Locating bilharzia transmission sites in South Africa: guidelines for public health personnel

Abstract

Bilharzia surveillance at local authority level in South Africa relies on public health personnel being able to locate transmission sites. Although several methods have been tried, the method of choice is collecting snails, identifying those that serve as intermediate hosts for bilharzia, and examining them for evidence of infection. Unfortunately, public health personnel are seldom trained to recognise these snails or the parasites’ larval stages, and few laboratories are able to assist. Therefore, the intention is that these guidelines will help to equip personnel with the basic information needed to collect and identify the bilharzia-carrying snails, and then examine them for infection. The intramolluscan or larval stages of trematode parasites likely to be encountered in dissected snails are described. However, emphasis is placed on the furcocercariae, a group which includes the infective stage of bilharzia flukes. A family key to furcocercariae is presented.