Tests to ascertain malaria

Malaria is an infectious disease caused by Plasmodium, a parasite that is transmitted to humans through the bite of mosquitoes of the genus Anopheles.

Humans are the only reservoir of the disease, and interhuman contagion is not possible.

Mosquitoes of the Anopheles genus breed in water-rich areas and usually sting during the hours of darkness, from dusk to dawn.

The numbers and survival of mosquitoes, and thus the possibility of malaria transmission, are greatly influenced by environmental conditions, particularly rainfall distribution, temperature, and humidity. In many places transmission is seasonal, peaking during and just after the rainy season.

Another factor that can affect the chance of getting sick is human immunity, especially among adults living in areas with moderate to intense transmission conditions. These individuals, after years of exposure to Plasmodium, develop partial immunity that reduces the risk of contracting severe forms of malaria. For this reason, most malaria deaths in Africa occur in young children, while in areas with lower transmission and low immunity all age groups are at risk.

There are several species of this parasite; the most common are Plasmodium falciparum and Plasmodium vivax; others are Plasmodium ovale and Plasmodium malariae.

The incubation period is variable: about 7-14 days for P. falciparum infection, 8-14 days for P. vivax and P. ovale, 7-30 days for P. malariae. For some strains of P. vivax incubation can extend for 8-10 months.

The symptomatology of malaria is usually nonspecific; the main symptoms are fever accompanied by chills, headache, backache, profuse sweating, muscle aches, nausea, vomiting, diarrhea, cough. Malaria can be suspected on the basis of the patient's travel history, symptoms, and findings from the clinical examination.
The most serious infection is that given by Plasmodium falciparum: this parasite, in fact, causes a serious, potentially fatal disease, so it is essential to start treatment as soon as possible.

Diagnosis can be made through different methodologies. Laboratory investigations usually show a mild anemia, a slight platelet decrease, and a increase in bilirubin and transaminase. The diagnostic gold standard is light microscopy in which a thin smear of blood is viewed under a microscope and the morphology of the parasite within the red blood cells, the species of the parasite, and the percentage of parasitemia can be recognized. Another test is the thick drop test, again performed on a blood sample, this test is more sensitive but more difficult to prepare and interpret so the accuracy of the results depends on the experience of the examiner. If the initial blood smear is negative, additional smears should be repeated at 12-24 h intervals until negativity of three consecutive tests is obtained. Because of the possibilities of these types of tests, recognizing species and estimating parasitemia, they are the most widely used in the world. In addition to the previously mentioned methods, rapid diagnostic tests are possible, capable of providing a result in 2 to 15 minutes, which detect the presence of antigens (molecules that can be recognized by the immune system) of Plasmodium or the enzymatic activity produced by it. The most widely used are tests that look for the HRP-2 protein associated with malaria parasites (especially a P. falciparum) and those that detect the enzyme lactate dehydrogenase associated with Plasmodium. These tests are the most widely used in areas of sub-Saharan Africa, although they do not allow differentiation of the species involved in infection and knowledge of parasitemia. Rapid tests based on HRP-2 protein recognition account for about 80% of all rapid tests on the market. The current issue is the increasing prevalence of P. falciparum with deletions of the hrp2/3 gene (gene required for HRP-2 protein production), which poses a serious threat to the reliability of these diagnostic tests. Although less widely used, there are other diagnostic methodologies such as molecular diagnosis by LAMP (Loop-mediated isothermal amplification) technique that allows detection of Plasmodium falciparum and PCR (Polymerase Chain Reaction) by which it is possible to recognize the specific DNA of each species of Plasmodium that can infect humans.

These are currently in the process of being developed.

A number of malaria vaccines are currently being tested.

Globally, there were an estimated 247 million cases of malaria in 2021, with the majority of cases, 82%, occurring in Africa, particularly in Nigeria (27%), the Democratic Republic of Congo (12%), Uganda (5%) Mozambique (4%), and Southeast Asia where 10% of cases were recorded. Globally, deaths from malaria declined steadily over the period 2000-2019, followed by an uptick of about 10% in 2020, from disruption of services due to the Covid-19 pandemic, and again declined slightly in 2021, when deaths were 619.000. An estimated 2 billion cases of malaria and 11.7 million deaths from this cause were prevented during the period 2000-2021 by all prevention, diagnostic and treatment measures implemented by the World Health Organization (WHO). The goals currently promoted by WHO are to reduce the incidence of malaria cases by at least 90 percent by 2030, reduce malaria mortality rates by at least 90 percent by 2030, eliminate malaria in at least 35 countries by 2030, and prevent the recurrence of malaria in all malaria-free countries.