Friday, October 14, 2016

Migratory Birds & The Spread Of Highly Pathogenic Avian Flu


For more than a dozen years there's been a debate over whether - and just how much - migratory and wild birds contribute to the distribution and evolution of highly pathogenic avian flu.

We've seen innumerable studies implicating migratory birds over the years, including:

Erasmus Study On Role Of Migratory Birds In Spread Of Avian Flu

PNAS: H5N1 Propagation Via Migratory Birds

EID Journal: A Proposed Strategy For Wild Bird Avian Influenza Surveillance

PLoS One: North Atlantic Flyways Provide Opportunities For Spread Of Avian Influenza Viruses

But the primary `smoking gun'  - the detection of large numbers of wild and migratory birds carrying HPAI - has remained elusive (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).

All of which has led some scientists and bird enthusiasts to claim that `sick birds don't fly', that migratory birds are not a major factor in the spread of these avian viruses, and that the blame lies primarily at the feet of the poultry industry. 

We explored this ongoing debate in Bird Flu Spread: The Flyway Or The Highway?, and while poultry industry practices are no doubt a major factor, it is hard to ignore the migratory bird link.

While we still lack definitive proof, yesterday the Journal Science published a strong argument for migratory birds being behind the international spread of HPAI H5N8.

The paper (and an accompanying editorial) are behind a paywall, but we have a press release and a CIDRAP News report to help fill in the gaps.

Science 14 Oct 2016:
Vol. 354, Issue 6309, pp. 213-217
DOI: 10.1126/science.aaf8852

Avian influenza viruses affect both poultry production and public health. A subtype H5N8 (clade virus, following an outbreak in poultry in South Korea in January 2014, rapidly spread worldwide in 2014–2015. Our analysis of H5N8 viral sequences, epidemiological investigations, waterfowl migration, and poultry trade showed that long-distance migratory birds can play a major role in the global spread of avian influenza viruses.

Further, we found that the hemagglutinin of clade virus was remarkably promiscuous, creating reassortants with multiple neuraminidase subtypes. Improving our understanding of the circumpolar circulation of avian influenza viruses in migratory waterfowl will help to provide early warning of threats from avian influenza to poultry, and potentially human, health.

You'll find an accompanying editorial called Sick birds don't fly…or do they? by Colin A. Russell in the same issue. 

CIDRAP News carried a brief report in their news scan last night. A few excerpts:

Study finds long-distance migrant birds key to US H5N8 outbreak in 2015

The 2014-15 outbreak of H5N8 avian flu in Europe and then North America was likely driven by long-distant migrant birds and an unusually "promiscuous" clade, a study published today in Science found.
Scientists from 32 global institutions who form the Global Consortium for H5N8 and Related Influenza Viruses analyzed migration patterns of wild birds that were found to be infected with H5N8. They also constructed phylogenetic trees of viruses collected from 16 different countries from 2004 to 2015 to track virus evolution.
Their data suggest that H5N8 was most likely carried by long-distance flights of infected migrating birds from Asia to Europe and North America via their Arctic breeding grounds. The authors write that the virus likely spread along two main migration routes: (1) from the east Asia coast/Korean peninsula, north to the Arctic coast of the Eurasian continent, then west to Europe and (2) from the Korean peninsula, then east across the Bering Strait and south along the northwest coast of North America.
Their genetic analysis also found that "the hemagglutinin of clade virus was remarkably promiscuous, creating reassortants with multiple neuraminidase subtypes." That led to rapid evolution of the highly pathogenic H5N8 strain.
(Continue. . . )

The University of Edinburgh released the following press summary as well.

University of Edinburgh

Monitoring the migration routes of wild birds could help to provide early warning of potential bird flu outbreaks, experts say.

The recommendation follows new research that shows migrating birds can help to spread deadly strains of avian flu around the world.

Some strains of bird flu viruses are highly lethal in birds they infect and pose a major threat to poultry farms worldwide. In rare cases, the viruses can also infect people and cause life-threatening illness.
Researchers investigated how a subtype of bird flu called H5N8 spread around the world following outbreaks in South Korea that began in early 2014.

The virus spread to Japan, North America and Europe, causing outbreaks in birds there between autumn 2014 and spring 2015.

Scientists analysed migration patterns of wild birds that were found to be infected with the H5N8 virus. The team then compared the genetic code of viruses isolated from infected birds collected from 16 different countries.

Their findings reveal that H5N8 was most likely carried by long-distance flights of infected migrating wild birds from Asia to Europe and North America via their breeding grounds in the Arctic.

The researchers say their findings reinforce the importance of maintaining strict exclusion areas around poultry farms to keep wild birds out.

Greater surveillance of wild birds at known breeding areas could help to provide early warning of threats of specific flu virus strains to birds and people, they add.

(Continue . . .)

Clade H5N8 has spread faster, and farther, than any other HPAI H5 virus we've seen to date. Along the way it has managed to reassort with local avian viruses, producing new, viable subtypes (H5N1, H5N2, etc.) in Taiwan and North America.

Last month, in FAO/EMPRES: H5N8 Clade Detected Over Summer In Russia, we looked at a follow up on reports from earlier in the summer that H5N8 had been detected in Russia, which prompted the FAO to warn:

Countries and places in Central Asia, the Caucasus, the Middle East, Europe and West Africa – especially those that have experienced outbreaks in 2005/06, 2009/10 and/or 2014/15 (as shown in Maps 2, 3 and 4) – should be on alert over the next 6 to 12 months, as westward and southern spread of the H5N8 virus is likely. If the virus enters Egypt or West Africa, where H5N1 HPAI viruses are already present or even entrenched in poultry populations it would further complicate disease control. 

South Asia may also be at risk of incursion of this H5N8 HPAI clade virus, potentially arriving there with fall migration in 2016. Based on past experience, this virus could also arrive in the Republic of Korea and Japan within the next 18 months. Clade virus is already circulating widely in China.

And it isn't just H5N8 we have to be concerned with, as the HPAI H5N6 - which, unlike H5N8, has proven highly pathogenic in humans, belongs to the same promiscuous and high flying clade.

While it hasn't yet spread beyond China, Vietnam and Laos, last year Hong Kong reported H5N6 in migratory birds several times.

All of which just adds to the need to monitor wild and migratory birds for HPAI viruses.