Platynosomum fastosum reported in a cat in Ontario

Emily Rätsep, Jacob Avula, Lindsay Ormesher

Animal Health Laboratory, University of Guelph, Kemptville, ON (Rätsep) and Guelph, ON (Avula); Mississauga Oakville Veterinary Emergency and Specialty Hospital, Mississauga, ON (Ormesher)

AHL Newsletter 2023;27(1):26.

In fall of 2022, samples of bile from the bile duct and gall bladder were received from a cat with history of having been obtained from Barbados.  Vomiting was noted in Barbados in May 2022.  Serum biochemistry performed June 2022 revealed mild hyperglobulinemia of 5.2 g/dL (RR: 2.8-5.1 g/dL), mild elevation in ALT of 295 U/L (RR: 12-130 U/L), and mild elevation in GGT enzyme activity of 7 U/L (RR: 0-4 U/L).  A progressive hepatic enzymopathy was noted on subsequent visits, and abdominal ultrasound identified multiple cystic structures within the liver.  The cat arrived in Canada and was presented to the internal medicine department at MOVEH in August 2022. 

The cat was small in stature with a firm cranial abdomen, but no distinct organomegaly or masses.  On ultrasound, heterogenous hepatic parenchyma was noted, and the previously-identified cystic structures were traced and confirmed as distension of all aspects of the biliary system.  Persistent elevation in ALT enzyme activity at 406 U/L (RR: 27 - 158 U/L) and a novel, mild elevation in AST enzyme activity of 125 U/L (RR:16 - 67 U/L) was noted.  Total and conjugated bilirubin were within normal limits. Functional liver parameters including glucose, urea, albumin and cholesterol were normal. 

Based on the history and abdominal ultrasound findings, infection with Platynosomum spp. was suspected.  Cholecystocentesis performed under sedation proceeded with separate aspirations of the gall bladder and the proximal bile duct.  Bile samples were submitted to the Animal Health Laboratory for centrifugal sedimentation which revealed moderate numbers of oval, golden brown, thick-shelled operculated eggs with miracidia (33.0 µm x 42.0 µm), consistent with Platysonosum fastosum (Figs. 1, 2).  An additional sample submitted to IDEXX confirmed many (>30) Platynosomum concinnum (fastosum) ova.

Resolution of the hepatic enzymopathy was noted following commencement of therapy.  On follow-up examination, it was considered that based on the prepatent period of the parasite, immature flukes that were not eliminated with the first treatment may have matured into adults; therefore, treatment was repeated.  It is uncertain if the observed ultrasound changes, considered secondary to injury and fibrosis induced by the flukes, would be permanent.  A repeat cholecystocentesis was performed in November 2022, and no liver fluke ova or other parasites were identified.

Platynosomum fastosum is a small liver fluke from the family Dicrocoeliidae that is found in biliary ducts and gall bladders of cats, though ectopic sites have been reported, including small intestines, lung and pancreas.  This parasite is generally found in tropical or subtropical areas, but has been reported world-wide.  The lifecycle is still not fully understood, but generally involves snail intermediate hosts (Sublima octona) with terrestrial isopods, lizards, toads and geckos acting as paratenic hosts.  Cats acquire the infection by ingesting infected lizards containing the encysted infective stage metacercariae, hence the commonly-recognized name of “lizard poisoning” in cats.  The metacercariae excyst in the small intestine of the cat, and travel through the duodenal papillae to the common bile duct, bile ducts and gall bladder where they mature into adult flukes.  Eggs are discharged intermittently in the feces of the infected cat.

While infection is often asymptomatic and considered an incidental finding, obstructive hepatobiliary disease with hepatic failure can occur in some cats with a heavier burden.  Clinical disease presents as jaundice, abdominal distension and weight loss.  Anorexia, diarrhea, vomiting, depression, hair loss and slight fever have also been reported, together with biochemical changes of elevated hepatic enzymes and total bilirubin vales.  Parasitic infection of bile ducts can result in cholangitis/cholangiohepatitis, characterized by hyperplasia of the epithelium, periductal fibrosis, inflammation, and occasionally, progressive obstruction due to the presence of adult flukes.  These lesions can present as feline cystic hepatic disease.

Diagnosis is based on history, clinical findings and detection of the adults or eggs in stool or bile, on ultrasound or during postmortem.  Shedding of eggs in stool is intermittent, and eggs may not appear if infection results in biliary obstruction.  Identification of the trematodes and/or eggs in bile aspirates is considered a more effective method of diagnosis.  P. fastosum ova can easily be differentiated from the more common Paragonimus kellicotti lung fluke eggs in fecal samples, as the latter are much larger in size, have a thickened ridge on the shell beside the operculum, and contain an embryonic cell mass.

Considering these findings, platynosomiasis should remain a potential differential diagnosis for felids with hepato-biliary dysfunction in Canada, especially in those with a history of travel to or from tropical and subtropical locations.   AHL

Figure 1. Platynosomum fastosum eggs obtained from centrifugal sedimentation of bile with measurements.	Figure 2.  Fluke eggs showing operculum (blue arrow) and miracidium (red arrow).

References

1. Xavier FG, et al. Cystic liver disease related to high Platynosomum fastosum infection in a domestic cat. JFMS 2007;9:51-55.

2. Ranaraja DMAE, et al. Hepatic trematode Platynosomum sp. (Dicrocoeliidae) from a domestic cat in Columbo, Sri Lanka: Case report and molecular identification. Vet Para 2022;34. https://doi.org/10.1016/j.vprsr.2022.100762

3. Basu AK, Charles RA. A review of the cat liver fluke Platynosomum fastosum Kossack, 1910 (Trematoda: Dicrocoeliidae). Vet Para 2014;200:1-7.