The malarial parasite, Plasmodium, is transmitted by female Anopheles mosquitoes. Mosquitoes pick up the parasites from infected people while sucking blood. The parasites traverse the mosquito’s gut and form oocysts that divide continuously. Mature oocysts release thousands of sporozoites into mosquito hemolymph. These reach the mosquito’s salivary glands to infect a new healthy person.
While switching from one stage to another, the Plasmodium population has to face strong innate immune responses from the mosquito. How do the parasites escape the mosquito’s immune system and manage the host’s resources for efficient reproduction?
Investigations by a group of researchers from the National Institute of Malaria Research, New Delhi and other universities in India now provide an answer.
The researchers fed female mosquitoes blood containing Plasmodium vivax from malaria patients. Then they dissected mosquito midgut, salivary gland and hemocytes and, using advanced technologies, examined the molecular network involved.
The plasmodium parasite, they found, limits the availability of iron and other nutrients to bacteria in the mosquito gut. This suppresses the proliferation of mosquito gut microbiota , which, in turn, reduces the immunity of the mosquito.
“Then, the parasite suppresses many salivary, midgut and immune-related proteins in the mosquito by altering its genetic makeup. Now the mosquito is helpless against invasion by the parasites”, says Rajnikant Dixit, ICMR-National Institute of Malaria Research, Delhi.
After the invasion, the parasite alters the molecular architecture of the mosquito to produce more catabolic and metabolic compounds and nutrient transport proteins. These compounds and macromolecules are used by the parasite for sexual development during interaction with hemocytes, the mosquito’s immune cells, .
Plasmodium oocysts suppress host gut metabolic activities and elevate secretary and immune protein activities for releasing sporozoites from oocysts which eventually enter the mosquito’s salivary glands. This causes a nutritional imbalance in the mosquito, enhancing host-seeking behavior to feed on multiple people.
According to the World Malaria 2020 report, nearly 230 million people were infected and more than 4 lakhs died of malaria last year. To reduce and prevent malarial infections, existing control methods depend on insecticide-treated bed nets. But this is leading to the development of resistance to the insecticide among mosquito populations. So, we need new and complementary tools.
To prevent malaria transmission, the researchers suggest enriching microbes like Microsporidia fungi and Wolbachia bacteria in mosquito gut. This could enhance mosquito metabolism and immunity, making mosquitoes more resistant to the malaria parasite.
Front. Immunol. 11: 609 (2020);
Curr. Res. Immunol. 2:12-22 (2021);
Reported by: G Sharath Chandra
Indian Institute of Horticultural Research
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