The OIE said that reports from the Chinese Veterinary Authorities had revealed that birds that had tested positive from the disease showed no symptoms, making it hard to trace the source of the human outbreak that has infected 63 people and killed 14.
“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, which has the potential to cause severe disease when it infects humans,” said OIE director general Dr Bernard Vallat.
The OIE added that its reference laboratory for avian influenza in China, the Harbin Veterinary Research Institute, was conducting “extensive analyses” on the animal source of the virus. However, it warned that it could be “some time” before an effective vaccine against avian influenza H7N9 was developed.
China’s authorities are continuing to investigate the possible animal sources of the avian influenza outbreak. So far, eight outbreaks of H7N9 have been notified in pigeons and chickens at markets in Shanghai and neighbouring provinces. The World Health Organisation (WHO) has said there is so far no evidence of human-to-human transmission.
The OIE’s warnings follow a statement from the UN Food and Agriculture Organisation earlier this month, which said that China would need to implement “strong biosecurity measures” in response to the H7N9 outbreak, because it was 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 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,” said Juan Lubroth, FAO chief veterinary officer.
“With the virus 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.”
China’s Ministry of Agriculture held a meeting with FAO officials last week to discuss the outbreak and measures taken to control it, including China’s proposal for a nationwide H7N9 avian influenza surveillance programme, which the MOA said would be implemented in the “near future”.
The two parties agreed to co-operate on H7N9 lab diagnosis, serological surveillance and epidemiological investigations.