Opisthorchis viverrini


Opisthorchis viverrini

Description, Causes and Risk Factors:

Opisthorchis viverriniis a food borne trematode, important because of the sheer numbers of people infected and its serious morbidities such as hepatobiliary diseases and cholangiocarcinoma. Although infections are identified throughout Southeast Asia, the epicenter is Northeast Thailand, where high prevalence coexists with a high incidence of cholangiocarcinoma. In this review, we present the basic population features and the factors influencing transmission between the different hosts.

The disease poses a serious threat to human health for it is a cofactor for the cancer of the bile ducts. It is transmitted to humans through the consumption of raw cyprinid fishes. Efforts made towards Opisthorchis viverrini control have placed greater interests on epidemiological and clinical studies of O. viverrini than the study of biogeography of O. viverrini and its intermediate hosts. While important, epidemiological and clinical studies alone are unable to provide a comprehensive picture of the cause and effects of O. viverrini.

The parasite has a complex life-cycle which involves an intermediate phase in cyprinoid fishes. Consumption of raw or undercooked fish infected with the metacercarial (larval) stage of O. viverrini results in infection, with adult worms living primarily in the intra-hepatic bile duct. In addition to the affects of the infection itself, O. viverrini is directly carcinogenic, with up to 70% of infected individuals in endemic regions developing malignant cholangiocarcinomas.

Control of the parasite relies exclusively on the use of praziquantel and little is known about the mechanisms through which O. viverrini stimulates carcinogenesis. An improved understanding of the Molecular biology of O. viverrini is needed.

Symptoms:

Signs and symptoms associated with O. viverrinican include eosinophilia and, in intense infections, diarrhea, epigastric pain, anorexia, pyrexia, jaundice and/or ascites.With chronic infection, the symptoms can be more severe, and hepatomegaly and malnutrition may be present. In rare cases, cholangitis, cholecystitis, and cholangiocarcinoma (CCA) may develop.

Diagnosis:

Microscopic diagnosis of O. viverriniis challenging even for experts because eggs of O. viverrini and Haplorchis taichui (minute intestinal fluke of no known clinical significance) are similar in size and shape and are indistinguishable by usual light microscopybut are identifiable by using potassium permanganate solution.

Antigens from Bithynia goniomphalos, the intermediate snail host of O. viverrini, work well for antibody detection with only occasional cross-reactions in hymenolepiasis and strongyloidiasis.

Earlier reports of antigen detection have not been followed-up.PCR, the new gold standard for detection of infections via O. viverrini DNA in stool,will also be useful for tracking infections in intermediate hosts and as a basis for improving tests for detection of specific antigens and antibodies.

Treatment:

In patients with asymptomatic and mild-to-moderate cases, praziquantel given three times after meals in has been reported to be effective. In those with heavy infections, a single dose of 50 mg/kg produces a cure rate of 97%. No eggs are recovered in the stool after about a week; however, clinical symptoms and gallbladder dysfunction may take several months to resolve. Any side effects can be minimized by administration of the single dose regimen at bedtime.

Mebendazole has also been given at 30 mg/kg/day for 3 or 4 weeks, with cure rates of 89 and 94% respectively. No adult worms were recovered after therapy.

It is important to remember that only 5% to 10% of cases are relieved with praziquantel alone and that relapsing cholangitis and obstructive jaundice may require the use of antimicrobials. In complicated cases, surgery may also be required. Unfortunately, cholangiocarcinoma associated with O. viverrini infection carries a poor prognosis.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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