Subclinical Infection With Avian Influenza A (H5N1) Virus in Cats

Michael Leschnik; Joachim Weikel; Karin Möstl; Sandra Revilla-Fernández; Eveline Wodak; Zoltan Bagó; Elisabeth Vanek; Viviane Benetka; Michael Hess; Johann G. Thalhammer

Disclosures

Emerging Infectious Diseases. 2007;13(2):243-247. 

In This Article

Abstract and Introduction

Abstract

Avian influenza A virus subtype H5N1 was transmitted to domestic cats by close contact with infected birds. Virus-specific nucleic acids were detected in pharyngeal swabs from 3 of 40 randomly sampled cats from a group of 194 animals (day 8 after contact with an infected swan). All cats were transferred to a quarantine station and monitored for clinical signs, virus shedding, and antibody production until day 50. Despite unfamiliar handling, social distress, and the presence of other viral and nonviral pathogens that caused illness and poor health and compromised the immune systems, clinical signs of influenza did not develop in any of the cats. There was no evidence of horizontal transmission to other cats because antibodies against H5N1 virus developed in only 2 cats.

Introduction

Avian influenza has attracted worldwide attention because highly pathogenic avian influenza virus subtype H5N1 can cause fatal infections in humans[1] and other mammals.[2] Domestic cats and wild cats in a zoo have reportedly shown severe clinical signs and they may die of natural or experimental infections.[3,4,5,6,7] Ingestion of infected birds was assumed to be the route of transmission in cats. However, horizontal transmission by experimentally infected cats has been demonstrated[3] and was also assumed under natural conditions in tigers in Thailand.[8] No data are available on nonlethal outcomes of H5N1 infection in cats and whether horizontal transmission between feline hosts occurs under natural conditions. Also unknown is whether domestic cats play a role in the epidemiology of avian influenza, which could be an undefined hazard for poultry and humans.[9]

During the first weeks of 2006, moribund or dead birds infected with avian influenza (H5N1) were found near water in Germany, Slovenia, and Austria. On February 14, 2006, a sick swan was found near the Mur River in Austria and transported to an animal shelter in Graz, Austria, where it died within 24 hours (day 1). PCR and egg culture identified avian influenza virus (H5N1) in the swan and in 13 of 38 other culled birds (swans, ducks, chickens) (day 4) housed with the swan at the same time. Only the swan developed clinical signs of disease. On day 4, the poultry area was disinfected after all 38 birds were removed.

In the same shelter were 194 cats; most had access to an outdoor enclosure near the poultry area and were separated from the birds by a wire-mesh fence. On several occasions, 1 or 2 unidentified cats were observed climbing the fence and entering the poultry area. Ingestion of birds by cats was not observed. Austrian authorities ordered random sampling of the cat population at the shelter because of spatial proximity of poultry and cats and the possible exposure of cats to infective debris of the birds. The bird area was left unoccupied while the cats were under observation. The purpose of this study was to monitor health status and possible transmission within a large cat population with proven natural exposure to H5N1 influenza virus.

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