Malaria is present in over 90 countries around the world but is mainly confined to the poorest tropical areas of Africa, Asia and Latin America. More than 90% of cases and the vast majority of deaths occur in tropical and equatorial Africa.
Plasmodium falciparum is the main type of malaria and is the cause of the deaths caused by the disease.
Although the distribution of malaria in the world has been reduced and confined mainly in tropical areas, the number of people at risk of infection has reached about 3 billion and this number is likely to increase. Every year, there are more than 200 million malaria cases worldwide with around 400,000 deaths. 90% of cases concern Sub-Saharan Africa, with a devastating impact on the economy and social development of most of the affected countries.
After the eradication campaigns of malaria in the world launched by the World Health Organization (WHO) in 1955, and interrupted for technical and economic reasons in the late 1960s, there has been a resurgence of malaria in the following years, not only in the areas that had benefited from the good results of the eradication campaigns, but also in Sub-Saharan Africa, mainly due to the onset of the resistance of Plasmodium falciparum to chloroquine and other antimalarial drugs.
Mutations in hemoglobin (S, C, beta and alpha-thalassemia), in the glucose-6-phosphate dehydrogens and pyruvate-kinase enzymes, protect against the serious forms of malaria caused by P. Falciparum in heterozygous carriers and, in the case of hemoglobin C, especially in homozygosity. The particular properties of the hemoglobin chains and the oxidative stress conditions caused by the infection itself can cause the hemolysis of erythrocytes, hindering the maturation of the trophozoites. Although these mutations are harmful (almost always lethal in homozygosity), thanks to the protection conferred against malaria they are found at high frequencies in populations living in endemic (or ex endemic) areas for malaria (Mediterranean basin, sub-Saharan Africa, Southeast Asia). Except for hemoglobin C, in these populations the frequency of resistance mutations is however destined to reach an equilibrium value (around 15-20%) which reflects the disadvantage due to the lethality of the mutation and the advantage over malaria. In non-malarial areas, these mutations are generally very rare or absent since their lethality is not balanced by positive effects.
A very interesting example is that of the evolution of the Duffy erythrocyte antigen, the receptor through which P. vivax merozoites penetrate the red blood cell. Erythrocytes that do not have this antigen (Duffy negative) are refractory to infection by that plasmodium. In West Africa, a mutation that eliminates the antigen from the surface of the erythrocytes but that has no other clinical consequences has reached (probably in several thousand years) the frequency of 100% and therefore most of the inhabitants of central and western Africa it is not infected with this species of plasmodium.
Already in the early 1950s, at the end of the five-year Antimalarial Struggle Campaign, Italy was in fact a malaria-free country but, as some sporadic cases of Plasmodium vivax malaria continued until 1962, WHO formalized this result. only in 1970. Since then, in consideration of the potential conditions for the reintroduction of malaria in Italy, a surveillance system has been activated.