The influence of host haematocrit on the blood feeding success of Anopheles stephensi: implications for enhanced malaria transmission

Two studies were carried out to determine the effect of the rodent malaria Plasmodium yoelii nigeriensis on the blood feeding success of Anopheles ste phensi. Initially, pairs of mice with similar packed cell volume (PCV) (mea sured by haematocrit) were selected. Following infection of one of the pair its PCV gradually fell. At various times post-infection, a comparison was made of the bloodmeal size (haemoglobin content) of mosquitoes feeding on t hese mice. The bloodmeal sizes increased with parasite-induced fall in PCV down to a haematocrit of 43-44%, which occurred approximately 48 h post-inf ection. Bloodmeals were significantly reduced, however, when mosquitoes fed on mice with higher parasitaemias and a haematocrit of 15-35%. Thus, at ea rly stages of infection, mosquitoes ingested a bloodmeal significantly grea ter than did the mosquitoes feeding on the control mice. However, mosquitoe s were not able to compensate for severe infection-associated anaemia. To c ompensate for variation due to innate differences in the mice, a second exp eriment was performed. Mosquitoes were fed on the same mice before (control ) and after infection, Again, the bloodmeal size increased with decreasing PCV down to haematocrits of 42-45%, but declined thereafter. In this host-p arasite-vector system, haematocrits that maximized erythrocyte intake were produced when gametocytes, capable of exflagellation, were present.