Abstract
The areas endemic for schistosomiasis in the Lao People’s Democratic Republic and in Cambodia were first reported 50 and 60 years ago, respectively. However, the causative parasite Schistosoma mekongi was not recognized as a separate species until 1978. The infection is distributed along a limited part of the Mekong River, regulated by the focal distribution of the intermediate snail host Neotricula aperta. Although more sensitive diagnostics imply a higher figure, the current use of stool examinations suggests that only about 1500 people are presently infected. This well-characterized setting should offer an exemplary potential for the elimination of the disease from its endemic areas; yet, the local topography, reservoir animals, and a dearth of safe water sources make transmission control a challenge. Control activities based on mass drug administration resulted in strong advances, and prevalence was reduced to less than 5% according to stool microscopy. Even so, transmission continues unabated, and the true number of infected people could be as much as 10 times higher than reported. On-going control activities are discussed together with plans for the future.
Highlights
The adult schistosomes are miniscule worms with a preference for abdominal capillaries of the definitive human host, where they release a large number of eggs
These are excreted with either urine or feces and infect the intermediate snail host, which releases many cercariae—a later developmental stage—into the water
Owing to the limited geographical distribution of Schistosoma mekongi to endemic areas in Cambodia and the Lao People’s Democratic Republic (Lao PDR), strategies aiming at its elimination and eventual eradication can be implemented more effectively than for other, more widespread species
Summary
The parasitic, trematode genus Schistosoma puts more than 800 million people in the world’s tropical areas at risk, infecting a third of them [1,2]. After schistosomiasis had been discovered in the Mekong River Basin (MRB), first in Lao PDR in 1957 [7] and 10 years later (1968) in Cambodia [8], biological research conducted in the 1970s demonstrated that the eggs from the MRB schistosomes were morphologically different from S. japonicum [8]. The former species had a different intermediate snail host [9,10] that could not infect water buffaloes [8] but was found in dogs [11]. This review features the more recent switch from morbidity control to elimination, followed by a discussion of the steps to achieve and the challenges involved
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