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Photo: CDC Female Anopheles mosquito
Of all the possible diseases you can get while traveling overseas, none of them cause more concern or strike up fear like malaria, and for good reason.
It is estimated to be up to a half a billion cases of malaria annually with about 1 million deaths, particularly among young children.
It is considered the most important parasitic disease affecting humans. The disease has great socio-economic importance and helps in keeping poor countries poor in a vicious cycle.
According to the Centers for Disease Control and Prevention (CDC), about 1,300 cases of malaria are diagnosed in the United States each year. The vast majority of cases in the United States are in travelers and immigrants returning from malaria-risk areas, many from sub-Saharan Africa and South Asia.
The protozoan parasite belongs from the genus Plasmodium. There are many species of Plasmodium that infect vertebrates, but only 4 that are important to humans. The four species are:
• Plasmodium falciparum (see below)
• Plasmodium vivax
• Plasmodium malariae
• Plasmodium ovale
There have been some documented cases of people getting simian malaria (P. knowlesi).
Human malaria is considered a tropical disease, but some cases happen outside the tropics. Most cases are found in Southeast Asia, China, India, and Africa, parts of the Middle East, Mexico, Central and South America.
For malaria to occur you must have the following; a susceptible population, malaria carriers and the right mosquito vector (the female Anopheles mosquito).
The life cycle for all the malaria species is essentially the same. It’s very complicated (with part in the mosquito and part in the human) but in a nutshell, in humans it goes like this: During a blood meal, a malaria-infected female Anopheles mosquito inoculates the parasite into the human host.
The parasite almost immediately infects liver cells and goes through a maturation series and ruptures. Just a side, P. vivax and P. ovale can have a dormant stage in the liver and can cause relapses in the blood weeks to years later.
The parasite then moves on to infect red blood cells. Blood stage parasites are responsible for the clinical manifestations of the disease.
The parasite is later ingested by an Anopheles mosquito during a blood meal and the cycle in the mosquito happens. It really is a vicious cycle.
The disease may manifest itself after an incubation of days to months. Once the parasites build up in the blood, symptoms are non-specific; fever, chills, body aches, diarrhea and vomiting. At this point the only way to confirm is finding the parasites in blood. These early stages resemble many other febrile diseases.
Paroxysms (due to rupture and release of the parasite and metabolic products into the system), happen every 48-72 hours depending on the species.
There is a cold stage which leads to teeth chattering, shaking chills followed by a hot stage (fever) where temperatures may reach 106°F. Convulsions may develop particularly in children.
Untreated P. falciparum (the life-threatening species) can lead to severe malaria. Severe malaria is characterized by cerebral malaria, severe anemia, renal filure (black water fever), respiratory distress and bleeding disorders and shock.
Prompt treatment for falciparum malaria is essential cause death from cerebral complications may occur.
The other human malarias are not usually life-threatening. People who are partially immune or non-immune but taking prophylactic anti-malarials, may show atypical symptoms and a longer incubation period.
Active malaria is most frequently diagnosed by observing the parasite in blood smears. There are molecular and antibody detection techniques to complement microscopic examination.
Treatment of malaria depends on several factors; The type (species) of the infecting parasite, the area where the infection was acquired and its drug-resistance status, the clinical status of the patient, any accompanying illness or condition, pregnancy, drug allergies, or other medications taken by the patient.
Chloroquine, Fansidar, mefloquine , Malarone, quinine, doxycycline and artemisin derivatives (not licensed for use in the United States, but often found overseas) can be used to treat malaria. See link for treatment guidelines.
As a traveler in a malaria endemic area, what preventive measures can you take?
There is no vaccine currently available for malaria. According to the CDC all travelers to malaria-endemic areas should be advised that taking an appropriate drug regimen and using antimosquito (insecticide treated bed nets, stay in well screened areas, DEET insect repellent) measures will help prevent malaria. Travelers should be informed that no method can protect completely against the risk for contracting malaria.
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