Tapeworm infection is often overlooked, underdiagnosed, and indertreated in dogs and cats throughout the Unites States. To reverse this trend, it's imperative that veterinarians and their team members understand and thoroughly educate clinets about the risk of tapeworm zoonoses and the importance of prevention.
Byron Blagburn, MS, PhD, Department of Pathobiology, College of Veterinary Medicine Auburn University, Auburn, AL
Dwight Bowman, MS, PhD, Department of Microbiology and Immunology, College of Veterinary Medicine Cornell University, Ithaca, NY
Jonathan Cooper, DVM, PhD, Co-Owner, Westbury Animal Hospital Houston, TX
Kevin Kazacos, DVM, PhD, Department of Comparative Pathobiology, School of Veterinary Medicine Purdue University, West Lafayette, IN
Susan Little, DVM, PhD, Department of Veterinary Pathobiology, Center for Veterinary Health Sciences Oklahoma State University, Stillwater, OK
It's often overlooked, underdiagnosed, and undertreated in dogs and cats throughout the United States. To reverse this trend, it's imperative that veterinarians and their team members understand and thoroughly educate clients about the risk of tapeworm zoonoses and the importance of prevention. This Q&A, moderated by Dr. Byron Blagburn, examines the prevalence and life cycle of common tapeworms and discusses strategies the veterinary team can use to manage and prevent infection.
Q: What is the most common tapeworm species, and what is its life cycle?
Susan Little: Dipylidium caninum is the most common tapeworm in North American dogs and cats. As most veterinary professionals know, it is acquired by ingesting infected fleas. A dog or cat with a Dipylidium caninum adult in its small intestine sheds egg-filled proglottids in its feces, and those proglottids in the environment are consumed by flea larvae. As the flea larva matures into an adult flea, the tapeworm egg develops into an infectious cysticercoid. When a dog or cat ingests the adult flea, the cysticercoid emerges in the animal's small intestine. The protoscolex attaches to the wall of the small intestine, where the adult tapeworm forms. It is a rapid process. Within two to three weeks of ingesting an infected flea, a dog or cat can shed proglottids in its feces.
Cat flea (Ctenocephalides felis)
Byron Blagburn: Would the same process occur if a small child happened to ingest a flea?
Little: Yes. Dipylidium tapeworms can develop and produce proglottids in a child when that child inadvertently ingests a flea containing the cysticercoid. The tapeworm will continue to develop in that child's small intestine, and the parents may find proglottids in the diaper or on the anus.
Preventing zoonotic infections
Q: How prevalent is Dipylidium infection?
Little: The estimates for infection rates are all over the map—from 4% to 50% or higher. It really depends on the flea prevalence in a particular area—the prevalence of Dipylidium follows. In addition, the proglottids are not evenly distributed throughout the feces. So if you do a fecal flotation on just 4 grams of feces, the odds of finding a proglottid are low. Fecal exams are not a good screening tool for Dipylidium infection.
Diagnosing tapeworm infection
Q: What is the life cycle of Taenia species?
Kevin Kazacos: The life cycle of Taenia species involves other mammals. Infected dogs and cats shed Taenia proglottids in their feces, just like with Dipylidium, but then other mammals acquire the organism by ingesting the eggs. The eggs hatch in that mammal and the larvae migrate into organs, usually the liver, and grow to form large fluid-filled larvae. The dog or cat becomes infected again by eating that infected mammal. The larva contains the tapeworm scolex—the tapeworm head that attaches to the intestinal wall and generates proglottids. So for Taenia species, carnivorism is necessary for tapeworm transmission back to the dog or cat.
Dogs acquire Taenia pisiformis by eating cottontail rabbits, and cats acquire Taenia taeniaeformis by eating infected mice. These are the two most common taeniids we see. Other Taenia species and Echinococcus, which includes zoonotic taeniids, are seen less often but are hard to distinguish from the aforementioned species. As with Dipylidium, Taenia is diagnosed by finding proglottids in the feces, on the rear end, or in the environment of dogs and cats.
Q: What are the effects of tapeworm infection on dogs and cats?
Dwight Bowman: Usually we think of adult tapeworms as fairly benign in dogs and cats. But there are reports of impactions, sometimes fatal, in young puppies with Dipylidium infection. I have an article in press on Taenia taeniaeformis in cats causing impaction that required surgery and removal of the worm.1 Although these cases occur, they are often not reported.
Q: How common is human exposure and infection?
Bowman: Dipylidium infection is probably the most common tapeworm zoonosis in the continental United States. It may be a little less common than it once was, probably because of better flea control. Again, a person becomes infected through ingestion of the intermediate host—the flea—and not ingestion of the stage passed by the dog or cat.
Kazacos: With the zoonotic Taenia species and Echinococcus, people become infected with the larval stages, and the method of infection is also different. With Dipylidium, you have to eat the flea and ingest the larvae to become infected with adult tapeworms. With the taeniids, you ingest infective eggs and become infected with tapeworm larvae. It is important to realize that an animal can have infective eggs in its perianal area and fur.
Bowman: Unlike hookworms or roundworms, these taeniids are infectious when they come out.
Kazacos: That's correct. With zoonotic taeniids, simple contact and accidental ingestion of those eggs can cause infection, and that is an important distinction. Proper sanitation and handwashing in the clinic are always good ideas, because taeniid infections may be hard to identify with certainty.
Q: What is the best way to treat and prevent tapeworms, and is reinfection a problem?
Jonathan Cooper: We use praziquantel as our tapeworm treatment and find it to be very effective. Oftentimes, if there is a major flea infestation and potential for reinfection, we readminister the praziquantel. My assumption is that the animals are being reinfected with fleas that transmit the tapeworms, so generally I discuss flea control with the pet owner.
Little: Reinfection is very common. In fact, many practitioners will prescribe a second treatment of praziquantel two weeks after the first treatment. The initial treatment is fully effective for the current infection, but it takes some time to get a flea problem under control, so these veterinarians assume reinfection will occur before the flea problem is resolved.
Blagburn: In east central Alabama, the only way we can manage chronic Dipylidium infection is by administering praziquantel every three to four weeks. There are times of year when administering it four or five months in a row is the only way we can bring the infection under control.
Q: Should a product like praziquantel be administered monthly as part of a broad-spectrum, continuous control program?
Cooper: In regions of the country where fleas are a huge problem and in areas where tapeworms are endemic, it would make a lot of sense. Similarly, in areas where Dipylidium as well as Taenia and Echinococcus are diagnosed, the benefit of preventing zoonotic disease has real value.
Blagburn: Obviously there is an interest in our industry to move toward more frequent administration of tapeworm medicines the way we've done with heartworm preventives and broad-spectrum internal parasiticides.
Bowman: As long as the treatment is part of another protocol, such as heartworm prevention or internal parasite control, I think most practitioners and owners would accept it. It would be different if the product were just targeting tapeworms.
Q: Clients are used to monthly heartworm preventives with other products added. But what do you tell clients who are resistant to administering additional frequent-use medications?
Kazacos: Some veterinarians think that if dogs are on a monthly heartworm combination product, all parasites are taken care of. I have seen some veterinarians stop doing routine fecal diagnostics for that very reason. Nothing could be further from the truth. Heartworm combination products, as good as they are, actually have a fairly narrow treatment spectrum. We have to consider that animals on these products may become infected with a variety of other parasites, including tapeworms.
Blagburn: I would tell clients that tapeworm control is additional insurance when we know that flea-control products, while very good, are not 100% effective all of the time. Just a few fleas can propagate a tapeworm infection.
Kazacos: We could add that the pet is not the only source of fleas. It is well-known that suburban wildlife, like raccoons and opossums, also carry fleas that infest dogs and cats. At night, suburban wildlife seed people's yards with flea eggs and, thus, help maintain the flea life cycle. So animals can become infected from other sources even though they are on appropriate flea control.
Cooper: Sometimes clients just don't want to see them or admit that their pet has a flea problem.
Blagburn: Clients often tell me they don't see fleas, but I can drag a comb through the hair coat and point out the flea dirt.
Q: Would it be hard to convince clients to use a broad-spectrum agent that included praziquantel in Dipylidium- and Taenia-endemic areas if cost wasn't prohibitive?
Cooper: I think clients would accept it if they and their veterinarian were convinced it was an effective and safe product.
Q: How important is it to mention the zoonotic potential of tapeworms, especially Dipylidium?
Cooper: It is very important. I don't think most owners understand or recognize the zoonotic potential, so making them aware of it certainly helps us convey the importance of parasite control.
1. Wilcox RS, Bowman DD, SC Barr, et al. Intestinal obstruction in a cat due to Taenia taeniaeformis. JAAHA 2007;in press.
2. Companion Animal Parasite Council. Cestodes: Tapeworm Guidelines I (Cyclophyllidean Cestodes*). Available at: www.capcvet.org/default.asp?p+Guidelines_Tapeworm_I&h=0&s=. Accessed March 18, 2008.