Malaria, a parasitic infection transmitted by the night-biting female Anopheles mosquito, is still causing significant deaths in the tropics and sub-tropics; approximately 3.2 billion people are exposed to the illness every year. The World Health Organization estimated that approximately 207 million people developed symptomatic malaria in 2012. Malaria deaths peaked at 1.82 million in 2004 and fell to 1.24 million in 2010. Over 80 percent of these occur in sub-Saharan Africa, with most cases attributed to Plasmodium falciparum, the deadliest form of malaria parasite. To understand why malaria hasn’t yet been eradicated across the globe, it’s necessary to consider three important factors – the mosquito, the illness-causing parasite, and human behavior.

The mosquito itself is one of the main reasons that malaria has not been eradicated. Of the approximately 400 known species of Anopheles mosquitoes, 30 to 40 species transmit malaria. Different species live in different ecosystems, so there is no one method of eradication, and they are becoming increasingly resistant to pesticides. Even if there were one pesticide that could eradicate all mosquitoes, spraying it over their habitats would have a large adverse effect on other organisms living in or near the sprayed area. Because all members of the food chain would be affected, mass spraying is not a feasible option.

Modifying human behavior to avoid mosquito bites is a more feasible method for eradication. This includes using insecticide-treated bed nets that provide a physical and chemical barrier, and spraying insecticide on indoor walls and ceilings. However, neither of these are permanent solutions; while they can control malaria, they won’t eradicate it.

Although Plasmodium falciparum is the most common and deadly species to cause malaria, there are four other species that can affect humans, each with different life cycles and antigens. The parasites that cause malaria also pass through multiple distinct forms during their life cycle and have evolved to evade the mammalian immune system; some have even become resistant to the drugs normally used to treat the illness. The ideal drug would protect humans from malaria at any stage in the parasites’ development, but current treatments only target them during one part of their life cycle. All these variables make it significantly more challenging to develop medications and vaccines that are effective against every stage and species of malaria.

In addition, the effectiveness of antimalarial drugs can be compromised for several reasons. Resistance to these drugs in humans can occur because of inappropriate prescribing and overuse; in many countries antimalarials can be bought over the counter. Often drugs are counterfeited, and people may be unaware that they are not taking the correct medication.

Social unrest affects many countries where the disease is common, so controlling malaria sometimes becomes a secondary issue. A successful effort to eradicate the illness would probably involve restricting travel, because refugees, immigrants, and tourists transport malaria into new areas and make it harder to contain. But the infrastructure in these countries is often poor, and other basic needs (food and water) are prioritized over the control of malaria.

The best chance for successful eradication lies in the development of a truly effective vaccine with a high efficiency that provides lifelong immunity and doesn’t require a booster. Cooperation between governments, social services, pharmaceutical companies and charities is critical for any successful program. Without simultaneously targeting the mosquito, the unique features of the parasite, and human behavior, eradication will remain a distant goal.