Bacteria or viral infections can lead to meningitis -- life-threatening inflammation of brain and spinal cord protective coverings.
A 2009 study detailed two cases of meningitis in newborns linked to pets. One came after a cat stole the newborn's pacifier and used it as a toy. The other was attributed to a dog licking the baby's face. Out of 38 babies who developed meningitis in their first month, 27 had been licked or sniffed by a dog, according to the study.
A 44-year-old woman got meningitis after a similar infection, according to a 2010 report. The woman reported regularly kissing her dog as well as feeding it food out of her own mouth.
In the U.S., hookworms and roundworms take top spot for dog parasites. In humans, roundworms transmitted from dog fur can cause ocular larva migrans (OLM) if they migrate to the eyes or visceral larva migrans (VLM) if they migrate to other organs. The painful conditions can lead to blindness, encephalitis, heart and lung complications and even death.
Sleeping with pets is a comfort for many. And although pets can transmit diseases to humans, it's rare, according to Dr. Karesh.
"It's difficult to interpret this report without an idea of how many millions of people had a dog lick their ear and didn't get an infection," Karesh said.
"People who have weakened immune systems and small children certainly need to be more careful. But for the majority of people in the U.S., it's probably more dangerous to sleep in a bed than it is to sleep with your pet," Karesh said, citing data from 2004 that suggests 450 people die each year in the U.S. falling out of bed.
Nevertheless, the report serves a good reminder to keep pets healthy with vaccinations and parasite control, Karesh said.