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Fifty-nine ewes, seronegative to Toxoplasma gondii, were allocated to four groups which received 2000, 200, 20 or no M1 strain toxoplasma oocysts 56 days before mating. Fifty-one of them subsequently became pregnant and were challenged with 10,000 oocysts between 78 and 83 days of gestation. Infection with 2000 oocysts induced a pyrexia, seroconversion and protective immunity in all the recipient animals. Ewes that received either 20 or no oocysts before pregnancy were susceptible to subsequent challenge and severe fetal mortality occurred. In this study 200 oocysts was the threshold value for the induction of toxoplasma infection in sheep, although not all the ewes that seroconverted to this dose were protected against further challenge.

The efficacy of various sodium stibogluconate formulations against Leishmania donovani has been investigated using a BALB/c mouse model of visceral leishmaniasis. Only one therapy, multiple dosing with drug loaded sonicated vesicles, liposomes or niosomes, was found to be effective against parasites in the liver, spleen and bone marrow. Other treatments significantly reduced parasite liver burdens but either failed to effect spleen and bone marrow parasites, or were effective but toxic. Prophylactic treatment with sodium stibogluconate preparations, six days before infection, reduced parasite multiplication in the liver (free, niosomal and liposomal drug) and the spleen (sonicated, drug loaded niosomes only), but had no suppressive effect on bone marrow parasite burdens compared with controls. These results indicate that in-vivo sodium stibogluconate persists in some compartments at parasiticidal concentrations and that failure to reach this concentration at some sites of infection such as bone marrow, is the cause of treatment failure and relapse.

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