Metacyclic promastigotes of Leishmania in the salivary glands of experimentally infected phlebotomine sandflies

Thirty one female Phlebotomus duboscqi experimentally infected with Leishmania tropica were found with metacyclic promastigotes in their salivary glands. The presence of parasites in the glands was correlated with heavy infections of metacyclic promastigotes in the stomodaeal valve and thoracic midgut of the fly and it is suggested that the parasites may have migrated through the gut wall into the glands which lie against the valve in the thorax of the fly. No evidence was found that gland invasion is an obligatory stage of the life-cycle of Leishmania, but reports of wild-caught flies with parasites in the glands, coupled with these laboratory observations, raise the possibility that regurgitation of parasites or the migration of metacyclic promastigotes into the mouthparts may not be the only mechanisms of transmission by bite.