Persistence of low-pathogenic H5N7 and H7N1 avian influenza subtypes in filtered natural waters.

Wild aquatic birds are the natural reservoir of avian influenza virus (AIV), and the virus is transmitted among birds through a fecal-oral route. Infected birds excrete significant amounts of AIV into the environment, and thereby sustain the circulation of AIV in the bird populations. Improved knowledge on the influence of environmental factors on the persistence of AIV in natural habitats would be valuable for risk assessments. The presented work investigated the persistence of two low-pathogenic AIV subtypes in natural water samples. The study included two AIVs formerly isolated from wild ducks, which were suspended in filtered natural fresh, brackish or sea water with salinity of 0, 8000 and 20,000 parts per million (ppm), respectively. Also sterilized brackish and sea waters were included in order to examine the influence of microbial flora on virus persistence. All water samples were incubated at temperatures representative for seasonal variation of ambient temperatures in Northern Europe (4, 17 and 25 °C). The results showed a clear correlation between persistence of viral infectivity and temperature, salinity and presence of microbial flora. While independent of virus subtype, the persistence of infectivity was negatively affected by increased temperature, salinity as well as presence of natural microbial flora. The study provides insight on impact of essential physical, chemical and biological parameters on persistence of AIV in aquatic environments. Studies determining the importance of additional environmental parameters and the detailed mechanisms of microbial inactivation of AIV should be encouraged.

Rapid detection of avian influenza virus in chicken fecal samples by immunomagnetic capture reverse transcriptase-polymerase chain reaction assay.

Avian influenza virus (AIV) causes great economic losses for the poultry industry worldwide and threatens the human population with a pandemic. The conventional detection method for AIV involves sample preparation of viral RNA extraction and purification from raw sample such as bird droppings. In this study, magnetic beads were applied for immunoseparation and purification of AIV from spiked chicken fecal sample. The beads were conjugated with monoclonal antibodies against the AIV nucleoprotein, which is conserved in all the AIV. The bead-captured virus was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) without RNA extraction because of effective removal of RT-PCR inhibitors. The developed bead-based assay showed a similar detection limit comparable to the RNA extraction and the classic virus isolation method. Using ready-to-use antibody-conjugated bead, the method requires less than 5 h. Furthermore, the method has potential to integrate into a Lab-on-a-chip system for rapid detection and identification of AIV.

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.

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.

Genetic analysis of avian influenza virus from wild birds and mallards reared for shooting in Denmark.

Denmark forms a geographical bottleneck along the migration route of many water birds breeding from northeastern Canada to north Siberia that gather to winter in Europe and Africa. Potentially, the concentration of such large numbers of water birds enhances the risk of avian influenza virus (AIV) introduction to domestic poultry. In 2003, Denmark initiated a nationwide survey of AIV in wild birds and mallards reared for shooting. Partial sequence analysis of the six internal genes from a total of 12 low pathogenic (LP) AIV isolates obtained in 2003 showed that genes from these viruses were closely related with genes from AIV circulating in northern Europe. For the Danish sequences only the PB2 and NS genes differ, so they cluster to more than one cluster in the phylogenetic trees. In spring 2006, highly pathogenic (HP) AIV H5N1 was detected in 44 cases of wild birds in Denmark. Sequence analysis of the HP H5N1 virus genome showed that it was not related to the LPAIV isolated previously, but closely related to the HPAIV H5 (Asian type) detected in the rest of Europe at that time. Even though only partial sequences were applied, this gave the idea for future full-length sequence studies.