Circulation of highly pathogenic avian influenza A/H5N1 in Savar and Dhamrai Upazila, Dhaka Bangladesh

Résumé fourni par la source

Bangladesh has experienced outbreaks of avian influenza(AI) frequently from 2007 until 2012 and thereafter only sporadic outbreaks were reported. In January 2017, a cluster of sick and dead poultry in Dhamrai Upazila was reported to Department of Livestock Services. The government reference laboratory confirmed Influenza A (H5N1) and notified to OIE. Subsequently, a joint investigation between the USAID PREDICT team and the Government of Bangladesh was conducted in Savar and Dhamrai to determine the extent of the outbreak and whether HPAI, including other subtypes, has been circulating in LBMs and among the wild birds and to identify the possible sources of AI for the reported event. The team surveyed nearby all live bird markets (LBM) in Savar and Dhamrai Upazila in Dhaka District and extended up to 24km radius in outbreak areas. Oropharyngeal and cloacal swab samples from dead crows (N=3) and environmental swab samples from LBMs (N=77) were collected. All swabs tested by real-time RT-PCR for Influenza-A (M gene) H5, H7, H9 and N1. Samples are also being tested using PREDICT’s pan-influenza consensus PCR to detect any additional subtypes that may be circulating. The team observed crows feeding on poultry wastage in neighboring LBMs and results expressed that, in crow 100% (n=3; 95%CI: 29-100) were positive for influenza A/H5N1. None of the LBM and crow samples were positive for H7 subtypes. Of the 77 environmental samples, 40% (95%CI: 29-52) were positive for influenza-A, including: A/H5 8% (n=6; 95%CI:3-16), A/H9 9% (n=7; 95%CI: 4-18) and A/untypable 23% (n=18; 95%CI:14-34). Twenty six percent of urban LBMs (n=23; 95%CI:10.2-48.4) were positive for influenza A/H5 and none of rural (n=22) LBMs were positive for A/H5. Presence of waterfowl having higher (75%; n=4; 95%CI:19- 99) A/H5 positive than others (7%; n=41; 95%CI: 2-20). The LBMs within 7km from the outbreak farm were found higher positive for A/H5 (28%; n= 18; 95%CI:10-53) compared to LBMs beyond the 7km (4%; n=27; 95%CI: 0-19). H5 positive LBM samples were tested for N1; results revealed that 50% H5 (n=6; 95%CI: 12-89) were positive for N1 and the remaining were negative which indicates that other N types might be co-circulating in LBMs. The evidence of a relationship between animals & humans in the disease or its transmission was not found. No human cases were reported. Our findings suggest that low pathogenicity and highly pathogenic avian influenza viruses are circulating in in LBMs. In a response to an outbreak of influenza A on a farm, we found that influenza A appears to be circulating in LBMs and crows. Consensus PCR assays that detect all Influenza A subtypes may be useful in identifying novel or less common subtypes.