The suppression of Plasmodium berghei in Anopheles coluzzii infected later with Vavraia culicis

The suppression of malaria parasites in the presence of an existing microsporidian infection of Vavraia culicis, was examined using fluorescent Plasmodium berghei. Younger hosts infected with V. culicis had a greater suppressive effect on the subsequent development of P. berghei than older infected hosts. This effect was density dependant on the numbers of microsporidian spores present, consequently it was also dependant on the age at which mosquitoes were infected with microsporidia, as larvae infected later harboured comparatively fewer V. culicis spores. The timing of primary and secondary infections of larval and adult mosquitoes (host age) with different parasites affects parasite development and hence disease outcomes. The use of green, fluorescent P. berghei enabled easier and rapid visualisation and separation of malaria oocysts from V. culicis spores. Different degrees of melanisation of V. culicis were seen in a number of hosts and merits further investigation.