Effects Of Plasmodium Falciparum Infected Blood On The Midgut Proteases Of Anopheles Gambiae S.S

ABSTRACT

Malaria is the leading cause of death in Africa among pregnant women and children under five years. Each year 350-500 million cases of malaria occur worldwide, and over one million people die, most of them young children in sub-Saharan Africa. In Africa, Anopheles gambiae mosquito is the main vector of Plasmodium falciparum, which causes malaria. All female Anopheles mosquitoes are usually haematophagous; they require a blood meal from a vertebrate host, either before or after mating, for egg development. Despite numerous control measures to reduce prevalence of Plasmodium transmission, morbidity and mortality rates continue to increase in the tropics and sub-tropics. Control measures have been hindered by the occurrence of insecticideresistant vectors and drug-resistant malaria parasites; therefore resulting to an urgent need of integrating current strategies with new ones. One effective measure is to block the development and transmission of Plasmodium by mosquitoes. Midgut proteases of dipterans are involved in many aspects of the vector-parasite relationship. These proteases are crucial for the parasites’ development in the vector. However, they are not fully understood, thus making it difficult to identify a useful transmission blocking mechanism. This study sought to determine the effects of Plasmodium falciparum and blood meals on the levels of midgut proteases (trypsin, chymotrypsin and aminopeptidase) as a basis to identify the potential of transmission blocking mechanisms in Anopheles gambiae. Replicates of four different groups of female Anopheles gambiae were fed on blood containing Plasmodium falciparum, human blood alone, hamster blood or 10% glucose in KEMRI, CBRD insectaries. These mosquitoes were then dissected after 6, 12, 18, 24 and 48 hours respectively and their midgut protease levels determined and recorded. The collected data were analyzed using SPSS. Comparisons for replicate test results and the different treatment groups were carried out using analysis of variance (ANOVA). Shapiro Wilk’s test was used to check on the normality of the data and Scheffe’s test was used for post-hoc testing. The mean differences in overall enzyme trends in the glucose treatment group when compared with those of the human blood and human blood infected with P. falciparum treatment groups were significant, thus indicating that human blood and human blood infected with P. falciparum alter the level of midgut proteases. Trypsin is essential in protein digestion because in all the blood-fed mosquitoes, trypsin activities peaked at 18-24 hours which coincided with the time taken to digest 80% of the blood meal, unlike in the sugar-fed mosquitoes. When multiple comparisons of chymotrypsin and aminopeptidase activities were made between the human blood treatment group and the human blood infected with P. falciparum treatment group with the glucose treatment group, the results showed that the differences were significant thus indicating that human blood and human blood infected with P. falciparum alter the levels of chymotrypsin and aminopeptidase in An. gambiae mosquitoes. Inhibition of these enzymes in the mosquitoes could lead to transmission blocking mechanisms thus further work needs to be carried out so as to identify the potential of transmission blocking mechanisms in the control of malaria.