A molecular epidemiological study of avian paramyxovirus type 1 (Newcastle disease virus) isolates by phylogenetic analysis of a partial nucleotide sequence of the fusion protein gene

First report of the emergence of novel sub-genotype XIII.2.3 of Newcastle disease virus in chickens from selected regions of Bangladesh

Newcastle disease (ND) is one of the most economically devastating infectious diseases impacting the poultry industry in Bangladesh. This study aimed to characterize the pathotype, genotype, evolutionary divergence, and mutations of circulating virulent Newcastle disease virus (NDV) in chickens from the Gazipur, Tangail, and Mymensingh districts of Bangladesh between October 2023 and December 2024. ND-suspected samples, including lung, trachea, and caecal tonsil tissues, were collected, processed, and inoculated into 10-12-day-old embryonated chicken eggs (ECEs) via the allantoic cavity. Allantoic fluids were harvested after 24 h of incubation, and virulent NDV was identified through RT-PCR targeting the fusion (F) gene using specific primers. Pathogenicity was assessed using the mean death time (MDT), intracerebral pathogenicity index (ICPI), and intravenous pathogenicity index (IVPI). The pathotype and genotype were confirmed by complete sequencing of the F gene and phylogenetic analysis. Further evolutionary divergence and mutations were analyzed using MEGA-11 software. RT-PCR yielded specific amplification of a 254-bp product indicative of virulent NDV. Pathogenicity indices-MDT (<60 h), ICPI (>1.5), and IVPI (>1.70)-confirmed a velogenic strain. Complete F gene sequencing revealed an F-protein cleavage site motif of "RRQKRF," while phylogenetic analysis classified the isolates as belonging to sub-genotype XIII.2.3 under genotype XIII. Evolutionary divergence (0.00-0.06) and mutations at neutralizing epitopes 1 and 2 (at the 74th and 170th amino acids, respectively) suggested moderate genetic diversity. This study represents the first report in Bangladesh identifying the emergence of the novel sub-genotype XIII.2.3 of genotype XIII NDV associated with chicken mortality in selected regions.

Identifying Causative Agents of a Paretic Syndrome in Waterbirds in Southern Portugal

Paretic and paralyzing syndromes affecting wild birds are widely described in the literature, with outbreaks showing an increase in frequency and intensity worldwide during recent years. In the Iberian Peninsula, a paretic clinical picture without known etiology affecting mostly gulls has been reported during the last few decades. This paretic syndrome (PS) affects waterbirds and is characterized by a set of signs of ascendent flaccid paralysis, dyspnea, and diarrhea at different levels of severity. This study presents the first macro-analysis of some potential etiological PS agents in wild birds in southern Portugal. Other possible etiologies of PS related to nutritional deficiencies and environmental pollutants were not studied but are also discussed here. A total of 571 samples, belonging to 377 individuals with (n = 336) and without (n = 41) PS signs, have been tested for seven different toxins groups (botulinum neurotoxin (BoNT), paralytic shellfish toxins (PSTs), domoic acid (DA), anatoxin-a (ATX-a), cylindrospermopsin (CYN), tetrodotoxins (TTXs), and microcystins (MCs)) and three viral infections (gull adenovirus (GA), Newcastle disease virus (NVD), and highly pathogenic avian influenza viruses (HPAIV)). Of all the birds tested for botulinum neurotoxin, those with PS signs were positive (100%) and those without PS signs were negative (0%), confirming an association between PS and botulism. Some samples were positive for PSTs and MCs, but the prevalence in birds with PS signs was not significantly higher (2.5% and 5.3%, respectively) than in birds without signs (5.4% and 5.4%, respectively). Two birds without PS signs were positive for highly pathogenic avian influenza virus. The presence of the rest of the toxins and viruses was negative for all the samples tested. Our results support the relevant contribution of botulinum neurotoxin in the PS outbreaks observed in several species of aquatic birds in the last decades in southern Portugal, suggesting it could be one of the main causes of mortality in waterbirds.

Newcastle disease virus genotype VII.1.1 identified from backyard chickens with low antibody titer: Jimma Zone, Southwest Ethiopia

BACKGROUND

Newcastle disease significantly impacts the global poultry industry and is prevalent in many African countries, including Ethiopia. The objective of this research is to determine the humoral immune response to Newcastle Disease Virus (NDV), identify the circulating NDV genotype, and evaluate the correlation between the diagnostic tests used in backyard chickens in the Jimma Zone, southwest Ethiopia.

METHODS

A total of 90 swab and blood samples were purposively collected from symptomatic backyard chicken in the period between February and April 2022. Samples were collected from Jimma town, Seqa Chekorsa and Tiro Afeta districts of Jimma zone. Enzyme linked immunosorbent assay (ELISA) was conducted and seropositivity was determined from the collected serum samples. From the swab samples, total RNA was extracted and the viral genomic material was detected by amplifying the Fusion gene by Reverse transcription polymerase chain reaction (RT-PCR). The interconnection between ELISA and RT-PCR was also analyzed. Further, positive swab samples were nucleotide sequenced and genotyped.

RESULTS

Of the 90 serum samples, 62 (68.8%) were seropositive. From the 90 swab samples, 14 (15.5%) were RT-PCR positive. No statistically significant association between risk factors (breed, age, sex) and virus exposure was observed by RT-PCR (P = 0.41, 0.44, 0.67) or ELISA (P = 0.85, 0.19, 0.11). However, local breeds, young, and male birds were at higher risk according to RT-PCR results, while young and female birds were more likely to be seropositive. The antibody titer study showed that RT-PCR positive birds produced less than half the mean antibodies of negative birds (x̄=854 vs. 1885) and positive birds produced similar amount of antibody (σ = 626). Local (x̄=1978), adult (x̄=2558), and female (x̄=2620) birds had higher mean antibody titers than their counterparts. The agreement between RT-PCR and ELISA in identifying positive samples was minimal (k = 0.05). Nucleotide-sequenced isolates were nearly identical (99.7%) to each other and identified as velogenic based on the F-gene cleavage site (RRQKRF) with genotype VII.1.1.

CONCLUSION

NDV was circulating in the study area, infecting birds with low antibody titers. High viral similarity between neighboring countries emphasizes the need for regional disease control strategy.

Protective efficacy of classical vaccines and vaccination protocols against an exotic Newcastle disease virus genotype VII.2 in Belgian layer and broiler chickens

Vaccination against Newcastle disease (ND) has been routinely implemented in the Belgian professional poultry sector since 1993, using genotype I and II vaccines. Despite this, an outbreak of genotype VII.2 avian paramyx-ovirus 1 (APMV-1) occurred in 2018, with 20 reported cases over the course of 3 months. Although the economic impact on the professional poultry sector was limited, this epizootic raised questions regarding the efficacy of implemented classical genotype I and II vaccines against phylogenetically distant exotic velogenic strains. The present study provides insights into the protective efficacy of standard vaccination programs applied in layer and broiler flocks against the introduction and transmission of this velogenic APMV-1 VII.2 strain. For fully field-vaccinated 26-week-old layer chickens, high levels of specific antibodies were measured at the time of the velogenic APMV-1 challenge, resulting in good clinical protection. However, despite the observed humoral immunity, viral excretion was not prevented, leading to transmission of the virus to non-infected sentinel birds. In fully field-vaccinated 4-week-old broiler chickens, assessment of vaccine uptake and coverage revealed low levels of ND specific antibodies despite double vaccination at day 1 and day 14. Consequently, poor protection against velogenic APMV-1 infection was observed, with both clinical signs and viral excretion occurring in both infected and sentinel birds. This study demonstrates that the introduction of velogenic APMV-1 VII.2 can lead to its dissemination among the Belgian avian poultry population despite the implementation of standard vaccination.

Genomic Diversity and Evolutionary Insights of Avian Paramyxovirus-1 in Avian Populations in Pakistan

The virulent form of Avian paramyxovirus-1 (APMV-1), commonly known as Newcastle Disease Virus (NDV), is a pathogen with global implications for avian health, affecting both wild and domestic bird populations. In Pakistan, recurrent Newcastle Disease (caused by NDV) outbreaks have posed significant challenges to the poultry industry. Extensive surveillance in Pakistan over 20 years has demonstrated a dynamic genetic diversity among circulating APMV-1 strains, emphasizing the potential necessity for customized vaccination strategies and continuous surveillance. In this study, 13 APMV-1-positive isolates harboring four different APMV-1 genotypes circulating throughout Pakistan were identified. These included the highly virulent genotypes VII and XIII, genotype XXI, commonly associated with Columbiformes, and genotype II, hypothesized to have been detected following vaccination. These findings underscore the intricate interplay of mutational events and host-immune interactions shaping the evolving NDV landscape. This study advances our understanding of the evolutionary dynamics of APMV-1 in Pakistan, highlighting the need for tailored vaccination strategies and continuous surveillance to enable effective APMV-1 management in avian populations, further emphasizing the importance of globally coordinated strategies to tackle APMV-1, given its profound impact on wild and domestic birds.

Genomic Diversity and Geographic Distribution of Newcastle Disease Virus Genotypes in Africa: Implications for Diagnosis, Vaccination, and Regional Collaboration

The emergence of new virulent genotypes and the continued genetic drift of Newcastle disease virus (NDV) implies that distinct genotypes of NDV are simultaneously evolving in different geographic locations across the globe, including throughout Africa, where NDV is an important veterinary pathogen. Expanding the genomic diversity of NDV increases the possibility of diagnostic and vaccine failures. In this review, we systematically analyzed the genetic diversity of NDV genotypes in Africa using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Information published between 1999 and 2022 were used to obtain the genetic background of different genotypes of NDV and their geographic distributions in Africa. The following genotypes were reported in Africa: I, II, III, IV, V, VI, VII, VIII, XI, XIII, XIV, XVII, XVIII, XX, and XXI. A new putative genotype has been detected in the Democratic Republic of the Congo. However, of 54 African countries, only 26 countries regularly report information on NDV outbreaks, suggesting that this number may be vastly underestimated. With eight different genotypes, Nigeria is the country with the greatest genotypic diversity of NDV among African countries. Genotype VII is the most prevalent group of NDV in Africa, which was reported in 15 countries. A phylogeographic analysis of NDV sequences revealed transboundary transmission of the virus in Eastern Africa, Western and Central Africa, and in Southern Africa. A regional and continental collaboration is recommended for improved NDV risk management in Africa.

Isolation and Genetic Characterization of a Novel Adenovirus Associated with Mass Mortality in Great Cormorants (Phalacrocorax carbo)

High mortality in great cormorants (Phalacrocorax carbo) was registered on the Alakol Lake in eastern Kazakhstan in 2021 when about 20% of juveniles died. High-throughput sequencing revealed the presence of a putative novel cormorant adenovirus significantly divergent from known aviadenoviruses. We suggest that this cormorant adenovirus can be considered an emerging threat to the health and conservation of this species.

Detection of Avian Orthoavulavirus-1 genotypes VI.2.1 and VII.1.1 with neuro-viscerotropic tropism in some backyard pigeons (Columbidae) in Eastern Saudi Arabia

Introduction

Avian orthoavulavirus-1 (AOAV1) has a wide host range, including domestic and wild birds. The present study aimed to identify the currently circulating AOAV1 strains from some outbreaks in some backyard pigeons in the eastern region of Saudi Arabia (ERSA).

Methods

Tracheal/cloacal swabs and tissue specimens were collected from eight backyards in Al-Ahsa, ERSA, between January 2021 and March 2023. Samples were tested for the presence of AOAV1 using commercial real-time RT-PCR. Part of the fusion gene was also amplified by gel-based RT-PCR, and the obtained amplicons were sequenced.

Results and discussion

AOAV1 was detected in samples from the eight flocks. The retrieved sequences from samples of 6/8 pigeon backyards are reported. Phylogenetic analysis based on the obtained sequences from these backyard pigeons showed the segregation of the obtained sequences in AOAV1 genotypes VI.2.1 and VII.1.1. Clinically, nervous manifestations were dominant in pigeons infected with both genotypes. Respiratory manifestations and significantly higher overall mortality rate were induced by genotype VI.2.1. The deduced amino acid sequences of the fusion protein cleavage site (FPCS) showed that all the detected isolates belong to velogenic strains. Differences in clinical profiles induced by the natural infection of pigeons with AOAV1 genotypes VI.2.1 and VII.1.1 were reported. The present findings highlight the potential roles of some backyard pigeons in the long-distance spread and cross-species transmission of the reported AOAVI genotypes. Further research is required to perform biotyping and pathotyping of the reported strains.

Phylogenetic Analysis of Newcastle Disease Virus Isolated from Poultry in Live Bird Markets and Wild Waterfowl in Zambia

Poultry production is essential to the economy and livelihood of many rural Zambian households. However, the industry is threatened by infectious diseases, particularly Newcastle disease virus (NDV) infection. Therefore, this study employed next-generation sequencing to characterise six NDV isolates from poultry in Zambia's live bird markets (LBMs) and wild waterfowl. Four NDV isolates were detected from 410 faecal samples collected from chickens in LBMs in Lusaka and two from 2851 wild birds from Lochinvar National Park. Phylogenetic analysis revealed that the four NDVs from LBM clustered in genotype VII and sub-genotype VII.2 were closely related to viruses previously isolated in Zambia and other Southern African countries, suggesting possible local and regional transboundary circulation of the virus. In contrast, the two isolates from wild birds belonged to class I viruses, genotype 1, and were closely related to isolates from Europe and Asia, suggesting the possible introduction of these viruses from Eurasia, likely through wild bird migration. The fusion gene cleavage site motif for all LBM-associated isolates was 112RRQKR|F117, indicating that the viruses are virulent, while the isolates from wild waterfowl had the typical 112ERQER|L117 avirulent motif. This study demonstrates the circulation of virulent NDV strains in LBMs and has, for the first time, characterised NDV from wild birds in Zambia. The study further provides the first whole genomes of NDV sub-genotype VII.2 and genotype 1 from Zambia and stresses the importance of surveillance and molecular analysis for monitoring the circulation of NDV genotypes and viral evolution.

In vivo challenge studies on vaccinated chickens indicate a virus genotype mismatched vaccine still offers significant protection against NDV

Although commercial vaccines against Newcastle Disease have been available for decades, outbreaks still occur in the face of vaccination Further vaccination may accelerate viral evolution resulting in a further reduction in vaccine efficacy. A key question is whether genotype-matched vaccines can confer better protection against contemporary type 1 Avian Paramyxoviruses. To assess this, an in vivo vaccine-challenge study was undertaken to assess protection afforded by 'genotype-matched' and commercial vaccine formulations. Groups of chickens were vaccinated twice (prime-boost) with an inactivated preparation of either La Sota Clone 30, AV632-chicken-Cyprus-13 (genotype VII.2), or mock vaccine, and later challenged with virulent AV632-chicken-Cyprus-13. Post vaccinal serological responses differed, although both vaccination/challenge groups showed similar levels of clinical protection compared to the unvaccinated group, where 100 % mortality was observed. Shedding was significantly reduced in the vaccinated groups compared to the unvaccinated group. Virus dissemination in the tissues of vaccinated birds was comparable, but onset of infection was delayed. Two mutations were observed in the HN gene of the heterologous vaccine group; H199N and I192M, the latter thought to be associated with increased fusogenic potential. These data demonstrate that existing vaccine formulations confer similar levels of clinical protection to contemporary strains and that the antigenic heterogeneity of circulating strains does not impact upon shedding profiles in immunised birds. In conclusion, the ability of virulent APMV-1 to cause disease in vaccinated flocks is unlikely to be the result of antigenic mismatch alone, and other factors likely contribute to vaccination failure and breakthrough.

Predominance of low pathogenic avian influenza virus H9N2 in the respiratory co-infections in broilers in Tunisia: a longitudinal field study, 2018-2020

Respiratory diseases are a health and economic concern for poultry production worldwide. Given global economic exchanges and migratory bird flyways, respiratory viruses are likely to emerge continuously in new territories. The primary aim of this study was to investigate the major pathogens involved in respiratory disease in Tunisian broiler poultry and their epidemiology. Between 2018 and 2020, broilers farms in northeastern Tunisia were monitored, and 39 clinically diseased flocks were sampled. Samples were screened for five viral and three bacterial respiratory pathogens using a panel of real-time PCR assays. The reemergence of H9N2 low pathogenic avian influenza virus (LPAIV) in commercial poultry was reported, and the Northern and Western African GI lineage strain was typed. The infectious bronchitis virus (IBV) GI-23 lineage and the avian metapneumovirus (aMPV) subtype B also were detected for the first time in broilers in Tunisia. H9N2 LPAIV was the most detected pathogen in the flocks tested, but rarely alone, as 15 of the 16 H9N2 positive flocks were co-infected. Except for infectious laryngotracheitis virus (ILTV), all of the targeted pathogens were detected, and in 61% of the respiratory disease cases, a combination of pathogens was identified. The major combinations were H9N2 + aMPV (8/39) and H9N2 + IBV (6/39), showing the high contribution of H9N2 LPAIV to the multifactorial respiratory diseases. This field survey provided evidence of the emergence of new respiratory viruses and the complexity of respiratory disease in Tunisia. A comprehensive and continuous surveillance strategy therefore is needed to better control respiratory pathogens in Tunisia.

Genetic Diversity of Newcastle Disease Virus Involved in the 2021 Outbreaks in Backyard Poultry Farms in Tanzania

Newcastle disease virus is a significant avian pathogen with the potential to decimate poultry populations all over the world and cause enormous economic losses. Distinct NDV genotypes are currently causing outbreaks worldwide. Due to the high genetic diversity of NDV, virulent strains that may result in a lack of vaccine protection are more likely to emerge and ultimately cause larger epidemics with massive economic losses. Thus, a more comprehensive understanding of the circulating NDV genotypes is critical to reduce Newcastle disease (ND) burden. In this study, NDV strains were isolated and characterized from backyard poultry farms from Tanzania, East Africa in 2021. Reverse-transcription polymerase chain reaction (RT-PCR) based on fusion (F) gene amplification was conducted on 79 cloacal or tracheal swabs collected from chickens during a suspected ND outbreak. Our results revealed that 50 samples out 79 (50/79; 63.3%) were NDV-positive. Sequencing and phylogenetic analyses of the selected NDV isolates showed that 39 isolates belonged to subgenotype VII.2 and only one isolate belonged to subgenotype XIII.1.1. Nucleotide sequences of the NDV F genes from Tanzania were closely related to recent NDV isolates circulating in southern Africa, suggesting that subgenotype VII.2 is the predominant subgenotype throughout Tanzania and southern Africa. Our data confirm the circulation of two NDV subgenotypes in Tanzania, providing important information to design genotype-matched vaccines and to aid ND surveillance. Furthermore, these results highlight the possibility of the spread and emergence of new NDV subgenotypes with the potential of causing future ND epizootics.

Analysis of Avian Orthoavulavirus 1 Detected in the Russian Federation between 2017 and 2021

Newcastle disease virus (NDV, Avian orthoavulavirus type 1, AOAV-1) is a contagious high-impact poultry pathogen with infections detected worldwide. In the present study, 19,500 clinical samples from wild bird species and poultry collected from 28 regions of Russia between 2017 and 2021 were screened for the presence of the AOAV-1 genome. NDV RNA was detected in 15 samples from wild birds and 63 samples from poultry. All isolates were screened for a partial sequence of the fusion (F) gene that included the cleavage site. Phylogenetic analysis demonstrated that lentogenic AOAV-1 I.1.1, I.1.2.1, and II genotypes were dominant among vaccine-like viruses in the territory of the Russian Federation. A vaccine-like virus with a mutated cleavage site (112-RKQGR^L-117) was detected in turkeys. Among the virulent AOAV-1 strains, viruses of the XXI.1.1, VII.1.1, and VII.2 genotypes were identified. The cleavage site of viruses of the XXI.1.1 genotype had a 112-KRQKR^F-117 amino acid sequence. The cleavage site of viruses with VII.1.1 and VII.2 genotypes had a 112-RRQKR^F-117 amino acid sequence. The data collected by the present study demonstrate the distribution and dominance of the virulent VII.1.1 genotype in the Russian Federation between 2017 and 2021.

Common viral and bacterial avian respiratory infections: an updated review

Many pathogens that cause chronic diseases in birds use the respiratory tract as a primary route of infection, and respiratory disorders are the main leading source of financial losses in the poultry business. Respiratory infections are a serious problem facing the poultry sector, causing severe economic losses. Avian influenza virus, Newcastle disease virus, infectious bronchitis virus, and avian pneumovirus are particularly serious viral respiratory pathogens. Mycoplasma gallisepticum, Staphylococcus, Bordetella avium, Pasteurella multocida, Riemerella anatipestifer, Chlamydophila psittaci, and Escherichia coli have been identified as the most serious bacterial respiratory pathogens in poultry. This review gives an updated summary, incorporating the latest data, about the evidence for the circulation of widespread, economically important poultry respiratory pathogens, with special reference to possible methods for the control and prevention of these pathogens.

Comparative pathogenesis of two genotype VI.2 avian paramyxovirus type-1 viruses (APMV-1) in pheasants, partridges and chickens

Newcastle disease (ND) is caused by virulent forms of avian paramyxovirus-1 (APMV-1) and is an economically important disease of poultry world-wide. Pigeon paramyxovirus 1 (PPMV-1), a sub-group of APMV-1 is endemic in Columbiformes and can cause infections of poultry. An outbreak of ND in partridges in Scotland, UK, in 2006 (APMV-1/partridge/UK(Scotland)/7575/06) was identified as a class II, genotype VI.2.1.1.2.1, more commonly associated with PPMV-1. It has been hypothesized that game birds may be a route of transmission into commercial poultry settings due to the semi-feral rearing system, which potentially brings them into contact with both wild-birds and poultry species. Therefore, the pathogenesis and transmission of APMV-1/partridge/UK(Scotland)/7575/06 in game birds and chickens was investigated, and compared to a contemporary PPMV-1 isolate, PPMV-1/pigeon/UK/015874/15. Viral shedding and seroconversion profiles demonstrated that pheasants were susceptible to infection with APMV-1/partridge/UK(Scotland)/7575/06 with limited clinical signs observed although they were able to excrete and transmit virus. In contrast, partridges and pheasants showed limited infection with PPMV-1/pigeon/UK/015874/15, causing mild clinical disease. Chickens, however, were productively infected and were able to transmit virus in the absence of clinical signs. From the data, it can be deduced that whilst game birds may play a role in the transmission and epidemiology of genotype VI.2 APMV-1 viruses, the asymptomatic nature of circulation within these species precludes evaluation of natural infection by clinical surveillance. It therefore remains a possibility that genotype VI.2 APMV-1 infection in game birds has the potential for asymptomatic circulation and remains a potential threat to avian production systems.RESEARCH HIGHLIGHTS Demonstration of infection of game birds with Pigeon paramyxovirus-1 (PPMV-1).There are differing dynamics of infection between different game bird species.Differing dynamics of infection between different PPMV-1 isolates and genotypes in game birds and chickens.

Evolutionary Trajectories of Avian Avulaviruses and Vaccines Compatibilities in Poultry

Newcastle disease virus (NDV) causes one of the highly infectious avian diseases in poultry leading to genuine financial misfortunes around the world. Recently, there has been an increasing trend in the number of ND-associated outbreaks in commercial Jordanian poultry flocks indicating a possible complex evolutionary dynamic of NDV infections in the country. To underpin the dynamics of circulating NDV strains and to assess the vaccine-escape potential, a total of 130 samples were collected from different poultry flocks in six Jordanian Governorates during 2019-2021. Twenty positive isolates, based on real-time reverse transcriptase PCR, were used for further genetic characterization and evolutionary analysis. Our results showed that there is a high evolutionary distance between the newly identified NDV strains (genotype VII.1.1) in this study and the commercially used vaccines (genotypes I and II), suggesting that circulating NDV field strains are under constant evolutionary pressure. These mutations may significantly affect flocks that have received vaccinations as well as flocks with insufficient immunity in terms of viral immunity and disease dynamics. To assess this further, we investigated the efficacy of the heterologous inactivated LaSota or homologous genotype VII.1.1 vaccine for their protection against virulent NDV in chicken. Vaccine-induced immunity was evaluated based on the serology, and protection efficacy was assessed based on clinical signs, survival rates, histopathology, and viral shedding. Chickens vaccinated with the inactivated genotype VII.1.1 based vaccine showed 100% protection with a significant reduction in virus shedding, and ameliorated histopathology lesions compared to LaSota vaccinated chicks that showed 60% protection. These results revealed that the usage of NDV inactivated vaccine from the circulating field strains can successfully ameliorate the clinical outcome and virus pathobiology in vaccinated chicks and will serve as an effective vaccine against the threat posed by commonly circulating NDV strains in the poultry industry.

Epidemiology of Newcastle disease in chickens of Ethiopia: a systematic review and meta-analysis

The objective of this systematic review was to estimate the overall pooled prevalence of Newcastle disease in chickens in Ethiopia and identify the sources of heterogeneity among and within studies. The seroprevalence of Newcastle disease was estimated using a single-group meta-analysis. Attempts were also made to identify study-level variables that could explain the heterogeneity in the apparent seroprevalence of the Newcastle disease. The findings were based on 16 published articles and 33 district-level reports and were limited to studies performed during 2005-2017. Due to the presence of heterogeneity, pooled analysis from different districts was conducted using random-effects meta-analysis. The single-group summary of Newcastle disease seroprevalence in chickens was estimated to be 21.47% (19.54-23.4%) with a 95% confidence interval. Our results indicated high inter-study variability (Cochran's Q statistic = 196.2, true variance (τ²) = 0.36, inverse variance index (I²) = 90.0%, p < 0.001). Of all variables analysed, diagnostic techniques and regions were the most significant predictors (p ˂ 0.05) of heterogeneity. According to the diagnostic technique-based meta-analysis of random pooled prevalence, the haemagglutination inhibition test had the highest prevalence, followed by the enzyme-linked immunosorbent assay. In conclusion, the high-pooled prevalence estimates of the disease, combined with the scarcity of published data for the entire country of Ethiopia, indicate a significant data gap on the distribution of Newcastle disease in the country. While the high pooled prevalence tells the need for intervention to control the disease, there is also a need to assess the disease prevalence in all other parts of the country.

Isolation, Identification, and Molecular Characterization of Newcastle Disease Virus from Field Outbreaks in Chickens in Afghanistan

Newcastle disease viruses (NDVs) in Afghanistan were isolated from three chicken farms and identified using a hemagglutination test and reverse transcription-polymerase chain reaction assay. Three isolates from each farm were sequenced to characterize the part of their fusion protein gene around the cleavage site. The characteristics of the fusion protein genes of the three isolates shown by phylogenic analysis indicated that the isolates were velogenic, belonged to the class II subgenotype VII 1.1, and were closely related to an identified Chinese NDV isolate. To our knowledge, this is the first time that NDV isolates from Afghanistan have been partially sequenced.

Epidemiology of Newcastle disease in poultry in Africa: systematic review and meta-analysis

The present study intended to determine the prevalence of Newcastle disease in unvaccinated backyard poultry in Africa. Using the PRISMA approach, a systematic review and meta-analysis of 107 epidemiological studies was conducted. The meta-analysis identified significant variation of both seroprevalence (I² = 99.38, P = 0.00) and Newcastle disease virus prevalence (I² = 99.52, P = 0.00) reported in various studies included in this review. Publication bias was not detected in either case. Seroprevalence of Newcastle disease was 40.2 (95%CI 32.9-47.8). Seroprevalence was significantly influenced by sampling frame and the African region where the studies were conducted. The prevalence of Newcastle disease virus (NDV) was 12% (95%CI 7.3-17.8), and the variation was influenced by sampling frame, diagnostic test, and regions where the studies were conducted. Also, Newcastle disease (ND) accounted for 33.1% (95%CI 11.9-58.1) of sick chickens. Results also indicated that genotypes VI and VII are widely distributed in all countries included in the study. However, genotype V is restricted in East Africa, and genotypes XIV, XVII, and XVIII are restricted in West and Central Africa. On the other hand, genotype XI occurs in Madagascar only. In addition, virulent genotypes were isolated from apparently healthy and sick birds. It is concluded that several genotypes of NDV are circulating and maintained within the poultry population. African countries should therefore strengthen surveillance systems, be able to study the viruses circulating in their territories, and establish control programs.

Response of three local chicken ecotypes of Ghana to lentogenic and velogenic Newcastle disease virus challenge

This study was carried out to assess the response of three Ghanaian local chicken ecotypes to LaSota (lentogenic) and virulent field strains of Newcastle disease virus (NDV). Local chickens sampled from the Interior Savannah (IS), Forest (FO) and Coastal Savannah (CS) agro-ecological zones were bred and their offspring were challenged with LaSota NDV at 4 weeks of age. The LaSota challenge was replicated four times with different chicken groups. A total of 1438 chicks comprising 509 Coastal Savannah, 518 Forest and 411 Interior Savannah ecotypes were used. Pre- and post-challenge anti-NDV antibody titre levels were determined via ELISA assays. A second trial was conducted by introducing sick birds infected with virulent NDV to a flock of immunologically naïve chickens at 4 weeks old. Body weights were measured pre- and post-infection. Sex of the chickens was determined using a molecular method. In both trials, there was no significant difference among ecotypes in body weight and growth rate. In the LaSota trial, anti-NDV antibody titre did not differ by ecotype or sex. However, there was a positive linear relationship between body weight and antibody titre. In the velogenic NDV trial, survivability and lesion scores were similar among the three ecotypes. This study confirms that a relatively high dose of LaSota (NDV) challenge has no undesirable effect on Ghanaian local chicken ecotypes. All three Ghanaian local chicken ecotypes were susceptible to velogenic NDV challenge. Resistance to NDV by Ghanaian local chickens appears to be determined more by the individual's genetic makeup than by their ecotype.

Pathogenesis of Velogenic Genotype VII.1.1 Newcastle Disease Virus Isolated from Chicken in Egypt via Different Inoculation Routes: Molecular, Histopathological, and Immunohistochemical Study

Newcastle disease virus (NDV) remains a constant threat to the poultry industry. There is scarce information concerning the pathogenicity and genetic characteristics of the circulating velogenic Newcastle disease virus (NDV) in Egypt. In the present work, NDV was screened from tracheal swabs collected from several broiler chicken farms (N = 12) in Dakahlia Governorate, Egypt. Real-time reverse transcriptase polymerase chain reaction (RRT-PCR) was used for screening of velogenic and mesogenic NDV strains through targeting F gene fragment amplification, followed by sequencing of the resulting PCR products. The identified strain, namely, NDV-CH-EGYPT-F42-DAKAHLIA-2019, was isolated and titrated in the allantoic cavity of 10 day old specific pathogen-free (SPF) embryonated chicken eggs (ECEs), and then their virulence was determined by mean death time (MDT) and intracerebral pathogenicity index (ICPI). The pathogenicity of the identified velogenic NDV strain was also assessed in 28 day old chickens using different inoculation routes as follows: intraocular, choanal slit, intranasal routes, and a combination of both intranasal and intraocular routes. In addition, sera were collected 5 and 10 days post inoculation (pi) for the detection of NDV antibodies by hemagglutination inhibition test (HI), and tissue samples from different organs were collected for histopathological and immunohistochemical examination. A series of different clinical signs and postmortem lesions were recorded with the various routes. Interestingly, histopathology and immunohistochemistry for NDV nucleoprotein displayed widespread systemic distribution. The intensity of viral nucleoprotein immunolabeling was detected within different cells including the epithelial and endothelium lining, as well as macrophages. The onset, distribution, and severity of the observed lesions were remarkably different between various inoculation routes. Collectively, a time-course comparative pathogenesis study of NDV infection demonstrated the role of different routes in the pathogenicity of NDV. The intranasal challenge was associated with a prominent increase in NDV lesions, whereas the choanal slit route was the route least accompanied by severe NDV pathological findings. Clearly, the present findings might be helpful for implementation of proper vaccination strategies against NDV.

Epitope Peptide-Based Predication and Other Functional Regions of Antigenic F and HN Proteins of Waterfowl and Poultry Avian Avulavirus Serotype-1 Isolates From Uganda

Uganda is a Newcastle disease (ND) endemic country where the disease is controlled by vaccination using live LaSota (genotype II) and I₂ (genotype I) vaccine strains. Resurgent outbreak episodes call for an urgent need to understand the antigenic diversity of circulating wild Avian Avulavirus serotype-1 (AAvV-1) strains. High mutation rates and the continuous emergence of genetic and antigenic variants that evade immunity make non-segmented RNA viruses difficult to control. Antigenic and functional analysis of the key viral surface proteins is a crucial step in understanding the antigen diversity between vaccine lineages and the endemic wild ND viruses in Uganda and designing ND peptide vaccines. In this study, we used computational analysis, phylogenetic characterization, and structural modeling to detect evolutionary forces affecting the predicted immune-dominant fusion (F) and hemagglutinin-neuraminidase (HN) proteins of AAvV-1 isolates from waterfowl and poultry in Uganda compared with that in LaSota vaccine strain. Our findings indicate that mutational amino acid variations at the F protein in LaSota strain, 25 poultry wild-type and 30 waterfowl wild-type isolates were distributed at regions including the functional domains of B-cell epitopes or N-glycosylation sites, cleavage site, fusion site that account for strain variations. Similarly, conserved regions of HN protein in 25 Ugandan domestic fowl isolates and the representative vaccine strain varied at the flanking regions and potential linear B-cell epitope. The fusion sites, signal peptides, cleavage sites, transmembrane domains, potential B-cell epitopes, and other specific regions of the two protein types in vaccine and wild viruses varied considerably at structure by effective online epitope prediction programs. Cleavage site of the waterfowl isolates had a typical avirulent motif of ¹¹¹GGRQGR'L¹¹⁷ with the exception of one isolate which showed a virulent motif of ¹¹¹GGRQKR'F¹¹⁷. All the poultry isolates showed the ¹¹¹GRRQKR'F¹¹⁷ motif corresponding to virulent strains. Amino acid sequence variations in both HN and F proteins of AAvV-1 isolates from poultry, waterfowl, and vaccine strain were distributed over the length of the proteins with no detectable pattern, but using the experimentally derived 3D structure data revealed key-mapped mutations on the surfaces of the predicted conformational epitopes encompassing the experimental major neutralizing epitopes. The phylogenic tree constructed using the full F gene and partial F gene sequences of the isolates from poultry and waterfowl respectively, showed that Ugandan ND aquatic bird and poultry isolates share some functional amino acids in F sequences yet do remain unique at structure and the B-cell epitopes. Recombination analyses showed that the C-terminus and the rest of the F gene in poultry isolates originated from prevalent velogenic strains. Altogether, these could provide rationale for antigenic diversity in wild ND isolates of Uganda compared with the current ND vaccine strains.

In silico prediction of B and T cell epitopes based on NDV fusion protein for vaccine development against Newcastle disease virus

Newcastle disease (ND) is known as the most common diseases of economic importance worldwide. Vaccination against virulent strains of Newcastle disease virus (NDV) has failed during some outbreaks. Here, we aimed to assess the epitopes of NDV fusion protein as targets for a peptide-based vaccine. To explore the most antigenic epitopes on the F protein, we retrieved virulent strains of genotype VII from National Center for Biotechnology Information (NCBI). Linear and conformational B-cell epitopes were identified. Moreover, T-cell epitopes with high and moderate binding affinities to human major histocompatibility complex (MHC) class I and class II alleles were predicted using bioinformatics tools. Subsequently, the overlapped epitopes of B-cell and MHC class I and MHC class II were determined. To validate our predictions, the best epitopes were docked, to chicken MHC class I (B-F) alleles using the HADDOCK flexible docking server. Seven ‘high ranked epitopes’ were identified. Among them, ‘LYCTRIVTF’ and ‘MRATYLETL’ showed the highest scores. The other five epitopes including LSGEFDATY, LTTPPYMALK, LYLTELTTV, DCIKITQQV and SIAATNEAV obtained very encouraging results as well. SIAATNEAV had been recognized as a neutralizing epitope of F protein using monoclonal antibodies before. Taken together, our results demonstrated that the identified epitopes needed to be tested by in vitro and in vivo experiments.

Antigenic and Molecular Characterization of Virulent Newcastle Disease Viruses Circulating in Ethiopia Between 1976 and 2008

Introduction

Newcastle disease virus (NDV) cultures held in the isolate collections in Ethiopia between 1976 and 2008 were not characterized using biological and molecular techniques. The already characterized NDV isolates belonged to genotype VI but the genetic nature of previously collected isolates, which could shade light on the history of introduction into the country and their evolutionary relationships, were not established.

Methods

A total of 14 NDVs (11 obtained from outbreak cases in chickens and three commercial vaccinal strains used in the country) were inoculated into specific pathogen free (SPF) embryonated chicken eggs (ECE). Allantoic fluids harvested from grown SPF ECE were tested by heamagglutination (HA) and heamagglutination inhibition (HI) tests. Partial F gene sequences were generated for all samples and molecular evolutionary relationships were reconstructed together with reference sequences freely available online. The pathogenicities of the isolates were assessed in vivo by determining their intracerebral pathogenicity index (ICPI) in day-old chicks and molecularly by determination of F gene cleavage sites.

Results

Of these, 12 viruses (two vaccines and 10 outbreaks) were successfully propagated as evidenced by a positive heamagglutination (HA) test. These 12 propagated viruses were further characterized by heamagglutination inhibition (HI) test, of which only three viruses reacted with monoclonal antibody (MAb 617/616) specific for pigeon paramyxovirus-1. In addition, all 14 viruses were characterized by partial fusion (F) gene sequencing and phylogenetic tree reconstruction. The Ethiopian NDV isolates clustered with genotype VI viruses, forming two clades (groups 1 and 2) that have ancestral relationships with Egypt-1990 and Sudan-1975 like viruses.

Discussion

The characterized genotype VI NDVs were genetically similar to currently circulating NDVs in Ethiopia. The isolates had cleavage sites consistent with mesogenic/velogenic NDV with a mean ICPI value of 1.76, indicating that the isolates were velogenic. Two and four highly virulent viruses were thermostable at 56°C for 2 hours and 1 hour, respectively. To reduce chicken mortality and production losses, proper control of the disease should be instituted using high quality and protective vaccines together with strong biosecurity measures.

Circulation of at Least Six Distinct Groups of Pigeon-Derived Newcastle Disease Virus in Iran Between 1996 and 2019

According to the latest Newcastle disease virus (NDV) classification system, Iranian PPMV-1 isolates were classified as either XXI.1.1 or XXI.2 subgenotypes only. However, a few recent studies have suggested the possible existence of other Iranian PPMV-1 genotypes/subgenotypes. Recently, we isolated a PPMV-1 closely related to the African origin subgenotype VI.2.1.2 from an ill captive pigeon in a park aviary in central Tehran (Pg/IR/AMMM160/2019). This subgenotype had never been reported from Iran or neighboring countries. We also isolated a subgenotype VII.1.1 NDV (Pg/IR/AMMM117/2018), usually reported from non-pigeon birds in Iran. The nucleotide distance of AMMM117 was 1.0-2.5% compared to other Iranian subgenotypes VII.1.1 isolates. However, usually the same year VII.1.1 viruses that we isolate from Iranian poultry farms show negligible distances (0.0-0.5%). More isolates are required to study if this difference is due to subgenotype VII.1.1 being circulated and mutated in pigeons. Here, we also characterized two other isolates, namely Pg/IR/AMMM168/2019 and Pg/IR/MAM39/2017. The latter is the first Iranian subgenotype XXI.1.1 to be featured in the NDV datasets of the international NDV consortium. We also investigated the phylogenetic relation of all the published Iranian pigeon-derived NDV to date and updated the grouping according to the latest classification system. We have concluded that at least six different groups of pigeon-derived NDV have been circulating in Iran since 1996, four of which have been reported from just one city over the last seven years. This study suggests that the Iranian pigeon-origin NDV have been more diverse than the Iranian poultry-derived NDV in recent years.

Comparison of genomic and antigenic properties of Newcastle Disease virus genotypes II, XXI and VII from Egypt do not point to antigenic drift as selection marker

Newcastle disease (ND), caused by avian orthoavulavirus type-1 (NDV), is endemic in poultry in many regions of the world and causes continuing outbreaks in poultry populations. In the Middle East, genotype XXI, used to be present in poultry in Egypt but has been replaced by genotype VII. We investigated whether virus evolution contributed to superseding and focussed on the antigenic sites within the hemagglutinin-neuraminidase (HN) spike protein. Full-length sequences of an NDV genotype VII isolate currently circulating in Egypt was compared to a genotype XXI isolate that was present as co-infection with vaccine-type viruses (II) in a historical virus isolated in 2011. Amino acid differences in the HN glycoprotein for both XXI and VII viruses amounted to 11.7% and 11.9%, respectively, compared to the La Sota vaccine type. However, mutations within the globular head (aa 126-570), bearing relevant antigenic sites, were underrepresented (a divergence of 8.8% and 8.1% compared to 22.4% and 25.6% within the protein domains encompassing cytoplasmic tail, transmembrane part and stalk regions (aa 1-125) for genotypes XXI and VII, respectively). Nevertheless, reaction patterns of HN-specific monoclonal antibodies inhibiting receptor binding revealed differences between vaccine-type viruses and genotype XXI and VII viruses for epitopes located in the head domain. Accordingly, compared to Egyptian vaccine-type isolates and the La Sota vaccine reference strain, single aa substitutions in 6 of 10 described neutralizing epitopes of HN were found. However, the same alterations in neutralization sensitive epitopes were present in old genotype XXI as well as in newly emerged genotype VII isolates. In addition, isolates were indistinguishable by polyclonal chicken sera raised against different genotypes including vaccine viruses. These findings suggest that factors other than antigenic differences within the HN protein account for facilitating the spread of genotype VII versus genotype XXI viruses in Egypt.

In Vitro and In Vivo Characterization of a Pigeon Paramyxovirus Type 1 Isolated from Domestic Pigeons in Victoria, Australia 2011

Significant mortalities of racing pigeons occurred in Australia in late 2011 associated with a pigeon paramyxovirus serotype 1 (PPMV-1) infection. The causative agent, designated APMV-1/pigeon/Australia/3/2011 (P/Aus/3/11), was isolated from diagnostic specimens in specific pathogen free (SPF) embryonated eggs and was identified by a Newcastle Disease virus (NDV)-specific RT-PCR and haemagglutination inhibition (HI) test using reference polyclonal antiserum specific for NDV. The P/Aus/3/11 strain was further classified as PPMV-1 using the HI test and monoclonal antibody 617/161 by HI and phylogenetic analysis of the fusion gene sequence. The isolate P/Aus/3/11 had a slow haemagglutin-elution rate and was inactivated within 45 min at 56 °C. Cross HI tests generated an R value of 0.25, indicating a significant antigenic difference between P/Aus/3/11 and NDV V4 isolates. The mean death time (MDT) of SPF eggs infected with the P/Aus/3/11 isolate was 89.2 hr, characteristic of a mesogenic pathotype, consistent with other PPMV-1 strains. The plaque size of the P/Aus/3/11 isolate on chicken embryo fibroblast (CEF) cells was smaller than those of mesogenic and velogenic NDV reference strains, indicating a lower virulence phenotype in vitro and challenge of six-week-old SPF chickens did not induce clinical signs. However, sequence analysis of the fusion protein cleavage site demonstrated an ¹¹²RRQKRF¹¹⁷ motif, which is typical of a velogenic NDV pathotype. Phylogenetic analysis indicated that the P/Aus/3/11 isolate belongs to a distinct subgenotype within class II genotype VI of avian paramyxovirus type 1. This is the first time this genotype has been detected in Australia causing disease in domestic pigeons and is the first time since 2002 that an NDV with potential for virulence has been detected in Australia.

Molecular Characterization of Velogenic Newcastle Disease Virus (Sub-Genotype VII.1.1) from Wild Birds, with Assessment of Its Pathogenicity in Susceptible Chickens

Simple Summary

Newcastle disease virus (NDV) is a highly contagious viral disease affecting a wide range of avian species. The disease can be particularly virulent in chickens, resulting in high mortality and morbidity. In this study, we characterized velogenic NDV sub-genotype VII.1.1 from wild birds and assessed its pathogenicity in susceptible chickens. One hundred wild birds from the vicinity of poultry farms with a history of NDV infection were examined clinically. Pooled samples from the spleen, lung, and brain were screened using real-time reverse transcriptase polymerase chain reaction (RRT-PCR) and reverse transcriptase polymerase chain reaction (RT-PCR) to detect the NDV F gene fragment, and phylogenetic analysis was carried out for identification of the genetic relatedness of the virus. Chickens were infected with the strains identified, and the major histopathological changes were assessed. Interestingly, NDV was detected in 44% of cattle egret samples and 26% of house sparrow samples by RRT-PCR, while RT-PCR detected NDV in 36% of cattle egrets examined and 20% of house sparrow samples. Phylogenetic analysis revealed close identity, of 99.7–98.5% (0.3–1.5% pairwise distance), between the isolates used in our study and other Egyptian class II, sub-genotype VII.1.1 NDV strains. Histopathological examination identified marked histopathological changes that are consistent with NDV. These findings provide interesting data in relation to the detection of NDV sub-genotype VII.1.1 in wild birds and reveal the major advantages of the combined use of molecular and histopathological methods in the detection and characterization of the virus. More research is needed to determine the characteristics of this contagious disease in the Egyptian environment.

Abstract

Newcastle disease (ND) is considered to be one of the most economically significant avian viral diseases. It has a worldwide distribution and a continuous diversity of genotypes. Despite its limited zoonotic potential, Newcastle disease virus (NDV) outbreaks in Egypt occur frequently and result in serious economic losses in the poultry industry. In this study, we investigated and characterized NDV in wild cattle egrets and house sparrows. Fifty cattle egrets and fifty house sparrows were collected from the vicinity of chicken farms in Kafrelsheikh Governorate, Egypt, which has a history of NDV infection. Lung, spleen, and brain tissue samples were pooled from each bird and screened for NDV by real-time reverse transcriptase polymerase chain reaction (RRT-PCR) and reverse transcriptase polymerase chain reaction (RT-PCR) to amplify the 370 bp NDV F gene fragment. NDV was detected by RRT-PCR in 22 of 50 (44%) cattle egrets and 13 of 50 (26%) house sparrows, while the conventional RT-PCR detected NDV in 18 of 50 (36%) cattle egrets and 10 of 50 (20%) of house sparrows. Phylogenic analysis revealed that the NDV strains identified in the present study are closely related to other Egyptian class II, sub-genotype VII.1.1 NDV strains from GenBank, having 99.7–98.5% identity. The pathogenicity of the wild-bird-origin NDV sub-genotype VII.1.1 NDV strains were assessed by experimental inoculation of identified strains (KFS-Motobas-2, KFS-Elhamoul-1, and KFS-Elhamoul-3) in 28-day-old specific-pathogen-free (SPF) Cobb chickens. The clinical signs and post-mortem changes of velogenic NDV genotype VII (GVII) were observed in inoculated chickens 3 to 7 days post-inoculation, with 67.5–70% mortality rates. NDV was detected in all NDV-inoculated chickens by RRT-PCR and RT-PCR at 3, 7, and 10 days post-inoculation. The histopathological findings of the experimentally infected chickens showed marked pulmonary congestion and pneumonia associated with complete bronchial stenosis. The spleen showed histocytic cell proliferation with marked lymphoid depletion, while the brain had malacia and diffuse gliosis. These findings provide interesting data about the characterization of NDV in wild birds from Egypt and add to our understanding of their possible role in the transmission dynamics of the disease in Egypt. Further research is needed to explore the role of other species of wild birds in the epidemiology of this disease and to compare the strains circulating in wild birds with those found in poultry.

Innate immune responses of domestic pigeons to the infection of pigeon paramyxovirus type 1 virus

Pigeon paramyxovirus type 1 (PPMV-1) is a globally distributed, virulent member of the avian paramyxovirus type-1. The PPMV-1-associated disease poses a great threat to the pigeon industry. The innate immune response is crucial for antiviral infections and revealing the pathogenic mechanisms of PPMV-1. In this study, we evaluated the pathogenicity of a PPMV-1 strain LHLJ/110822 in one-month-old domestic pigeons, as well as the host immune responses in PPMV-1-infected pigeons. We observed typically clinical sign in infected pigeons by 3 dpi. The morbidity rate and the mortality in pigeons inoculated with the PPMV-1 strain were up to 100% and 30%, respectively. The virus could replicate in all of the examined tissues, namely trachea, lung, liver, spleen, and bursa of Fabricius. In addition, the infected pigeons had developed anti-PPMV-1 antibodies as early as 8 dpi; and the antibody level increased over the time in this study. The expression level of toll-like receptor (TLR) 2, TLR3 TLR15, IFN-γ, and IL-6 were significantly upregulated by the PPMV-1 infection in some tissues of pigeons. By contrast, PPMV-1 infection results in downregulation of IL-18 expression in most of investigated tissues except for bursa of Fabricius in this study. The current results confirmed that this virus could replicate in pigeons and induce host immune responses, then leading to produce serum antibody titers. Meanwhile, the PPMV-1 infection induces strong innate immune responses and intense inflammatory responses at early stage in pigeon which may associate with the viral pathogenesis.

Co-circulation of genotypes XIV.2 and XVIII.2 of avian paramyxovirus-1 (Newcastle disease virus) in backyard poultry in Niger

The causative agent of Newcastle disease (ND) of poultry is the avian paramyxovirus-1, also commonly known as ND virus (NDV). Like in many developing countries, ND is endemic in Niger and has significant economic impact on commercial and backyard poultry production. NDVs were characterized in Niger between 2006 and 2008 and shown to belong to genotypes XIV.1 and XVII. In order to determine the current situation regarding the virus in Niger, tracheas (n = 384) were collected for the detection of NDV from both healthy (n = 335) and sick (n = 49) backyard poultry in 2019. Of these samples, 24 from sick chickens were positive for NDV by conventional RT-PCR. Sequencing of the fusion protein gene and phylogenetic analysis revealed that the viruses belonged to either genotype XIV.2 or XVIII.2. No NDVs of genotype XIV.1 or XVII were identified in the current study highlighting the dynamic nature of NDV circulation in Niger and the region.

Rapid Development of an Effective Newcastle Disease Virus Vaccine Candidate by Attenuation of a Genotype VII Velogenic Isolate Using a Simple Infectious Cloning System

Genotype-matched vaccines provide ideal protection against infection caused by new Newcastle disease virus (NDV) genotypes or variants even in the vaccinated chickens. In this study, we report a protocol for attenuation and rapid development of a velogenic NDV isolate as an effective vaccine candidate, using a simple and reliable infectious cloning platform. Based on DHN3, a genotype VII velogenic NDV isolate, recombinant rDHN3 was rescued by co-transfection of plasmids expressing the genomic RNA, NDV proteins NP, P and L, and the T7 polymerase without using a helper virus. Subsequently, an attenuated strain rDHN3-mF was produced by substitution of residues from amino acids 112 to 117 in the DHN3 F protein with the corresponding sequence from the LaSota strain. Both rDHN3 and rDHN3-mF are genetically stable during propagation in cell culture and chicken embryos. Further characterization through determination of EID₅₀, MDT and clinical assessments confirmed that rDHN3 is velogenic and rDHN3-mF lentogenic. Vaccination of one-week-old SPF chicks with inactivated rDHN3-mF produced much higher anti-DHN3 antibody response and better protection against live DHN3 challenge than did the commercial LaSota vaccine, providing 100% protection and much earlier viral clearance. This attenuated NDV isolate would merit further development into a vaccine product.

Comparative pathogenicity of two closely related Newcastle disease virus isolates from chicken and pigeon respectively

Newcastle disease (ND), caused by virulent Newcastle disease virus (NDV), is a highly contagious disease that has led to tremendous economic losses worldwide. Pigeon paramyxovirus type 1 (PPMV-1) is an antigenic and host variant of NDV. However, limited in-depth studies are available concerning side-by-side comparison of pathogenicity of PPMV-1 and its phylogenetically close NDV both in chickens and pigeons. To this end, two phylogenetically closely related NDV isolates, Kuwait 256 and JS/07/04/Pi from chicken and pigeon respectively were pathotypically and genotypically characterized in this study. The results indicated that Kuwait 256 was a velogenic strain, while JS/07/04/Pi was a mesogenic strain based on the mean death time of chick embryos (MDT) and intracerebral pathogenicity index in 1-day-old chicks (ICPI). Pathogenicity tests showed that Kuwait 256 caused severe clinical signs and 100 % mortality, while JS/07/04/Pi caused no apparent disease in chickens. Interestingly, both Kuwait 256 and JS/07/04/Pi caused morbidity and mortality in pigeons. Notably, pigeons infected with JS/07/04/Pi exhibited viral shedding for longer time compared to Kuwait 256-infected pigeons. Collectively, the findings of this study suggested that PPMV-1 decreased the pathogenicity in chickens but gained a survival advantage over NDV of chicken origin after its adaptive variation in pigeons based on the previous evidence that PPMV-1 originated from chicken-origin viruses. This study laid the foundation for the elucidation of the molecularmechanism underlying difference in pathogenicity of PPMV-1 and chicken-origin NDV in chickens.

First molecular characterization of avian paramyxovirus-1 (Newcastle disease virus) in Botswana

Avian paramyxovirus-1 (APMV-1), the causative agent of Newcastle disease (ND) in domestic and wild avian species, has recently been reported and characterized in five southern African countries (i.e. Mozambique, Namibia, South Africa, Zambia and Zimbabwe). Since APMV-1s have never been characterized in Botswana, this study was undertaken to determine the genotype circulating in the country. Fourteen samples were collected from ND outbreaks in poultry in 2014, 2018 and 2019 and the complete fusion protein gene was sequenced. Phylogenetic analysis revealed that all of the viruses from Botswana clustered in genotype VII.2 (previously subgenotype VIIh) and that they were more related to viruses from South Africa and Mozambique than the other southern African countries (i.e. Namibia, Zambia and Zimbabwe).

Efficacy of inactivated velogenic Newcastle disease virus genotype VII vaccine in broiler chickens

Newcastle disease (ND) causes severe economic losses in poultry production. Despite the intensive vaccination regimes of NDV in Egypt, many outbreaks are being reported. The present study focused on the preparation and evaluation of inactivated velogenic Newcastle disease virus vaccine (genotype VII) isolated from Egyptian broiler chicken during 2015-2016. Fifty-five tissue samples including trachea, lung, liver, proventriculus, intestine, and kidney collected from commercial broiler chickens were used for virus isolation in specific pathogen-free embryonated chicken eggs (ECE) and identified using RT-PCR and sequencing. The isolates were classified by sequencing as velogenic NDV genotype VIId containing F0 protein cleavage site motifs (¹¹²RRQKRF¹¹⁷). A selected isolate was served as a master seed for the preparation of inactivated NDV vaccine with or without Montanide ISA70 adjuvant and evaluated in SPF chicks. Nine NDV isolates were isolated on ECE and the highest infectivity titer of the virus was 7.50 log₁₀ EID₅₀ mL^-1 by the 5^th passage. Vaccinated chicks with NDV-Montanide ISA70 adjuvanted vaccine exhibited antibody titer of 5.20 log₂ at the 3^rd-week-post-vaccination (WPV) with the highest titer (8.90 log₂ mL^-1) at the 6^th-WPV. Protective antibodies values were persisted to 12^th WPV followed by a gradual decrease to the end of the experiment (16^th weeks). Vaccination of chicks with inactivated NDV isolate without adjuvant failed to induce protective HI antibodies all over the experiment. Chickens vaccinated with the ISA70 adjuvant vaccine were passed homologous challenge tests with 100% protective efficiency, while the unadjuvanted vaccine could not provide any protective efficiency. In conclusion, the preparation of inactivated oil adjuvant vaccine from NDV field circulating strains was efficient in controlling the disease in Egypt.

Cormorants as Potential Victims and Reservoirs of Velogenic Newcastle Disease Virus (Orthoavulavirus-1) in Central Asia

Virulent strains of avian orthoavulavirus 1, historically known as Newcastle disease virus (NDV), are widespread and cause high levels of mortality in poultry worldwide. Wild birds may play an important role in the maintenance of Avian orthoavulavirus 1 in nature. Prior to 2014, most of the lentogenic NDV strains isolated from Central Asia were obtained from the avian order Anseriformes (ducks and geese). Wild birds were monitored from 2014-2016 to detect the circulation of NDV. A total of 1522 samples belonging to 73 avian species were examined, and 26 positive samples were identified. The isolates of Avian orthoavulavirus 1 belonged to three genotypes: viruses from doves (Columbiformes) and cormorants (Suliformes) were attributed to the velogenic genotypes VI and XIII, respectively, while the isolate from poultry belonged to lentogenic genotype I. The isolation of Avian orthoavulavirus 1 from doves may confirm their role as a reservoir of pigeon paramyxoviruses (antigenic variant of the genotype VI NDV) in nature and indicates the potential threat of introduction of velogenic strains into the poultry population. Our study describes an epizootic scenario in Kazakhstan among cormorants with mortality among juveniles of up to 3 wk of age and isolation of the NDV from apparently healthy birds. These observations may support the idea that cormorants are one of the potential reservoirs and victims of velogenic Avian orthoavulavirus 1 in Central Asia. The seasonal migrations of cormorants may partially contribute to viral dissemination throughout the continent; however, this hypothesis needs more evidence.

Development of an Effective and Stable Genotype-Matched Live Attenuated Newcastle Disease Virus Vaccine Based on a Novel Naturally Recombinant Malaysian Isolate Using Reverse Genetics

Genotype VII Newcastle disease viruses are associated with huge economic losses in the global poultry industry. Despite the intensive applications of vaccines, disease outbreaks caused by those viruses continue to occur frequently even among the vaccinated poultry farms. An important factor in the suboptimal protective efficacy of the current vaccines is the genetic mismatch between the prevalent strains and the vaccine strains. Therefore, in the present study, an effective and stable genotype-matched live attenuated Newcastle disease virus (NDV) vaccine was developed using reverse genetics, based on a recently isolated virulent naturally recombinant NDV IBS025/13 Malaysian strain. First of all, the sequence encoding the fusion protein (F) cleavage site of the virus was modified in silico from virulent polybasic (RRQKRF) to avirulent monobasic (GRQGRL) motif. The entire modified sequence was then chemically synthesized and inserted into pOLTV5 transcription vector for virus rescue. A recombinant virus termed mIBS025 was successfully recovered and shown to be highly attenuated based on OIE recommended pathogenicity assessment indices. Furthermore, the virus was shown to remain stably attenuated and retain the avirulent monobasic F cleavage site after 15 consecutive passages in specific-pathogen-free embryonated eggs and 12 passages in one-day-old chicks. More so, the recombinant virus induced a significantly higher hemagglutination inhibition antibody titre than LaSota although both vaccines fully protected chicken against genotype VII NDV induced mortality and morbidity. Finally, mIBS025 was shown to significantly reduce both the duration and quantity of cloacal and oropharyngeal shedding of the challenged genotype VII virus compared to the LaSota vaccine. These findings collectively indicate that mIBS025 provides a better protective efficacy than LaSota and therefore can be used as a promising vaccine candidate against genotype VII NDV strains.

Comparative protective immunity provided by live vaccines of Newcastle disease virus or avian metapneumovirus when co-administered alongside classical and variant strains of infectious bronchitis virus in day-old broiler chicks

This study reports on the simultaneous administration of live NDV or aMPV subtype B vaccines alongside two live IBV (Massachusetts-H120 and 793B-CR88) vaccines in day-old maternal-antibody positive commercial broiler chicks. In the first experiment, chicks were divided into four groups; one unvaccinated and three groups vaccinated with live NDV VG/GA-Avinew, live H120 + CR88, or VG/GA-Avinew + H120 + CR88. In the second experiment, live aMPV subtype B vaccine was used in place of NDV. Clinical signs were monitored daily and oropharyngeal swabs were taken at regular intervals for vaccine virus detection. Blood was collected at 21 dpv for serology. 10 chicks from each group were challenged with virulent strains of M41 or QX or aMPV subtype B. For IBV, after 5 days post challenge (dpc), tracheal ciliary protection was assessed. For aMPV, clinical scores were recorded up to 10 dpc. For NDV, haemagglutination inhibition (HI) antibody titres were assayed as an indicator of protective immunity. In both experiments, ciliary protection for IBV vaccinated groups was maintained above 90%. The protection against virulent aMPV challenge was not compromised when aMPV, H120 and CR88 were co-administered. NDV HI mean titres in single and combined NDV-vaccinated groups remained above the protective titre (>3 log2). Both experiments demonstrated that simultaneous administration of live NDV VG/GA-Avinew or aMPV subtype B alongside H120 and CR88 vaccines does not interfere with protection conferred against NDV, IBV or aMPV.

A class Ⅰ lentogenic newcastle disease virus strain confers effective protection against the prevalent strains

The traditional vaccine strains, such as LaSota, do not completely prevent the shedding of NDV. An ideal vaccine which could not only prevent the clinical signs, but significantly reduce the shedding of NDV is urgently needed for the eradication of ND. In this study, an NDV isolate APMV-1/Chicken/China (SC)/PT3/2016 (hereafter referred as PT3) was identified as a class Ⅰ NDV and a lentogenic strain. The antigenic relationship between PT3 and 3 other NDV strains, including vaccine strain LaSota and 2 prevalent genotype Ⅶd and Ⅵb strains were analyzed. The protective efficacy of PT3 and LaSota against challenge with genotype Ⅶd and Ⅵb strains were assessed. The antigenic analysis result showed that 4 strains belong to the single serotype and the PT3 antiserum exhibited the highest HI titer against 3 other NDV strains. The results of protective efficacy showed that both of LaSota and PT3 could provide 100% survivability for infected chickens. However, PT3 performed better in inducing higher humoral responses and reducing virus shedding than the LaSota strain. Lentogenic strains from Class I NDV appear to be promising vaccine candidates for the control of ND, and allows for the easy discrimination of field NDV and vaccine strains.

Molecular and biological characterization of some circulating strains of Newcastle disease virus in broiler chickens from Eastern Saudi Arabia in 2012-2014

Background and Aim:

Newcastle disease (ND) is a worldwide poultry disease that is historically known to cause severe losses in the poultry industry. In the present study, attempts were made to characterize ND virus (NDV) recovered from broiler chickens in the Eastern Region of Saudi Arabia from January 2012 to March 2014.

Materials and Methods:

Reverse transcription-polymerase chain reaction was used for the detection of NDV followed by partial sequencing of the fusion (F) gene. The intracerebral pathogenicity index (ICPI), mean death time (MDT), and complete sequencing of the hemagglutinin-neuraminidase (HN) gene were also used for further biological and molecular characterization.

Results:

NDV was detected at a rate of 9.6% (11/115) of the tested flocks, most of which were vaccinated against ND. F gene-based phylogeny and motifs of the fusion protein cleavage site (FPCS) showed segregation of Saudi isolates into two groups. The first group contained 10 isolates and was located in genotype II with the lentogenic motif ¹¹²GRQGRL¹¹⁷ at the FPCS. The second group contained one isolate and was located in genotype VII with velogenic motif ¹¹²RRQKRF¹¹⁷. Further characterization using the ICPI and MDT of two representative isolates showed virulence of both tested isolates. Phylogenetic analysis of the HN gene showed close nucleotide identity between the two isolates. A BLAST search for sequences similar to HN gene sequences showed high identity with isolates from the surrounding region.

Conclusion:

The present findings showed a low detection rate of NDV, possibly due to the wide application of vaccines, and the circulation of at least two NDV genotypes, II and VII, in the Eastern Region of Saudi Arabia. The present Saudi isolates may share common ancestors with isolates from the surrounding region.

Characterization of a Novel Avian Avulavirus 1 of Class I isolated from a Mute Swan (Cygnus Olor) in Macedonia in 2012

Avian avulavirus type 1 (AAvV-1) belongs to the family Paramyxoviridae, genus Avulavirus. Even though belonging to a single serotype, there is great genetic variability between these viruses. On the basis of the available complete fusion (F) gene and whole genome sequences and using the genotype classification system, AAvV-1 viruses are divided in two major groups: class I and class II. Class I viruses are predominantly avirulent viruses and majority of the isolations come from waterfowl and domestic poultry from live bird markets in USA and China although isolations from wild birds are reported globally. In our study we used classical, molecular and phylogenetic tools to characterize an AAvV-1 isolated from a mute swan in Macedonia. Based on the complete F gene sequence, we have concluded that the virus designated as AAvV-1/mute swan/Macedonia/546/2012 (KP123431) belongs to the class I of AAvV-1 with an avirulent cleavage site motif 112ERQER*L117. The virus could not be assigned to any of the four currently existing subgenotypes (1a, 1b, 1c or 1d) of the single genotype 1 of class I viruses. Two distant viruses, isolated from goose in Alaska in 1991 and from goose in Ohio in 1987, shared the highest nucleotide sequence identity of the complete F gene with the isolate in our study: 92.7% and 92.8%, respectively. This is the first report of isolation of class I AAvV-1 in Southeastern Europe. The asymptomatic nature and the underreporting of sequences from the class I viruses impede the understanding of the molecular epidemiology and evolution of this group of viruses.

Updated unified phylogenetic classification system and revised nomenclature for Newcastle disease virus

Several Avian paramyxoviruses 1 (synonymous with Newcastle disease virus or NDV, used hereafter) classification systems have been proposed for strain identification and differentiation. These systems pioneered classification efforts; however, they were based on different approaches and lacked objective criteria for the differentiation of isolates. These differences have created discrepancies among systems, rendering discussions and comparisons across studies difficult. Although a system that used objective classification criteria was proposed by Diel and co-workers in 2012, the ample worldwide circulation and constant evolution of NDV, and utilization of only some of the criteria, led to identical naming and/or incorrect assigning of new sub/genotypes. To address these issues, an international consortium of experts was convened to undertake in-depth analyses of NDV genetic diversity. This consortium generated curated, up-to-date, complete fusion gene class I and class II datasets of all known NDV for public use, performed comprehensive phylogenetic neighbor-Joining, maximum-likelihood, Bayesian and nucleotide distance analyses, and compared these inference methods. An updated NDV classification and nomenclature system that incorporates phylogenetic topology, genetic distances, branch support, and epidemiological independence was developed. This new consensus system maintains two NDV classes and existing genotypes, identifies three new class II genotypes, and reduces the number of sub-genotypes. In order to track the ancestry of viruses, a dichotomous naming system for designating sub-genotypes was introduced. In addition, a pilot dataset and sub-trees rooting guidelines for rapid preliminary genotype identification of new isolates are provided. Guidelines for sequence dataset curation and phylogenetic inference, and a detailed comparison between the updated and previous systems are included. To increase the speed of phylogenetic inference and ensure consistency between laboratories, detailed guidelines for the use of a supercomputer are also provided. The proposed unified classification system will facilitate future studies of NDV evolution and epidemiology, and comparison of results obtained across the world.

Investigation of suspected Newcastle disease (ND) outbreaks in Egypt uncovers a high virus velogenic ND virus burden in small-scale holdings and the presence of multiple pathogens

Highly contagious Newcastle disease (ND) is associated with devastating outbreaks with highly variable clinical signs among gallinaceous birds. In this study we aimed to verify clinical ND suspicions in poultry holdings in Egypt suffering from respiratory distress and elevated mortality, comparing two groups of ND-vaccinated poultry holdings in three governorates. Besides testing for Newcastle disease virus (NDV), samples were screened for infectious bronchitis virus (IBV) and avian influenza virus (AIV) by RT-qPCR as well as by non-directed cell-culture approach on LMH-cells. Virulent NDV was confirmed only in group A (n = 16) comprising small-scale holdings. Phylogenetic analysis of the fusion protein gene of 11 NDV-positive samples obtained from this group assigned all viruses to genotype 2.VIIb and point to four different virus populations that were circulating at the same time in one governorate, indicating independent epidemiological events. In group B, comprising large commercial broiler farms (n = 10), virulent NDV was not present, although in six farms NDV vaccine-type virus (genotype 2.II) was detected. Besides, in both groups, co-infections by IBV (n = 10), AIV H9 (n = 3) and/or avian reovirus (ARV) (n = 5) and avian astrovirus (AastVs) (n = 1) could be identified. Taken together, the study confirmed clinical ND suspicion in small scale holdings, pointing to inefficient vaccination practices in this group A. However, it also highlighted that, even in an endemic situation like ND in Egypt, in cases of suspected ND vaccine failure, clinical ND suspicion has to be verified by pathotype-specific diagnostic tests. RESEARCH HIGHLIGHTS Velogenic NDV circulates in small-scale poultry holdings in Egypt. Viral transmission occurred among neighbouring farms and over long distances. Co-infections with multiple pathogens were identified. Pathotype specific diagnostic tests are essential to verify ND suspicions.

A comparative genomic and evolutionary analysis of circulating strains of Avian avulavirus 1 in Pakistan

Newcastle disease, caused by Avian avulavirus 1 (AAvV 1), is endemic to many developing countries around the globe including Pakistan. Frequent epidemics are not uncommon even in vaccinated populations and are largely attributed to the genetic divergence of prevailing isolates and their transmission in the environment. With the strengthening of laboratory capabilities in Pakistan, a number of genetically diverse AAvV 1 strains have recently been isolated and individually characterized in comparison with isolates reported elsewhere in the world. However, there lacks sufficient comparative genomic and phylogenomic analyses of field circulating strains that can elucidate the evolutionary dynamics over a period of time. Herein, we enriched the whole genome sequences of AAvV reported so far (n = 35) from Pakistan and performed comparative genomic, phylogenetic and evolutionary analyses. Based on these analyses, we found only isolates belonging to genotypes VI, VII and XIII of AAvV 1 in a wide range of avian and human hosts. Comparative phylogeny revealed the concurrent circulation of avulaviruses representing different sub-genotypes such as VIg, VIm, VIIa, VIIb, VIIe, VIIf, VIIi, XIIIb and XIIId. We found that the isolates of genotype VII were more closely associated with viruses of genotype XIII than genotype VI. An inter-genotype comparative residue analysis revealed a few substitutions in structurally and functionally important motifs. Putative recombination events were reported for only one of the captive-wild bird (pheasant)-origin isolates. The viruses of genotype VII had a high genetic diversity as compared to isolates from genotypes VI and XIII and, therefore, have more potential to evolve over a period of time. Taken together, the current study provides an insight into the genetic diversity and evolutionary dynamics of AAvV 1 strains circulating in Pakistan. Such findings are expected to facilitate better intervention strategies for the prevention and control of ND in disease-endemic countries across the globe particularly Pakistan.

Epidemiology, control, and prevention of Newcastle disease in endemic regions: Latin America

Newcastle disease (ND) infects wild birds and poultry species worldwide, severely impacting the economics of the poultry industry. ND is especially problematic in Latin America (Mexico, Colombia, Venezuela, and Peru) where it is either endemic or re-emerging. The disease is caused by infections with one of the different strains of virulent avian Newcastle disease virus (NDV), recently renamed Avian avulavirus 1. Here, we describe the molecular epidemiology of Latin American NDVs, current control and prevention methods, including vaccines and vaccination protocols, as well as future strategies for control of ND. Because the productive, cultural, economic, social, and ecological conditions that facilitate poultry endemicity in South America are similar to those in the developing world, most of the problems and control strategies described here are applicable to other continents.

Surveillance and investigative diagnosis of a poultry flock in Great Britain co-infected with an influenza A virus and an avirulent avian avulavirus type 1

A detailed veterinary and laboratory investigation revealed an unusual case of concurrent avian avulavirus type 1 (AAvV-1, formerly called avian paramyxovirus type 1) and low pathogenicity avian influenza (LPAI) virus infections of chickens during March 2010 in a mixed poultry and livestock farm in Great Britain. Respiratory signs and daily mortality of 5-6 birds in a broiler flock 8-weeks of age prompted submission of two carcasses to an Animal and Plant Health Agency (APHA) regional laboratory. Infectious bronchitis virus infection was suspected initially and virus isolation in SPF embryonated fowls' eggs was attempted at APHA-Weybridge. Avirulent AAvV-1 was detected in the first sampling. Both in vitro nucleotide sequencing of the fusion gene and in vivo pathotyping by intracerebral pathogenicity index revealed an avirulent AAvV-1 not definitively ascribed to licensed vaccine. Upon initial detection of the AAvV-1 virus, statutory restrictions were placed on the farm, an official veterinary visit was performed and further samples were submitted to APHA-Weybridge for official statutory disease investigation. An H2N3 LPAI virus was subsequently isolated from tissue samples and swabs submitted from the follow-up statutory investigation. The subtype was confirmed by haemagglutination inhibition test (HAIT) and neuraminidase inhibition (NI) tests on egg-amplified virus. As neither virus was notifiable according to the internationally recognized EU and OIE standards, and/or definitions of disease, statutory farm restrictions were lifted. Veterinary investigations identified the broiler flock to be free-range, next to a river and duck pen, reinforcing the suspicion of wild bird origin for both viruses which may have been co-circulating in ducks. It could not, however, be established as to whether there were separate introductions of the two viruses or whether there had been a single co-introduction of the viruses. The described case highlights the value of integrated surveillance and laboratory approaches, including veterinary field investigations, international standards and definitions of notifiable avian disease, validated RRT-PCR assays, and virus isolation in achieving rapid and accurate diagnostic results.

Development of an avian avulavirus 1 (AAvV-1) L-gene real-time RT-PCR assay using minor groove binding probes for application as a routine diagnostic tool

Newcastle disease is a devastating disease of poultry caused by Newcastle disease virus (NDV), a virulent form of avian avulavirus 1 (AAvV-1). A rapid, sensitive and specific means for the detection of NDV is fundamental for the control of this notifiable transboundary virus. Although several real-time RT-PCR assays exist for the detection of AAvV-1, diagnostic sensitivity and specificities can be sub-optimal. In this study, we describe a modification to an existing AAvV-1 l-gene RT-PCR screening assay, where the original probe set was replaced with minor groove binding (MGB) probes, to create the MGB l-gene assay. The diagnostic sensitivity and specificity of this assay was evaluated against a broad panel of both Class I and Class II AAvV-1 viruses of diverse and representative lineages/genotypes in both clinical samples and amplified viruses, and compared with a number of previously published real-time RT-PCR screening assays for AAvV-1. The MGB l-gene assay outperformed all other assays in this assessment, with enhanced sensitivity and specificity, detecting isolates from a broad range of virus lineages/genotypes (including contemporaneously-circulating strains). The assay has also proved its value for screening original clinical samples for the presence of AAvV-1, thus providing an improved screening assay for routine detection of this notifiable disease agent.

Genotype Diversity of Newcastle Disease Virus in Nigeria: Disease Control Challenges and Future Outlook

Newcastle disease (ND) is one of the most important avian diseases with considerable threat to the productivity of poultry all over the world. The disease is associated with severe respiratory, gastrointestinal, and neurological lesions in chicken leading to high mortality and several other production related losses. The aetiology of the disease is an avian paramyxovirus type-1 or Newcastle disease virus (NDV), whose isolates are serologically grouped into a single serotype but genetically classified into a total of 19 genotypes, owing to the continuous emergence and evolution of the virus. In Nigeria, molecular characterization of NDV is generally very scanty and majorly focuses on the amplification of the partial F gene for genotype assignment. However, with the introduction of the most objective NDV genotyping criteria which utilize complete fusion protein coding sequences in phylogenetic taxonomy, the enormous genetic diversity of the virus in Nigeria became very conspicuous. In this review, we examine the current ecological distribution of various NDV genotypes in Nigeria based on the available complete fusion protein nucleotide sequences (1662 bp) in the NCBI database. We then discuss the challenges of ND control as a result of the wide genetic distance between the currently circulating NDV isolates and the commonest vaccines used to combat the disease in the country. Finally, we suggest future directions in the war against the economically devastating ND in Nigeria.