Intense circulation of A/H5N1 and other avian influenza viruses in Cambodian live-bird markets with serological evidence of sub-clinical human infections

Abstract

Surveillance for avian influenza viruses (AIVs) in poultry and environmental samples was conducted in four live-bird markets in Cambodia from January through November 2013. Through real-time RT-PCR testing, AIVs were detected in 45% of 1048 samples collected throughout the year. Detection rates ranged from 32% and 18% in duck and chicken swabs, respectively, to 75% in carcass wash water samples. Influenza A/H5N1 virus was detected in 79% of samples positive for influenza A virus and 35% of all samples collected. Sequence analysis of full-length haemagglutinin (HA) and neuraminidase (NA) genes from A/H5N1 viruses, and full-genome analysis of six representative isolates, revealed that the clade 1.1.2 reassortant virus associated with Cambodian human cases during 2013 was the only A/H5N1 virus detected during the year. However, multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of HA and NA genes revealed co-circulation of at least nine low pathogenic AIVs from HA1, HA2, HA3, HA4, HA6, HA7, HA9, HA10 and HA11 subtypes. Four repeated serological surveys were conducted throughout the year in a cohort of 125 poultry workers. Serological testing found an overall prevalence of 4.5% and 1.8% for antibodies to A/H5N1 and A/H9N2, respectively. Seroconversion rates of 3.7 and 0.9 cases per 1000 person-months participation were detected for A/H5N1 and A/H9N2, respectively. Peak AIV circulation was associated with the Lunar New Year festival. Knowledge of periods of increased circulation of avian influenza in markets should inform intervention measures such as market cleaning and closures to reduce risk of human infections and emergence of novel AIVs.

Insight into live bird markets of Bangladesh: an overview of the dynamics of transmission of H5N1 and H9N2 avian influenza viruses

“…3 , 4 , 5 , 6 However, in Bangladesh, a country with one of the highest human population densities, where people rely heavily on domestic fowl for both sustenance and income, little is known about what relative effect the live poultry industry has on both the currently circulating strains of AIVs and the risk to the general public. Active surveillance involving the repeat collection of hundreds of samples from poultry and the environment in live bird markets (LBMs) and farms on a monthly basis has enabled infections and outbreaks in Bangladesh to be closely monitored.…”

Seroprevalence and Transmission of Human Influenza A(H5N1) Virus before and after Virus Reassortment, Cambodia, 2006–2014

“…Recent studies, however, have shown a >2.5-fold increase in the circulation of avian H5N1 virus in live bird markets in Cambodia during 2013 compared with 2011 ( 10 , 11 ). The peak in confirmed human infections with H5N1 reassortant virus during 2013-2014 may therefore be linked to this increased circulation of H5N1 reassortant virus among poultry, but it may also reflect improved surveillance in the public health sector because our 2014 seroprevalence study does not suggest increased transmissibility of the virus to humans.…”

Blockage of regulatory T cells augments induction of protective immune responses by influenza virus-like particles in aged mice

“…This requirement, together with the immunosenescence in aged hosts, poses a difficult challenge to the development of an effective influenza vaccine for the aged population. Further elucidation of deficiencies of influenza vaccines and the mechanism of immune protection against influenza virus infection in aged hosts is of high importance for developing more efficacious influenza vaccine to protect the aged population, especially for developing vaccines against emerging highly pathogenic H5N1 as well as H7N9 avian influenza viruses that are now endemic in poultry species and continuing to cause human infections and outbreaks [49, 50]. …”