With warmer months approaching, it will soon be time to take your canine family members in for their yearly heartworm and parasite prevention. Commonly, deworming medication prevents heartworm, roundworm, and hookworm infections. Based on your dog’s lifestyle, you may want to ask your veterinarian about tapeworm prevention as well. Ontario was thought to be free of a zoonotic species of tapeworm called Echinococcus multilocularis, however, a recent study published February 2019 has found 25-37% of coyotes and foxes in southwestern Ontario to be infected with E. multilocularis.
Lifecycle
Tapeworms such as E. multilocularis live in the intestine of wild canid species such as coyotes and foxes. Segments of the tapeworm containing eggs are then shed in the feces. In a normal lifecycle, an intermediate host such as small rodents ingest these eggs which hatch inside the GI tract and then migrate to different tissues in the body to develop into infective cysts. These rodents are then ingested by wild canid species where the worms mature into adults in the intestines, and the cycle begins again. Eggs will be shed in the feces five weeks after ingesting an infected intermediate host.
Domestic dogs may become infected in two ways: if they are hunters and ingest an infected rodent, they will have an intestinal infection and shed tapeworms in their feces. If they are exposed to infected feces with tapeworm segments or eggs, they may instead become intermediate hosts where the immature tapeworms spread to different tissues in their body and form cysts. Dogs may be infected with both the intestinal form and the cystic form of the tapeworm at the same time, for example, if they eat a rodent, become infected, and then ingest their feces.
Zoonosis
Humans may become infected with E. multilocularis as well and become accidental intermediate hosts if they ingest eggs that are shed in the feces of infected wildlife or their own dogs. The immature tapeworms will migrate to different tissues in the body and form cysts. Most common sites of migration are the liver, lungs, and brain. Signs of infection would be abdominal pain, weight loss, and signs similar to liver cancer and cirrhosis of the liver. Because the cysts are very slow growing, humans may be infected but not show any signs for 5-15 years.
Prevention
Dogs that are infected with the adult form of this tapeworm in their intestines do not show any clinical signs, however, due to the human health risk of infection, it is recommended that dogs that have a potential of exposure are treated regularly for tapeworm.
Dogs that ingest rodents or that like to eat or roll in feces are at risk for tapeworm infection. Prevention and treatment of tapeworm infection are with a dose of a medication called praziquantel once a month during periods of high risk of exposure.
For prevention of human transmission, it is also recommended to wash your hands after petting your dog and wash all wild-picked foods well before ingesting.
Written by: Dr. Connie Tuck, DVM
Further reading:
https://www.wormsandgermsblog.com/2019/01/articles/animals/dogs/echinococcus-multilocularis-ontario-canada/