Cashew’s Case: An Emerging Parasitic Threat

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Despite veterinarian recommendations, many pet owners struggle to successfully provide year-round parasite protection for their pet, leaving them vulnerable to serious health risks.^1,2

Although ectoparasites such as fleas and ticks often receive pet owner attention due to their visibility, other more “invisible” parasites that still have serious health implications for both pets and humans may go unnoticed. Emerging zoonotic threats are making it more important than ever for veterinarians to stay vigilant and educate clients on the risks that may be present in their pet’s environment.

Meet Cashew

Cashew, a 2-year-old neutered male Staffordshire terrier, was presented for his annual examination and preventive care. His owners reported that he was current on monthly heartworm and flea and tick prevention, although they were unsure which brands they were using. They reported that he was eating, drinking, and acting normally at home, but he occasionally had soft stools. He lived an active lifestyle on the family farm and had been a great addition to the family since his adoption last year.

Physical Examination & Diagnostics

Cashew was bright, alert, and responsive during his visit. Physical examination was unremarkable. His owners agreed to the recommended vaccines, baseline CBC and serum chemistry testing, heartworm testing, SNAP Giardia spp test, and fecal examination. Heartworm test results and SNAP Giardia spp results were negative, and the veterinary team explained they would call in the coming days with results of the additional testing.

The next day, the results of Cashew’s CBC, serum chemistry, and fecal testing came back. Although blood work showed no concerns, fecal PCR testing was positive for the tapeworm Echinococcus multilocularis.

Echinococcus spp & Zoonotic Risk

Echinococcus spp are tapeworms of emerging concern in the United States and Canada. Although the most common tapeworms of dogs and cats, Dipylidium caninum, is spread through ingestion of fleas, the Echinococcus spp life cycle does not involve fleas.³ In dogs, Echinococcus spp infection most commonly occurs after consumption of an intermediate host such as rodents or livestock.⁴ Adult tapeworms then develop in the small intestine, shedding eggs in stool and causing contamination of water and soil in the area.⁴ Although infected dogs generally show no clinical signs of enteric echinococcosis, some infected dogs will, in fact, present with diarrhea or weight loss.⁵

The zoonotic risk for Echinococcus spp (with the primary risk coming from E multilocularis and E granulosus) is of particular concern, as it can cause serious or even deadly disease in humans.⁶ After tapeworm eggs are ingested and then develop to larvae, the larvae migrate through the circulatory system, traveling to distant organ sites and developing into cysts. These cysts can be difficult to diagnose, difficult to treat, and mimic metastatic disease in humans.⁴ In some instances of Echinococcus spp infections, dogs may also serve as aberrant intermediate hosts and develop a similar serious cystic disease known as canine alveolar echinococcosis.⁶

Active tapeworm infestations with the most common tapeworms species (ie, Taenia spp, Echinococcus spp, Dipylidium spp) can be treated with anticestodal praziquantel and/or epsiprantel.⁷ In addition to treating an existing infection, care must be taken to eliminate exposure to the intermediate host (eg, fleas, livestock, rodents) to help prevent recurrence of tapeworm infestation.

In Cashew’s case, a routine fecal PCR, a highly sensitive fecal test, was run as part of his clinic’s annual visit protocol.⁸ It is important to note that, because pets with tapeworms often do not have clinical signs, they may be more likely to go undiagnosed. In addition to a lack of clinical signs, tapeworm infestations may be difficult to detect in patients due to the low sensitivity of common fecal testing methods, resulting in infections being underdiagnosed.⁷ Echinococcus spp have been of growing concern in recent years, with cases showing a much wider distribution in Canada and the United States than in previous years, including emergence in novel areas (Colorado, Nevada, Wyoming, Montana, Illinois, Washington, Idaho, Kansas, and Oregon).⁵ To prevent zoonotic infections, the Companion Animal Parasite Council recommends routine monthly praziquantel in dogs residing in areas where E multilocularis is endemic.⁹

Cashew’s Parasite Management Plan

After Cashew’s diagnosis with E multilocularis, the zoonotic risks were explained to the owner. Praziquantel was administered to Cashew. The risk for reinfection was also explained, and a monthly parasiticide containing praziquantel was recommended. Cashew was scheduled to return in 4 weeks to repeat the fecal PCR to ensure resolution of infection, and his family was encouraged to talk to their human healthcare provider to further discuss zoonotic risk.