Vitamin A dietary supplementation reduces the mortality of velogenic Newcastle disease significantly in cockerels

Newcastle Disease Genotype VII Prevalence in Poultry and Wild Birds in Egypt

Newcastle Disease Virus (NDV) genotype VII is a highly pathogenic Orthoavulavirus that has caused multiple outbreaks among poultry in Egypt since 2011. This study aimed to observe the prevalence and genetic diversity of NDV prevailing in domestic and wild birds in Egyptian governorates. A total of 37 oropharyngeal swabs from wild birds and 101 swabs from domestic bird flocks including chickens, ducks, turkeys, and pelicans, were collected from different geographic regions within 13 governorates during 2019–2020. Virus isolation and propagation via embryonated eggs revealed 91 swab samples produced allantoic fluid containing haemagglutination activity, suggestive of virus presence. The use of RT-PCR targeted to the F gene successfully detected NDV in 85 samples. The geographical prevalence of NDV was isolated in 12 governorates in domestic birds, migratory, and non-migratory wild birds. Following whole genome sequencing, we assembled six NDV genome sequences (70–99% of genome coverage), including five full F gene sequences. All NDV strains carried high virulence, with phylogenetic analysis revealing that the strains belonged to class II within genotype VII.1.1. The genetically similar yet geographically distinct virulent NDV isolates in poultry and a wild bird may allude to an external role contributing to the dissemination of NDV in poultry populations across Egypt. One such contribution may be the migratory behaviour of wild birds; however further investigation must be implemented to support the findings of this study. Additionally, continued genomic surveillance in both wild birds and poultry would be necessary for monitoring NDV dissemination and genetic diversification across Egypt, with the aim of controlling the disease and protecting poultry production.

Seroprevalence and risk factors of Newcastle disease virus in local chickens in Njombe and Bahi districts in Tanzania

Newcastle disease virus (NDV) causes significant losses of poultry in Tanzania. Like in many African countries, the regular surveillance of NDV is important for the control of disease. The objective of this study was to determine seroprevalence of NDV in unvaccinated backyard poultry in Bahi and Njombe districts of Tanzania over the rainy (May) and dry (November) seasons in 2016. Using hemaglutination inhibition test, the overall seroprevalence was determined to be 26.8%. The significant differences in seroprevalence were between seasons (higher (34.9%) in dry season, p < 0.0001) and age (higher (30.3%), p < 0.0001 in adult birds). There were no significant differences in seroprevalence between the districts or sex. The higher levels of "protective" antibody titers were significantly associated with location: Njombe (RR 1.15), dry season (RR 1.08), and age: adult birds (RR 1.16); however, the prevalence of these titers was not high enough to conclude any herd immunity among these flocks. This study therefore concludes that local chickens are naturally exposed to NDV and the birds in highlands, dry season, and adults are more protected. Future studies focusing on transmission, strain type, and monthly dynamics of NDV in backyard flocks will provide greater insight into the disease dynamics and allow new practical strategies to alleviate the effects of NDV for the smallholder farmers.

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.

Pathology of Komarov vaccine in Hitchner B1 vaccinated and unvaccinated broilers

Newcastle disease (ND) is a major problem of poultry production worldwide. Control is by biosecurity and vaccination. In this project, we studied the pathology of Komarov vaccine which is commonly used in many countries of Africa on the Hitchner B1 (HBI) vaccinated and unvaccinated broilers. Seventy-five Arbor Acres broilers were obtained at 1 day old. Twenty-five of the broilers were given HB1 vaccine at the hatchery and Komarov vaccine at 5 weeks of age (group HK). A second group of 25 broilers were given only Komarov vaccine at 5 weeks of age (group K). The third group remained as unvaccinated (UU). All the groups were observed for clinical signs and lesions. Depression, sneezing, coughing and noisy respiration were observed in group K broilers from day 2 post Komarov vaccination (PKV). Leg paralysis occurred in 6 broilers on day 8 PKV. The clinical signs were milder in the HK broilers. Only one broiler showed leg paralysis in this group on day 18 PKV. No mortality occurred in the three groups. The bursa, spleen and thymus showed mild to moderate enlargement, atrophy and depletion of lymphocytes on days 3, 5, 8 and 14 PKV in HK and K groups. The trachea and lungs were congested. The haemagglutination inhibition (HI) antibody titres in the K group were higher than those of HK and UU groups on days 7, 24 and 21 PKV. The above observations show that Komarov vaccine may cause no mortality in vaccinated and unvaccinated broilers and higher HI antibodies are produced in broilers that have not been vaccinated earlier.

Infection-Associated Thymic Atrophy

The thymus is a vital organ of the immune system that plays an essential role in thymocyte development and maturation. Thymic atrophy occurs with age (physiological thymic atrophy) or as a result of viral, bacterial, parasitic or fungal infection (pathological thymic atrophy). Thymic atrophy directly results in loss of thymocytes and/or destruction of the thymic architecture, and indirectly leads to a decrease in naïve T cells and limited T cell receptor diversity. Thus, it is important to recognize the causes and mechanisms that induce thymic atrophy. In this review, we highlight current progress in infection-associated pathogenic thymic atrophy and discuss its possible mechanisms. In addition, we discuss whether extracellular vesicles/exosomes could be potential carriers of pathogenic substances to the thymus, and potential drugs for the treatment of thymic atrophy. Having acknowledged that most current research is limited to serological aspects, we look forward to the possibility of extending future work regarding the impact of neural modulation on thymic atrophy.

Triple La Sota re-vaccinations can protect laying chickens for 3 months against drop in egg production caused by velogenic viscerotropic Newcastle disease virus infection

One hundred and ten Isa Brown layers were vaccinated with La Sota, once at point of lay at 18 weeks and three times at peak of lay which occurred at 27–29 weeks of age. Thereafter, they were weekly monitored for haemagglutination inhibition (HI) antibody decline. The first batch A of the layers were challenged with velogenic viscerotropic Newcastle disease (vvND) virus (vvNDV) on day 24 post‐vaccination (PV), when the geometric mean titre (GMT) was 84.4, batch B were challenged on day 48 PV at GMT of 42.2, while batch C were challenged on day 97 PV at GMT of 21.1. The individual chicken HI antibody titres of the 10 layers in batch C at the day of challenge were: 7 layers had HI titres of 16, 2 layers had HI titres of 32 and 1 layer had HI titres of 64. Each challenge in the three batches produced no clinical signs including drop in egg production. But there was initial swelling of the spleen followed by atrophy with high antibody responses. The virus was recovered in all the cloacal swabs on days 3–9 post‐challenge (PC) at low titres. On days 145 PV and 48, post‐Batch C challenge the remaining hyperimmunized unchallenged layers demonstrated a drop in total % egg production (p < .05) and changes in egg quality. The HI GMT was 256. The virus was recovered in all the cloacal swabs on days 3–9 following appearance of clinical signs. There was no mortality in the experiment. Based on the above observations, it is concluded that triple La Sota re‐vaccination can protect layers against a drop in egg production in areas where vvNDV infection is enzootic.

La Sota vaccination may not protect against virus shedding and the lesions of velogenic Newcastle disease in commercial turkeys

The aim of this project is to study the clinical signs and lesion of velogenic Newcastle disease (vND) in commercial turkeys, and also to find out if La Sota vaccination offered protection against these signs and lesions. The cockerels were included as positive controls. One hundred and twenty turkey poults and cockerels were divided into eight groups as follows: unvaccinated unchallenged turkeys (UUT), unvaccinated challenged turkeys (UCT), vaccinated unchallenged turkeys (VUT), vaccinated challenged turkeys (VCT), and along the same lines, the cockerel groups were UUC, UCC, VUC and vaccinated challenged cockerels (VCC). Vaccination was at 3 weeks of age while challenge was at 6 weeks of age. The unvaccinated turkeys and cockerels (UCT and UCC) showed different degrees of depression, diarrhoea and later paralysis at challenge. Total mortality was 100% in cockerels within 6 days, but 60% in turkeys. Similar but milder clinical signs were found in the VCC with a total mortality of 13.3%. The VCT showed mild drop in feed and water consumption, and no mortality. All the challenged groups had significant (p < 0.05) loss of weight when compared with their controls. Necropsy showed that while the UCC had severe proventricular haemorrhages, intestinal and caecal tonsil ulcers, the UCT had no digestive tract lesion. There was severe atrophy of the lymphoid organs in all the challenged groups. Histopathological sections of the bursa, spleen and thymus in all the challenged groups with special emphasis on the vaccinated and unvaccinated turkeys with mortalities of 0 and 60%, respectively, had very severe necrosis and depletion of the lymphoid tissue. Virus was isolated from the cloacal swabs. The haemagglutination inhibition antibodies were significantly higher (p < 0.05) in the challenged groups than the unchallenged. The above observations in the intestinal tracts of UCT are of diagnostic significance while the gross and microscopic lesions in the UCT and VCT show that La Sota vaccination may not protect turkeys against the destruction of the lymphoid organs by vND as earlier reported in chickens. This may lead to immunosuppression and production problems in areas where vND is enzootic.

Atrophy of the lymphoid organs and suppression of antibody response caused by velogenic Newcastle disease virus infection in chickens

This project was undertaken to study the immunosuppressive capabilities of velogenic viscerotropic pathotype of Newcastle disease virus (VVNDV) infection in cockerels. Two hundred six-week-old cockerels were divided into four groups. Groups B/VUC and C/VC were vaccinated with LaSota in drinking water at 6 weeks of age. Groups C/VC and D/UC were challenged with VVNDV at 8 weeks of age. Three days post challenge (PC), the cockerels in group D/UC came down with clinical signs which included depression and greenish diarrhoea. Total mortality was 74.6 %. The C/VC cockerels showed no clinical signs. But both challenged groups showed significant weight loss, significant loss of total serum proteins, globulin and albumen (P < 0.05). These losses were more severe in the D/UC than in the C/VC. There was severe atrophy of the bursa, spleen and thymus in both groups. Histopathology showed severe necrosis and depletion of the lymphocytes in the three lymphoid organs. However, the lesions were more severe in the D/UC than in C/VC cockerels. On day 28, PC groups B/VUC, C/VIC and D/UIC were revaccinated with LaSota. The haemagglutination inhibition antibody response on days 35, 42 and 49 PC was very low in groups C/VIC and D/UIC when compared with B/VUC cockerels. These observations show that VVNDV infection both clinical and subclinical can cause immunosuppression and vaccine failure due to severe destruction of the lymphocytes in the lymphoid organs. This will be a serious problem for poultry production in those countries where the disease is enzootic.