eMedicine Specialties > Pediatrics: General Medicine > Parasitology

Malaria

Author: Parang N Mehta, MD, Consulting Staff, Department of Pediatrics, Mehta Hospital, Surat, India
Contributor Information and Disclosures

Updated: Apr 28, 2009

Introduction

Background

Malaria is an ancient scourge of humanity. Although almost eradicated from industrialized nations, malaria continues to extract a heavy toll of life and health in a substantial part of the world. Almost half the world's population lives in countries where the disease is endemic, and almost every country in the world encounters imported malaria. Children are the worst affected, especially children aged 6 months to 5 years. In parts of the world where malaria is endemic, it may cause as many as 10% of all deaths in children.

In the 1950s, the World Health Organization launched an ambitious plan to control or eradicate malaria. After initial successes, the plan foundered; today malaria is returning to areas where it was once controlled and it is entering new areas. Because of plasmodial and mosquito resistance to drugs and insecticides, the danger of malaria has worsened, and the disease is now a major global problem.

Pathophysiology

The bite of an infected mosquito introduces asexual forms of the parasite, called sporozoites, into the bloodstream. Sporozoites enter the hepatocytes and form schizonts, which are also asexual forms. Schizonts undergo a process of maturation and multiplication known as preerythrocytic or hepatic schizogony. In Plasmodium vivax and Plasmodium ovale infection, some sporozoites convert to dormant forms called hypnozoites, which can cause disease after months or years.

Rupture of a large number of erythrocytes at the same time releases a large amount of pyrogens, which causes the paroxysms of malarial fever. The periodicity of malarial fever depends on the time required for the erythrocytic cycle and is definite for each species. Plasmodium malariae needs 72 hours for each cycle, leading to the name quartan malaria. The other 3 species each take 48 hours for one cycle and cause fever on alternate days (tertian malaria). However, this periodicity requires all the parasites to be developing and releasing simultaneously; if this synchronization is absent, periodicity is not observed.

Frequency

United States

Approximately 1300 cases are diagnosed every year, most of them acquired outside the country. Only about 1% of patients acquire the infection in the United States. Over half the cases are acquired in Africa. Usually fewer than 10 deaths are reported in the United States annually.

International

Malaria is a major health problem in Africa, Asia, Central America, Oceania, and South America. About 40% of the world's population lives in areas where malaria is common.¹ Approximately 300-500 million cases of malaria occur every year, and 1-2 million deaths occur, most of them in young children.

Mortality/Morbidity

• Cerebral malaria: Most of the mortality of malaria is due to this complication of Plasmodium falciparum malaria, an acute illness that is mostly observed in children aged 6 months to 3 years. Early diagnosis and prompt treatment with a drug to which the parasite is susceptible is important to save the life of the child.
• Anemia: Anemia is so common in malaria that it is considered almost a part of the disease. The degree of anemia is much greater than can be explained by destruction of parasitized erythrocytes. Malarial anemia can be quite severe, sometimes causing death.
• Repeated frequent seizures: Even without cerebral malaria, a child can experience prolonged, frequent convulsions, which can lead to prostration and death.

Race

People of all races are affected, with some exceptions. People of West African origin who do not have the Duffy blood group are not susceptible to P vivax malaria.

Sex

Malaria affects females and males equally.

Age

Children of all ages living in nonmalarious areas are equally susceptible to malaria. In endemic areas, children younger than 5 years have repeated and often serious attacks of malaria. The survivors develop partial immunity. Thus, older children and adults often have asymptomatic parasitemia (ie, presence of plasmodia in the bloodstream without clinical manifestations of malaria). Most deaths resulting from malaria occur in children younger than 5 years.

Clinical

History

Elicit any history of travel through, or immigration from, a malarious area. Even a few hours at an airport in an endemic area is significant. Obtain history of blood transfusion, organ transplantation, and (for newborns) malaria in the mother.

Young children manifest this disease in many different ways, but the classic picture of malaria, with periodic fever, shivering, and sweating, is not observed. Malaria can mimic any febrile illness and should be suspected in any febrile child who has recently been in a malarious area. Older children may manifest the classic periodicity of fever with chills and shivering.

• Prodrome: After the mosquito bite, children are asymptomatic while the parasites complete the liver cycle and one erythrocytic cycle, which takes 8-18 days, depending on the species. Children then become restless, drowsy, apathetic, and anorexic. Older children may report aching body, headache, and nausea.
• Fever: Fever is usually continuous and may be very high (40°C) from the first day.
• Respiratory symptoms: Many children have only flulike respiratory symptoms at presentation, with mild cough and cold. These symptoms abate in 1-2 days, with or without treatment.
• GI symptoms: Vomiting is very common in children with malaria and may make oral therapy ineffective. Mild diarrhea is often observed, with dark green mucoid stools. Occasionally, profuse diarrhea with dehydration and circulatory failure is observed.
• Febrile convulsions: Seizures are common and may occur at the onset of the disease, even before high fever has set in. Differentiating postictal impairment of consciousness from cerebral malaria is often difficult.
• Congenital malaria: Parasitemia in neonates within 7 days of birth implies transplacental transmission. This congenital malaria is usually associated with placental parasitemia, which sometimes persists even after adequate treatment with antimalarial drugs. Babies have fever, are irritable, refuse feeds, and often develop anemia, jaundice, and hepatosplenomegaly.
• Malaria in immune children: Children living in an area where malaria is endemic have repeated frequent infections and develop and maintain partial immunity. These children often develop only a low-grade fever, anemia, poor appetite, and malaise. Tiredness, restlessness, cough, and diarrhea are other symptoms that may occur.
• Relapses and recrudescences: Depending on the species of Plasmodium involved, relapses and recrudescences vary in their effects. P vivax and P ovale both give rise to hypnozoites in the liver. P vivax malaria may relapse for up to 3 years and P ovale for 1-1.5 years. P falciparum and P malariae do not form hypnozoites, so they do not have true relapses. However, the disease recrudesces because of surviving erythrocytic forms. Although P falciparum can recrudesce for up to 1 year, P malariae may continue to cause clinical malarial attacks even 20 years after the original infection. Only the sporozoites (introduced by the mosquitoes themselves) can penetrate the liver cells. Thus, if malaria is acquired by blood transfusion or transplacentally, no infection of the liver occurs and relapses do not occur.

Physical

• Fever: Fever can be very high from the first day. Temperatures of 40°C and higher are often observed. Fever is usually continuous or irregular. Classic periodicity may be established after some days.
• Hepatomegaly: The liver may be slightly tender.
• Splenomegaly: Splenomegaly takes many days, especially in the first attack in nonimmune children. In children from an endemic area, huge splenomegaly sometimes occurs.
• Anemia: Prolonged malaria can cause anemia, and malarial anemia causes significant mortality.
• Jaundice: With heavy parasitemia and large-scale destruction of erythrocytes, mild jaundice may occur. This jaundice subsides with the treatment of malaria.
• Dehydration: High fever, poor oral intake, and vomiting all contribute to dehydration.

Causes

• Malaria is caused by Plasmodium species, which are protozoal blood parasites. The following 4 species can infect humans:
  • P vivax
  • P falciparum
  • P malariae
  • P ovale
• Most malaria acquired in Africa is due to P falciparum. P vivax dominates in Asia and the Americas.
• Transmission of malaria
  • The bite of an infected female Anopheles mosquito transmits malaria. Species of mosquito capable of transmitting malaria are found in all 48 of the contiguous states of the United States.
  • Malaria can be transmitted through blood transfusion. Among people living in malarious areas, semi-immunity to malaria allows donors to have parasitemia without any fever or other clinical manifestations. The malaria transmitted is by the merozoites, which do not enter the liver cells. Because the liver stage is not present, curing the acute attack results in complete cure.
  • Organ transplantation may transmit malaria.
  • Transplacental malaria (ie, congenital malaria) can be significant in populations who are semi-immune to malaria. The mother may have placental parasitemia, peripheral parasitemia, or both, without any fever or other clinical manifestations. Vertical transmission of this infestation may be as high as 40% and is associated with anemia in the baby.
• Risk factors
  • Residence in, or travel through, a malarious area
  • No previous exposure to malaria (hence no immunity)
  • No chemoprophylaxis or improper chemoprophylaxis

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