Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 10, 2013
Publication Date: N/A
Interpretive Summary: Avian influenza virus can be divided into two basic groups, highly deadly strains and low-pathogenicity strains that cause less severe illness. These less powerful strains cause mild illness in poultry, including decline in egg production. They are common in waterfowl where the virus is thought to be transmitted via water contaminated with feces from infected birds. Transmission efficiency likely depends on how long the virus can survive in water. We studied the feeding effect of the common water flea, Daphnia, on survival of a low-pathogenicity strain isolated from an Alaskan duck. Water fleas are eaten in large quantities by some ducks, and, as filter feeders, water fleas might incidentally accumulate avian influenza virus in their bodies, providing a shortcut in the transmission route from virus in water to ingestion by birds. Our experiments showed Daphnia quickly accumulates avian influenza virus in its body during feeding; but when we isolated ingested virus from Daphnia tissue, it was not infective, suggesting the feeding activity killed the virus. Correspondingly, when Daphnia were feeding in water, the avian influenza virus concentration in that water decreased; the Daphnia were in effect clearing the water of virus, which would benefit waterfowl by reducing the likelihood of infection. We cannot completely dismiss the idea that Daphnia serves as an avian influenza vector. At time scales shorter than our measurements, infective virus might have been present in Daphnia tissue. Another possibility is we might have detected infective virus inside Daphnia by using more sensitive methods. Understanding the ecology and transmission of avian influenza virus in the environment among its natural hosts is important for preventing infections in poultry and people.
Technical Abstract: The principle mode of avian influenza A virus (AIV) transmission among wild birds is thought to occur via an indirect fecal-oral route, whereby individuals contract the virus from the environment through contact with virus-contaminated water. AIV can remain viable for periods of months to years in water; however, little is known regarding the influence of the biotic community (i.e., aquatic invertebrates) on virus persistence and infectivity in aquatic environments. We conducted laboratory experiments to investigate the ability of an aquatic filter-feeding invertebrate, Daphnia magna, to accumulate virus from AIV-dosed water and act as a potential vector of AIV to waterfowl hosts. We placed live Daphnia in test tubes dosed with low pathogenic AIV (H3N8 subtype isolated from a wild duck), and sampled Daphnia tissue and the surrounding water using RT-qPCR at 3 – 120 minute intervals for up to 960 minutes following dosing. Concentrations of viral RNA averaged 3 times higher in Daphnia tissue than the surrounding water shortly after viral exposure, but concentrations decreased exponentially through time for both. In the presence of Daphnia, we suspect that AIV persistence is a function of Daphnia density and filtration rate, such that viral concentrations in water are reduced with each filtration event. Our results suggest Daphnia can accumulate AIV RNA and effectively remove virus particles from water; however, their effect on virus infectivity remains unresolved. Although extracts from Daphnia tissue were negative for AIV by cell culture, concentrations of viral RNA were consistently higher in Daphnia tissue than the surrounding water, suggesting that Daphnia may represent a vector facilitating AIV infection to aquatic birds.