Medical Matters: Pooches with parasites and toxic tomcats - hazards of household pets

All pets are a theoretical risk, with bites, scratches, saliva and contact with faeces among the common routes of infection

We have just welcomed a new kitten to the house. A cheeky ball of black fur, whose hair stands up as if he is in permanent contact with a Van de Graaff generator, he defies you not to play with him. Which we do, while trying to remember to wash our hands after each contact.

For all their attractive qualities, household pets can transmit infection to people. When we are healthy, the risk of pet-associated disease is low; however, pregnant women, young children and people with cancer are more vulnerable.

A review earlier this year in the Canadian Medical Association Journal (CMAJ) looked at different types of infection, how they are transmitted from pets, prevention and the role of healthcare providers. "Studies suggest physicians do not regularly ask about pet contact, nor do they discuss the risks of zoonotic diseases with patients, regardless of the patient's immune status," writes the lead author, Dr Jason Stull of the department of veterinary preventive medicine, Ohio State University, Columbus, Ohio.

Zoonosis is the scientific name for disease passed from animals to humans, which, unsurprisingly, pose a greater threat to cancer patients and others whose immune systems are compromised. All pets are a theoretical risk, with bites, scratches, saliva and contact with faeces among the common routes of infection, while psittacosis or parrot fever is contracted when humans breathe in aerosolised droplets containing secretions from infected birds.

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But the most common zoonotic diseases come from parasites and bacteria that are transmitted through the gastrointestinal route: by touching the pet or litter tray and then your mouth.

According to Dr Vincent Ho, a gastroenterologist at the University of Western Sydney, toxoplasmosis is one of the most common gastrointestinal zoonoses. "Toxoplasmosis is caused by the single-celled parasitic organism toxoplasma gondii. The parasite undergoes sexual reproduction in cats and is excreted in faeces as a thick-walled structure known as an oocyst," he says. "Oocysts passed in a cat's faeces are not immediately infectious to other animals. They must first undergo a process called sporulation, which can take one to five days depending on environmental conditions."

While toxoplasmosis in adults is usually asymptomatic, people with suppressed immune systems are at risk of flu-like illness from infection. However, in pregnant women infected during the first trimester, the parasite can cause congenital abnormalities.

One of the commonest zoonotic infection in children is toxocariasis caused by parasitic roundworms, commonly found in the intestine of dogs and cats. Puppies can contract toxocara canis from the mother before birth or from her milk. Toxocara larvae multiply rapidly in the puppy's intestine. When the puppy is a few weeks old, they begin to produce large numbers of eggs. Young children become infected by ingesting soil contaminated with animal faeces. The parasite can then migrate to the liver, lungs and eyes.

But pets are good for health too. Finnish research found babies who grew up in homes with a pet dog or cat were 44 per cent less likely to develop an ear infection and 29 per cent less likely to receive antibiotics in their first year of life. Separate research has linked pets with a lower risk of allergies among babies. And cats and other pets have proven benefits for mental health.

Here are tips from the CMAJ experts to keep your pet relationship joyful: Wear protective gloves to clean aquariums and cages and remove faeces.

Proper handwashing after pet contact.

Discourage pets from licking humans’ faces.

Cover playground boxes when not in use.

Avoid contact with exotic animals.

Undertake regular cleaning and disinfection of animal cages, feeding areas and bedding.

Locate litter boxes away from areas where eating and food preparation occur.

Wait to acquire a new pet until immune system has recovered.

Schedule regular veterinary visits for all pets.

mhouston@irishtimes.com muirishouston.com