The parasites' presence in the lymph nodes almost certainly has implications for the mammalian immune response, said Robert Ménard, a Howard Hughes Medical Institute (HHMI) international research scholar who led the study.
Ménard and colleagues report their findings in the February issue of the journal Nature Medicine, published online on January 22, 2006.
When a mosquito infected with Plasmodium bites a mammal, the immature parasites travel to the animal's liver, which, until now, scientists thought was the only place they could develop, Ménard said. Once they have fully developed, the parasites burst out of the liver cells and infect red blood cells, beginning the onset of malaria.
Although researchers understand this life cycle, no one has measured directly how many parasites a mosquito bite transmits or where else in a mammal's body they travel, said Ménard. To find out, he and his colleagues infected mosquitoes with fluorescently tagged Plasmodium parasites, and then allowed the mosquitoes to bite a mouse. From each mosquito bite, they found an average of 20 fluorescent parasites embedded in the animal's skin. Ménard found that the parasites moved through the skin in a random, circuitous path at a speed that is amongst the fastest recorded for any migrating cell. After leaving the skin, the parasites frequently invaded blood vessels. That was no surprise to Ménard, since they need to travel through blood vessels to get to the liver. However, many of the parasites also invaded lymphatic vessels. About 25 percent of the parasites injected by the mosquito bites were drained by lymphatic vessels and ended up in lymph nodes close to the site of the bite. Their journey seemed to stop there,
Source:Howard Hughes Medical Institute