Although waterfowl (ducks & geese) and gallinaceous birds (turkeys, grouse, chickens & quail) are most often associated with carriage of HPAI H5 viruses, terrestrial birds such as crows, starlings, pigeons, and sparrows are also known to carry, and shed, theses viruses 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. In 2012, and again in 2014 India saw numerous wild bird die offs that were blamed on the avian flu virus (see Media Report: H5N1 Killing Crows In Jharkhand).While once a major hotbed of H5N1 activity, including the detection of 8 human cases, reports have become far more sporadic from Bangladesh over the past few years with only one outbreak reported in all of 2016.
This year (2017) has been only slightly more active, with 1 report of H5N1 in a poultry flock last January, quickly followed by two reports of H5N1 killing crows at the Rajshashi Medical College Campus, and again 200 miles away in Dhaka.
Today, however, the OIE is reporting two incidents in Dhaka - roughly less than 5 miles apart and on the same day (11/25/17) - involving the deaths of 63 crows.
While not exactly a unique occurrence, this is a reminder that the H5N1 virus continues to circulate in the environment, and can return to areas where it hasn't been seen in months, or even years.
Although the incidence of terrestrial bird carriage of HPAI viruses is poorly understood and its significance remains hotly debated, recent studies and surveillance suggests their role may be greater than previously believed.
- The Survey of H5N1 Flu Virus in Wild Birds in 14 Provinces of China from 2004 to 2007, published in 2009, found 26 positive samples distributed across 9 species from among 7320 passerine samples tested, providing a very low incidence of 0.36%. However, among tree sparrows tested, the prevalence was three times higher at 1.09%.
- The 2012 PLoS One Study A Survey of Avian Influenza in Tree Sparrows in China in 2011, found serological evidence of prior H5 subtype HPAI infection in 94 of 800 (11.75%) of sparrows tested, showing that HPAI H5 infection need not always prove fatal in that species.
- In 2013, in Pathogenesis in Eurasian tree sparrows inoculated with H5N1 highly pathogenic avian influenza virus and experimental virus transmission from tree sparrows to chickens by Yamamoto Y, Nakamura K, Yamada M, Mase M., the authors found that inoculated birds lived up to 11 days and shed copious amounts of the virus during that time, and suggested that Eurasian tree sparrows could be potential vectors to housed poultry.
- And a 2015 study - Avian Path: Susceptibility of Wild Passerine Birds To HPAI H5N1 - examined the susceptibility of three passerine bird species (reed buntings, brown-eared bulbuls and pale thrushes) to HPAI H5N1, and finds that 2 out of 3 (buntings & bulbuls) sickened and died, while pale thrushes seroconverted exhibited no clinical signs of infection.
With the emergence of new avian flu viruses around the globe nearly every year, and an expansion of their host ranges, the research into their interactions with thousands of non-aquatic bird species has only just begun.