Indian House Crow – Photo Credit Wikipedia
While China, Cambodia, Vietnam, and South Korea have garnered most of the avian flu headlines this winter, the H5N1 virus remains endemic in other countries as well, including much of Asia and parts of the Middle East. In many of these regions, surveillance and reporting is less than optimal, so the true extent of this virus is hard to measure.
Although debate over the incidence and importance of wild birds spreading the avian flu virus remains contentious (see India: The H5N1 & Migratory Birds Debate), we have often seen wild and migratory birds test positive for the H5N1 virus.
In addition to having infected more than 20 mammalian species, the H5N1 virus has been detected in more than 150 different types of wild birds (See USGS List of Species Affected by H5N1 (Avian Influenza)).
Waterfowl (ducks & geese) and gallinaceous birds (turkeys, grouse, chickens & quail) are most often associated with carriage of the H5N1 virus, but terrestrial birds such as crows, starlings, pigeons, and sparrows are also known to carry, and shed, the virus as well (see 2007’s EID Journal Role of Terrestrial Wild Birds in Ecology of Influenza A Virus (H5N1).
As far back as 2008, we saw reports out of India of crows dying from the H5N1 virus. A little over two years ago India was again plagued with numerous wild bird die offs that were blamed on the avian flu virus (see Media Report: H5N1 Killing Crows In Jharkhand).
By mid-December of 2011 the Indian Veterinary Research Institute (IVRI), Bhopal, confirmed that the H5N1 virus was behind at least some of these deaths. (see EpiSouth eweb_195_15_12__11.pdf). Over the next few months, even more reports came in, involving thousands of dead birds (see The Kolkata Crow Mystery & H5N1: A Murder Of Crows) that spread across several northern states.
While India has reported a number of H5N1 outbreaks in Poultry since then - and at least one die off in pigeons (see Nov. 2012 Pigeon Droppings) - reports of the virus in wild birds have been noticeably absent the past 18 months.
At least, until this week, when the OIE was notified of two dead house crows from Keonjhar District, in Orissa state in Eastern India that were found to be infected with the virus.
Two dead house crows may not seem terribly important, but as the study below indicates, changes in the behavior of the virus in the wild can sometimes be a tip off that something is changing with the virus. This from just last October, in the Archives of Virology:
Salah Uddin Khan, LaShondra Berman, Najmul Haider, Nancy Gerloff, Md Z. Rahman, Bo Shu, Mustafizur Rahman, Tapan Kumar Dey, Todd C. Davis, Bidhan Chandra Das . . . .
We investigated unusual crow mortality in Bangladesh during January-February 2011 at two sites. Crows of two species, Corvus splendens and C. macrorhynchos, were found sick and dead during the outbreaks. In selected crow roosts, morbidity was ~1 % and mortality was ~4 % during the investigation. Highly pathogenic avian influenza virus H5N1 clade 184.108.40.206 was isolated from dead crows.
All isolates were closely related to A/duck/India/02CA10/2011 (H5N1) with 99.8 % and A/crow/Bangladesh/11rs1984-15/2011 (H5N1) virus with 99 % nucleotide sequence identity in their HA genes. The phylogenetic cluster of Bangladesh viruses suggested a common ancestor with viruses found in poultry from India, Myanmar and Nepal.
Continuation of surveillance in wild and domestic birds may identify evolution of new avian influenza virus and associated public-health risks.
As the H5N1 virus continues to evolve into new clades or strains, its behavior across various species is likely to change as well. Two years ago, in Differences In Virulence Between Closely Related H5N1 Strains, we looked at a study that found that genetically similar strains can exhibit significantly different pathogenicity in specific hosts.
Making any perceived change in how the virus presents or spreads worth noting.