Malaria : Climate Effects, Symptoms and Diagnosing

by National Institute of Health

(Page 3 of 5)

Climate affects both parasites and mosquitoes. Mosquitoes cannot survive in low humidity. Rainfall expands breeding grounds, and in many tropical areas, malaria cases increase during the rainy season. Mosquitoes must live long enough for the parasite to complete its development within them. Therefore, environmental factors that affect mosquito survival can influence malaria incidence. Plasmodium parasites are affected by temperature - their development slows as the temperature drops. P. vivax stops developing altogether when the temperature falls below 60° F. P. falciparum stops at somewhat higher temperatures. This explains why parasites can be found in various parts of temperate areas.

Effect of Human Intervention

People have worked for centuries to control malaria and were successful in eradicating it from most of the New World early in the 20th century. Certain human activities, however, have inadvertently worsened the spread of malaria.

City conditions can create new places for mosquito larvae to develop. Agricultural practices also can affect mosquito breeding areas. Although draining and drying of swamps gets rid of larval breeding sites, water-filled irrigation ditches may give mosquitoes another area to breed. In addition, because farmers use the same pesticides on their crops as those used against malaria vector mosquitoes, the problem of insecticide-resistant mosquitoes is growing. Modern transportation also contributes to the spread of the disease, moving travelers between malaria-endemic and non-endemic regions.

Blood

Malaria is transmitted occasionally by transfusions of blood from infected individuals, sharing of needles to inject intravenous drugs, or from an infected pregnant woman to her unborn child. In the United States, however, transmission rarely occurs through blood transfusions because blood donors are not allowed to donate for specified periods of time after traveling to or living in a malarious area.

Symptoms of Malaria

Malaria typically produces a string of recurrent attacks, or paroxysms, each of which has three stages - chills, followed by fever, and then sweating. Along with chills, the person is likely to have headache, nausea, and vomiting. Within an hour or two, the person's temperature rises, and the skin feels hot and dry. Then, as the body temperature falls, a drenching sweat begins. The person, feeling tired and weak, is likely to fall asleep.

The symptoms first appear some 10 to 16 days after the infectious mosquito bite and coincide with the bursting of infected red blood cells. When many red blood cells are infected and break at the same time, malaria attacks can recur at regular time periods - every 2 days for P. vivax malaria and P. ovale, and every 3 days for P. malariae.

With P. vivax malaria, the patient may feel fine between attacks. Even without treatment, the paroxysms subside in a few weeks. A person with P. falciparum malaria, however, is likely to feel miserable even between attacks and, without treatment, may die. One reason P. falciparum malaria is so virulent is that the parasite can infect red blood cells in all stages of development, leading to very high parasite levels in the blood. In contrast, P. vivax parasites infect only young red blood cells, which means the number of parasites in the blood does not reach the same high levels as seen in P. falciparum infection.

Diagnosing Malaria

A doctor or other health care worker should suspect malaria whenever a person who has been in the tropics recently or received a blood transfusion develops a fever and other signs that resemble the flu. A doctor will examine blood smears, taken from a finger prick, under a microscope. the diagnosis is confirmed. A "thick" smear makes it possible for the health care worker to examine a large amount of blood. Then, the species of parasite can be identified by looking at a corresponding "thin" smear. This is important for deciding on the best treatment.

Mixed infections are possible. or example, a person can be infected with P. vivax as well as the more dangerous P. falciparum. In the unusual event that parasites cannot be seen immediately in a blood smear, but the patient's condition and prior activities strongly suggest malaria, the doctor may decide to start treatment before being sure the patient has malaria.

Treating Malaria

In most cases, malaria can be successfully treated, although the recuperating patient may find it takes several weeks to recover full strength. on the best medicine to use, the doctor should try to identify the species of parasite responsible for the disease and where the patient got the infection. Up-to-date information on the geography of malaria, such as which species are present in which areas, whether chloroquine-resistant parasites are present, and which seasons of the year carry the greatest risk, is available at international travel clinics, CDC, and WHO.

In the United States, patients with P. falciparum malaria are usually hospitalized and treated as medical emergencies because their conditions may get worse quickly. Patients should talk with a doctor who specializes in infectious diseases and is knowledgeable about diagnosing and treating malaria and its complications.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.