Final answer:
Pregnant women, children under five in Africa, and non-immune individuals are the main groups at risk of dying from untreated malaria. The disease is caused by Plasmodium species, particularly P. falciparum, and is transmitted by Anopheles mosquitoes with high risks in areas with drug resistance.
Step-by-step explanation:
The primary groups of people at risk of dying from malaria when it is left untreated include pregnant women, children under the age of five residing in Africa, and individuals without immunity to the disease. Malaria is a deadly parasitic disease mainly transmitted to humans by the bite of the infected female Anopheles gambiae mosquito.
Plasmodium falciparum is recognized as the most lethal cause of malaria, commonly known as falciparum malaria. The mortality rate can be as low as 0.1 percent with prompt and correct treatment, but in areas where the parasite has developed drug resistance, the disease's severity and the mortality risk increase substantially.
Pregnant women are considered to be especially at high risk of malaria, with non-immune pregnant women facing acute and severe clinical disease, potentially leading to fetal loss in up to 60% of such cases and maternal deaths in more than 10%.
In the case of semi-immune pregnant women with malaria infection, the risk of severe illness also poses a significant danger.
The evolutionary aspect of this disease is highlighted by the prevalence of the sickle-cell allele (S allele) in populations where malaria is endemic, due to heterozygotes (AS) possessing a natural resistance to malaria, thus influencing the gene pool.