Pets and zoonoses

MOST AUSTRALIANS lin? in urban and suburban communities. In common with similar societies in Western Europe and North America, 60010 of Australian homes have pets of one type or another. Dogs, cats, and birds are the favourite additions to the family. These animals have their own diseases, some of which are transferable to human beings. This set of diseases, the zoonoses, are of relatively low prevalence in Australia.' Fortunately, some zoonoses of major public health significance, like rabies, arc completely absent here. Despite their low prevalence, many should be considered in the differential diagnosis both of localised and of generalised disease of children and adults. Virtually everyone in the community is in contact with either animals, or their products, or their excreta. Human toxoplasmosis,' toxocariasis, J and hydatid disease' all result from the ingestion of faeces of cats or dogs containing oocysts or eggs of parasites resident in the intestines of these animals. All cause a wide range of clinical signs. While lymphadenopathy is its usual manifestation in humans, toxoplasmosis may also cause fetal abnormalities. Young children are more likely to be affected by toxocariasis. Signs are protean, but eosinophilia is commonly present. Infestation with Echinococcus granulosus occurs in urban dogs as well as in those in the countryside with ready access to uncooked viscera of sheep. All dogs should, therefore, be suspected as potential sources of hydatid disease which, in Australia, usually follows cyst development in the liver. Salmonellosis is the most commonly diagnosed zoonosis in Australia. S Although meat is the most likely vehicle, dogs and cats have both clinical and subclinical infections with a variety of serotypes." These animals have been incriminated as sources of infection in households. 7 Furthermore, unprocessed pet food is frequently heavily contaminated with Salmonella and is a potential source of infection through transfer to uncooked human food in the kitchen.' Sarcoptes scabiei var. canis causes mange in dogs. This parasite does not burrow in human skin nor complete its life cycle other than on its specific host. It does, however, cause dermatitis-papules, erythema, vesicle formation and pruritus-in some people to whom it transfers when affected dogs are nursed. A number of contacts with affected animals may be necessary, and the offending animal may not necessarily be in the same household as the patient. Other mites (Cheyletiella spp.) which may either be saprophytic feeders or mild pathogens in dogs, cats and rabbits, might cause dermatitis in people." Dermatomycosis (ringworm caused by Microsporum canis) may be acquired from subclinical infections in cats as well as from more obvious lesions in dogs. Bites and scratches inflicted both by dogs and by cats are perhaps more important than the zoonoses. They cause physical damage and shock; bites introduce oral bacterial flora into damaged tissue. The oral flora of these animals includes Gram-negative anaerobes as well as pathogens like Pasteurella multocida which cause serious local infections. Thorough cleaning, debridement and rational antibiotic therapy are essential components of treatment. Cat-scratch disease is a specific illness usually associated with prior injury 311