Plasmodium berghei: development of an irreversible experimental malaria model in Wistar rats

A protocol to infect five-week-old Wistar rats by Plasmodium berghei which resulted in 100% mortality was developed in this work. In order to accomplish this goal, the effect of the administration of 10(7) and 10(8) parasitized erythrocytes by i.v. and i.p. route was investigated. The animals inoculated with 10(7) parasitized red blood cells by i.p. and i.v. routes showed 25 and 50% mortality, respectively. Inoculation with 10(8) parasitized erythrocytes by both routes resulted in a 100% lethal infection. The i.v. inoculation showed less scattered results and it was preferred over the i.p. route. The suitability of the protocol developed was evaluated by treating infected Wistar rats with chloroquine (30 mg/kg/day). A decreased parasitemia after the treatment was observed until the complete eradication of the parasite, around 10 days post-inoculation. Parasitemia depression after chloroquine treatment demonstrates the utility of the model developed to test new antimalarial drugs.     

The establishment of Plasmodium berghei in mosquitoes of a refractory and a susceptible line of Anopheles atroparvus

The events between the ingestion of Plasmodium berghei-infected mouse blood and the establishment of the ookinetes in the epithelium of the midgut in refractory (R) and susceptible (S) Anopheles atroparvus are described. Simultaneously fed, fully engorged female mosquitoes were randomly assigned to dissection at 22, 28, 32, 48 h and 10 days (controls) after the infective feed (post-infection: p.i.). Serial transverse sections of 6 micron were cut. Every 10th section was studied. The maturation of ookinetes was monitored at 16, 19 and 22 h p.i. The infections in R and S mosquitoes developed similarly with regard to the maturation of ookinetes and the number of mature ookinetes in the lumen of the midgut. The semiquantitative evaluation of the envelopment of the food bolus by the peritrophic layer showed that this layer cannot function as a physical barrier against migrating ookinetes. In the midgut epithelium the number of ookinetes decreased significantly with time in both R and S mosquitoes, but a similar number of penetrations was recorded for both types of mosquito. In S mosquitoes maximal 1% of the ookinetes present in the midgut formed an oocyst. In both R and S mosquitoes a substantial loss of parasites was found, first in the lumen of the midgut and second after penetration of the midgut epithelium by the mature ookinetes. Relatively few parasites develop into oocysts in S, but hardly any do so in R individuals. The factors in control of refractoriness are likely to operate on early oocyst development.