Zoonoses

No, not the noses of zoo animals, but the diseases that can spread from animals to humans. It comes from the Greek “zoon” for animals and “nosos” for diseases, whereas the nose on your face gets its name from ancient Anglo-Saxon roots. Coincidence.

            Zoonoses have been on my mind because of two items in the news recently. One is at the top of every news feed right now and the other you’d have to scroll some distance to find, and only on certain sites.

            The first is coronavirus.

            Depending on happens with the current coronavirus epidemic in Wuhan, China, and depending on when you’re reading this, you may have to look back through the news archives to remind yourself of the details, or you may be dead from it, in which case you’re probably not reading this anyway. Some strains of coronavirus can be considered zoonotic. The current one in China, for example, is thought to have originated in wildlife, possibly pangolins. Middle Eastern Respiratory Syndrome (MERS) is another coronavirus, and it jumped from camels to people. SARS was also a coronavirus, and it seemed to have been passed from civets (a kind of cat-like creature).

            And now I have shocking news for you. Are you ready? Dogs get coronavirus too. Quite commonly, in fact. This is common enough knowledge that vet clinics have seen a surge in requests for coronavirus vaccination in the last few days. Yes, we do have a vaccine, but we rarely use it. We rarely use it because it is a really mild disease, at worst causing diarrhea, mostly in puppies. It has nothing to do with SARS, MERS or Wuhan corona, other than belonging in the same very general family of viruses. Being afraid of canine corona because other coronas are potentially lethal is like being afraid of garter snakes because cobras and rattlesnakes can kill you. For sure, some people are afraid of all snakes, but they (hopefully) understand that this is an irrational phobia, not a rational basis for decision making. Ditto for viruses. I get it if you’re germophobic, but don’t panic as a result. Your dog’s diarrhea will not kill you. It might be the end of your carpet, but not of you.

            The other zoonosis in the news is, I think, more interesting. A woman in Alberta was diagnosed with rare and aggressive liver cancer. In a surgical Hail Mary pass, the doctors planned to remove a large part of her liver and a number of nearby tissues. Then the surprise. It was not cancer, it was a parasite. It was a zoonotic tapeworm called Echinococcus multilocularis. Creepy, eh? This has been around for millennia, but in parts of the world, including western and northern Canada, it may be on the increase. Nobody knows for sure where this woman contracted it, but normally it’s through canid feces. Canid, not necessarily canine. But possibly. Echinococcus cycles between a definitive host, usually a coyote, wolf or fox, and an intermediate host, usually a rodent. The adult worm sets up shop in the intestines of the definitive host, shedding eggs in the feces for the intermediate host to ingest. The eggs then hatch into larvae which migrate and form cysts somewhere in the intermediate host, such as in the liver, waiting to be eaten by the definitive host and thus completing one of nature’s more disturbing circles of life (cue Elton John).

            Now read back over the third last sentence in the paragraph above. Note the use of the word “usually”, twice. The definitive host is usually a coyote, wolf or fox, but it could be a dog if the dog eats rodents. And the intermediate host is usually a rodent, but it could be a human if the human snuggles with their rodent-eating dog and then goes to eat a corned beef on rye sandwich without washing their hands first. To be clear, it doesn’t have to be a corned beef on rye, or any sandwich at all, but I’m sure you sorted that out for yourself. I was just trying to create a more memorable mental image. So, if you suspect your dog of eating rodents you should mention it to your vet (we don’t always ask, although I think we will be doing so more often now) because there are effective deworming medications for this, and you should always wash your hands before eating. I know I sound like your mother. Well, she was right. At least about this. Just imagine how much more insistent she would have been if she knew about worms that formed giant cysts in your liver.

            This is still very rare, so please don’t panic. However, while no concern whatsoever is warranted for canine coronavirus, some mild attentive concern is appropriate for Echinococcus. This frontier between human medicine and veterinary medicine is fascinating. One list I saw had 64 different zoonoses on it, from African sleeping sickness (from cattle via tsetse flies) to Zika fever (from primates via mosquitoes), and while most are tropical and passed through insect vectors from their animal hosts, some are direct from your pet to you. Of these, really only rabies is fatal and it is very rare here because of vaccination. Everything else, from ringworm (incidentally, not a worm and not always in a ring – rashfungus would be a better name) to scabies to giardia are not especially common or especially serious, unless you have a weakened immune system.

            In closing, I have to wonder if camels at the zoo with MERS sneezed on you, would that be a zoonosis from zoo noses? (Sorry.)

Update: 
Today there was an item in the news reporting that a dog in Hong Kong had caught the corona virus, now officially known as COVID-19. This will cause silly people to panic. In case you are feeling like you are in peril of becoming silly yourself, let me explain why you shouldn't do that. 
First of all, this is all highly unsurprising. COVID came from another mammal in the first place, so it reasonable to assume that it could pass to yet more different mammals. This is in no way unusual. Ferrets can get human flu for example. The happy news though is that when a virus jumps species it always changes. Usually it gets much weaker. Sometimes, rarely, it gets stronger. Given the thousands of dogs and cats exposed, if COVID was getting stronger after going into them, we would know about it by now. This is one single dog and this dog isn't even sick, he just tested positive. COVID apparently isn't even replicating in this dog, so he definitely can't pass it on. The virus has indeed gotten much weaker. So don't be silly and panic. Not about this, anyway. There are plenty of far worthier things to panic about.