Our dogs can apparently catch a nasty germ called novovirus from us humans, a group of English and French scientists have affirmed this month, backing earlier research from Finland indicating that very thing. But can dogs return the favor? Could man and his best friend be caught in a rather revolting vicious circle of infection?
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About a half of American homes have dogs, as do a third of English households, and (as of 2012) there were well over 400,000 dogs in Israeli homes.
Given that, and given that that around 20 million Americans and 3 million English people are diagnosed with novoviral gastroenteritis each year, one would like to know whether man and his best friend are giving each other something beyond love.
Also known in England as "the winter vomiting bug" or, with sublime indifference to scientific accuracy, stomach flu, novovirus is a fiercely contagious germ that is transmitted chiefly by unhygienic bathroom habits. It can also be transmitted by unclean food, surfaces and the air. Novovirus is often implicated in mass illness on cruise ships and in hospitals – note that there at least, dogs can't have caused it.
In people, norovirus can cause violent vomiting, abdominal pain and diarrhea, as well as the usual symptoms of viral malaise – headache, weakness and fever. The symptoms usually last from a day to three at most. The virus, in its various strains, isn't usually deadly, except to people with weak immune systems, including the elderly and babies: it is believed to cause about 800 deaths a year in the U.S.
There is also a specific form of canine novovirus, which again exists in multiple strains, and which has similar symptoms, though whether it causes its furry sufferers headache too is not known.
Usually viruses are species-specific, though through mutation, some can make the interspecies leap, for instance avian flu or swine infecting humans. In the case of novovirus, what the scientists found is antibodies to the human virus in some dogs, according to the paper published on April 1 in the Journal of Clinical Microbiology.
"This strongly suggests that these dogs have been infected with the virus," said first author Sarah Caddy, a veterinarian and PhD student at the University of Cambridge, and Imperial College, London, U.K. "We also confirmed that that human norovirus can bind to the cells of the canine gut, which is the first step required for infection of cells."
Fido has the runs
How do we know the dogs caught human novovirus? The researchers found antibodies to the human strain in the canine serum, that's how. They did not find actual human norovirus particles in doggie doo, not even dogs with diarrhea.
Also, the antibodies were only found in serum samples of about one seventh of the 325 dogs they tested.
While the researchers did not find evidence of the human virus in the dogs' emissions, the fact that they produce the antibody indicates that they did suffer active, if possibly low-key, infection, they explain.
To sum this up, the evidence indicates that our pooches can catch the virus from us, but they're not likely to.
It is not known whether human novovirus can cause clinical disease in dogs. Their doggie cells may not be easily enslaved to produce the human-viral particles, though it bears saying that they don't have to produce that many to infect us doting dog-lovers. Clinical investigators have estimated that as few as 18 virus particles can cause human infection, Caddy says.
That's not your slippers the dog's carrying
Having proven again that humans can infect dogs with novovirus, the next question is whether the dogs can become carriers and then, whether dog-to-human transmission exists too.
That suspicion first arose in 1983, during an outbreak of gastroenteritis at an old-age home that got traced to one elderly man and his diarrhetic dog. The dog proved to have antibodies to human novovirus, while control dogs tested at the time had no such antibodies.
Later, an epidemiological study in 2004 showed that humans had a greater tendency to test positive for novovirus antibodies if there was a dog in the household.
The bottom line is that science doesn't know yet whether Spot can infect you with human novovirus that he picked up heaven knows where, but given the indications, it makes sense to take extra precautions when either he, or anybody he's come into contact with, has gastroenteritis.
Caddy notes anecdotal evidence of the people and dogs in a household having the runs at the same time, but bemoans the lack of rigorous scientific research on that curious coincidence.
The Health Ministry begs to point out that novovirus isn't among the diseases that Israeli doctors have to report to the central authority, except in cases of outbreaks, such as at hospitals. But if there's a case in the house, the ministry suggests being extra particular an hygiene.
By the way, there are indications that farm animals such as cows and pigs may also be susceptible to catching the human novovirus. But not many of us keep cows and pigs in the house and sleep with them in the bed, or clean up their poop from the city streets.