The malaria parasites can develop in the lymph nodes also, according to a recent research, led by Robert Ménard. This reportedly has implications for the mammalian immune response.
The dreaded disease is caused when a mosquito infected with Plasmodium bites a mammal, and the immature parasites travel to the animal's liver. Once they have fully developed, the parasites burst out of the liver cells and infect red blood cells, beginning the onset of malaria. After leaving the skin, the parasites frequently invaded blood vessels, as they need to travel through them to get to the liver.
However, scientists also found that many of the parasites also invaded lymphatic vessels, and about 25% 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.
The researchers found that though within about four hours of the mosquito bite, many of the lymph-node parasites appeared degraded, and were also seen interacting with key mammalian immune cells, suggesting that the immune cells were destroying them, a small number of the parasites in the lymph nodes escaped degradation and began to develop into forms usually found only in the liver.
Dr Ménard said that the development of malarial parasites in the lymph nodes may be a reason why the body was so tolerant to the parasites. The study showed that 52 hours after the mosquito bites, no parasites remained in the lymph nodes, thus suggesting that they cannot develop completely there. Dr Ménard said that as only fully developed parasites can infect red blood cells and cause malaria, the lymph-node parasites probably don't contribute to the appearance of malaria symptoms. However, they could still affect how the immune system responds to infection.
He further explained that parasites developing in the lymph nodes could have two opposite effects on the body's immune response. On one hand they might alert the body that an invader is present and activate a protective immune response, while on the other their presence in the lymph nodes might desensitize the body to the parasites, blunting the immune system's response to liver and blood cell infection.