Yesterday we had a lunch and learn, very similar to in vet school where a pharmaceutical rep comes in to teach us about their newest release, in this case it was for flea/tick/intestinal parasite control and we eat pizza.
Recently in the news, it was discovered that a woman initially thought to have cancer of her liver, actually had the hydatid form of a tapeworm called Echinococcus multilocularis. If you’re a veterinarian you probably remember studying the lifecycle of this tapeworm. If you’re not then I will briefly summarize for your enjoyment. The primary (definitive) host is usually a canid (foxes and coyotes in Southern Ontario, also in the prairie provinces where I studied veterinary medicine). Sometimes dogs will also act as a primary host. These dog-like species carry the adult tapeworms, and the eggs are defecated in tapeworm segments (proglottids) into the environment. If you own a dog with these tapeworms, that means the poop is in your yard. Adult worms do not shed consistently, which also means that even if you are doing annual fecal tests on your dog, then you could be missing these worms. But, in order for your dog (or fox or coyote or wolf) to be infected with the adult tapeworms, they have to ingest the worms in a type of larval stage that we call the hydatid cyst or metacestode in the secondary (intermediate) host. In the case of E. multilocularis it is typically a rodent like a mouse. The mouse got infected by consuming the eggs from the environment. See the graphic for more info.
So now that you have a slight understanding of the lifecycle of the parasite. How did this woman get the hydatid cyst, you may ask? From eating tapeworm eggs. Maybe this woman had a dog, and accidentally consumed feces or eggs. Maybe there were containments on vegetables from a local farm that weren’t washed thoroughly or cooked prior to ingestion. We may never know because the cysts are thought to be growing inside her for ten years.
What was interesting in this new‘s article was that they use Albendazole to treat the hydatid form of the parasite. This drug is very close to a deworming medication we use for puppies to treat giardia called fenbendazole. So I guess if I am ever suspicious of hydatid disease in a dog, then some panacur may be on the list!
But, standard treatment for adult tapeworms in dogs is praziquantel. If you treat your dog with a praziquantel product, this will clear the adult worms and prevent the spread of the parasite to any intermediate host including your itchy-bum sucky-thumb children.
The reason it peaked my interest is that we are switching to an all-in-one parasite control medicated chew that will cover for fleas, ticks, some intestinal parasites like hookworms and roundworms, as well as heartworm prevention. Roundworms and fleas are pretty common, and if you control fleas then you don’t get the other tapeworm (dipylidium). Then I would say ticks are the next most common in our practice. Heartworm is rare in Toronto, but it’s there and can be a killer if a dog gets infected. From a human health perspective I would say that Lyme disease is the most devastating. So while tick protection for your dog‘s health is recommended, more importantly if your dog sleeps in your child’s bed, you definitely don’t want the dog bringing home a crawly friend!
But this all-in-one chew, doesn’t cover for tapeworms. So if your dog is a hunting dog, if your dog consumes rodents, if they are off-leash anywhere in wooded or grassy areas where there might be mice, or carcass of mice, you will want some praziquantel!
Edit March 29, 2020: For more information from a specialist in emerging infectious diseases, head to Dr. Scott Weese's blog "Worms and Germs".