Academic journal article Bulletin of the World Health Organization

Guidelines for Treatment of Cystic and Alveolar Echinococcosis in Humans

Academic journal article Bulletin of the World Health Organization

Guidelines for Treatment of Cystic and Alveolar Echinococcosis in Humans

Article excerpt

Introduction

Human echinococcosis is a zoonotic infection caused by larval forms (metacestodes) of tapeworms of the genus Echinococcus found in the small intestine of carnivores. The eggs of these tapeworms excreted by carnivores may infect various species of natural intermediate host animals and humans. Among the four recognized species of Echinococcus (20). two are of special medical importance. -- E. granulosus and E. multilocularis -- causing cystic echinococcosis (CE) and alveolar echinococcosis (AK) in humans, respectively.

The annual incidence of AE is generally low in most of the endemic areas (0.03-1.2 per 100000 inhabitants) but in untreated or in inadequately treated patients mortality is >90% within 10-15 years of diagnosis (1. 2, 17). The annual incidence of CE can range from <1 to 220 per 100000 inhabitants in various endemic areas (16 17). The mortality rate (about 2-4%) from CE is lower than that from AE but it may increase considerably if medical treatment and care are inadequate (1, 2).

In view of the public health significance of CE and AE in many countries (16,17), WHO initiated in 1981 a multicentre clinical study on the chemotherapy of human echinococcosis, because individual studies undertaken since 1977 had produced inconsistent results (6, 7) a Progress and problems in the treatment of human echinococcosis were discussed at two meetings by the WHO Informal Working Group on Echinococcosis (9).b The results of these discussions are presented here but it should be borne in mind that the efficacy and safety of some of the methods are not yet clearly defined and require further evaluation. Readers are referred for detailed information and scientific discussion to various published reviews and WHO reports (1, 2, 8,14-18, 20-24).(a)

Cystic echinococcosis

In primary echinococcosis, metacestode cysts develop in various sites from oncospheres after ingestion of E. granulosus eggs. In secondary echinococcosis, larval tissue spreads from the primary site and proliferates after spontaneous or trauma-induced cyst rupture or after release of viable parasite material during invasive treatment procedures.

Organ localization

In primary echinococcosis. the metacestodes may develop in almost any organ. Most patients (up to 80%) have a single organ involved and harbour a solitary cyst, localized in approximately two-thirds of cases in the liver and in about 20% in the lungs. In each site cysts are surrounded by the host tissue (pericyst), encompassing the endocyst of metacestode origin. The endocyst consists of an outer acellular "laminated" layer, which is covered on its inner side by a multipotential germinal layer giving rise to the production of brood capsules and protoscolices. The central cavity of E. granulosus cysts is typically filled with clear fluid. which in "fertile" cysts contains brood capsules and protoscolices. In addition, "daughter" cysts of variable size are often present inside or outside the 'mother" cysts.

Course of infection

During the natural course of infection, the fate of E. granulosus cysts is variable. Some cysts may grow (average increase: 1-30mm per year) and then persist without a noticeable change for many years; others may spontaneously rupture or collapse and can completely disappear. Spillage of viable protoscolices after spontaneous or traumatic cyst rupture or during interventional procedures, may result in secondary echinococcosis. Calcified cysts are not uncommon.

After an undefined and variable incubation period, infections may become symptomatic if active cysts exert pressure on adjacent tissue and induce other pathologic events. Usually, cysts do not induce clinical symptoms until they have reached a particular size; sudden onset of symptoms may be due to cyst rupture.

Diagnosis

The diagnosis of CE is based on clinical findings, morphological features detected by imaging techniques, and immunological as well as other laboratory tests. …

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