The Role of Anopheles Gambiae Mosquitoes in Malaria Transmission

Malaria is a disease, which infects more than 300 million people all over the world and is estimated to be responsible for more than 1.5 million deaths each year. It is a tropical disease, which continues to haunt countries in the Sub-Saharan Africa than it does in other tropical countries. Malaria eradication programmes which came into being in the 1950s and 1960s failed to capitalize on initial successes and many other factors have since then contributed to re-emergence of malaria especially in the African region.

What made malaria to re-emerge in the past decade?

According to the WHO, malaria has re-emerged at an alarming rate, especially in the region of sub-Saharan Africa. They have recognized several factors which might have lead to this resurgence and these include,

-Development of resistance to commonly used antimalarial drugs,

-Necessity for large groups of people to settle in endemic areas due to being displaced from their original settlements following armed conflicts,

-Migration of people who are non-immune and were residing in low malaria prevalent areas towards highly endemic areas,

-Changing rainfall patterns and the initiation of irrigation projects which leads to new mosquito breeding sites,

-Poor socio economic status, which would prevent people from obtaining adequate treatment and adhere to preventive strategies,

-Rapid increase in the birth rate that leads to an expansion of the highly susceptible population below the age of 5 years,

-Changing patterns in the vector behavior such as the biting habits.

From the above list, it is evident that environmental changes and behavior patterns of the vector have contributed towards the re-emergence of malaria and certain elements in the life cycle of Anopheles gambiae have contributed to maintain its place as the most efficient vector for malaria.

How does malaria transmit?

Malaria is caused by parasites belonging to the genus plasmodia and among them, the most deadliest form would be the Plasmodium falciparum. The parasites gain entry to human beings following a bite from an infected mosquito belonging to the genus anopheles. In the African region, one of the primary mosquitoes to transmit malaria has been recognized as belonging to Anopheles gambiae complex while scientists have unraveled the existence of around seven species within same complex.

Although the different species of Anopheles gambiae are morphologically indistinguishable, there are certain behavior patterns different from one another. Thus, not all mosquito species belonging to Anopheles gambiae complex would transmit malaria in humans. Among Anopheles gambiae species transmitting malaria in humans, Anopheles gambiae sensu stricto would be the primary vector while the same species is known to be the most efficient of all such vectors transmitting malaria.

Why is Anopheles gambiae more effective in transmitting malaria parasite than other vectors?

Among those who study malaria parasites and its vectors, Anopheles gambiae would be the most efficient vector among all anopheles species for several reasons.

One of the reasons is the strong affinity by these mosquitoes to feed on humans than on the blood of other animals. Therefore, Anopheles gambiae falls into the category of anthropophily where most of the other anopheles species fall into the category of mixed feeding habits.

Furthermore, having multiple sub-species would mean that they can tolerate many different habitats such as salt water, standing water on puddles and in irrigation ditches, water in hollows of trees, as well as in barren areas. This would mean Anopheles gambiae would tolerate most environments in the tropics with adequate hydration to sustain life.

At the same time, researchers are eyeing a split in the Anopheles gambiae sensu stricto species, which would further complicate the control measures undertaken to tackle the emergence of malaria.

What does the future hold in controlling Anopheles gambiae?

At present, the techniques used for controlling or preventing malaria in endemic regions of Africa does not seem to perform adequately to lower the number of cases. At the same time, scientists have almost completed the Anopheles gambiae genetic sequence, which would enable them to understand how these vectors adapt and behave during the process of disease transmission. In light of these new findings, scientists are hopeful that they can break the jinx of controlling the most influential malaria vector and bring down the number of cases or else the case fatality rate in the endemic areas.


The Ethology of Anopheles gambiae, the Vector of Malaria –

Malaria: A Reemerging Disease in Africa – Thomas C. Nchinda
World Health Organization, Geneva, Switzerland.