While owning a pet is linked to numerous mental and physical health benefits, pets can also harbour infectious diseases that can sometimes be passed on to humans.
For most people, the risk is low, write Sarah McLean and Enzo Palombo in The Conversation, but some, like pregnant women and those with weakened immune systems, face a greater risk of getting sick from animals.
What diseases can pets carry?
Infectious diseases that move from animals to humans (zoonotic diseases or zoonoses) are increasing, and more than 70 pathogens of companion animals are known to be transmissible to people.
While sometimes a pet with a zoonotic pathogen may look sick, often, there may be no visible symptoms at all, making it easier for people to catch it, because they don’t suspect their pet of harbouring germs.
Zoonoses can be transmitted directly from pets to humans – through contact with saliva, bodily fluids and faeces – or indirectly, through contact with contaminated bedding, soil, food or water.
Studies suggest the prevalence of pet-associated zoonoses is low. However, the true number of infections may be under-estimated, as many zoonoses are not notifiable, or may have multiple exposure pathways or generic symptoms.
Dogs and cats are major reservoirs of zoonotic infections (meaning the pathogens naturally live in their population) caused by viruses, bacteria, fungi and parasites. In endemic regions in Africa and Asia, dogs are the main source of rabies, transmitted through saliva.
Dogs also commonly carry Capnocytophaga bacteria in their mouths and saliva, which can be transmitted to people through close contact or bites. Most people won’t get sick, but these bacteria can occasionally cause infections in people with weakened immune systems, resulting in severe illness and sometimes death.
Cat-associated zoonoses include a number of illnesses spread by the faecal-oral route, such as giardiasis, campylobacteriosis, salmonellosis and toxoplasmosis. This means it’s especially important to wash hands or use gloves whenever handling a cat’s litter tray.
Cats can also sometimes transmit infections through bites and scratches, including the aptly named cat scratch disease, caused by the bacterium Bartonella henselae.
Both dogs and cats are also reservoirs for methicillin-resistant bacterium Staphylococcus aureus (MRSA), with close contact with pets identified as an important risk factor for zoonotic transmission.
Birds, turtles and fish also transmit disease
Pet birds can occasionally transmit psittacosis, a bacterial infection which causes pneumonia. Contact with pet turtles has been linked to Salmonella infections in humans, particularly in children, while even pet fish have been linked to various bacterial infections in humans, including vibriosis, mycobacteriosis and salmonellosis.
Close contact with animals – and some behaviours in particular – increase the risk of zoonotic transmission. A study from the Netherlands found half of owners allowed pets to lick their faces, and 18% allowed dogs to share their bed. (Sharing a bed increases the duration of exposure to pathogens carried by pets.)
The same study found 45% of cat owners allowed their cat to jump on to the kitchen sink.
Kissing pets has also been linked to occasional zoonotic infections in pet owners. In one case, a woman in Japan developed meningitis due to Pasteurella multicoda infection, after regularly kissing her dog’s face. These bacteria are often found in the oral cavities of dogs and cats.
Children are also more likely to engage in behaviours that increase their risk of getting sick from animal-borne diseases – like putting their hands in their mouth after touching pets. They are also less likely to wash their hands properly after handling pets.
Although anybody who comes into contact with a zoonotic pathogen via their pet can become sick, certain people are more likely to suffer from serious illness, including the young, old, pregnant and immunosuppressed.
Sarah McLean, Lecturer in environmental health, Swinburne University of Technology, Melbourne, Australia.
Enzo Palombo, Professor of Microbiology, Swinburne University of Technology, Melbourne, Australia.
Zoonotic parasites in faecal samples and fur from dogs and cats in The Netherlands (Open access)
Zoonoses in the bedroom (Open access)
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