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Home Eurosurveillance Weekly Release  2006: Volume 11/ Issue 15 Article 4 Printer friendly version
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Eurosurveillance, Volume 11, Issue 15, 13 April 2006
Articles

Citation style for this article: Influenza team (ECDC). H5N1 infections in cats – public health implications. Euro Surveill. 2006;11(15):pii=2942. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=2942

H5N1 infections in cats - public health implications

Influenza team (influenza@ecdc.europa.eu), European Centre for Disease Prevention and Control, Stockholm, Sweden

The natural reservoir of influenza viruses is generally considered to be wild waterbirds. In this animal group, many types of influenza viruses circulate without seeming to cause much disease, and are therefore known as 'low pathogenic' avian influenza viruses. As well as waterbirds, a number of other animals (including humans) are occasionally infected with influenza viruses (Table). However, a distinction needs to be made between species which can occasionally be infected by a particular influenza but who rarely transmit onwards - so called 'dead end hosts' and those species where it seems that the viruses are better adapted and are transmitted - 'propagating hosts' (Table).

Species Some influenza types that infect
Cats Type A/H5N1
Dogs Type A/H3N8
Horses Type A/H7N7 and H3N8
Humans (pandemic and seasonal influenza) Type A, H3N2 and H1N1 also Types B and C
Marine mammals (seals) Type A/H7N7
Mustelids (including ferrets, mink and wild mustelids) H3N2, H10N4 and H5N1
Pigs (swine fever) Type A/H1N1, H1N2, H3N2

Cats are among the species which can, and have been, infected with influenza type H5N1. The first time that this happened, and was reported, was in December 2003 when a few large cats (leopards and tigers) died in a zoo in Thailand after being fed with infected poultry [1]. The second natural event was a much larger H5N1 outbreak in zoo tigers, also in Thailand, which had been fed chicken carcasses. Over 140 tigers died, or were euthanised, and there was convincing evidence of tiger to tiger transmission [1,2].

Experimentally, it has been shown that domestic cats can be infected with H5N1 through eating infected material and that these infected cats can transmit influenza to other cats. These experimentally infected cats, though limited in number, all became seriously ill when infected and did not seem to shed the virus until they had symptoms [3]. To date the only domestic cats that have been conclusively shown to be infected have been those found ill or dead in the intense epizootic of H5N1 in wild birds on Rügen island in Germany in February 2006 [1,4]. There have been anecdotal reports of increased mortality in cats during H5N1 outbreaks in other countries (China, Iraq and Indonesia) but these have not been confirmed by laboratory tests [5].

Unconfirmed reports of infections and deaths from H5N1 in cats elsewhere should always be interpreted cautiously. A recent preliminary report of infected cats in Austria was eventually not confirmed. Reports of positive serology for H5N1 infection in non-bird species should be treated with particular caution, especially if these involve healthy animals and there has been no actual evidence of H5N1 virus (PCR or viral isolation). Serology for H5N1 may be helpful but it needs to be undertaken in laboratories used to handling H5N1 serology and able to exclude the cross reactions that can occur with H5N1 [6].

So what should be the recommended actions for cat owners when H5N1 is reported in wild birds, and what is the risk to humans? The Food and Agriculture Organization has produced guidance (Box). The difficult decision is when to apply this guidance. This would be highly recommended and reasonable guidance concerning a poultry outbreak or in an intense epizoonotic such as on Rügen Island. However, the actions would probably be considered unreasonable and over cautious where there have perhaps just one or two single birds infected. Veterinary authorities in European Union countries have not always tried to enforce guidance like this in the latter circumstances. Also as cat owners have pointed out, there are practical difficulties for some of the guidance like trying to keep cats in houses.

Box. FAO Recommended Actions in Areas where H5N1 HPAI has been diagnosed or is suspected in poultry or wild birds [1]:
  • Report any evidence of significant bird mortality (both wild and domestic) to the local veterinary authority
  • Be especially vigilant for any dead or sick cats and report such findings to the local vet
  • Make sure contact between cats and wild birds or poultry (or their faeces) is avoided and/or keep cats inside
  • If cats bring a sick or dead bird inside the house, put on plastic gloves and dispense of the bird in plastic bags for collection by local veterinary animal handlers
  • Keep stray cats outside the house and avoid contact with them
  • If cats show breathing problems or nasal discharge, a veterinarian should be consulted
  • Do not touch or handle any sick-looking or dead cat (or other animal) and report to the authorities
  • Wash hands with water and soap regularly and especially after handling animals and cleaning their litter boxes or coming in contact with faeces or saliva
  • Dogs can only be taken outside the premises if kept restraint
  • Do not feed any water birds
  • Disinfect (eg, with bleach 2%-3 %) cages or other hardware with which sick animals have been transported or been in contact with.
  • Wash animal blankets with soap or any other commercial detergent
  • Those living on farms should also be aware of the risk that semi-domestic cats (feral domesticated and farm cats) could shed the virus into poultry feed or housing, leading to exposure of poultry.

The risk to humans from an H5N1 infected cat is hard to quantify [6]. Cats naturally hunt wild birds, will choose sick birds and have close contact with humans as companion animals. Given that one cat can infect another, the risk to humans cannot be zero. Though as H5N1 remains poorly adapted to humans the cat's infection will not cross over easily [7]. The present evidence is that cats with infectious H5N1 are quite ill, so the risk of acquiring H5N1 from a well cat may be negligable. Also, risk will be minimal in areas where there there is no H5N1. While it could be argued that owners should be cautious around cats with respiratory infections, cats (like humans) catch many of these. For example, there are common infections confusingly called 'cat 'flu', which are not caused by an influenza virus at all but are due to either a cat calcivirus or herpes virus. Humans are actually at considerably greater risk from other zoonoses in cats such as toxocara, toxoplasmosis and ringworm, and basic hygiene measures for handling companion animals are important to protect against these.

For more information on avian influenza, see http://www.ecdc.europa.eu/influenza/update_influenza.php.

 

References:
  1. Food and Agriculture Organization . Animal Health Special Report H5N1 in Cats FAO 2006 (http://www.fao.org/ag/againfo/subjects/en/health/diseases-cards/avian_cats.html)
  2. Thanawongnuwech R, Amonsin A, Tantilertcharoen R, Damrongwatanapokin S, Theamboonlers A, Payungporn S, et al. Probable tiger-to-tiger transmission of avian influenza H5N1. Emerg Infect Dis 2005; 11: 699-701. (http://www.cdc.gov/ncidod/EID/vol11no05/05-0007.htm)
  3. Rimmelzwaan GF, Van Riel D, Baars M et al Influenza A virus (H5N1) infection in cats causes systemic disease with potential novel routes of viral spread with and between hosts. Am J Path 2006; 168: 176-183
  4. European Commission. Statement of the Standing Committee on the Food Chain and Animal Health Brussels 1 March 2006 (http://www.europa.eu.int/rapid/pressReleasesAction.do?reference=MEMO/06/104&format=HTML&aged=0)#uage=EN&guiLanguage=en)
  5. Kuiken T, Fouchier R, Rimmelzwaan G, Osterhaus A, Roeder P. Feline friend or potential foe? Nature 2006: 440; 741-2
  6. Puzelli S, Di Trani L, Fabiani C, Campitelli L, De Marco MA, Capua I, Aguilera JF, Zambon M, Donatelli I. Serological analysis of serum samples from humans exposed to avian H7 influenza viruses in Italy between 1999 and 2003. J Infect Dis 2005; 192: 1318-22
  7. European Centre for Disease Prevention and Control. The Public Health Risk from Highly Pathogenic Avian Influenza Viruses Emerging in Europe with Specific Reference to type A/H5N1. 5 January 2005. (http://www.ecdc.europa.eu/avian_influenza/H5N1_European_Risk_Assessment_ECDC_051019.pdf)

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