Can mosquitoes die from malaria? 

Researchers show: After feeding on blood, the malaria parasite is the least of the mosquito's problems.

Researchers at the Max Planck Institute for Infection Biology have shown how the mosquito's immune system responds to feeding on blood that contains the malaria parasite. Surprisingly, while the immune system recognizes the malaria parasite, it does not appear to prioritize eliminating it. Mosquitoes encounter many microbes while feeding on nectar, but it is blood-feeding that exposes them to the malaria parasite. But how do mosquitoes react to it? In fact, it is not the parasite but the nutritious blood meal that mosquitoes need to reproduce that poses a major threat to their lives: its nutrients cause the mosquito's intestinal bacteria to multiply very rapidly. The study reveals how the mosquito’s immune system tightly controls this bacterial overgrowth in the gut; if it fails to keep the microbes in check, the mosquito dies. Notably, one of the proliferating bacterial species is harmful to both mosquitoes and the invading malaria parasites. These findings open new avenues in the fight against malaria by focusing on the mosquitoe’s intestinal bacteria.

In our part of the world, mosquitoes are mainly a nuisance. In African countries south of the Sahara, however, they are a major problem: there, they transmit deadly pathogens such as the malaria parasite. Every year, more than 250 million people contract malaria, and around half a million—mostly young children—die.

What activates the mosquito’s immune system?

In order to understand how malaria parasites are transmitted, researchers at the Max Planck Institute for Infection Biology in Berlin are studying the mosquito itself. Like humans, mosquitoes have an immune system that protects them from pathogens such as bacteria, viruses, and parasites.

After a bite, the mosquito’s immune system is activated. Researchers long assumed that its activation is caused by malaria parasites. This assumption has now been turned on its head by scientist Suzana Zakovic.

Doubles its body weight in seconds: bloodsucking as a stress test

Zakovic discovered that it is not the malaria parasite, but rather the mosquito's gut microbiome that becomes a stress test for the immune system after a blood meal. This microbiome consists of various bacteria that support blood digestion in the mosquito's gut. However, as blood is rich in proteins and fats that female mosquitoes need for egg production, this oversupply of nutrients causes the bacteria to multiply rapidly.

As Zakovic explains, the blood meal is extremely stressful: “In a few seconds, the mosquito, which normally feeds on flower nectar, consumes the size of its body weight. Such amounts of nutrients are equivalent to a festive roast.”

When the microbiome becomes a problem

Under these conditions, some bacteria multiply to life-threatening levels. “We discovered that the immune system is activated after a blood meal to keep the bacteria in check,” says Zakovic. If the immune system fails to contain this bacterial overgrowth, the mosquito dies.

Suzana Zakovic has uncovered the molecular mechanisms behind this process. Her research focused on the main activator of the immune defense in the mosquito intestine. It has long been believed that the genes activated by it also kill the invading malaria parasites. To investigate the interaction between the immune response, the microbiome, and the parasites, Zakovic used the molecular CRISPR/Cas9 scissors to specifically switch off the immune activator in mosquitoes.

The mosquito immune system reacts to microbiome shifts

To her surprise, some intestinal bacteria in mosquitoes with defective immune systems multiplied almost uncontrollably, causing a shift in the microbiome composition that eventually killed the mosquitoes. Surprisingly, such shift in microbiome composition did not render mosquitoes more susceptible to malaria parasites.

Zakovic refuted the previous assumption: the immune regulator does not protect the mosquito from the malaria parasite, but from its own microbiome, which threatens to go haywire after a blood meal. While the mosquito is busy digesting and containing the microbiome, it seems to pay little attention to the parasite. “The burden of the increasing bacteria loads is so great that the malaria parasites ingested with the blood are not even a footnote for the immune system,” explains Zakovic.

Microbiome shifts harm mosquitoes and malaria parasites

During her experiments, the researchers made another surprising discovery: mosquitoes with functioning immune systems often had more parasites in their intestines than those in which the immune activator under investigation had been switched off.

They concluded that it may be the derailed microbiome that hinders the parasite's development. When Zakovic examined the microbiome of the immune-compromised mosquitoes, she found that, although it contained more bacteria, its diversity was greatly reduced.

In this “perturbed” microbiome, one type of bacteria called Serratia dominates, causing the high mortality rate of the mosquitoes. Surprisingly, Serratia harms both the mosquito and the malaria parasite. There were significantly fewer parasites in mosquitoes in which Serratia dominated the microbiome. “However, we still need to understand exactly how Serratia kills mosquitoes and malaria parasites in the gut,” the researcher adds.

How the environment affects malaria transmission

Through evolution, the malaria parasite has co-evolved with the mosquito, tuning its life cycle to the mosquito’s survival. “It is interesting that the parasite uses the moment to colonize the mosquito gut when the mosquito is busy digesting blood, producing eggs, and controlling the immune response to a surging microbiome ,” Zakovic reflects.

This study shows how both mosquito health and parasite survival hinge on a balanced microbiome. As the microbial composition of the mosquito gut is shaped by the environment in which they live and feed, the outcomes of key life events, such as blood meals, are environmentally driven. Thus, the parasite’s fate rises and falls with mosquito gut health, making transmission between humans contingent on local bacterial exposures. This dependency provides a valuable clue for decoding the biology of parasite-transmitting mosquitoes and links ecology to malaria transmission.