Malaria

Overview

Malaria is a serious and sometimes fatal disease caused by a parasite that commonly infects a certain type of mosquito which feeds on humans. Malaria produces recurrent attacks of chills and fever.

While the disease is uncommon in temperate climates, malaria is still prevalent in tropical and subtropical countries, including parts of the Americas, Asia, and Africa. Each year, there are approximately 515 million cases of malaria, killing an estimated 660,000 people each year, the majority of whom are young children in Sub-Saharan Africa. Ninety percent of malaria-related deaths occur in Sub-Saharan Africa. Malaria is commonly associated with poverty, but is also a cause of poverty and a major hindrance to economic development. World health officials are trying to reduce the incidence of malaria by distributing bed nets to help protect people from mosquito bites as they sleep. Scientists around the world are working to develop a vaccine to prevent malaria.

Infection with malaria parasites may result in a wide variety of symptoms, ranging from absent or very mild symptoms to severe disease and even death. People who get malaria are typically very sick with high fevers, shaking chills, and flu-like illness. In general, malaria is a curable disease if diagnosed and treated promptly and correctly. Treatment depends on many factors including disease severity, the species of malaria parasite causing the infection and the part of the world in which the infection was acquired.

If you're traveling to locations where malaria is common, take preventive medicine before, during and after your trip. Many malaria parasites are now immune to the most common drugs used to treat the disease.

Symptoms

A malaria infection is generally characterized by recurrent attacks with the following signs and symptoms:

  • Moderate to severe shaking chills
  • High fever
  • Sweating

Other signs and symptoms may include:

  • Headache
  • Vomiting
  • Diarrhea
  • Arthralgia (joint pain)
  • Anemia (caused by hemolysis)
  • Hemoglobinuria, retinal damage, and convulsions

Malaria signs and symptoms typically begin within a few weeks after being bitten by an infected mosquito. However, some types of malaria parasites can lie dormant in your body for up to a year.

The classic symptom of malaria is cyclical occurrence of sudden coldness followed by rigor and then fever and sweating lasting four to six hours, occurring every two days in P. vivax and P. ovale infections, while every three for P. falciparum

Causes

Malaria is caused by protozoan parasites of the genus Plasmodium (phylum Apicomplexa). In humans malaria is caused by P. falciparum, P. malariae, P. ovale, P. vivax and P. knowlesi. P. falciparum is the most common cause of infection and is responsible for about 80% of all malaria cases, and is also responsible for about 90% of the deaths from malaria.

Parasitic Plasmodium species also infect birds, reptiles, monkeys, chimpanzees and rodents. There have been documented human infections with several simian species of malaria, namely P. knowlesi, P. inui, P. cynomolgi, P. simiovale, P. brazilianum, P. schwetzi and P. simium; however, with the exception of P. knowlesi, these are mostly of limited public health importance.

Although avian malaria can kill chickens and turkeys, this disease does not cause serious economic losses to poultry farmers. However, since being accidentally introduced by humans it has decimated the endemic birds of Hawaii, which evolved in its absence and lack any resistance to it.

Mosquito transmission cycle:

  • Uninfected mosquito. A mosquito becomes infected by feeding on a person who has malaria.
  • Transmission of parasite. If you're the next person this mosquito bites, it can transmit malaria parasites to you.
  • In the liver. The parasites then travel to your liver — where some types can lie dormant for as long as a year.
  • Into the bloodstream. When the parasites mature, they leave the liver and infect your red blood cells. This is when people typically develop malaria symptoms.
  • On to the next person. If an uninfected mosquito bites you at this point in the cycle, it will become infected with your malaria parasites and can spread them to the next person it bites.

Other modes of transmission:

Because the parasites that cause malaria affect red blood cells, people can also catch malaria from exposures to infected blood, including:

  • From mother to unborn child
  • Through blood transfusions
  • By sharing needles used to inject drugs

Risk factors

The biggest risk factor for developing malaria is to live in or to visit tropical areas where the disease is common. Many different subtypes of malaria parasites exist. The variety that causes the most lethal complications is most commonly found in:

  • African countries south of the Sahara Desert
  • The Asian subcontinent
  • Solomon Islands, Papua New Guinea and Haiti

Risks of more severe disease

People at increased risk of serious disease include:

  • Young children and infants
  • Travelers coming from areas with no malaria
  • Pregnant women and their unborn children
  • Poverty, lack of knowledge, and little or no access to health care also contribute to malaria deaths worldwide.

Immunity can wane

Residents of a malaria region may be exposed to the disease so frequently that they acquire a partial immunity, which can lessen the severity of malaria symptoms. However, this partial immunity can disappear if you move to a country where you're no longer frequently exposed to the parasite.

Complications

Malaria can be fatal, particularly the variety that's common in tropical parts of Africa. The Centers for Disease Control and Prevention estimate that 90 percent of all malaria deaths occur in Africa — most commonly in children under the age of 5.

In most cases, malaria deaths are related to one or more serious complications, including:

  • Cerebral malaria. If parasite-filled blood cells block small blood vessels to your brain (cerebral malaria), swelling of your brain or brain damage may occur. Cerebral malaria may cause coma.
  • Breathing problems. Accumulated fluid in your lungs (pulmonary edema) can make it difficult to breathe.
  • Organ failure. Malaria can cause your kidneys or liver to fail, or your spleen to rupture. Any of these conditions can be life-threatening.
  • Anemia. Malaria damages red blood cells, which can result in anemia.
  • Low blood sugar. Severe forms of malaria itself can cause low blood sugar, as can quinine — one of the most common medications used to combat malaria. Very low blood sugar can result in coma or death.

Malaria may recur

Some varieties of the malaria parasite, which typically cause milder forms of the disease, can persist for years and cause relapses.

Prevention

Methods used 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. The continued existence of malaria in an area requires a combination of high human population density, high mosquito population density, and high rates of transmission from humans to mosquitoes and from mosquitoes to humans.

Diagnosis

Blood tests can show the presence of the parasite and help tailor treatment by determining:

  • Whether you have malaria
  • Which type of malaria parasite is causing your symptoms
  • If your infection is caused by a parasite resistant to certain drugs
  • Whether the disease is affecting any of your vital organs

Areas that cannot afford even simple laboratory diagnostic tests often use only a history of subjective fever as the indication to treat for malaria. Using Giemsa-stained blood smears from children in Malawi, one study showed that unnecessary treatment for malaria was significantly decreased when clinical predictors (rectal temperature, nailbed pallor, and splenomegaly) were used as treatment indications, rather than the current national policy of using only a history of subjective fevers (sensitivity increased from 21% to 41%).

Prognosis

When properly treated, the patient can expect a complete recovery.

Treatment

Active malaria infection with P. falciparum is a medical emergency requiring hospitalization. Infection with P. vivax, P. ovale or P. malariae can often be treated on an outpatient basis. Treatment of malaria involves supportive measures as well as specific antimalarial drugs.

The types of drugs and the length of treatment will vary, depending on:

  • Which type of malaria parasite you have
  • The severity of your symptoms
  • Your age
  • Whether you're pregnant

Medications:

The most common antimalarial drugs include:

  • Chloroquine (Aralen)
  • Quinine sulfate (Qualaquin)
  • Hydroxychloroquine (Plaquenil)
  • Mefloquine
  • Combination of atovaquone and proguanil (Malarone)

The history of antimalarial medicine has been marked by a constant struggle between evolving drug-resistant parasites and the search for new drug formulations. In many parts of the world, for instance, resistance to chloroquine has rendered the drug ineffective.

  • Topical repellents. The most effective repellents contain DEET as the active ingredient. Follow the label instructions.
  • Dress for success. Mosquitoes are active during nighttime hours, so wear long pants and a long-sleeved shirt to avoid exposure. In warm, tropical climates, light cotton pants and tops are a good choice for eveningwear.
  • Bug spray. Bring insect spray for your sleeping area. Try using an insect-repelling incense stick or candle to help to keep the mossies at bay--chances are the locals will have a home-brewed version that works well.
  • Mosquito netting. If you are not staying in well-screened accommodations, use a bed net. These can be purchased at camping supply stores. Nets will probably be provided in moderate and deluxe accommodation, but be sure to ask.

Resources

Refer to Research Publications.