Malaria

MALARIA

Malaria has been a major disease of humankind for thousands of years. Despite the availability of drugs for treatment, malaria is still one of the most important infectious diseases of humans, with approximately 200–500 million new cases and 1–2.5 million deaths each year. Protozoa of the genus Plasmodium cause malaria and four species are responsible for the disease in humans: P. falciparum, P. vivax, P. ovale and P. malariae. P. falciparum and P. vivax account for the vast majority of cases, although P. falciparum causes the most severe disease. Other species of plasmodia infect reptiles, birds and other mammals. Malaria is spread to humans by the bite of female mosquitoes of the genus Anopheles but transmission by inoculation of infected blood and through congenital routes is also seen. These mosquitoes feed at night and their breeding sites are primarily in rural areas.

Disease

The most common symptom of malaria is fever, although chills, headache, myalgia and nausea are frequently seen and other symptoms such as vomiting, diarrhoea, abdominal pain and cough occasionally appear. In all types of malaria, the periodic febrile response (fever) is caused by rupture of mature schizonts (one of the cell forms arising as part of the life cycle). In P. vivax and P. ovale malaria fever occurs every 24–48 hours, whereas in P. malariae, maturation occurs every 72 hours. In falciparum malaria fever may occur every 48 hours, but is usually irregular, showing no distinct periodicity. Apart from anaemia, most physical findings in malaria are often nonspecific and offer little aid in diagnosis, although enlargement of some organs may be seen after prolonged infection. If the diagnosis of malaria is missed or delayed, especially with P. falciparum infection, potentially fatal complicated malaria may develop. The most frequent and serious complications of malaria are cerebral malaria and severe anaemia.