Malaria

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Malaria is a life-threatening parasitic disease affecting approximately 40% of the world’s population. More than 500 people become severely ill annually. While most cases and deaths are in sub-Saharan Africa, Asia, Latin America, the Middle East, and some parts of Europe are also affected. It typically occurs in the warmer regions of the world, particularly the tropics and subtropics. The high temperatures in these areas allow the mosquito vector of the parasites to thrive. Among the high-risk groups are upland subsistence farmers, forest-related workers, indigenous peoples, settlers on frontier areas, migrant agricultural workers, and soldiers assigned in endemic areas. Travelers from malaria-free regions with little or no immunity are also highly vulnerable.

It was once thought that the disease originated from fetid marshes, hence the name mal aria, meaning “bad air.” In 1880, it was discovered by scientists that the actual causative agent of the disease is a one-celled parasite called Plasmodium. Later on, it was found that the parasite is transmitted among persons through a vector, the female Anopheles mosquito, which requires human blood to nurture its egg.

Four species of Plasmodium can infect humans: P. falciparum, P. vivax, P. ovale, and P. malariae. Of these, P. falciparum and P. vivax are the common species of malaria parasites in the Philippines, where 70% of malaria cases are caused by the former and 30% are P. vivax cases. Incidence of P. malariae infection contributes to approximately less than 1% of the total malaria cases. If not treated immediately, P. falciparum malaria can lead to severe cases like cerebral malaria and even death. P. vivax, on the other hand, does not lead to cerebral malaria but may cause relapse in incomplete treatment.


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Transmission

Malaria transmission differs in intensity and regularity depending on local factors such as rainfall patterns, proximity of mosquito breeding sites and mosquito species. In the Philippines is perennial and incidence is higher during the rainy season. Endemic areas are usually rural, hilly or mountainous, and hard to reach. People get infected when they are bitten at night by an infected female Anopheles mosquito, specifically A. flavirostris in the Philippine setting. These mosquitoes become infected through a previous blood meal on an infected host. The parasites, which are in their sporozoite form, are inoculated into the human bloodstream during the bite. After a single sporozoite is carried to the liver, it invades a liver cell, grows and divides in 6 days to produce 30,000-40,000 daughter cells called merozoites. These forms are released into the bloodstream when the liver cell ruptures and infect the host’s erythrocytes or red blood cells. The parasites grow within 48 hours and divide into 8-24 daughter cells. The human erythrocyte is ruptured during the process, leading to the release of the parasites. Some parasites move on to invade other erythrocytes and some mature into male and female gametocytes. These forms are sucked by the female Anopheles mosquito when it takes a blood meal on the infected host. Inside the mosquito, the gametocytes undergo sexual development, mate, and produce sporozoites. After about a week, as the mosquito takes its next blood meal, the sporozoites mix with the mosquito’s saliva and are injected into the next host.

Because the parasites are found in red blood cells of an infected person, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. The disease may also be transmitted from a mother to her unborn infant before or during delivery, a condition called congenital malaria. Pregnant women have increased susceptibility to Plasmodium falciparum malaria; in malaria-endemic countries, P. falciparum contributes to 8-14% of low birth weight, which in turn decreases the chance of a baby’s survival.


Symptoms

Symptoms usually occur 10-15 days after infection. In some people, the symptoms may appear after 4 weeks and even a year. The periodic destruction of erythrocytes during and the release of parasites into the circulation to re-invade other red blood cells cause typical intermittent chills, fever and sweating. Other symptoms include headaches, nausea, vomiting, muscle aches, and malaise. The disease may also cause anemia and jaundice (yellowish color of the skin and eyes) due to the loss of red blood cells. If left untreated, the disease can proceed to become life-threatening as blood supply to the vital organs is disrupted.

Infection by P. vivax and P. ovale can occur again, a condition termed relapsing malaria. These parasites can remain dormant in the liver for several months up to about 4 years after an infectious mosquito bite. Symptoms will appear when the parasites come out of hibernation and begin invading red blood cells. Infection with P. falciparum may cause kidney failure, seizures, mental confusion, coma, and death, if not promptly treated.


Diagnosis

Diagnosis of the disease is simply though blood testing. Blood sample from the patient is examined under a microscope for the presence of the parasites. The test should be performed without delay if symptoms have started to appear and one has any suspicion of malaria (i.e., recent travel to a malaria-risk area).


Treatment and Prevention

Although a life-threatening disease, malaria is treatable and preventable. Malaria can be controlled by two key points: early diagnosis and prompt treatment. These strategies shorten the duration of the disease and prevent the development of complications and deaths. As such, access to disease management should be established as a fundamental right of all populations at risk.

Contemporary methods of control focus more on curing patients than reducing parasite reservoirs. The World Health Organization currently recommends the marketing of artemisinin-based combination therapies (ACTs) as treatment for uncomplicated malaria, especially for those countries with cases of drug resistance greater than 10%. The use of artemisinin alone poses a risk of resistance, as evidenced by the developed resistance of the parasite, particularly P. falciparum, to conventional treatment , such as chloroquine and sulfadoxine-pyrimethamine when used singly.

ACTs involve the combination of artemisinin derivatives with another effective antimalarial drug. Presently, the medicine is considered the most effective one available for malaria treatment. ACTs have been deployed on an increasingly large scale. It has been shown that the medicine produces a very rapid therapeutic response and carries the potential of reducing the transmission of malaria. When the correct combination is used, artemisinin reaches 95% effectiveness in curing the disease, with a very low probability of the parasite developing resistance. It is imperative that the partner drug of artemisinin be considered, as the efficacy of ACTs depends on it. For example, there is a high falciparum resistance against chloroquine and the drug therefore does not produce an effective combination with artemisinin.

Children of any age are at risk for malaria and should be on antimalarial drugs when traveling to a hazardous area. However, some drugs are not recommended for children and doses are based on the child’s weight.

Malaria increases the risk of serious pregnancy, including premature births, miscarriage, and stillbirth. Thus, travel of pregnant women to malaria-risk areas is best postponed. If circumstances do not allow postponement, an effective prophylaxis regimen is necessary. There is no evidence that chloroquine and mefloquine cause congenital defects; however, it essential to keep in mind that preventive drugs are not completely effective. Consultation with the health care provider is best recommended.

There is limited data available regarding antimalarial drugs and breastfeeding. The amount of the drug excreted to the mother’s breast milk is thought to be harmless, although not likely enough to provide immunity against malaria for the infant.

Other measures endorsed for malaria prevention include:

  • Using insecticide-laden bed nets
  • Wearing insect repellent and long-sleeved clothing if outdoors at night
  • Spraying insecticides in risk areas at home


Malaria Eradication in the Philippines

In the Philippines, attempts of the Department of Health and others have been made to eradicate the disease. As of November 2007, 22 of the 57 provinces endemic for malaria have been cleared, the more recent ones being Marinduque, Sorsogon, Albay in Luzon; Eastern and Western Samar in the Visayas; and Surigao del Norte.


Sources

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