Avian Flu Diary: H9N2: Part Of A Crowded Viral Field

# 5958

Although chickens often bear the brunt of the blame in the media, aquatic waterfowl are actually the natural host (and likely the principal culprits in spreading) of avian influenza.

Unlike poultry and some species of wild birds which tend to visibly sicken and often die from HPAI (Highly Pathogenic Avian Influenza) viruses - ducks and waterfowl can frequently carry these viruses with little or no ill effects.

The influenza virus in birds is primarily a gastrointestinal infection, and is spread through feces. Where ducks and chickens intermingle – a common occurrence in Asia – the virus can easily jump to poultry.

The focus over the past few years has been on HPAI H5N1, because of its tremendous impact on the poultry industry around the world and the horrendously high mortality rate in the small number of human infections.

But other avian flu viruses are in circulation, and of concern as well.

In 2003, an outbreak of H7N7 at a poultry farm in the Netherlands went on to infect at least 89 people (mostly mildly, but 1 death), and many more may have been infected subclinically.

In Egypt - in 2004 - 2 infants were shown to be infected by the H10N7 avian flu virus.

In 2006 1 person in the UK was confirmed to have contracted H7N3, and the following year, 4 people tested positive for H7N2 – both following local outbreaks in poultry.

But in terms of concern, the closest runner up to H5N1 virus right now is probably H9N2 – which is known to have infected a handful of humans, mostly in Asia – and has the World Health Organization concerned enough that they are working on the creation of a candidate vaccine (see WHO Report : Antigenic & Genetic Characteristics of H5N1 & H9N2 Viruses).

Admittedly, the next influenza virus to successfully jump species could come out of left field, as we saw in 2009 with the H1N1 swine flu.

All of which serves as prelude to a new study that has just been published in the Archives of Virology that looks at the panorama of influenza pathogens detected in Vietnamese ducks over the past couple of years.

Below you’ll find excerpts from the abstract (reparagraphed for readability).

Arch Virol. 2011 Nov 9. [Epub ahead of print]

Characterization of avian influenza viruses isolated from domestic ducks in Vietnam in 2009 and 2010.

Nomura N, Sakoda Y, Endo M, Yoshida H, Yamamoto N, Okamatsu M, Sakurai K, Hoang NV, Nguyen LV, Chu HD, Tien TN, Kida H.

Abstract

In the surveillance of avian influenza in Vietnam, 26 H9N2, 1 H3N2, 1 H3N8, 7 H4N6, 3 H11N3, and 1 H11N9 viruses were isolated from tracheal and cloacal swab samples of 300 domestic ducks in April 2009, and 1 H9N6 virus from 300 bird samples in March 2010.

Out of the 27 H9 virus isolates, the hemagglutinins of 18 strains were genetically classified as belonging to the sublineage G1, and the other nine belonged to the Korean sublineage.

Phylogenetic analysis revealed that one of the 27 H9 viruses was a reassortant in which the PB2 gene belonged to the Korean sublineage and the other seven genes belonged to the G1 sublineage.

Three representative H9N2 viruses were intranasally inoculated into ducks, chickens, pigs, and mice. On the basis of experimental infection studies, it was found that each of the three viruses readily infected pigs and replicated in their upper respiratory tracts, and they infected chickens with slight replication.

Viruses were recovered from the lungs of mice inoculated with two of the three isolates. The present results reveal that H9 avian influenza viruses are prevailing and genetic reassortment occurs among domestic ducks in Vietnam.

It is recommended that careful surveillance of swine influenza with H9 viruses should be performed to prepare for pandemic influenza.

Although 7 different avian flu viruses were detected, 2/3rds were of the H9 variety. And their `fitness’ for replication in other species, particularly swine, is concerning.

Today only H5 and H7 avian viruses are required to be reported to the OIE, and given that H9N2 often spreads asymptomatically in poultry, its actual prevalence is probably underestimated around the globe.

In 2009, in the Journal of Clinical Virology, we saw a study out of China that looked for serological signs of human infection by both H7 and H9 influenza viruses.

Serological reports of human infections of H7 and H9 avian influenza viruses in northern China.

Jia N, de Vlas SJ, Liu YX, Zhang JS, Zhan L, Dang RL, Ma YH, Wang XJ, Liu T, Yang GP, Wen QL, Richardus JH, Lu S, Cao WC.

(EXCERPT)

A total of 583 sera collected from farmers in Xinjiang were tested, and 10 (1.7%) were positive for H9 virus infection. Out of 200 sera collected from Liaoning, two (1.0%) were infected by H9 virus. No H7 virus infection was detected in the above serum samples. Neither H7 nor H9 virus infection was identified in 277 poultry workers of Shandong and in 407 residents of Shanxi.

CONCLUSIONS:

Although H9 virus infection was limited in farmers from Xinjiang and Liaoning, a public health alert is needed as novel pandemic influenza strains may develop unnoticed given the presence of subclinical infections, and the possibility of re-assortment with prevailing H5N1 virus in these regions.

In another study (see Evidence for Subclinical Avian Influenza Virus Infections Among Rural Thai Villagers), testing of 800 villagers found:

38 (4.7%) who were seropositive for the Hong Kong H9N2 flu strain
45 (5.6%) had antibodies to A/Thailand/676/2005 H5N1
28 (3.5%) were shown to be seropositive to A/Thailand/384/2006 H5N1.

While the absolute number of positive detections so far have been small, these studies reinforce the idea that H5N1 isn’t the only bird flu game in town.

A few notable H9N2 stories from the past include: