Environmental, Social, and Genetic Risk Factors for Malaria

Malaria Risk Factors Malaria, as Viewed through the Expanded Risk Factor Model Malaria is caused by infection of red blood cells by the parasites Plasmodium falciparum, P. vivax, P. malariae, and P. ovale and transmitted from human to human by the vector, Anopheles mosquitoes, according to the information provided by the U.S. Centers for Disease Control and Prevention (CDC, 2012a).

The ability of the female Anopheles mosquito to thrive in proximity to humans, in addition to the presence of the malaria parasite, therefore determines the prevalence and incidence of malaria infections (CDC, 2012b). The only exceptions to this rule is when malaria is transmitted from human to human through pregnancy or exposure to biological substances, such as during a blood transfusion, organ transplantation, or drug use requiring the sharing of needles.

These latter modes of transmission occur rarely, however, therefore the vector, Anopheles mosquitoes, plays a dominant role in determining the risk of malarial infection. Anopheles mosquitoes thrive where rainfall is allowed to collect and provide an aquatic breeding ground (CDC, 2012b). As long as warm ambient temperatures and sufficient humidity persist the malaria parasite will complete its growth cycle and the female mosquito vector will survive, 9-21 days depending on the temperature. For these reasons, tropical and semitropical climates at lower altitudes represent the primary environmental risk factor for malaria.

These regions include the Caribbean, Central and South America, South Central and Southeast Asia, and Sub-Saharan Africa (Feder & Mansilla-Rivera, 2013). Social factors based on climate also play a role in malaria risk. These include the tendency for humans to sleep outside or without the protection of mosquito nets when the weather turns hot and humid. The risk of nighttime infection is great because the Anopheles mosquitoes are most active between dusk and dawn.

Field workers may also chose to sleep in the fields in preparation for another days work, also without the protection of mosquito nets. Notably, the working class and poor would be most susceptible because they would be least likely to have air conditioning in their homes and therefore seek relief from the heat by sleeping outside or without nets. Other social factors include the accumulation of debris capable of collecting rainfall and providing breeding grounds for the mosquito, which is common where humans reside.

This is especially true in poorer communities where it is common for old tires, discarded cans, and plastic debris to collect. Wealthier communities, in contrast, tend to police neighborhoods by removing trash. Some benefit is conferred to long-term residents of malaria-endemic regions of the world in the form of partial immunity, but this benefit is rapidly lost should they immigrate to non-endemic regions of the globe (Feder & Mansilla-Rivera, 2013). This also implies that travelers from non-endemic regions of the world are particularly susceptible to parasite-infected Anopheles mosquito bites.

For example, of the 18 million American traveling to malaria-endemic regions each year approximately 1,500 will return with the disease. Protection against malaria is afforded by the human genetic factor that results in sickle cell disease (Sabahelzain & Hamamy, 2014). When infected by the malaria parasite the red blood cells of individuals with the sickle cell trait will change shape to resemble a sickle, resulting in destruction.