Filter-feeding bivalves can remove avian influenza viruses from water and reduce infectivity

Avian influenza (AI) viruses are believed to be transmitted within wild aquatic bird populations through an indirect faecal-oral route involving contaminated water. This study examined the influence of filter-feeding bivalves, Corbicula fluminea, on the infectivity of AI virus in water. Clams were placed into individual flasks with distilled water inoculated 1 : 100 with a low pathogenic (LP) AI virus (A/Mallard/MN/190/99 (H3N8)). Viral titres in water with clams were significantly lower at 24 and 48 h post-inoculation compared to LPAI-infected water without clams. To determine whether clams affected the infectivity of AI viruses, 18 wood ducks (Aix sponsa) were divided into test groups and inoculated with a variety of treatments of clam supernatants, whole clams and water exposed to a high pathogenic (HP) AI (A/whooper swan/Mongolia/244/05 (H5N1)). None of the wood ducks inoculated with HPAI-infected water that was filtered by clams or that was inoculated with or fed tissue from these clams exhibited morbidity or mortality. All wood ducks exposed to either HPAI-infected water without clams or the original viral inoculum died. These results indicate that filter-feeding bivalves can remove and reduce the infectivity of AI viruses in water and demonstrate the need to examine biotic environmental factors that can influence AI virus transmission.