Malaria

Malaria is a protozoan disease transmitted by the bite of infected Anopheles mosquitoes. It is the most important of the parasitic diseases of humans, with transmission in 107 countries containing 3 billion people and causing 1–3 million deaths each year.

Etiology

Four species of the genus Plasmodium cause nearly all malarial infections in humans.  These are P. falciparum, P. vivax, P. ovale, and P. malariae. Almost all deaths are caused by falciparum malaria.

Epidemiology

Malaria occurs throughout most of the tropical regions of the world. P. falciparum predominates in Africa, New Guinea, and Haiti; P. vivax is more common in Central America. P. malariae is found in most endemic areas, especially throughout sub-Saharan Africa, but is much less common. P. ovale is relatively unusual outside of Africa and, where it is found, comprises <1% of isolates.

Clinical Features

Malaria is a very common cause of fever in tropical countries. The first symptoms of malaria are nonspecific; the lack of a sense of well-being, headache, fatigue, abdominal discomfort, and muscle aches followed by fever are all similar to the symptoms of a minor viral illness. Nausea, vomiting and orthostatic hypotension are also commonly occurring symptoms. The classic malarial paroxysms, in which fever spikes, chills, and rigors occur at regular intervals, are relatively unusual and suggest infection with P. vivax or P. ovale.

Although childhood febrile convulsions may occur with any of the malarias, generalized seizures are specifically associated with falciparum malaria and may herald the development of cerebral disease.

Diagnosis

Demonstration of the Parasite on Microscopy

The diagnosis of malaria rests on the demonstration of the parasite in stained peripheralblood smears. After a negative blood smear, repeat smears should be made if there is a high degree of suspicion.

Both thin and thick blood smears should be examined. In the thick blood smear the level of parasitemia is expressed as the number of parasitized erythrocytes per 1000 RBCs. The thick blood film should be of uneven thickness, having the advantage of concentrating the parasites and thus increasing diagnostic sensitivity.

Antigen tests

For areas where microscopy is not available, or where laboratory staff are not experienced at malaria diagnosis, there are commercial antigen detection tests that require only a drop of blood. Immunochromatographic tests have been developed, distributed and field tested. These tests use finger-stick or venous blood, the completed test takes a total of 15–20 minutes, and the results are read visually as the presence or absence of colored stripes on the dipstick, so they are suitable for use in the field. One disadvantage is that dipstick tests are qualitative but not quantitative – they can determine if parasites are present in the blood, but not how many.

Prevention of Malaria

Methods used in order to prevent the spread of disease, or to protect individuals in areas where malaria is endemic, include prophylactic drugs, mosquito eradication and the prevention of mosquito bites.

Known malaria prophylactic drugs, most of which are also used for treatment of malaria, can be taken preventatively. Modern drugs used include mefloquine (Lariam^®), doxycycline (available generically), and the combination of atovaquone and proguanil hydrochloride (Malarone^®). Doxycycline and the atovaquone and proguanil combination are the best tolerated with mefloquine associated with higher rates of neurological and psychiatric symptoms.

Efforts to eradicate malaria by eliminating mosquitoes have been successful in some areas by the draining of wetland breeding grounds and better sanitation. Other efforts such as Indoor Residual Spraying (IRS), where there is spraying of insecticides on the interior walls of homes in malaria affected areas, together with mosquito nets help to keep mosquitoes away from people, greatly reducing infection and transmission of malaria.

Education in recognizing the symptoms of malaria in the early stages has reduced the number of mortalities in some areas of the developing world by as much as 20%. Further education on vector control also cuts down the prevalence of malaria.

Malaria treatment

It is important to attempt to differentiate between uncomplicated and severe malaria. Patients

with uncomplicated malaria include: those who have mild symptoms, are ambulant and have

no evidence of organ dysfunction either clinically or on laboratory tests and in whom the

parasite count is less than 5% .

However, uncomplicated malaria may progress to severe malaria rapidly if the patient is not treated appropriately.

For patients with uncomplicated malaria, the recommended chemotherapy is artemether plus lumefantrine (Coartem^®) or alternatively quinine plus either doxycycline or clindamycin.

Patients should experience a clinical response to therapy within 24 – 48 hours, although fever

may persist for up to five days after treatment has commenced. A repeat peripheral blood smear should be performed where possible after 72 hours of treatment by which time a decrease of at least 75% of the initial parasite count is expected with effective treatment. Complicated malaria should be treated with parenteral antibiotics and meticulous medical care. Combinations of anti-malarial drugs are used, according to drug resistance and sensitivity.

Conclusion

Malaria has a very high mortality rate and causes great morbidity if not detected early and treated promptly.