Epidemiology and Evolutionary Dynamics of High Pathogenicity Avian Influenza (HPAI) H5N1 in Bangladesh

Abstract

Understanding disease clustering and transmission patterns improves the prevention and control of disease. Herein, we described the epizootic characteristics and spatiotemporal dynamics of High Pathogenicity Avian Influenza (HPAI) H5N1 outbreaks as well as clade diversity and phylodynamics of H5N1 over time and across host species in Bangladesh. We used Moran’s I, Geary’s C, Getis-Ord Gi∗, and a space-time permutation model to analyze the spatiotemporal patterns of H5N1 outbreaks. We used Bayesian phylogenetic analysis to generate a time-scaled maximum clade credibility (MCC) tree. Our study revealed nine HPAI H5N1 epizootic waves between 2007 and 2020 that invariably peaked in the wintertime. After vaccination of poultry against H5N1 was introduced in 2012, the incidence of HPAI H5N1 outbreaks and poultry mortality decreased significantly over time. Nonetheless, our research revealed that the virus continued circulating unabatedly in Bangladesh. The various spatiotemporal analyses were identified up to nine space-time clusters across Bangladesh, with the most significant clustering and hotspots of H5N1 outbreaks in and around the district of Dhaka. Since 2007, four H5N1 clades have been detected in Bangladesh, with only clade 2.3.2.1a continuing to circulate since 2011, which was followed up by the reassorted clade 2.3.2.1a in 2012. The HA gene of the H5N1 clade 2.3.2.1a has been reassorted into at least nine subgroups (R1–R9). After 2016, the first eight groups disappeared, with only the R9 group remaining. Spatiotemporal patterns and phylodynamics of H5N1 outbreaks are crucial for developing targeted and appropriate HPAI control and prevention measures. We recommended intensive monitoring of biosecurity measures and disease records in high-priority areas, along with assessing vaccine efficacy to better control HPAI outbreaks in Bangladesh.

The role of vaccination and environmental factors on outbreaks of high pathogenicity avian influenza H5N1 in Bangladesh

“…In case flocks are found infected, the virus should be stamped out to stop the spread. This means that vaccination should also be accompanied by improved farm and LBM biosecurity practices to reduce the chance of infection, even in vaccinated populations [ 8 , 83 ]. Additionally, vaccination against H5N1 in Bangladesh is currently focused on commercial chicken farms, while 9.7% of HPAI outbreaks are reported in backyard chickens [ 8 ].…”

“…This means that vaccination should also be accompanied by improved farm and LBM biosecurity practices to reduce the chance of infection, even in vaccinated populations [ 8 , 83 ]. Additionally, vaccination against H5N1 in Bangladesh is currently focused on commercial chicken farms, while 9.7% of HPAI outbreaks are reported in backyard chickens [ 8 ]. Furthermore, domestic ducks appear to be an important host reservoir and may play a central role in the maintenance, amplification, and spread of HPAI viruses in Bangladesh [ 84 , 85 ].…”

“…Since October 2021, viruses belonging to Clade 2.3.4.4b have caused a panzootic of unprecedented magnitude, spreading to all continents except Australia and Antarctica, thus far leading to the loss of more than half a billion poultry and high mortality across a great variety of species of wild birds [ [4] , [5] , [6] ]. Furthermore, HPAI H5N1, including the present panzootic clade 2.3.4.4b H5N1 viruses, have demonstrated the ability to cross the barrier between birds and mammals, resulting in infections in humans and other mammalian species [ [6] , [7] , [8] ], including a range of marine mammal species (such as south American sea lions, harbor seals, porpoises and dolphins) [ 9 , 10 ]. Since its emergence, the virus has led to at least 878 laboratory-confirmed human cases in 23 different countries [ 8 , 11 ].…”

“…Furthermore, HPAI H5N1, including the present panzootic clade 2.3.4.4b H5N1 viruses, have demonstrated the ability to cross the barrier between birds and mammals, resulting in infections in humans and other mammalian species [ [6] , [7] , [8] ], including a range of marine mammal species (such as south American sea lions, harbor seals, porpoises and dolphins) [ 9 , 10 ]. Since its emergence, the virus has led to at least 878 laboratory-confirmed human cases in 23 different countries [ 8 , 11 ]. This event has increased calls to implement poultry vaccination against HPAI more widely [ 5 , 12 ].…”

Association of biosecurity and hygiene practices with avian influenza A/H5 and A/H9 virus infections in turkey farms

“…There have been increased reports of both HPAI and low pathogenicity avian influenza (LPAI) in the Southeast Asian poultry industry ( 5 , 6 ), including Bangladesh, affecting various poultry production systems ( 7 , 8 ). Since the first reported HPAI H5N1 outbreak in poultry in Bangladesh ( 9 ), more than 580 HPAI H5N1 outbreaks have been recorded in poultry and wild birds in Bangladesh ( 10 , 11 ), where the maximum cases originated from commercial poultry farms ( 12 ). In Bangladesh, people come into close contact with poultry in different production systems ( 13 , 14 ), which enhances the transmission of avian influenza viruses (AIVs) from birds to humans.…”