Plasmodium sporozoites trickle out of the injection site

LM Yamauchi, A Coppi, G Snounou… - Cellular …, 2007 - Wiley Online Library
LM Yamauchi, A Coppi, G Snounou, P Sinnis
Cellular microbiology, 2007Wiley Online Library
Plasmodium sporozoites make a remarkable journey from the skin, where they are
deposited by an infected Anopheline mosquito, to the liver, where they invade hepatocytes
and develop into exoerythrocytic stages. Although much work has been done to elucidate
the molecular mechanisms by which sporozoites invade hepatocytes, little is known about
the interactions between host and parasite before the sporozoite enters the blood
circulation. It has always been assumed that sporozoites rapidly exit the injection site …
Summary
Plasmodium sporozoites make a remarkable journey from the skin, where they are deposited by an infected Anopheline mosquito, to the liver, where they invade hepatocytes and develop into exoerythrocytic stages. Although much work has been done to elucidate the molecular mechanisms by which sporozoites invade hepatocytes, little is known about the interactions between host and parasite before the sporozoite enters the blood circulation. It has always been assumed that sporozoites rapidly exit the injection site, making their interactions with the host at this site, brief and difficult to study. Using quantitative PCR, we determined the kinetics with which sporozoites leave the injection site and arrive in the liver and found that the majority of infective sporozoites remain in the skin for hours. We then performed sub‐inoculation experiments which confirmed these findings and showed that the pattern of sporozoite exit from the injection site resembles a slow trickle. Last, we found that drainage of approximately 20% of the sporozoite inoculum to the lymphatics is associated with a significant enlargement of the draining lymph node, a response not observed after intravenous inoculation. These findings indicate that there is ample time for host and parasite to interact at the inoculation site and are of relevance to the pre‐erythrocytic stage malaria vaccine effort.
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