Dogs host various species of tapeworms but to be transmitted from pets to people, you'd have to swallow tapeworm eggs or larvae. Since nobody does that on purpose, dog-to-human transmission is rare. Even when it happens, in most cases, the disgusting creatures are easily killed by medications. That's the good news. The bad news is that in certain regions, human tapeworm infections contracted from dogs aren't cured easily and can be not only serious but deadly.
Disgusting but Largely Harmless Tapeworms
For a parent, recovering from the shock of seeing tapeworm segments squirming on the anal area or in the feces of a child may be more difficult than getting rid of the parasite. These "proglottids," about the size of a grain of rice, contain the eggs of Dipylidium caninum, the most common dog-infesting tapeworm, which can grow to lengths of 20 inches. To contract it, dogs must ingest infested fleas or lice, which can happen easily when they groom themselves. Among human victims, children are most vulnerable. If a dog with a partially digested flea in his mouth licks someone's face, or children playing in a flea-infested indoor or outdoor area put dirty hands in their mouths, they can contract the infection. According to Dr. Alan Greene, pediatrician, author and founder of the award-winning website DrGreene.com, based in Danville, California, infections have been reported in infants as young as 5 weeks. Prescription pills quickly dissolve these parasites.
Serious and Sometimes Fatal Tapeworms
The Echinococcus granulosus tapeworm doesn't need fleas to do its dirty work. Though this parasite can infest many animals, it's especially fond of sheep and cattle. Dogs contract it by eating raw meat from infected livestock, then shed eggs in their feces. If eggs get into the fur of infected dogs, people who pet them can get them on their hands and transfer them to their mouth. Eating produce grown in soil where infected dogs have defecated without washing it first also can transmit the infection, says the Centers for Disease Control and Prevention. This tapeworm's eggs are so resilient that they survive cold winters. The worms typically multiply inside the lungs, muscles, organs, bones or brain for 10 to 20 years before symptoms, usually obstructions within an affected organ, develop. Treatment involves surgery and drugs but an information brochure issued by the American Academy of Family Physicians notes that the mortality rate is 4 to 5 percent.
"Almost Always Fatal" Tapeworms
Some dogs love rolling in feces but if their pile of preference contains the eggs of the E. multilocularis tapeworm, the consequences for humans can be catastrophic. Thankfully, the disease these tapeworms cause, alveolar echinococcosis, is rare but according to the CDC, the parasite's North American range includes the north central region from eastern Montana to central Ohio, although human cases have also been reported in Alaska and Canada. In addition to hand-to-mouth transmission from contaminated dog fur, humans can be exposed to infection by contact with the feces of dogs who have eaten infected rodents. Worm-filled cysts usually start colonizing the liver and over many years, spread throughout the body, destroying surrounding tissue, before the disease is detected. At best of times, it's difficult to impossible to treat but left untreated, is "almost always fatal," says the AAFP.
Prevention Is the Best Medicine
Strict adherence to flea control is the best way to ensure that your dog doesn't piggyback D. caninus into your household. More sound advice from the CDC: Wherever you live, after you've touched your dog or cat, wash your hands thoroughly with soap and warm water before handling food. If you have kids, teach them to do the same. Don't allow your pets to wander freely. If you live in an area where E. multilocularis is known to exist and think your dog may have eaten a rodent, ask your vet what to do. And if you enjoy fruit and vegetables gathered from the wild or picked directly from the ground, wash them thoroughly, or cook them, before eating them.
- Centers for Disease Control and Prevention: Dipylidium FAQs
- DrGreene.com: Dog Tapeworms and Children
- Medical News Today: What Are Tapeworms? What Causes Tapeworm Infection?
- Centers for Disease Control and Prevention: Cystic Echinococcosis (CE) FAQs
- American Family Physician: Echinococcosis—An Emerging Parasite in the Immigrant Population
- The Merck Manual Professional Edition: Echinococcosis (Hydatid Disease)
- Centers for Disease Control and Prevention: Alveolar Echinococcosis (AE) FAQs
- DrGreene.com: Meet Dr. Greene