泰国一个家庭中的15只猫感染了H5N1，其中14只已经死亡。泰国卫生部门对这家人进行了健康检查和监测，人与病猫接触是否会感染还有待证实。1970、1972、1981年均有实验室研究发现猫可以感染禽流感，但自然条件下的感染是首次发现，猫是否会成为除了猪以外的第二种人流感、禽流感混合载体，还需要进一步证实。
Reports of infection in domestic cats (Thailand)
WHO is aware of reports of H5N1 infection in a single household of domestic cats in Thailand. Investigations are under way and no firm conclusions can be made at present. However, concern is great and several specific questions are being raised about risks to humans in close contact with infected cats and the need for surveillance of disease in cat populations.
H5N1 infection in two out of three dead domestic cats was announced today by the Faculty of Veterinary Sciences at Thailand’s Kasetsart University. The animals are part of a single household of 15 cats. Of these, 14 have died. Contact of one cat with dead chickens was observed by the owner.
Thailand’s Ministry of Public Health is investigating the incident in cats and is monitoring the health of human contacts. FAO is also contributing expertise.
While conclusions are premature pending the results of these investigations, confirmation of H5N1 infection in cats is not considered likely to enhance the present risks to human health. Nor is it considered likely to influence the future evolution of the outbreak in humans in any significant way.
Several studies have shown that a small number of mammalian species, including pigs, seals, whales, mink, and ferrets, are susceptible to natural infection with influenza viruses that are purely avian in their genetic make-up. Of these species, only the pig has significance for human health. Pigs can be co-infected with both avian and human influenza viruses and can thus serve as the “mixing vessel” for the mingling of genetic material, possibly resulting in the emergence of a new influenza virus subtype. Most experts agree that pigs played a role in the emergence of pandemic viruses in 1957 and 1968.
Up to now, domestic cats have not been considered susceptible to disease caused by natural infection with influenza viruses. Some older studies, from 1970, 1972, and 1981, reported experimental infection of domestic cats under laboratory conditions. Although infection occurred (virus was recovered from the respiratory tract), all of the cats remained healthy. None developed typical symptoms of influenza, including fever, nasal discharge, coughing or sneezing. These findings are important in that they strongly suggest that, should additional cats become infected with H5N1, they would not shed large quantities of the virus.
In contrast, H5N1 virus replicates in the intestines as well as the respiratory tract of birds. In the present outbreak, very large quantities of virus are being excreted in the faeces of infected birds, resulting in widespread contamination of the environment. This wide presence of the H5N1 virus in the environment creates one of the most important risks for human exposure and subsequent infection. Should domestic cats prove to be easily infected with H5N1, which is considered unlikely, their infection is not expected to contribute in a significant way to the presence of H5N1 virus in the environment.
Avian influenza viruses, including the specific strain implicated in the present outbreak, lack the receptors needed to infect mammals efficiently. However, the infection of humans observed in this and two previous H5N1 outbreaks demonstrates that transmission from birds to mammals can occur despite this lack of receptors. The very small number of human cases – despite abundant and widespread opportunities for exposure and subsequent infection – strongly suggests that transmission of H5N1 from birds to mammals, including cats as well as humans, is a rare event.
The reported infection of domestic cats with H5N1 is an unusual event in what is an historically unprecedented situation. Results from the investigation undertaken by Thai authorities will shed critical light on this unusual event.
Influenza viruses are highly unstable and their behaviour cannot be predicted. Vigilance for suspected cases in various mammalian species is presently high and should be continued. Reporting by veterinarians of suspected or confirmed cases to national authorities, as happened in the present situation, is a key component of this continuing vigilance.
WHO is collaborating closely with FAO and OIE as part of international efforts to understand the continuing evolution of the outbreaks in humans and animals, which are closely inter-related.
