Symptoms of malaria infection range from mild to severe, including death, depending upon the age and health of the infected person and the species of parasite. The incubation period, the time between when a person is bitten by a malaria-infected mosquito and the onset of symptoms, is generally 7-30 days (CDC, 2010b).
Malaria typically produces a series of recurrent attacks, each of which has three stages: chills, followed by fever, and then sweating (NIAID). Symptoms can begin mildly, as drowsiness, irritability, loss of appetite, or trouble sleeping. These symptoms typically escalate within 24 hours into the recurring cycles of chills, fever, and sweating. Chills typically last for 1 to 2 hours and can be accompanied by convulsions or violent shaking. Along with chills, the person is likely to have headache, malaise, fatigue, muscular pains, occasional nausea, vomiting, and diarrhea. During the fever stage, body temperature rises (as high as 107 degrees F; CDC, 2010b) and the skin feels hot and dry. After three or four hours of fever, body temperature returns to normal, signaling the beginning of the “wet stage” of profuse sweating, which lasts 2 to 4 hours.
Two or three days later, the cycle begins again. The cycle may be compounded by other complications such as an enlarged spleen, kidney problems that hinder normal urination, convulsions, loss of consciousness, and pain throughout the entire back and abdomen region. If the infected person does not receive treatment, this debilitating and painful cycle can continue for years. Over time, the symptom-free periods between cycles become longer as the body slowly builds immunity to the parasites in the blood (CDC, 2010b).
Two types of malaria exist: uncomplicated (mild) or complicated (severe) (CDC, 2010b). Symptoms of the two types are similar within the first two weeks of infection—lethargy, dizziness, chills, sweats, fever, and muscular pain. Uncomplicated malarial symptoms remain essentially the same as those described above, although anemia can become a problem over time.
In complicated malaria, however, after the first two weeks, symptoms progress from the fever cycle to include severe anemia, convulsions, low blood sugar, failure of circulation (shock), repeated general convulsions, acidic blood, renal failure, spontaneous bleeding, red urine, pneumonia, jaundice, and high fevers. Complicated malaria also can produce cerebral malaria, which is life threatening (WHO Factsheet, 2012). Severe cases of malaria usually require hospitalization (CDC, 2010b).
Children under the age of five years have the highest malaria morbidity and mortality (Winstanley, 2000). Malaria is also especially dangerous for pregnant women and fetuses. Symptoms for pregnant women include sepsis or bleeding after deliver and increased risk of death during delivery. Fetal complications include abortion or still birth, fetal anemia, low birth weight, retarded growth and premature delivery (CDC, 2010).
Individuals affected during childhood can develop a ‘partial immunity’ after successive exposures to the falciparum parasite, which reduces their risk of developing the severe disease (Winstanley, 2000).
Malaria diagnosis, particularly in remote areas lacking laboratory support, frequently relies on the patient’s symptoms. However, for a definitive diagnosis to be made, laboratory tests must demonstrate the presence of the malaria parasites or their components. Parasites can be identified by examining a drop of the patient’s blood under the microscope; more sophisticated diagnostic techniques use molecular or immunological approaches. Much effort has been devoted to developing Rapid Diagnostic Tests (RTDs), which can provide results in minutes and identify the presence of parasite antigens. Before malaria RDTs can be widely adopted, however, issues such as accuracy, cost, and performance in the field must be addressed.
In order to respond to outbreaks of malaria and identify preventive measures, health care workers need to monitor its occurrence. Malaria surveillance can be classified as either active surveillance or passive surveillance. In active surveillance, health care workers actively screen for cases of malaria in a particular region. In passive surveillance, cases are monitored based on the number of patients who seek medical treatment due to severe symptoms. In areas with vigorous active surveillance programs, estimates of the incidence of malaria determined by active surveillance are commonly several fold higher than those based on passive surveillance. In contrast, in areas with limited active surveillance programs, passive surveillance dominates the percentage of cases identified likely leading to an underestimate of malaria incidence (Tren, 2000).