Liver Fluke

(Opisthorchis viverrini, Clonorchis sinensis)

Opisthorchis viverrini and Clonorchis sinensis are trematodes of fish-eating mammals including dogs, cats and humans in Asia. Liver flukes are zoonotic.

Parasite: Opisthorchis viverrini, Clonorchis sinensis
Common name: Southeast Asian liver fluke, Chinese or Oriental liver fluke
Hosts: fish eating mammals such as dogs, cats, pigs, humans.
Pre-patent period: 3-4 weeks
Location of adults: bile duct, liver, gallbladder, pancreatic duct
Distribution: Southeast Asia and Far East Asia
Transmission route: eating raw or undercooked freshwater fish infected with metacercariae
Zoonotic: Yes

Distribution

O.viverrini has been reported in Thailand, Laos, central Vietnam and Cambodia, while C. sinensis has been reported in Korea, China, Taiwan and northern Vietnam.

Clinical signs

In most cases, liver fluke infection in dogs is asymptomatic. When clinical signs occur they include lethargy, diarrhoea and dehydration. Migration of immature flukes can cause acute hepatitis and pancreatitis.

Diagnosis

The diagnosis of liver flukes infection in dogs is based on the detection of characteristic operculated eggs with a fully developed miracidium (Fig 1) by faecal sedimentation (SOP 4).

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

Treatment

Off-label use of praziquantel 40 mg/kg given as a single oral dose is reported effective at killing adult liver flukes.

Control

Owners should be advised not to feed their dog raw or undercooked freshwater fish. For further control options, refer to the General Considerations and Recommendations section.

Public health considerations

Humans become infected through the ingestion of undercooked fish infected with metacercariae of liver flukes. Dogs may act as reservoirs for human infection by contaminating the environment with liver fluke eggs. Humans infected with liver fluke are mostly asymptomatic however chronic infection may lead to biliary and hepatic disease and cholangiocarcinoma.