Opisthorchiasis is a parasitic disease caused by certain species of genus Opisthorchis (specifically, Opisthorchis viverrini and Opisthorchis felineus). Chronic infection may lead to cholangiocarcinoma, a cancer of the .
Medical care and loss of wages caused by Opisthorchis viverrini in Laos and in Thailand costs about $120 million annually.[Muller R. & Wakelin D. (2002). Worms and human disease. CABI. page 43-44.] In Asia, infection by Opisthorchis viverrini and other affects the poorest people.[.]
Signs and symptoms
Symptoms of opisthorchiasis are indistinguishable from
clonorchiasis.
About 80% of infected people have no symptoms, though they can have
eosinophilia.
Asymptomatic infection can occur when there are less than 1000 eggs in one gram of feces.
Infection is considered heavy when there are 10,000-30,000 eggs in one gram of feces.
Symptoms of heavier infections may include
diarrhea,
Epigastrium and right upper quadrant pain, lack of appetite,
fatigue,
jaundice and mild
fever.
These parasites are long-lived and cause heavy chronic infections that may lead to accumulation of fluid in the legs (edema) and in the peritoneal cavity (ascites),
Chronic opisthorchiasis and cholangiocarcinoma
experimental and epidemiological evidence strongly implicates
Opisthorchis viverrini infections in the etiology of a malignant cancer of the bile ducts (cholangiocarcinoma) in humans which has a very poor prognosis.
[ ] Clonorchis sinensis and
Opisthorchis viverrini are both categorized by the International Agency for Research on Cancer (IARC) as Group 1 carcinogens.
In humans, the onset of cholangiocarcinoma occurs with chronic opisthorchiasis, associated with hepatobiliary damage, inflammation, periductal fibrosis and/or cellular responses to antigens from the infecting fluke.
In regions where Opisthorchis viverrini is highly endemic, the incidence of cholangiocarcinoma is unprecedented.
Diagnosis
The medical diagnosis is usually established by finding eggs of
Opisthorchis viverrini in feces
using the
Kato technique.
[World Health Organization (1995). Control of Foodborne Trematode Infection. WHO Technical Report Series. 849. PDF part 1, PDF part 2. page 89-91.]
Alternatively, an antigen of
Opisthorchis viverrini can be detected by
ELISA test.
A polymerase chain reaction test that can be performed on faeces has been developed and evaluated in a rural community in central Thailand.
[.]
Prevention
Cholangiocarcinoma is typically incurable at diagnosis.
Because of this, intervention strategies are focused on the prevention or treatment of liver fluke infection. Prevention can be accomplished through education (by persuading people not to consume raw or undercooked fish), but the ancient cultural custom to consume raw, undercooked or freshly pickled fish persists in endemic areas. One community health program, known as the Integrated Opisthorchiasis Control Program, has achieved success in the Lawa Lakes region south of
Khon Kaen.
Cooking or deep-freezing (-20 °C for 7 days)[World Health Organization (2004). REPORT JOINT WHO/FAO WORKSHOP ON FOOD-BORNE TREMATODE INFECTIONS IN ASIA. Report series number: RS/2002/GE/40(VTN). 55 pp. PDF. pages 15-17.] of food made of fish is an effective method of prevention.[.]
Treatment
Treatment of opisthorchiasis is usually accomplished with
praziquantel. A single dose of praziquantel of 40 mg/kg is effective against opisthorchiasis (and also against
schistosomiasis).
Despite the efficacy of this compound, the lack of acquired immunity to infection predisposes humans to reinfection in endemic regions. In addition, under experimental conditions, the treatment of
Opisthorchis viverrini-infected
with praziquantel induced a dispersion of parasite antigens, resulting in adverse immunopathological changes following re-infection with
Opisthorchis viverrini, a process which has been proposed to initiate and/or promote the development of cholangiocarcinoma in humans.
[ ] Albendazole can be used as an alternative.
A randomized controlled trial published in 2011 showed that tribendimidine, a broad-spectrum anthelmintic, appears to be at least as efficacious as praziquantel.[.]
Epidemiology
Opisthorchiasis is prevalent where raw
Cyprinidae fishes are a staple of the diet.
Prevalence rises with age; children under the age of 5 years are rarely infected by
Opisthorchis viverrini. Males may be affected more than females.
The WHO estimates that foodborne trematodiases (infection by worms or "flukes", mainly
Clonorchis,
Opisthorchis,
Fasciola and
Paragonimus species) affect 56 million people worldwide and 750 million are at risk of infection.
80 million people are at risk of opisthorchiasis (67 million from infection with
Opisthorchis viverrini in Southeast Asia and 13 million from
Opisthorchis felineus in Kazakhstan, Russia, and Ukraine).
In the lower
Mekong basin, the disease is highly endemic, and more so in lowlands,
with a prevalence up to 60% in some areas of northeast Thailand. However, estimates using polymerase chain reaction-based diagnostic techniques indicate that prevalence is probably grossly underestimated.
In one study from the 1980s, a prevalence of over 90% was found in persons greater than 10 years old in a small village near Khon Kaen in northeast Thailand in the region known as
Isan.
Sporadic cases have been reported from Malaysia, Singapore, and the Philippines.
Although the overall prevalence has declined since initial surveys performed in the 1950s, an increase has occurred since the 1990s in some areas, possibly related to large increases in
aquaculture.
Research
Using
CRISPR in animal models, researchers have been able to eliminate the genes responsible for symptoms of opisthorchiasis, which may lead to further research toward novel treatment and control of this disease and its sequelae.
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