A bird-flu virus closely related to the strain that has infected South African ostriches has been found in pigs on several farms in China, according to an announcement from Chinese scientist Chen Hualan posted on the Science and Development Network website.
She could not yet confirm whether the pigs are infected or have merely come into contact with the disease.
The virulent H5N1 strain is highly infectious in poultry and can spread from birds to humans, although for now this remains a rare event. BBC Online says scientists fear that if the pigs are infected by both bird and human flu viruses, the two strains could combine to create a strain easily capable of infecting people.
However, the World Health Organisation (WHO) told the Agence France Presse that it is treating the news with caution, insisting that more information is needed before an accurate risk assessment can be made. Pigs can carry flu viruses in their snouts, from sniffing at the ground, without necessarily becoming infected and developing the disease in their bloodstream.
Strains could interact with deadly consequences
A spokesperson said that if the pigs are harbouring both bird and human flu viruses, the two strains could interact to create a strain easily capable of transferring to humans. Furthermore, other researchers say the bird-flu virus can combine its genes with those from a contemporary human influenza virus that is endemic to pigs in southern China.
The virus responsible for recent bird-flu outbreaks — including those that resulted in human fatalities — is so widespread among poultry in Asia that it poses a serious threat to animal and human health in the region and is becoming increasingly difficult to eradicate, according to the findings of a five-year study.
Recent developments “pose a threat to public and veterinary health in the region and potentially the world, and suggest that long-term control measures are required”, say the authors of the study, which was published in Nature.
Dominant strain emerges
The researchers, from China, Thailand, the United States and Vietnam, studied the evolution of the bird-flu virus, and showed that a single dominant form emerged in 2002. This form was responsible for outbreaks in China and seven other Asian countries in the next two years.
Their study “is a huge stepping stone”, says John Oxford, professor of virology at the Queen Mary School of Medicine, London, who adds that he has never previously “known a virus to be traced so cunningly and accurately”.
The now-dominant form of the virus is called “Z” by the researchers. Since its emergence in both chickens and ducks, it has replaced the 15 other genetically distinct types of the bird-flu virus.
This indicates that the virus’s rapid evolution is increasing its ability to survive. The authors warn that the “Z viruses” could continue to evolve “to achieve greater viral fitness”.
Two mutations found by the team in most samples of the Z virus could make bird flu increasingly difficult to control.
One mutation, found in all human and bird-flu viruses in samples from Thailand and Vietnam, confers resistance to a group of antiviral drugs used to treat human influenza. The other could help it avoid the host’s antibody response — an aspect of our immune response that helps kill an intruding virus.
Countries worry about bad publicity
But it would appear that many countries are more interested in minimising the negative publicity around the bird-flu virus than in actually reducing its threat.
Affected countries have been asked to provide samples of the virus to the WHO to help study the disease and assess the threat it poses. But according to the journal Science, despite months of being asked, a number of them have failed to comply.
The United Nations’s Food and Agriculture Organisation is now advising governments in affected areas to initiate vaccinations, since the culling of millions of birds has failed to stop the disease from spreading.
But the success of a vaccination programme depends to a large extent on careful monitoring of the vaccinated birds. This is something that worries Ilaria Capua, director of virology at the Veterinary Public Health Institute in Padua, Italy, who fears that poorer countries may be unable to carry out such monitoring.
Until now, authorities have favoured culling over vaccination since vaccinated birds can still carry and shed the virus. However, the new strategy is hoped to reduce the viral load enough to bring the outbreak under control. The bird vaccine costs just a few US cents per shot, but according to research published in the journal Nature, a vaccination programme will still be expensive since the number of shots could run into billions.
Currently, bird flu does not transmit easily from poultry to humans and there is no conclusive evidence of human-to-human transmission. But this may change, as extensive exposure of the virus to the human population increases the likelihood that it will mutate or combine with a human influenza virus to become more infectious and dangerous to humans.
“It is imperative that outbreaks in poultry in Asia are rapidly and sustainably controlled,” say the researchers. “Governments in the region face an endemic and recurrent problem that presents a serious threat to human health.”
The authors suggest that migratory birds may help the virus to travel quickly across Asia.
Bird-flu outbreaks have occurred almost simultaneously across the region, from China to Indonesia, and in areas that are not adjacent. The timing of outbreaks in China since 2001 has coincided with the general period of bird migration into southern China, and the Z form of the bird flu virus has been found in five species of migratory birds. — SciDev.Net
This overview was compiled from a series of articles available on the Science and Development Network