Abstract
Pre-clinical transmission assays are essential for proof-of-concept for transmission blocking strategies but are hazardous to laboratory personnel and animal hosts as it entails exposure of live rodents to infected vectors. Conventional transmission assay methods include the use of anesthesia (associated with undesired side effects). In addition, animal handlers risk being bitten by experimental animals and vectors during anesthesia due to a lack of safe and effective alternatives. Robustness of rodent to vector transmission was determined by comparing the number of oocysts. Vector-to-rodent transmission was determined by measuring parasitemia, gametocytemia, changes in body weight and survival time. A completely randomized design was used in this study. Rodent-to-vector transmission was analyzed by log linear model. Fecundity, gametocytemia, parasitaemia and changes in body weight were analyzed by regression analysis. Survival times were analyzed Kaplan-Meier method for determination of survival distribution function. Rank test of homogeneity were used to determine the effect of restraining method infection on survival times. There was no significant difference (p<0.001) in fecundity of mosquitoes fed on anesthetized mice; 122±22.1 eggs compared to INFECTRA®-Kit group with 110±14.1 eggs. Oocyst production increased gradually though not significantly (p<0.001) in both groups of mice with the number of mosquitoes. The INFECTRA®-Kit group increased from 2.7%±0.3 (1 mosquito) to 9.3%±0.3 (6 mosquitoes), the conventional group was 3.7%±0.3 to 8.6%±0.3 (6 mosquitoes). Parasitemia progression was characterized by two waves in INFECTRA®-Kit and three waves in the conventional group. The highest parasitaemia peak was 22% attained on 22dpi for the INFECTRA®-Kit and 17.8% attained on 26 dpi for the conventional group. Gametocytes were detected on 16 dpi in both groups and thereafter increased significantly (p<0.001) with dpi. In the INFECTRA®-Kit group, gametocytemia was represented by two oscillations while the conventional group was three cycles with peak gametocytes increasing with each subsequent peak. Disease progression was higher and survival times shorter with INFECTRA<sup>®</sup>-Kit than with anesthetized mice and there was no significant difference (p<0.05) between the two methods in body weight and gametocytemia. INFECTRA<sup>®</sup>-Kit is equivalent to that of anesthesia method but more advantageous given the more ethical and humane treatment of animals.
Highlights
Malaria is a mosquito-borne infectious disease of humans and other animals caused by parasitic protozoans of the genus Plasmodium (Bartoloni et al, 2012)
There was no evidence that the increase in INFECTRA®-Kit was significantly different from conventionally restrained mice and the rate of change in Gametocytemia % with dpi did not significantly vary from one treatment group to the other
The increase in INFECTRA®-Kit restrained mice was marked with two oscillation cycles/waves with the first cycle extending between 14 and 20 dpi and a peak of 0.44% followed by a second cycle with a peak of 1.33% at 22 dpi
Summary
Malaria is a mosquito-borne infectious disease of humans and other animals caused by parasitic protozoans (a type of unicellular microorganism) of the genus Plasmodium (Bartoloni et al, 2012). Symptoms associated with malaria include fever and headache and in severe cases infection progress to coma and death. Plasmodium falciparum, one of the five Plasmodium species that infect humans, is the most lethal parasite and contributes to the majority of deaths from the disease (Greenwood et al, 2008). The host specificity of this human malaria parasites represents a major constraint on in vivo studies (Ozwara et al, 2003, Vaughan et al, 2012) making studies on drugs and vaccine development using laboratory animals difficult. Murine malaria parasites like Plasmodium berghei is used in these type of studies as it is similar to human malaria parasites in most essential aspects of morphology, physiology and life cycle studies aimed at the development of new drugs or a vaccine against malaria (Carter and Diggs, 1977)
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