Immunity in kala-azar

Abstract
1. 1) The leishmanin test is described and its interpretation discussed in the light of recent work. This test becomes positive 6–8 weeks after treatment has been completed in kala-azar, and a similar period after the intradermal inoculation of rodent strains of L. donovani . This positive reaction may revert to negative in either case with the passage of time. 2. 2) Where over 5 per cent. of the population of an area show a positive leishmanin reaction, then kala-azar is endemic in that area. 3. 3) A positive leishmanin reaction denotes resistance to superinfection with any strain of L. donovani , but not of L. tropica . This immunity, which is complete in the early stages, fades with time but can be at least partially restored by subsequent inoculations of leptomonad cultures. 4. 4) The ground-squirrel strain of L. donovani isolated by Heisch (1957) is perfectly safe for use as a live vaccine to protect against kala-azar, since it does not produce visceral lesions in man when inoculated by the dermal route. Subjects immunized with this strain are immune to challenge from East African, Sudanese, Mediterranean and Indian strains of L. donovani , but show no immunity to any strains of L. tropica . 5. 5) There is complete cross immunity between all strains of L. donovani , but none between L. donovani and L. tropica .

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