Direct Microscopic Quantification of Dynamics of Plasmodium berghei Sporozoite Transmission from Mosquitoes to Mice

Abstract

The number of malaria sporozoites delivered to a host by mosquitoes is thought to have a significant influence on the subsequent course of the infection in the mammalian host. We did studies with Anopheles stephensi mosquitoes with salivary gland infections of Plasmodium berghei sporozoites expressing a red fluorescent protein. After individual mosquitoes fed on an ear pinna or the ventral abdomen of a mouse, fluorescence microscopy was used to count numbers of sporozoites. Mosquitoes allowed to feed on the ear for periods of 3 versus 15 min deposited means of 281 versus 452 sporozoites, respectively, into the skin; this may have epidemiological implications because mosquitoes can feed for longer periods of time on sleeping hosts. Mosquitoes feeding on the ventral abdomen injected sporozoites not only into the skin but also into the underlying peritoneal musculature. Although mosquitoes injected fewer sporozoites into the abdominal tissues, more of these were reingested into the mosquito midgut, probably a consequence of easier access to blood intake from the abdominal area. The most consistent parameter of sporozoite transmission dynamics under all conditions of mosquito probing and feeding was the relatively slow release rate of sporozoites (ϳ1 to 2.5 per second) from the mosquito proboscis. The numbers of sporozoites introduced into the host by mosquitoes and the transmission efficiencies of sporozoite delivery are multifactorial phenomena that vary with length of probing time, skin site being fed upon, and numbers of sporozoites within the salivary glands. Malaria infection is initiated by anAnopheles stephensi mosquito injecting sporozoites into the skin of its mammalian host while probing for a blood meal (1,15,16,21,25,28). Continuation of the malaria infection depends upon these sporozoites leaving the skin via dermal blood vessels and then traveling to the liver and developing into exoerythrocytic forms (EEF). The relatively large number of studies attempting to quantify the dynamics of this process attests to the importance with which it has been viewed by malariologists; the history and rationale for such attempts have been reviewed previously (6,24,26). The approaches used have included assessment of numbers of sporozoites released by mosquitoes into liquid media (reviewed in reference 6) or onto glass slides (12), counting of EEF after mosquito feeding on rodent hosts (26), and determination of sporozoite 18S rRNA (16) or ␤-galactosidase expressed by transgenic sporozoites (8) within the skin of a mouse after sporozoite introduction by mosquitoes.Each of these approaches has had both advantages and limitations. We believe that the most biologically appropriate approach requires direct feeding of infected mosquitoes on a living host and that the most accurate and precise means of quantification is direct microscopic observation and counting of injected sporozoites. Aside from the unequivocal nature of direct counts of morphologically recognizable sporozoites, this method allows correlation of specifi...

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“…6). In both groups of mice, this was relatively longer compared to previously observed results which had prepatent period at 7 days post infection (Yamei Jin, et al, 2007). Thereafter, parasitaemia in the two groups of restrained mice was characterized by high levels and this was in agreement with previous studies (Basir et al, 2012).…”

A Baculovirus Dual Expression System-Based Malaria Vaccine Induces Strong Protection againstPlasmodium bergheiSporozoite Challenge in Mice

“…One of these routes was bites of P. berghei-infected mosquitoes. This route was chosen because it closely mimics the natural route of malaria transmission (27,56). During blood feeding, mosquitoes probe the skin to search for blood vessels and inject sporozoites along with saliva into the host skin.…”

Distinct Malaria Parasite Sporozoites Reveal Transcriptional Changes That Cause Differential Tissue Infection Competence in the Mosquito Vector and Mammalian Host

“…Salivary gland sporozoites gain significant infection capacity for the mammalian liver, but in contrast, they loose infectivity for the salivary glands (36,37). During the bites of infected mosquitoes, only a few dozen to a few hundred sporozoites are inoculated into a new mammalian host (10,14). This is sufficient to ensure infection, because each of the highly infective salivary gland-derived sporozoites can initiate development of an intrahepatic liver stage, which can produce more than 10,000 red blood cell-infectious merozoite stages (4,39).…”