CALLISTO encountered the favour of the European Commission and is arising attention and great expectations because an increasing number and range of companion animals are being kept in close interaction with human beings, achieving nearly 50% of the households in industrialised societies. Most of these keep classical pets such as dogs, cats, rabbits, small rodents, birds and fish, but an increasing number of companion animals are exotic and wild animals, posing a poorly understood risk for both human and food animal health, due to the unfamiliarity with the infectious agents they may harbour and poor regulation of the wildlife trade.

As companion animals share the same environment with people, there is a need to clarify the role of companion animals as sources of zoonotic infectious diseases. In addition to the public health and occupational health risks to companion animal owners, care takers and veterinarians, food animals also are at risk of infection with (emerging) pathogens from companion animal species.

These infectious diseases can be caused by viruses, bacteria, fungi or parasites transmitted through physical injuries, direct contact, environmental contamination, ingestion of contaminated food or water, or arthropod vectors.

Zoonotic viruses

An important and probably best known example of a zoonotic viral disease from companion animals is rabies, which should be considered in the differential diagnosis of any patient presented with encephalitis in endemic areas. In recent years, a number of other zoonotic viruses from companion animals have emerged. Highly pathogenic avian influenza virus H5N1, which causes severe respiratory disease in humans, has been diagnosed in dogs and cats.

Zoonotic bacteria and fungi

Traditionally, the most common bacterial zoonoses include bite wound infections (Pasteurella multocida and Capnocytophaga canimorsus), cat scratch disease (Bartonella henselae) and campylobacteriosis (Campylobacter jejuni, C. coli and C. upsaliensis) in household pets; salmonellosis (S. enterica) in cold-blooded animals as well as in various mammalian and avian species; and psittacosis (Chlamydophila psittaci) in birds. In addition to traditional zoonoses, opportunistic pathogens such as Escherichia coli and staphylococci are exchanged between pets and humans sharing the same household.

Zoonotic parasites

Parasitic zoonoses associated with companion animals are among the most widely spread infections of humans in a European context. These include toxoplasmosis, leishmaniosis, and helminth infections of canines or felines (e.g., echinococcosis, toxocarosis, ancylostomiosis and dirofilariosis). Companion animals may also carry strains of Giardia. In addition to that, arthropod parasites of companion animals, such as ticks, fleas, mosquitoes, flies and sand flies may transmit a variety of infectious agents to humans. Increased mobility of companion animals especially from and to the Mediterranean basin area, has resulted in transmission of zoonotic parasitic pathogens, such as Leishmania infantum.