Plasmodium vivax: Ookinete destruction and oocyst development arrest are responsible for Anopheles albimanus resistance to circumsporozoite phenotypeVK247 parasites

Anopheles albimanus and An. pseudopunctipennis differ in their susceptibili ties to Plasmodium vivax circumsporozoite phenotypes. An. pseudopunctipenni s is susceptible to phenotype VK247 but almost refractory to VK210. In cont rast, An. albimanus is almost refractory to VK247 but susceptible to VK210. To investigate the site in the mosquito and the parasite stage at which re sistance mechanisms affect VK247 development in An. albimanus, parasite dev elopment was followed in a series of experiments in which both mosquitoes s pecies were simultaneously infected with blood from patients. Parasite phen otype was determined in mature oocysts and salivary gland sporozoites by us e of immunofluorescence and Western blot assays and/or gene identification. Ookinete maturation and their densities within the bloodmeal bolus were si milar in both mosquito species. Ookinete densities on the internal midgut s urface of An. albimanus were 4.7 times higher than those in An. pseudopunct ipennis; however, the densities of developing oocysts on the external mid-u t surface were 6.12 times higher in the latter species. Electron microscopy observation of ookinetes in An. albimanus midgut epithelium indicated seve re parasite damage. These results indicate that P. vivax VK247 parasites ar e destroyed at different parasite stages during migration in An. albimanus midguts. A portion, accumulated on the internal midgut surface, is probably destroyed by the mosquito's digestive enzymes and another portion is most likely destroyed by mosquito defense molecules within the midgut epithelium . A third group, reaching the external mid-ut surface, initiates oocyst dev elopment, but over 90% of them interrupt their development and die. The ide ntification of mechanisms that participate in parasite destruction could pr ovide new elements to construct transgenic mosquitoes resistant to malaria parasites. (C) 2001 Academic Press.