Susceptibility of Muscovy (Cairina Moschata) and mallard ducks (Anas Platyrhynchos) to experimental infections by different genotypes of H5N1 avian influenza viruses.

It is a fact that in Viet Nam, Muscovy ducks are raised in large populations (approximately 8 million), usually kept in small flocks together with mallards and chickens. As a result, it is a great concern for epidemiologists to elucidate possible differences in relation to these species being exposed to infection with H5N1. To do this, an experimental study on infections with different genotypes of H5N1 in mallards and Muscovy ducks have been conducted, where it was found that the mortality of the inoculated Muscovy ducks was at least 80%, regardless of the virus strain employed. In contrast, the mortality of the mallards ranged from nil to 100%, which suggests that Muscovy ducks are more susceptible to HPAIV H5N1 infection in terms of disease development and mortality. It was also found that higher virus titers developed in vital organs of Muscovy ducks compared to mallards, particularly in the brain. Due to their high susceptibility, it is unlikely that Muscovy ducks act as a silent reservoir. The virus strains used in this study, to a certain degree, differed in their virulence properties to the bird species in question.

Virulence of H5N1 influenza virus in Cattle Egrets (Bubulcus ibis).

In Vietnam, Cattle Egrets (Bubulcus ibis) are common in a variety of habitats, such as freshwater marshes, beaches, and paddy fields. They are also found associated with cattle (Bos spp.) and occasionally with pigs (Sus scrofa), goats (Capra hircus), and horses (Equus caballus) and are kept for insect control in households. In this study, six Cattle Egrets were experimentally infected intranasally with highly pathogenic avian influenza (AI) A/duck/Vietnam/40D/04 (H5N1) to investigate a possible epidemiologic role for Cattle Egrets in outbreaks of H5N1 AI in Vietnam. The Cattle Egrets were highly susceptible to the infection and either died within a week or had to be euthanized. Five uninfected chickens housed with the inoculated Cattle Egrets from day 1 to day 8 postinfection showed no signs of disease or mortality. This observation was most probably due to the low-level virus shedding by the Cattle Egrets. We concluded that Cattle Egrets are not significant reservoir hosts for H5N1 AI virus.