Biological characteristics of praziquantel-resistant and -susceptible isolates of Schistosoma mansoni

If there is a change in the biological characteristics of schistosomes asso ciated with the development of resistance to praziquantel, this could affec t the transmission and pathology of the diseases they cause. To investigate this possibility, the host-parasite relationships of five praziquantel-res istant and five praziquantel-susceptible isolates of Schistosoma mansoni we re compared in Biomphalaria glabrata snails and outbred CD1 albino mice. Wh ether praziquantel-resistant or -susceptible, all the laboratory-selected i solates gave similar results in B. glabrata. However, the snails infected w ith any of three field-collected isolates from Senegal, each of which has b een shown to be praziquantel-resistant, shed fewer cercariae and survived l onger than the snails infected with the drug-susceptible or laboratory-sele cted, drug-resistant isolates. There were no differences between isolates i n terms of their infectivity to mice. However, mice infected with any of fo ur of the five drug-resistant isolates shed more eggs in their faeces than mice carrying the drug-susceptible parasites, and mice infected with any of the resistant isolates also had larger numbers of eggs in their tissues. A lthough granuloma sizes were generally similar for all isolates, the praziq uantel-resistant isolates may be more pathogenic in mice than the susceptib le ones because of their relatively high egg productions.