Pets are part of the family for most people. They're cuddled with and talked to, and sometimes the dog will sit on the sofa with other family members, or the cat will sleep with them in their bed.
To avoid unnecessary health risks, however, experts say you shouldn't overdo displays of affection towards your four-legged cohabitants, and this applies particularly to children and people with weakened immune systems.
Kissing the animals is a no-no, and patting them should always be followed by carefully washing your hands.
The health risks posed by pets include injuries – especially bites – allergies and transmitted infections known collectively as zoonoses. Although some countries, such as Germany, have a reporting system for infectious diseases, the source of the infection isn't always found.
It's usually unclear whether the patient was infected by another person, an animal or a food, says Hendrik Wilking, a veterinarian who does research on zoonoses at the Berlin-based Robert Koch Institute (RKI), which is responsible for disease control and prevention.
In Germany, the most dangerous pet-borne pathogen is probably the parasite Toxoplasma gondii, according to Wilking. "An infection can lead to very serious complications in people whose immune system has been suppressed," he says.
The resulting disease, toxoplasmosis, may cause flu-like symptoms in some people. Cats are the host of this parasite, and people can be directly infected by the cats, or by eating meat contaminated by the parasite.
Women who become infected for the first time just before or during pregnancy can pass the infection to the baby. According to an RKI study, every year, more than 4,000 pregnant women in Germany contract toxoplasmosis, and more than 300 kids are born with clinical symptoms of the disease.
"(The symptoms) include neurological damage," Wilking points out. "Expectant mothers should practise proper hygiene around cats."
Another RKI study found that having a cat increases the risk of contracting Lyme disease, a tick-borne illness. "Cats pick up the ticks outdoors and can transmit them when cuddled, for instance," Wilking says.
Should people do without pets altogether to be on the safe side?
"Certainly not," Wilking says, citing studies showing pets to be beneficial to the health of their owners, who are more satisfied with their lives than the petless, get more exercise – by walking the animals and taking care of them – and have more social contacts.
While humans have been cohabitating with dogs and cats for millennia, having an exotic reptile as a pet became popular only in recent decades. A consequence of this, the RKI says, is an increase in salmonella infections in infants and young kids, since most snakes, geckos and bearded dragons shed the bacteria with their faeces. A salmonella infection can cause severe diarrhoea.
"Reptiles shouldn't be kept in children's rooms, bathrooms and especially in the kitchen," says Frank Mutschmann, a veterinarian in Berlin who specialises in reptiles. Rodents don't pose a risk of serious illness, says Maximilian Reuschel, a research associate at the University of Veterinary Medicine Hannover.
However, rabbits can transmit "snuffles", he says, a common upper respiratory infection most often caused by a bacteria known as Pasteurella multocids. Hamsters are often infested with tropical rat mites, whose bites can cause mild, reddish pustules on humans. – dpa