Are poultry or wild birds the main reservoirs for avian influenza in Bangladesh?

Avian influenza viruses (AIV) are of great socioeconomic and health concern, notably in Southeast Asia where highly pathogenic strains, such as highly pathogenic avian influenza (HPAI) H5N1 and other H5 and H7 AIVs, continue to occur. Wild bird migrants are often implicated in the maintenance and spread of AIV. However, little systematic surveillance of wild birds has been conducted in Southeast Asia to evaluate whether the prevalence of AIV in wild birds is higher than in other parts of the world where HPAI outbreaks occur less frequently. Across Bangladesh, we randomly sampled a total of 3585 wild and domestic birds to assess the prevalence of AIV and antibodies against AIV and compared these with prevalence levels found in other endemic and non-endemic countries. Our study showed that both resident and migratory wild birds in Bangladesh do not have a particularly elevated AIV prevalence and AIV sero-prevalence compared to wild birds from regions in the world where H5N1 is not endemic and fewer AIV outbreaks in poultry occur. Like elsewhere, notably wild birds of the orders Anseriformes were identified as the main wild bird reservoir, although we found exceptionally high sero-prevalence in one representative of the order Passeriformes, the house crow (Corvus splendens), importantly living on offal from live bird markets. This finding, together with high sero- and viral prevalence levels of AIV in domestic birds, suggests that wild birds are not at the base of the perpetuation of AIV problems in the local poultry sector, but may easily become victim to AIV spill back from poultry into some species of wild birds, potentially assisting in further spread of the virus

Modelling H5N1 in Bangladesh across spatial scales : model complexity and zoonotic transmission risk

Highly pathogenic avian influenza H5N1 remains a persistent public health threat, capable of causing infection in humans with a high mortality rate while simultaneously negatively impacting the livestock industry. A central question is to determine regions that are likely sources of newly emerging influenza strains with pandemic causing potential. A suitable candidate is Bangladesh, being one of the most densely populated countries in the world and having an intensifying farming system. It is therefore vital to establish the key factors, specific to Bangladesh, that enable both continued transmission within poultry and spillover across the human–animal interface. We apply a modelling framework to H5N1 epidemics in the Dhaka region of Bangladesh, occurring from 2007 onwards, that resulted in large outbreaks in the poultry sector and a limited number of confirmed human cases. This model consisted of separate poultry transmission and zoonotic transmission components. Utilising poultry farm spatial and population information a set of competing nested models of varying complexity were fitted to the observed case data, with parameter inference carried out using Bayesian methodology and goodness-of-fit verified by stochastic simulations. For the poultry transmission component, successfully identifying a model of minimal complexity, which enabled the accurate prediction of the size and spatial distribution of cases in H5N1 outbreaks, was found to be dependent on the administration level being analysed. A consistent outcome of non-optimal reporting of infected premises materialised in each poultry epidemic of interest, though across the outbreaks analysed there were substantial differences in the estimated transmission parameters. The zoonotic transmission component found the main contributor to spillover transmission of H5N1 in Bangladesh was found to differ from one poultry epidemic to another. We conclude by discussing possible explanations for these discrepancies in transmission behaviour between epidemics, such as changes in surveillance sensitivity and biosecurity practices

The impact of surveillance and control on highly pathogenic avian influenza outbreaks in poultry in Dhaka division, Bangladesh

In Bangladesh, the poultry industry is an economically and socially important sector, but it is persistently threatened by the effects of H5N1 highly pathogenic avian influenza. Thus, identifying the optimal control policy in response to an emerging disease outbreak is a key challenge for policy-makers. To inform this aim, a common approach is to carry out simulation studies comparing plausible strategies, while accounting for known capacity restrictions. In this study we perform simulations of a previously developed H5N1 influenza transmission model framework, fitted to two separate historical outbreaks, to assess specific control objectives related to the burden or duration of H5N1 outbreaks among poultry farms in the Dhaka division of Bangladesh. In particular, we explore the optimal implementation of ring culling, ring vaccination and active surveillance measures when presuming disease transmission predominately occurs from premises-to-premises, versus a setting requiring the inclusion of external factors. Additionally, we determine the sensitivity of the management actions under consideration to differing levels of capacity constraints and outbreaks with disparate transmission dynamics. While we find that reactive culling and vaccination policies should pay close attention to these factors to ensure intervention targeting is optimised, across multiple settings the top performing control action amongst those under consideration were targeted proactive surveillance schemes. Our findings may advise the type of control measure, plus its intensity, that could potentially be applied in the event of a developing outbreak of H5N1 amongst originally H5N1 virus-free commercially-reared poultry in the Dhaka division of Bangladesh

Monthly distribution of animal diseases and vaccination status in Bangladesh, 2010–2012.

<p>It represents the estimated number of diagnosed cases and vaccination of anthrax, foot and mouth disease, haemorrhagic septicaemia, peste des petits ruminants and dog bite/rabies reported in livestock (cattle, goats, sheep and buffaloes) in the country.</p

Species distribution of estimated number of diagnosed cases and death cases of anthrax, foot and mouth disease, haemorrhagic septicaemia, peste des petits ruminants and dog bite/rabies in livestock in Bangladesh, 2010–2012.

δ<p>Abbreviated: FMD = Foot and mouth disease, HS = Haemorrhagic septicaemia, PPR = Peste des petits ruminants.</p>θ<p>CFR = Case fatality rate.</p><p>*Statistically significant at the p<0.01 level.</p

A Retrospective Study on the Epidemiology of Anthrax, Foot and Mouth Disease, Haemorrhagic Septicaemia, Peste des Petits Ruminants and Rabies in Bangladesh, 2010-2012

<div><p>Anthrax, foot and mouth disease (FMD), haemorrhagic septicaemia (HS), peste des petits ruminants (PPR) and rabies are considered to be endemic in Bangladesh. This retrospective study was conducted to understand the geographic and seasonal distribution of these major infectious diseases in livestock based on data collected through passive surveillance from 1 January 2010 to 31 December 2012. Data analysis for this period revealed 5,937 cases of anthrax, 300,333 of FMD, 13,436 of HS, 247,783 of PPR and 14,085 cases of dog bite/rabies. While diseases were reported in almost every district of the country, the highest frequency of occurrence corresponded to the susceptible livestock population in the respective districts. There was no significant difference in the disease occurrences between districts bordering India/Myanmar and non-border districts (p>0.05). Significantly higher (p<0.01) numbers of anthrax (84.5%), FMD (88.3%), HS (84.9%) and dog bite/rabies (64.3%) cases were reported in cattle than any other species. PPR cases were reported mostly (94.8%) in goats with only isolated cases (5.2%) in sheep. The diseases occur throughout the year with peak numbers reported during June through September and lowest during December through April, with significant differences (p<0.01) between the months. The annual usages of vaccines for anthrax, FMD, HS and PPR were only 7.31%, 0.61%, 0.84% and 11.59% of the susceptible livestock population, respectively. Prophylactic vaccination against rabies was 21.16% of cases. There were significant differences (p<0.01) in the administration of anthrax, FMD and HS vaccines between border and non-border districts, but not PPR or rabies vaccines. We recommend that surveillance and reporting of these diseases need to be improved throughout the country. Furthermore, all suspected clinical cases should be confirmed by laboratory examination. The findings of this study can be used in the formulation of more effective disease management and control strategies, including appropriate vaccination policies in Bangladesh.</p></div

Estimated number of diagnosed cases, death cases and vaccination coverage of anthrax, foot and mouth disease, haemorrhagic septicaemia, peste des petits ruminants and dog bite/rabies in livestock (cattle, goats, sheep and buffaloes) in Bangladesh, 2010–2012.

<p>*CI = Confidence intervals.</p>δ<p>Calculated based on the number of livestock (cattle, buffaloes, sheep and goats) examined, which is 1,576,562 in 2010; 1,896,815 in 2011; and 1,255,145 in 2012 (only sheep and goats 576,936 in 2010; 695,845 in 2011; and 415,007 in 2012).</p>†<p>Calculated based on susceptible livestock population (buffaloes, cattle, goats and sheep) in Bangladesh, which is 42,594,399 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104435#pone.0104435-BangladeshBureauof1" target="_blank">[5]</a>.</p>‡<p>Calculated based on goat and sheep population only, which is 17,459,061 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104435#pone.0104435-BangladeshBureauof1" target="_blank">[5]</a>.</p>θ<p>The term “dog bite” is used for a suspected rabies case as every animal bite (mostly dog bite) is potentially suspected as rabid animal bite, as the rabies control program in animals is nonexistent in Bangladesh <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104435#pone.0104435-Hossain1" target="_blank">[22]</a>.</p><p>Calculated based on reported dog bite cases assuming that all death cases are from rabies.</p

Map of Bangladesh showing 64 districts (top left): 1) Bagerhat, 2) Bandarban, 3) Barguna, 4) Barisal, 5) Bhola, 6) Bogra, 7) Brahmanbaria, 8) Chandpur, 9) Chittagong, 10) Chuadanga, 11) Comilla, 12) Cox’s Bazar, 13) Dhaka (the capital), 14) Dinajpur, 15) Faridpur, 16) Feni, 17) Gaibandha, 18) Gazipur, 19) Gopalganj, 20) Habiganj, 21) Jamalpur, 22) Jessore, 23) Jhalokathi, 24) Jhenaidaha, 25) Joypurhat, 26) Khagrachhari, 27) Khulna, 28) Kishoreganj, 29) Kurigram, 30) Kushtia, 31) Laksmipur, 32) Lalmonirhat, 33) Madaripur, 34) Magura, 35) Manikganj, 36) Meherpur, 37) Moulvibazar, 38) Munshiganj, 39) Mymensingh, 40) Naogaon, 41) Narail, 42) Narayanganj, 43) Natore, 44) Nawabganj, 45) Netrokona, 46) Nilphamari, 47) Noakhali, 48) Norsingdi, 49) Pabna, 50) Panchgarh, 51) Patuakhali, 52) Pirojpur, 53) Rajbari, 54) Rajshahi, 55) Rangamati, 56) Rangour, 57) Satkhira, 58) Shariatpur, 59) Sherpur, 60) Sirajganj, 61) Sunamganj, 62) Sylhet, 63) Tangail, 64) Thakurgaon.

<p>The maps illustrate district distribution of the estimated number of diagnosed cases of anthrax, foot and mouth disease, haemorrhagic septicaemia, peste des petits ruminants and dog bite/rabies cases reported in livestock (cattle, goats, sheep and buffaloes) in the country, 2010–12.</p

Modeling and roles of meteorological factors in outbreaks of highly pathogenic avian influenza H5N1.

The highly pathogenic avian influenza A virus subtype H5N1 (HPAI H5N1) is a deadly zoonotic pathogen. Its persistence in poultry in several countries is a potential threat: a mutant or genetically reassorted progenitor might cause a human pandemic. Its world-wide eradication from poultry is important to protect public health. The global trend of outbreaks of influenza attributable to HPAI H5N1 shows a clear seasonality. Meteorological factors might be associated with such trend but have not been studied. For the first time, we analyze the role of meteorological factors in the occurrences of HPAI outbreaks in Bangladesh. We employed autoregressive integrated moving average (ARIMA) and multiplicative seasonal autoregressive integrated moving average (SARIMA) to assess the roles of different meteorological factors in outbreaks of HPAI. Outbreaks were modeled best when multiplicative seasonality was incorporated. Incorporation of any meteorological variable(s) as inputs did not improve the performance of any multivariable models, but relative humidity (RH) was a significant covariate in several ARIMA and SARIMA models with different autoregressive and moving average orders. The variable cloud cover was also a significant covariate in two SARIMA models, but air temperature along with RH might be a predictor when moving average (MA) order at lag 1 month is considered