Written by: Dr. Chip Coombs
In recent months there has been a great deal of media attention to an emerging disease risk that involves a tapeworm called Echinococcus multilocularis. This tapeworm has been around for a long time and is worldwide in its distribution, although it is primarily found in the Northern hemisphere. It is known to exist presently in the Arctic and from B.C to Ontario. Prior to 2009, it had never been diagnosed in a dog in Canada. However, recent studies conducted by researchers at the Ontario Veterinary College have noted that this tapeworm is far more prevalent in Ontario’s wild Canidae population than was originally thought. It is estimated that presently about 1 in 4 coyotes/ foxes have this tapeworm and it will only be a matter of time before it will become even more widespread.
Although Echinococcus multilocularis is a tapeworm that is usually found in wild Canidae, it can be transmitted to domestic dogs and cats. The reason it is gaining so much attention is that, not only is the incidence of the tapeworm on the rise but, under certain circumstances, it can also be transmitted to humans (making it a zoonotic disease).
Although outdoor cats that are hunters could become infected, the risk of them transmitting the eggs to humans is considered to be very low. This is because the viable egg numbers that they shed in their feces is much lower than that which occurs in domesticated or wild Canidae.
All tapeworms follow a typical pattern for their normal life-cycle. They have a resident host (in this case, the coyote / fox) and require an intermediate host in order to complete their life cycle (a rodent, in the case of Echinococcus multilocularis). The adult tapeworm resides in the coyote’s intestinal tract, and eggs from the tapeworm are shed in the coyote’s feces. These will disperse through the soil, and the grass is eaten by any one of many members of the rodent family. The eggs then develop into larvae, which form cysts within the liver of the rodent, which is then later eaten by another coyote. The cysts within the rodent’s liver then develop into adults again within the coyote’s intestinal tract, completing the life cycle which takes about 3-4 weeks.
Although the rodent is the natural intermediate host, the eggs can be ingested by other species. Furthermore, rodents and their remains can be eaten by domestic dogs and cats. What this ultimately means is that there are a number of different ways that people can be infected.
If the eggs from coyote fecal matter come in contact with wild fruit (berries) or with food in a vegetable garden, neither of which have been washed properly, then there could be human ingestion of the eggs. If this tapeworm were to develop into adult worms within a domesticated dog, then the eggs would be shed in their feces and could become attached to the haircoat around their back end. Our pets are also notorious for scent rolling on another animal’s feces, which is an excellent way to get eggs on their coat. Normal petting and grooming of that pet would then expose the owner to direct contact with the tapeworm eggs, which could then be inadvertently ingested by the owner through hand to mouth transfer.
When people ingest these eggs, as an accidental host, the same process that takes place in rodents could potentially occur. The eggs could develop into larval cystic structures within the person’s liver and grow very slowly over many years to very large masses. These masses are not easy to treat through surgery and medication, and could potentially be fatal. Our domesticated dogs, if they ate a rodent would normally experience a similar life cycle pattern of this tapeworm, as that which occurs in a wild canid. However, if they were to directly eat the infected feces of a fox of coyote, then they could be ingesting a very large egg burden. In this case, instead of the typical lifecycle of Echinococcus taking place in the intestines, the dog runs the risk of developing a liver infestation similar to what occurs in people, with equally dire potential consequences. The obvious course of action is prevention of this zoonotic potential.
Hunters, trappers and veterinarians are naturally at greater risk because of their work. If your lifestyle includes eating wild berries or growing your own vegetables, then ensure they are thoroughly washed before being consumed. The major source for people, though, is through their pet dog. One can try to minimize the consumption of foreign mystery material when out on walks or rolling in who knows what, but if they are ever off leash, this is very difficult. Not every dog’s lifestyle is a concern for their owner, because they are walked on a leash on the sidewalk. For those, however, who have dogs often off leash either in city ravines, or at a cottage or on a farm, then the potential for the dog to get exposed to this tapeworm increases significantly. For these dogs, the simplest solution is to routinely deworm them orally with a drug called praziquantel, which is a very safe drug. Echinococcus multilocularis is a tougher tapeworm to get rid of than most, and requires a higher dose of praziquantel than most other types of tapeworms. 5 mg/kg should be effective, and a pet owner can discuss with their veterinarian how frequently they should be giving the medication, as well as what form or product is best suited for their dog. Washing your hands, and encouraging your children to wash their hands thoroughly, after petting or grooming your pet is an excellent preventive.
It seems every so often, something new crops up when it comes to our pets that deserves an owner’s attention. It is important to keep the risk relative to your lifestyle and that of your pet in perspective. However, this recent emerging problem is on the increase and it behooves having a conversation with your veterinarian to monitor its progression, and to determine if and how preventive measures should be undertaken based on the lifestyle of your dog.
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