Attenuation of XXXX cercariae with a molluscicide derived from Millettia thonningii.

@entity19 @entity3636 @entity380
A @entity3636 extract of molluscicidal plant secondary compounds from the seeds of a West African legume Millettia thonningii was used to attenuate cercariae of @entity380 prior to infection of NMRI female @entity19 . Exposure of cercariae to 0.3, 0.6, 1.3, 2.5, 10 or 20 mg/l concentrations of extract for 30 min, immediately before standardized infection, was associated with a concentration-dependent decline in worm establishment at 55 days post-infection. The mean numbers of adult worms established declined from about 17 worms/ @entity19 with control cercariae and those exposed to 0.3 mg/l Millettia to 0.1 worms/ @entity19 after 10 mg/l pre-treatment. @entity19 exposed to cercariae after 20 mg/l pre-treatment had no adult worms at 55 days post-infection. The activities of cercariae 30 min after exposure to Millettia extract at concentrations up to 2.5 mg/l were similar to those of control larvae: none was immobile. Exposure to higher concentrations of Millettia progressively reduced swimming activity and increased the proportion of immobile cercariae. After pretreatment with 20 mg/l Millettia the majority of larvae were immobile. Levels of anti-parasite antibodies (estimated by ELISA assay using an adult worm-based antigen preparation) rose between 21 and 55 days p.i. with control cercariae and those pre-treated with 2.5 mg/l Millettia. After 5 mg/l pre-treatment, cercariae induced a reduced antibody rise, while @entity19 exposed to cercariae after 10 mg/l pre-treatment showed no rise in anti-parasite antibody levels. These results are discussed in the context of protocols which could possibly use Millettia-attenuated cercariae to induce useful levels of protection in @entity19 towards further cercarial challenge.
