Friday, July 22, 2016

Sci Rpts: Intense Circulation Of A/H5N1 In Cambodian LBMs & Evidence Of Subclinical Human Infection

Cambodia's H5N1 surge


Between 2011 and 2014 Cambodia reported a significant surge in human H5N1 infections, primarily among young children.  In the previous 6 years (2005-2010) they had only reported a total of 10 cases, but between 2011 and 2014, they reported 46 new cases and 29 deaths. 

In 2013 we saw reports suggesting a new reassortment of H5N1 (between clade 1.1 and clade viruses) had emerged in Cambodia (see Cambodia’s H5N1 Surge & the `M’ Word), although its role in this spike in human cases remains unknown. 

Then - just as abruptly as it began - Cambodia's H5N1 surge ceased, and we've not seen a case reported there since the spring of 2014.

Whether the circulating virus mutated to a less virulent strain, or local public health education efforts were finally successful in halting transmission, or perhaps something changed with Cambodia's reporting and surveillance, is simply unknown.

Nevertheless, even without a case reported in the last 2 years Cambodia remains ranked 4th in the world with documented H5N1 cases and deaths, exceeded only by Egypt, Indonesia, and Vietnam.

Considering Cambodia's much lower population (15 million vs Egypt's 82 million and Vietnam's 89 million), the per capita rate of infection in Cambodia is nearly equal to Egypt's and more than twice that of Vietnam.

It is against this backdrop that we get the following surveillance and seroprevalence study conduced during the height of the H5N1 human outbreaks in 2013 at four live bird markets in Cambodia.

Researchers not only found an incredibly high incidence of H5N1 infected poultry (35%), they found a plethora of other LPAI subtypes (HA1, HA2, HA3, HA4, HA6, HA7, HA9, HA10 and HA11) as well. 
Seroprevalence studies also found evidence of sub-clinical H5N1 and H9N2 infection in LMB workers, and additional seroconversions were documented during the course of the 11 month study.

The full (open access) study is well worth reading. The link and abstract follow.

Citation: Emerging Microbes & Infections (2016) 5, e70; doi:10.1038/emi.2016.69

Published online 20 July 2016

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


Srey Viseth Horm1,*, Arnaud Tarantola1, Sareth Rith1, Sowath Ly1, Juliette Gambaretti1, Veasna Duong1, Phalla Y1, San Sorn2, Davun Holl2, Lotfi Allal3, Wantanee Kalpravidh4, Philippe Dussart1, Paul F Horwood1,* and Philippe Buchy1,5,*

Correspondence: PF Horwood, E-mail:; P Buchy, E-mail:

Received 29 January 2016; Revised 13 April 2016; Accepted 25 April 2016


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.
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