Worm Recovery and Pathology in the Olive baboon, Papio anubis, Immunized Against Schistosoma mansoni with Snail Soluble Proteins

Abstract

Schistosomiasis is estimated to infect over 200 million people worldwide. Chemotherapy remains the major means of intervention but has the challenge of rapid re-infection, high cost and risk of drug resistance. A vaccine would have a long term effect and complement chemotherapy but none is in the market. Pilot studies in mice model showed that two proteins derived from Biomphalaria pfeifferri RT (soluble proteins from the rest of snail tissue) and DG (soluble proteins from the digestive gland) were protective against S. mansoni in terms of worm reduction and reduced pathology. Both met the World Health Organization criteria of over 40% protection. This study was done to investigate the efficacy of DG and RT in olive baboons challenged with Schistosoma mansoni. Baboons were in three groups: DG, RT and IC (infected control). DG and RT were immunized and boosted twice with their specific soluble snail antigens in Montanide at weeks 0, 3 and 6. They were challenged 2 weeks post final booster with 600 Schistosoma mansoni cercariae. DG had significant worm reduction of 11.4%. It had least gross pathology and histopathology. DG offered better protection against S. mansoni in baboon than RT, although lower than in mouse model.

Keywords: Schistosoma mansoni, Biomphalaria pfeifferi, Snail soluble protein, immunization