Cestodes and Trematodes

Taenia, Echinococcus, Dipylidium, Diphyllobothrium 

Species of veterinary importance include Taenia pisiformis, T. krabbei, T. hydatigena, and T. taeniaeformis; these species are not zoonotic.

Host range: Dogs and cats serve as definitive hosts, with a wide range of wildlife intermediate hosts.

Geographic range: Widespread, wherever dogs and cats have access to wildlife.

Life cycle: Dogs and cats harbour adult cestodes in their small intestine and pass segments and eggs in feces. Wild-life intermediate hosts are infected by ingestion of eggs in environment. Dogs and cats are infected by consumption of larval stage (metacestode, usually a cysticercus) in the tissues of intermediate hosts.

Diagnosis: Segments can be observed in feces by owners. Taeniid-type eggs (indistinguishable from Echinococcus spp.) can be detected on microscopy following fecal flotation or sedimentation, but these techniques have low sensitivity. Infected dogs and cats generally show no clinical signs.

Management: Prevent access of pets to wildlife intermediate hosts and don’t feed raw offal/meat. Routine deworming with praziquantel or epsiprantel is recommended for high-risk animals. Reactive deworming is indicated if taeniid-type eggs are detected in feces, especially since these are indistinguishable from Echinococcus spp. Note that only some praziquantel products are specifically labeled for treatment of Echinococcus spp.

Species of importance in Canada include E. canadensis (E. granulosus G8 and G10) and E. multilocularis. Both are zoonotic.

Host range: Dogs (and cats for E. multilocularis) serve as definitive hosts. Wildlife intermediate hosts for E. canadensis are cervids (moose, elk, caribou, deer). Wildlife intermediate hosts for E. multilocularis are rodents (lemmings, voles, deer mice), and dogs can serve as aberrant intermediate hosts. People can serve as aberrant intermediate hosts for
both species.

Geographic range: E. canadensis is present through-out Canada where suitable wildlife hosts (wolves, coyotes, cervids) exist; it is not thought to be present in the Atlantic provinces and Island of Newfoundland. E. multilocularis is present in northwestern Canada, especially the prairie provinces, and appears to be expanding its range into Ontario.

Life cycle: Dogs (and, rarely, cats for E. multilocularis) harbour adult cestodes in their small intestine and pass eggs in feces. Wildlife intermediate hosts are infected by ingestion of eggs in environment. Dogs and cats are infected by consumption of larval stage (metacestode, a cystic hydatid for E. canadensis and alveolar hydatid for E. multilocularis) in the tissues of intermediate hosts. Rarely, dogs may also develop alveolar hydatid cysts (alveolar echinococcosis).

Diagnosis: Segments are very small and will not be observed in feces by owners. Taeniid-type eggs (indistinguishable from Taenia spp.) can be detected on microscopy following fecal flotation or sedimentation, but these techniques have low sensitivity. Infected dogs and cats generally show no clinical signs as definitive hosts. Dogs with alveolar echinococcosis may have severe clinical disease and lesions can be detected on medical imaging.

Management: Prevent access of pets to wildlife intermediate hosts and don’t feed raw offal. Routine deworming with praziquantel is recommended for high-risk animals in endemic regions (note: only some praziquantel products are specifically labeled for treatment of Echinococcus spp.). Reactive deworming is indicated if taeniid-type eggs are detected in feces. Alveolar echinococcosis in dogs is best managed with complete surgical resection, if possible, and/or life-long albendazole treatment.

There is only one species, and it is considered zoonotic, but not directly from dogs or cats.

Host range: Dogs and cats serve as definitive hosts, with fleas (Ctenocephalides spp.) and, less commonly, dog chewing lice (Trichodectes canis), serving as intermediate hosts.

Geographic range: Wherever dogs and cats have fleas (southern BC and MB, ON, QC, and the Atlantic provinces).

Life cycle: Dogs and cats harbour adult cestodes in their small intestine and pass segments and egg packages in feces. Flea larvae are infected by ingestion of eggs in environment. Dogs, cats, and people (usually children) are infected by consumption of adult fleas (or chewing lice) containing the larval cestode (a cysticercoid).

Diagnosis: Segments can be observed in feces by owners. Characteristic egg packages can be detected on microscopy following fecal flotation or sedimentation, but these techniques have low sensitivity. Infected dogs and cats generally show no clinical signs.

Management: Flea control is key to prevention and management of Dipylidium caninum. Routine deworming with praziquantel or epsiprantel is recommended for high-risk animals (where access to fleas cannot be controlled).

There are multiple species, the most common in Canada in dogs being D. latum, D. dendriticum, and D. ursi. Spirometra is a related species that may rarely infect dogs and cats. These are considered zoonotic, but not directly from dogs.

Host range: Dogs and other fish-eating vertebrates serve as definitive hosts, with aquatic wildlife serving as intermediate and paratenic hosts.

Geographic range in Canada: Wherever dogs and cats have access to locally harvested fresh fish (whitefish, salmon, trout, char, grayling, burbot, perch, walleye, pike, sticklebacks, etc).

Life cycle: Dogs and cats harbour adult cestodes in their small intestine and pass segments and eggs in feces. Aquatic crustaceans (first intermediate hosts) are infected by ingestion of hatched eggs in environment. Dogs, cats, and people are infected by consumption of the larval stage (plerocercoid) in the tissues of fish serving as second inter-mediate or paratenic hosts.

Diagnosis: Segments and long ribbons can be observed in feces by owners. Characteristic operculate eggs can be detected on microscopy following fecal flotation or sedimentation, but these techniques have low sensitivity. Infected dogs and cats generally show no clinical signs.

Management: Treatment involves high-dose, off-label praziquantel. Prevention involves eliminating access to raw fish (owners should feed only cooked or previously solidly frozen fish) and preventing dogs from fecally contaminating water.

Species of veterinary importance include Alaria spp., Metorchis conjunctus, and Nanophyetus salmincola. These species are considered zoonotic, but not directly from dogs.

Host range: Dogs and cats serve as definitive hosts, with aquatic wildlife serving as intermediate and paratenic hosts.

Geographic range: Wherever dogs and cats have access to aquatic wildlife.

Life cycle: Dogs and cats harbour adult flukes in their small intestine (Alaria, Nanophyetus) or gall bladder
(Metorchis, dogs only) and pass eggs in feces. Aquatic snails serve as first intermediate hosts for all trematodes. Second intermediate host species are frogs for Alaria, salmonid fish for Nanophyetus, and sucker fish for Metorchis. Dogs, cats, and people are infected by consumption of larval stages (metacercariae) in the tissues of second intermediate hosts, or a small mammal paratenic host (for Alaria). Transmammary transmission may occur in cats with Alaria. 

Diagnosis: Characteristic, operculate trematode eggs can be detected on microscopy following fecal flotation or, preferably, sedimentation, but these techniques have low sensitivity. Eggs of Alaria float more readily than those of other flukes and are large and yellow. Eggs of Metorchis have a prominent lip on the operculum. Infected dogs and cats generally show no clinical signs, although liver abscesses have been reported for Metorchis. A rare but potentially fatal rickettsial disease called salmon poisoning is associated with Nanophyetus in coastal British Columbia

Management: Treatment involves off-label praziquantel. Prevention involves eliminating access to raw frogs or fish
(owners should feed only cooked or previously solidly frozen fish) and preventing dogs from fecally contaminating water. Treatment for salmon poisoning requires antirickettsial drugs such as doxycycline.