Characterisation of highly pathogenic avian influenza viruses in Myanmar

Longitudinal Analysis of Influenza A(H5) Sero-Surveillance in Myanmar Ducks, 2006-2019

Between 2006 and 2019, serological surveys in unvaccinated domestic ducks reared outdoors in Myanmar were performed, using a haemagglutination inhibition (HI) test, to confirm H5 avian influenza virus circulation and assess temporal and spatial distribution. Positive test results occurred every year that samples were collected. The annual proportion of positive farms ranged from 7.1% to 77.2%. The results revealed silent/sub-clinical influenza A (H5) virus circulation, even in years and States/Regions with no highly pathogenic avian influenza (HPAI) outbreaks reported. Further analysis of the 2018/19 results revealed considerable differences in seroconversion rates between four targeted States/Regions and between years, and showed seroconversion before and during the sampling period. By the end of the trial, a high proportion of farms were seronegative, leaving birds vulnerable to infection when sold. Positive results likely indicate infection with Gs/GD/96-lineage H5Nx HPAI viruses rather than other H5 subtype low-pathogenicity avian influenza viruses. The findings suggested persistent, but intermittent, circulation of Gs/GD/96-lineage H5Nx HPAI viruses in domestic ducks, despite the veterinary services' outbreak detection and control efforts. The role of wild birds in transmission remains unclear but there is potential for spill-over in both directions. The findings of this study assist the national authorities in the design of appropriate, holistic avian influenza control programs.

Molecular detection and genetic characterization of infectious laryngotracheitis virus in poultry in Myanmar

BACKGROUND

Avian infectious laryngotracheitis (ILT) is a highly contagious viral disease that causes severe economic losses to the poultry industry worldwide. In Southeast Asian countries, including Myanmar, poultry farming is a major industry. Although it is known that infectious respiratory pathogens, including infectious laryngotracheitis virus (ILTV), are a major threat to poultry farms, there are no data currently available on the epidemiology of ILTV in Myanmar. Therefore, in this study, we conducted a molecular detection of ILTV in 20 poultry farms in Myanmar.

RESULTS

Of the 57 tested oropharyngeal swabs, 10 were positive for ILTV by polymerase chain reaction of a 647 bp region of the thymidine kinase (TK) gene, giving a prevalence of ILTV of 17.5% (10/57). Further sequencing analysis of infected cell protein 4 (ICP4) gene and glycoprotein B, G, and J (gB, gG, and gJ) genes indicated that these isolates were field strains. Phylogenetic analysis revealed that the Myanmar strains clustered together in a single branch and were closely related to other reference strains isolated from Asian countries.

CONCLUSIONS

This study demonstrated the presence of ILTV in poultry farms in Myanmar. The genetic characterization analysis performed provides the fundamental data for epidemiological studies that monitor circulating strains of ILTV in Myanmar.

Molecular detection and genetic characterization of Mycoplasma gallisepticum, Mycoplama synoviae, and infectious bronchitis virus in poultry in Myanmar

BACKGROUND

In Southeast Asian countries, including Myanmar, poultry farming is a major industry. In order to manage and maintain stable productivity, it is important to establish policies for biosecurity. Infectious respiratory diseases are a major threat to poultry farming. Avian influenza and Newcastle disease have been reported in Myanmar, but no scientific information is available for other respiratory pathogens, such as mycoplasmas and infectious bronchitis virus (IBV). Identifying the genotypes and serotypes of IBVs is especially important to inform vaccination programs. In this study, we detected Mycoplasma gallisepticum (MG), M. synoviae (MS), and IBV in several poultry farms in Myanmar.

RESULTS

Samples were collected from 20 farms in three major poultry farming areas in Myanmar, and MG, MS, and IBV were detected on two, four, and eight farms, respectively, by polymerase chain reaction. Phylogenetic analysis revealed that the observed MG and MS isolates were not identical to vaccine strains. Three different genotypes of IBV were detected, but none was an unknown variant.

CONCLUSIONS

Mycoplasmas and IBV were detected on poultry farms in Myanmar. Periodic surveillance is required to establish the distribution of each pathogen, and to institute better vaccine protocols.

Avian influenza in the Greater Mekong Subregion, 2003-2018

The persistent circulation of avian influenza viruses (AIVs) is an ongoing problem for many countries in South East Asia, causing large economic losses to both the agricultural and health sectors. This review analyses AIV diversity, evolution and the risk of AIV emergence in humans in countries of the Greater Mekong Subregion (GMS): Cambodia, Laos, Myanmar, Thailand and Vietnam (excluding China). The analysis was based on AIV sequencing data, serological studies, published journal articles and AIV outbreak reports available from January 2003 to December 2018. All countries of the GMS have suffered losses due repeated outbreaks of highly pathogenic (HP) H5N1 that has also caused human cases in all GMS countries. In Laos, Myanmar and Vietnam AIV outbreaks in domestic poultry have also been caused by clade 2.3.4.4 H5N6. A diverse range of low pathogenic AIVs (H1-H12) have been detected in poultry and wild bird species, though surveillance for and characterization of these subtypes is limited. Subtype H3, H4, H6 and H11 viruses have been detected over prolonged periods; whilst H1, H2, H7, H8, H10 and H12 viruses have only been detected transiently. H9 AIVs circulate endemically in Cambodia and Vietnam with seroprevalence data indicating human exposure to H9 AIVs in Cambodia, Thailand and Vietnam. As surveillance studies focus heavily on the detection of H5 AIVs in domestic poultry further research is needed to understand the true level of AIV diversity and the risk AIVs pose to humans in the GMS.

Transmission of an H5N8-Subtype Highly Pathogenic Avian Influenza Virus from Infected Hens to Laid Eggs

We showed here that an H5N8-subtype highly pathogenic avian influenza virus (HPAIV) was transmitted to both the internal contents and shells of eggs laid by white leghorn hens experimentally infected with the virus. Seven of eight HPAIV-infected hens laid eggs until 4 days postinoculation (dpi). The mean number of eggs laid per head daily decreased significantly from 0.58 before inoculation to 0.18 after viral inoculation. The virus was detected in the eggs laid by three of the seven hens. Viral transmission was detectable beginning on 3 dpi, and virus titers in tracheal and cloacal swabs from the hens that laid the contaminated eggs exceeded 2.9 log10 EID50. The level of viral replication and its timing when virus replicates enough to be detected in oviduct after virus inoculation appear to be key factors in the transmission of H5N8 HPAIV from infected hens to laid eggs.

Investigating a crow die-off in January-February 2011 during the introduction of a new clade of highly pathogenic avian influenza virus H5N1 into Bangladesh

We investigated unusual crow mortality in Bangladesh during January-February 2011 at two sites. Crows of two species, Corvus splendens and C. macrorhynchos, were found sick and dead during the outbreaks. In selected crow roosts, morbidity was ~1 % and mortality was ~4 % during the investigation. Highly pathogenic avian influenza virus H5N1 clade 2.3.2.1 was isolated from dead crows. All isolates were closely related to A/duck/India/02CA10/2011 (H5N1) with 99.8 % and A/crow/Bangladesh/11rs1984-15/2011 (H5N1) virus with 99 % nucleotide sequence identity in their HA genes. The phylogenetic cluster of Bangladesh viruses suggested a common ancestor with viruses found in poultry from India, Myanmar and Nepal. Histopathological changes and immunohistochemistry staining in brain, pancreas, liver, heart, kidney, bursa of Fabricius, rectum, and cloaca were consistent with influenza virus infection. Through our limited investigation in domesticated birds near the crow roosts, we did not identify any samples that tested positive for influenza virus A/H5N1. However, environmental samples collected from live-bird markets near an outbreak site during the month of the outbreaks tested very weakly positive for influenza virus A/H5N1 in clade 2.3.2.1-specific rRT-PCR. Continuation of surveillance in wild and domestic birds may identify evolution of new avian influenza virus and associated public-health risks.

Epidemiology of Highly Pathogenic Avian Influenza Virus Strain Type H5N1

Highly pathogenic avian influenza (HPAI) is a severe disease of poultry. It is highly transmissible with a flock mortality rate approaching 100% in vulnerable species (Capua et al. 2007a). Due to the potentially disastrous impact the disease can have on affected poultry sectors, HPAI has received huge attention and is classified as a notifiable disease by the World Organisation for Animal Health (OIE).

Implications of global and regional patterns of highly pathogenic avian influenza virus H5N1 clades for risk management

This paper analyses the publicly available data on the distribution and evolution of highly pathogenic avian influenza virus (HPAIV) H5N1 clades, whilst acknowledging the biases resulting from the non-random selection of isolates for gene sequencing. The data indicate molecular heterogeneity in the global distribution of HPAIV H5N1, in particular in different parts of East and Southeast Asia. Analysis of the temporal pattern of haemagglutinin clade data shows a progression from clade 0 (the 'dominant' clade between 1996 and 2002) to clade 1 (2003-2005) and then to clade 2.3.4 (2005 onwards). This process continuously produces variants, depending on the frequency of virus multiplication in the host population, which is influenced by geographical variation in poultry density, poultry production systems and also HPAI risk management measures such as vaccination. Increased multilateral collaboration needs to focus on developing enhanced disease surveillance and control targeted at evolutionary 'hotspots'.