History

An approximately 3-year-old male cat presented September 2024 (day 1) for diarrhea of unknown duration. He had been surrendered the day prior to a local rescue organization near Calgary, Alberta, Canada. The cat’s previous ecto- and endoparasite prevention and vaccination status were unknown. The rescue organization reported that the cat was a stray. Other history included that he was found on a rural property with a barn, and other dogs and cats lived on the premises. On physical examination, the cat was found to be intact, malodorous, and in good body condition at a weight of 4.8 kg (body condition score, 6/9). No other physical examination abnormalities were noted.

Diagnostic Findings and Interpretation

On day 1 of presentation, a fecal sample was submitted for fecal quantitative PCR (qPCR) testing to assess for infectious causes of the cat’s diarrhea, such as fecal parasites. Empirical treatment with metronidazole (14.5 mg/kg, PO, q 12 h) was started, pending results of the fecal panel. The fecal qPCR tests ([1] KeyScreen GI Parasite PCR and [2] Diarrhea FastPanel; Antech Diagnostics, Mars Petcare Science & Diagnostics) detected DNA of the following organisms: Echinococcus multilocularis, Toxocara cati, Cryptosporidium felis, and Campylobacter jejuni. These results were confirmed by repeat DNA extraction and qPCR of the same sample (Antech Diagnostics’ laboratory, Mississauga, ON, Canada) and by Antech Diagnostics’ research and development R&D department (Fountain Valley, CA). Additionally, the E multilocularis qPCR results were confirmed by the Animal Health laboratory at the University of Guelph, Ontario, and the Zoonotic Parasite Research Unit, University of Saskatchewan, as previously described.¹

A CBC, serum biochemistry, T₄, FeLV/FIV test, and urinalysis were performed due to ongoing diarrhea on day 18. A mild elevation in ALT (123 U/L; reference range, 10 to 100 U/L) was the only hematological abnormality. On urinalysis assessment, collected via cystocentesis, there were > 50 RBCs/hpf (normal, 0 to 3/hpf), occult blood 3+ (normal, negative), and 2+ protein (normal, negative).

Treatment and Outcome

After communication of the fecal qPCR result to the primary veterinarian, the cat was treated with a milbemycin oxime/praziquantel product (Milbemax for Cats, Elanco; 3.3 mg/kg milbemycin and 8.3 mg/kg praziquantel) on day 3, with this treatment repeated on day 4. Recheck fecal testing (KeyScreen GI Parasite PCR and Diarrhea FastPanel; Antech Diagnostics, Mars Petcare Science & Diagnostics) was submitted on day 10. Cryptosporidium felis was the only organism detected. As the diarrhea was ongoing, the cat was treated by the primary veterinarian (day 11) with a probiotic and tylosin (15 mg/kg, q 12 h, for 14 days) for suspected C felis–associated clinical signs. The cat was reported to have ongoing diarrhea on day 24; however, clinical signs were reported as resolved by day 77.

In Alberta, Canada, E multilocularis is not reportable or categorized as a notifiable disease. Despite this, and due to zoonotic risk, the Office of the Chief Provincial Veterinarian was informed of the detected results. Recommendations by the primary veterinarian, in consultation with the Antech Diagnostics Internal Medicine Consultation Service, were made to the rescue organization and veterinary clinic that all in-contact personnel reach out to their human healthcare providers for guidance related to potential E multilocularis exposure risk since E multilocularis eggs are immediately infective in feces. Similarly, the rescue organization was advised to reach out to the person(s) who surrendered the cat given the suspected common environment risk and risk of E multilocularis to the other cats, dogs, and humans on the property.

Comments

Echinococcus multilocularis is an emerging parasite of One Health concern in the US and Canada.^1–3 Wild canids (eg, wolves and foxes) are the typical definitive hosts for E multilocularis, and they are infected by preying on the rodent intermediate hosts (eg, deer mice, voles) that contain metacestode larvae (hydatid cysts). The canid definitive host sheds proglottids with eggs in the feces. Besides these wild canids, dogs and cats can serve as definitive hosts in the lifecycle of E multilocularis. These fecal shed proglottids are rarely observed in feces, and the eggs contained within feces are immediately infective, making human risk associated with fecal shedding from domestic pets a significant concern. Humans, and dogs, can be aberrant hosts for E multilocularis, and if infected, both can develop hydatid cysts, a condition referred to as alveolar echinococcosis. This is a rare infection in humans but is considered an underrecognized disease that can be fatal for both dogs and people.

In wild dogs (hunted or road-killed wolves), the prevalence of E multilocularis in the area around Calgary, Alberta, where this cat originated, has been reported as 20.5%.² A recent study¹ using fecal qPCR screening (KeyScreen; Antech Diagnostics, Mars Petcare Science & Diagnostics) on owned dogs in the US and Canada described 26 E multilocularis–detected dogs, of which 4 dogs lived in Alberta, Canada, with 3 dogs originating from Calgary. These studies,³ others, and human cases reflect regional One Health parasite risk.

While canids are the main definitive hosts, patent intestinal infections can occur in felids. The prevalence of E multilocularis detection in cats is currently unknown in the US and Canada. To date, the only reports of this parasite in cats, in either country, are from the 1970s and were morphological descriptions of worms present on necropsy. These necropsy findings were reported in 3 cats from Saskatchewan, Canada, in 1971 and from 2 US cats in North Dakota in 1972.³ In enzootic regions of Europe, local fox E multilocularis prevalence rates are as high as 35% (France), 48.2% (Poland), and 53% (Switzerland).^4,5 Detection of E multilocularis in cats in these countries has been reported as between 7% and 9.3% (France), 6% (Poland), and < 1% (Switzerland), respectively, likely indicating environmental “spillover” as the parasite circulates more widely in other, more competent definitive hosts, such as foxes, wolves, or coyotes.^4,5

The cat in our report was a stray cat from a rural environment and likely survived by hunting rodents. Hunting behavior is an established risk factor for E multilocularis infection because of ingestion of infected intermediate hosts, like small rodents (eg, mice, rats). Cats, whether stray or not, are avid hunters when allowed outside, and 1 study⁴ on cats in Poland showed no difference in the prevalence of E multilocularis detection between shelter and owned cats. Given prevalence data in other endemic countries, there needs to be veterinary and public health awareness of the risk for undetected and untreated cats in the US and Canada. This need for awareness is compounded by several factors specific to cats, including lack of routine veterinary care, such as fecal screening, for many owned cats. For example, according to the AVMA Pet Ownership and Demographics information from 2024, only 57% of owned cats are seen by a veterinarian for routine care.

Another compounding factor impacting the detection of E multilocularis in dogs and cats is that routine fecal centrifugation and flotation is an insensitive way of detecting patent infections¹ and that eggs cannot be distinguished microscopically from Taenia species. Of the 26 dogs with E multilocularis from the recent study in the US and Canada, Taenia-type eggs were detected in only 8 of 17 (47%) PCR-positive dogs that had a concurrent zinc centrifugal floatation performed.¹ Unfortunately, the cat in this report did not have sufficient fecal sample remaining to perform fecal floatation. As larger data sets are collected in cats through routine veterinary fecal qPCR screening, and as advised by parasite guidelines in both countries, this information could be used to inform human exposure risk in endemic and emerging areas.

This case highlights the potential value of fecal testing for suspected infectious causes of diarrhea and the promotion of routine veterinary fecal screening in cats, particularly those with outdoor access and hunting behavior. Routine deworming with praziquantel in endemic areas as recommended by the Companion Animal Parasite Council and cestoidal treatment as advised by the Canadian Parasitology Expert Panel may decrease human risk of exposure. However, routine treatment without testing would fail to alert to emerging parasite risk.

Patent intestinal E multilocularis infections are believed to be uncommon in cats in the US and Canada. Consequently, little is known regarding treatment, management, or outcome for this parasite when detected. Coprophagy, with the detection of ingested but passively transiting eggs, could also be an explanation for the detection of E multilocularis on fecal qPCR. However, this behavior is much less common in cats than dogs, and due to public health risk, detection of the parasite warrants treatment. In the cat in our report, E multilocularis was not detected by PCR after treatment with 8.3 mg/kg praziquantel given on 2 consecutive days. At this time, while patent infections in cats have been documented in other studies,⁴ their true role in infectivity to intermediate hosts remains unknown despite their serving as a broad indicator of zoonotic risk and highlighting that the parasite is circulating in the environment.^4,5

While E multilocularis is not a reportable disease in Alberta, the Office of the Chief Provincial Veterinarian was informed of the detected result and all at-risk humans were alerted and advised to discuss concerns with their human healthcare provider. The other cats and dogs on the property where the patient originated were not tested, but they were all treated with 5 mg/kg of praziquantel and repeated 24 hours later. Further work, and larger data set evaluation, may assist to better establish E multilocularis prevalence in cats from endemic and emerging regions and determine the potential role cats play in parasite spread and zoonotic risk. It is important that veterinarians, pet owners, and human healthcare providers, especially in endemic areas, be aware of this evolving One Health risk and educated on fecal screening of cats and dogs (fecal PCR), along with clinical management of E multilocularis.

Disclosures

Drs. Langs Rund, Evason, and Leutenegger are employees of Antech Diagnostics, Mars Petcare Science & Diagnostics, Loveland, CO.

No AI-assisted technologies were used in the composition of this manuscript.

Funding

The authors have nothing to disclose.