Health Informer - Medical News: Bird Flu Blamed for Seal Deaths

Tuesday, July 31, 2012

Bird Flu Blamed for Seal Deaths - MedPage Today

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ByÂ Michael Smith, North American Correspondent, MedPage Today

Published: July 31, 2012

ReviewedÂ byÂ Dori F. Zaleznik, MD; Associate Clinical Professor of Medicine, Harvard Medical School, Boston

Action Points

Explain that an H3N8 influenza strain previously found in birds was found to be the cause of an outbreak of fatalities among New England harbor seals in 2011.
Note that this avian H3N8 strain appears to have acquired virulence mutations that affect transmissibility among mammals as well as promoting cell death, inflammation, and secondary bacterial pneumonia -- the latter of which was found among the dead seals.

First there was swine flu. Now there may be seal flu.

In the wake of a pneumonia outbreak that killed 162 harbor seals in New England last year, researchers are blaming the deaths on an avian flu virus.

The virus is similar to one circulating in North American birds since 2002 but shows signs of having recently adapted to mammals, according to according to Ian Lipkin, MD, of Columbia University's Mailman School of Public Health in New York City and colleagues.

Among the adaptations are some genetic changes that have been associated with increased virulence and transmissibility among mammals, Lipkin and colleagues reported in the July/August issue of the journal mBio.

The outbreak is "particularly significant," they wrote, because the virus has naturally acquired mutations that may make it a candidate to cause disease in humans.

"Our findings reinforce the importance of wildlife surveillance in predicting and preventing pandemics," Lipkin said in a statement, adding that a range of human pathogens â€" including HIV, West Nile virus, and influenza itself â€" "are all examples of emerging infectious diseases that originated in animals."

From September through December last year, dead or dying seals were found along the New England coast at a rate about four times the expected mortality for the region and time, the researchers reported.

Five animals were collected for testing; all had pneumonia and ulcers on the skin and oral mucosa, Lipkin and colleagues reported. Genetic testing also showed that all five were positive for influenza A.

When the investigators sequenced the genes for the viral proteins hemagglutinin and neuraminidase, they found the flu was subtype H3N8, typically found in birds, but also in horses and dogs.

The virus is closely related to one isolated in 2002 from a blue-winged teal in Ohio â€" the two are identical in 96.07% of their respective genomes.

But the 37 changes in amino acid sequence from the older subtype to the seal virus include several that are potentially worrisome, the researchers said.

For instance, the second RNA segment of the virus encodes the PB1 protein and in some strains a second protein, dubbed PB1-F2, which has been associated with increased cell death, inflammation, and secondary bacterial pneumonia.

The 2009 pandemic H1N1 flu lacked the PB1-F2 protein, which some experts have suggested may have limited its virulence.

The seal H3N8 virus, on the other hand, has the protein â€" and all five tested seals had evidence of apoptosis and secondary bacterial pneumonia.

The genetic sequences were also missing a section whose deletion â€" previous work on the highly pathogenic H5N1 avian flu has shown â€" is associated with the ability of influenza to use human-like cellular receptors and to transmit among mammals.

The seal virus also has a mutation â€" dubbed D701N â€" that has been experimentally shown to increase pathogenicity and transmissibility. In previous seal flu outbreaks, the mutation was absent, but it is commonly found in H3N8 viruses in horses and dogs, the researchers reported.

Taken together, Lipkin and colleagues argued, the findings suggest that the virus may have evolved the ability to persist within the seal population.

As well, they noted, the virus has already acquired mutations in key genes "that are often, though perhaps not exclusively, regarded as prerequisites for pandemic spread."

The study had support from the NIH, the National Science Foundation, the Library of Medicine, USAID PREDICT, and the Defense Threat Reduction Agency. The researchers did not report any conflicts.

Primary source: mBio
Source reference:
Anthony SJ, et al "Emergence of fatal avian influenza in New England harbor seals" mBio 2012; DOI: 10.1128/mBio.00166-12.