ACCORDING to official reports veterinary authorities in China sent to the World Organization for Animal Health (OIE), poultry that tested positive for the presence of influenza virus A(H7N9) -- and are also suspected of being the source of reported human cases -- do not show any visible signs of disease, making it very difficult to detect this virus in poultry, OIE said April 11.
"Based on the information currently available, we are facing a rather exceptional situation, because we are dealing with an influenza virus of very low pathogenicity for poultry that has the potential to cause severe disease when it infects humans," OIE director general Dr. Bernard Vallat said.
OIE assured that it is fully involved in the global effort to manage new risks presented by the H7N9 virus. To support the effort, the OIE reference laboratory for avian influenza in China at the Harbin Veterinary Research Institute is currently conducting extensive analyses on the animal source of the virus.
OIE said humane culling is the best option to eliminate the virus from infected animal production units. However, in addition to culling, the agency said another key option for controlling the influenza virus at the animal source and preventing its regional and global spread is a suitably adapted vaccination program of limited duration.
During a previous crisis involving the H5N1 virus, OIE managed regional vaccine banks but emphasized that it may be some time before an effective vaccine to protect against H7N9 can be made available in sufficient quantities.
The U.N. Food & Agriculture Organization (FAO) noted that the H7N9 outbreak requires strong biosecurity measures because it is hard to detect in poultry.
"Unlike H5N1, where chickens were dying off on a large scale, with this virus, we don't have a red flag that immediately signals an infection. This means farmers may not be aware that the virus is circulating in their flock. Biosecurity and hygiene measures will help people protect themselves from virus circulating in seemingly healthy birds or other animals," FAO chief veterinary officer Juan Lubroth said April 5.
He added that because the virus is "harder to detect, good biosecurity measures become even more essential to reducing the risk of virus transmission to humans and animals. Good biosecurity and hygiene measures implemented by farmers, livestock producers, transporters, market workers and consumers represent the first and most effective way to protect the food chain."
H7N9 in China
To date, OIE said it has been notified of eight outbreaks of low-pathogenic avian influenza A(H7N9) in pigeons and chickens in live markets, all located in Shanghai, China, and neighboring provinces.
The China Animal Disease Control Centre and the country's animal health services, including the OIE Reference Laboratory at Harbin, are still investigating the precise animal source or the possible reservoir of the H7N9 virus.
According to China's Xinhua news agency, a top Chinese biology laboratory ascribed the H7N9 avian influenza to genetic reassortment of wild birds from East Asia and chickens from eastern China.
Xinhua said the researchers determined that no genes in H7N9 were traceable to pigs, thus excluding swine as intermediate hosts for the new strain of avian flu.
The report came from the Chinese Academy of Sciences Key Laboratory of Pathogenic Microbiology & Immunology.