Liver Flukes

Liver flukes are digenean trematodes that can infect a wide range of definitive hosts, including cats. They are indirect (food-borne) zoonoses.

Parasite species: Platynosomum concinnum (syn. P. fastosum, P. illiciens), Amphimerus pseudofelineus, Clonorchis sinensis, Opisthorchis felineus, Opisthorchis viverrini, Metorchis conjunctus, and many other species
Common name: Liver fluke
Hosts: Wild and domestic carnivores, including dogs and cats
Pre-patent period: 2-4 weeks
Location in the host: Gallbladder and/or bile ducts; some species can occasionally be found in the pancreatic duct or the small intestine
Distribution: Worldwide
Transmission route: Predation of intermediate and paratenic hosts (e.g. freshwater fish, lizards, frogs, toads and potentially mice and birds)
Zoonotic: Yes

Distribution

Platynosomum concinnum is found in Malaysia, Hawaii, West Africa, South America, the Caribbean, and areas surrounding the Gulf of Mexico [1,2]. Amphimerus pseudofelineus is found in the Americas. Clonorchis sinensis is found in northern Vietnam, China [3]. Opisthorchis felineus has been reported from Europe and Russia. Opisthorchis viverrini is found in southern Vietnam, Thailand, Laos, Malaysia, and India [3]. Metorchis conjunctus is found in North America.

Clinical signs

Cats infected by P. concinnum may present diarrhoea, depression, anorexia, weight loss, jaundice, liver enlargement and vomiting. Amphimerus pseudofelineus-infected cats may present anorexia, weight loss, diarrhoea, vomiting, icterus, and liver enlargement; some cats may develop severe cirrhosis of the liver and ultimately die [2]. Clonorchis sinensis may also cause cirrhosis. Metorchis conjunctus can cause icterus, haematuria, diarrhoea, chronic cholangiohepatitis, cirrhosis, emaciation, ascites and jaundice.

Figure 1. Liver fluke eggs with distict ‘shoulder’ below the operculum ‘cap’ (Image credit: Shutterstock)

Diagnosis

Liver fluke infections can be confirmed by faecal sedimentation. Eggs are operculated and measure approximately 34-50 x 20-35 μm in P. concinnum, 27 x 15 µm in A. pseudofelineus, 28-35 x 12-19 µm in C. sinensis, 30 x 11 µm in O. felineus, 27 x 15 µm in O. viverrini and 22-32 x 11-18 μm in M. conjunctus [1].

Treatment

The following treatments represent off-label use of praziquantel. Praziquantel at 20 mg/kg PO or IM once daily for 3-5 days, repeated 12 weeks later is considered to be the most effective drug against P. concinnum infections in cats [4]. For feline opisthorchiasis, a single dose of 40 mg/kg praziquantel was effective and safe for the treatment of cats [5].

Prevention and Control

The control of liver fluke infections can be achieved by preventing cats from hunting and eating intermediate or paratenic hosts. Infection in humans is due to consumption of intermediate or paratenic hosts.

Public health considerations

Many species of liver flukes that infect cats have been reported in humans [1]. Cats may act as a zoonotic reservoir for human infection in communities where fish-borne trematode zoonoses is endemic.

References

[1] Bowman DD, Hendrix CM, Lindsay DS, Barr SC. Feline Clinical Parasitology. Iowa State University Press, Ames, USA. 2002.

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

[3] Petney TN, Andrews RH, Saijuntha W, Wenz-Mücke A, Sithithaworn P. The zoonotic, fish-borne liver flukes Clonorchis sinensis, Opisthorchis felineus and Opisthorchis viverrini. Int J Parasitol. 2013;43:1031-1046.

[4] Lathroum CN, Shell L, Neuville K, Ketzis JK. Efficacy of praziquantel in the treatment of Platynosomum fastosum in cats with natural infections. Vet Sci. 2018;5(2):E35.

[5] Sereerak P, Upontain S, Tangkawattana P, Mallory FF, Sripa B, Tangkawattana S. Efficacious and safe dose of praziquantel for the successful treatment of feline reservoir hosts with opisthorchiasis. Parasitol Int. 2017;66:448-452.