Researchers from the U.S. and abroad used a contact ferret model to evaluate transmissibility of influenza viruses in humans and found that some strains currently circulating throughout the world may transmit better than others in mammals. The researchers report their findings in the July 2007 issue of the Journal of Virology. The study found that both Vietnam “avian-like” viruses caused neurological symptoms and death in ferrets while the Hong Kong and Turkey “human-like” viruses caused only mild non-lethal symptoms. Transmission of H5N1 influenza viruses is of great concern worldwide as their geographic and host ranges continue to expand. Currently transmission to humans has been inefficient. Although there is limited knowledge of potential routes and determinants required for transmission, researchers predict genetic reassortment and mutation during adaptation in the host to be the two most likely avenues.
In the study experimental groups consisting of one inoculated ferret and two contact ferrets were used to monitor the transmissibility of four human H5N1 viruses isolates collected in Hong Kong (A/Hong Kong/213/03), Vietnam (A/Vietnam/1203/04 and A/Vietnam/JP36-2/05) and Turkey (A/Turkey/65-596/06) between 2003 and 2006. The selected isolates differed in their pathogenicity and affinity for “avian-like” and “human-like” receptors. Results showed that one contact ferret developed neutralizing antibodies to A/Hong Kong/213/03 but did not exhibit clinical signs or virus shedding. In two of the groups two contact ferrets had detectable virus following 6 to 8 days exposure with the A/Vietnam/JP36-2/05 virus-inoculated ferrets. Infected contact ferrets displayed severe clinical signs despite little or no virus detection in nasal washes. The absence of secondary transmission among ferrets housed together was attributed to minimal virus shedding. The effect of viral pathogenicity and receptor binding specificity on transmissibility showed that both Vietnam “avian-like” viruses caused neurological symptoms and death in ferrets while the Hong Kong and Turkey “human-like” viruses caused only mild non-lethal symptoms. “Here we demonstrated a useful animal model system to evaluate the transmissibility of H5N1 viruses,” say the researchers. “We propose that future selection of H5N1 vaccine candidates among new antigenic variants should take into account the transmissibility of the virus.”
August 21, 2007
Original web page at Science Daily