WHO on flu in cats

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[1] WHO update 28: cats, suspected human cases

Fri 20 2004

ProMED-mail<promed

Source: World Health Organisation (WHO), Communicable Disease Surveillance

and Response (CSR), Disease Outbreak News, Fri 20 Feb 2004 [edited]

<http://www.who.int/csr/don/2004_02_20/en/>

 

 

Avian influenza A (H5N1) Virus Infection - WHO Update 28

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Thailand: Reports of infection in domestic cats

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WHO is aware of reports of avian influenza a (H5N1) virus 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.

 

Avian influenza A (H5N1) virus infection in 2 out of 3 dead domestic cats

was announced today by the Faculty of Veterinary Sciences at Thailandís

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. Thailandís 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

[also] susceptible to natural infection with influenza viruses that are

purely avian in their genetic makeup. 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,

from1970, 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, avian influenza A (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 2 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.

 

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