Cross-species infection of the novel coronavirus is uncertain but unlikely, The Washington Post reported. Despite one possible recorded case of human-to-dog transmission, concrete evidence of zoonotic infection has not appeared. Zoonosis is the process of disease jumping from an animal to a human.
The relative newness of the current coronavirus pandemic has raised questions among animal owners, animal lovers, and others concerned about whether it has zoonotic properties.
“Based on available evidence, there’s little reason to avoid petting, according to the American Veterinary Medical Association,” The Washington Post article said. “One dog in Hong Kong tested ‘weak positive’ for the virus that causes COVID-19, in what city officials said was a likely case of human-to-dog transmission, but the dog showed no symptoms, and researchers say that single case is not strong evidence that dogs can catch the virus.
“Because other diseases are known to spread between people and animals, the association recommends that people always wash their hands before and after dog petting.”
These other diseases are called zoonotic diseases.
One of the most common and best-known examples of zoonosis is the rabies virus.
“After a bite, or even a scratch by an infected animal, the virus can enter the body through the skin,” said Dr. Barry Fox, Clinical Professor of Medicine at University of Wisconsin Medical School. “If the wound goes unnoticed, which might occur with scratches, the virus next establishes itself in the local nerves where the injury occurred. Over the course of the next weeks or months, the virus is able to travel insidiously from the skin nerves to deeper nerves in the body.”
Dr. Fox said that by the time “local neurological symptoms” develop, rabies is virtually always fatal, as it leads to deadly inflammation of the brain and spinal cord. He added that vaccinations in the United States mean that very few domestic animals transmit rabies; over 90 percent of rabies comes from wildlife.
“Around 40,000 people in the U.S. every year get rabies shots after exposure to wild animals,” he said. “The estimated cost of receiving these vaccinations is more than $300 million, so please try to avoid the temptation to feed or handle wild animals.”
Cat Scratch Fever
Vaccine regulations keep most of the United States from contracting rabies from their domestic animals and it seems unlikely that dogs can spread SARS-CoV-2 to humans. However, that doesn’t make our most common pets—cats and dogs—completely innocent. Cats specifically carry two other common zoonotic diseases.
“Cat-scratch disease is a bacterial disease by a germ called Bartonella henselae,” Dr. Fox said. “Most people with cat-scratch illness have been bitten or scratched by a cat [and] they usually develop a mild infection near the injury site. Lymph nodes become swollen, and fever and flu-like symptoms can occur for several days.”
Dr. Fox said that up to 40 percent of cats carry this germ asymptomatically. Fortunately, its cases rarely develop into serious problems for cats or humans alike. Cats also carry toxoplasmosis, which they often contract from one of their favorite pastimes.
“Cats can become infected [with toxoplasmosis] after eating infected tissue of rodents, or, less commonly, cattle,” he said. “Infectious cyst forms are shed by cats, and the humans become infected through accidental contact with feline fecal material. Based on blood sample testing, only nine percent of the U.S. population has been exposed to toxoplasmosis; but in other areas of the world, the rate is as high as 50 percent.”
Dr. Fox added that most human cases of toxoplasmosis are asymptomatic, though occasionally, whole-body lymph node enlargement with flu-like symptoms develops. Finally, pregnant woman who contract toxoplasmosis can transmit it to their fetuses, which can result in babies born blind or with mental disabilities. This is the reason why pregnant women are discouraged from scooping litter boxes.
SARS-CoV-2 seems unlikely to be zoonotic, which is good news for pet owners and animal lovers around the world. However, keeping up to date on the subject via reputable medical and scientific websites is always a good idea.
Dr. Barry C. Fox contributed to this article. Dr. Fox is Clinical Professor of Medicine at University of Wisconsin Medical School. He received his undergraduate degree in Molecular Biophysics and Biochemistry from Yale University and his medical degree from Vanderbilt University.