Malaria

Malaria

Disease characteristics

          Malaria is a contagious disease. Anopheles mosquito is a carrier of Plasmodium, which is a single cell in the class of Sporozoa. It has a life cycle that can be found in both vertebrates and mosquitoes. Malaria is a very important public health problem. Thirty six percent of the population of more than 90 countries around the world live in malaria-endemic areas. For Thailand, malaria remains a major public health problem as well. Although this disease has a low morbidity and mortality rate, since 1996, the morbidity and mortality rate has tended to increase.

Cause

          There are four types of Plasmodium that cause disease in humans: P.falciparum, P.vivax, P.malariae, and P.ovale. P.ovale. In Thailand, P.falciparum and P.vivax are mostly found. Mosquito vectors found in Thailand are Anopheles dirus, An.minimus, An. maculatus, An. sundaicus, An. aconitus and An. pseudowillmori.

Transmission

          When an infected with malaria female Anopheles mosquito bites a human, mosquitoes release malaria (sporozoites) from their salivary glands into the human bloodstream. The infection then travels to the liver where asexual cell division takes place, producing thousands of merozoites. The liver cells then mature and burst, releasing merozoites into the bloodstream. At this stage, patients will begin to show symptoms of the disease, such as fever, chills, and headache. For P.vivax and P.ovale, some of the bacteria remain in the liver cells called "hypnozoites", causing relapsing.

After the merozoite enters the bloodstream, the organism then travels to erythrocytes where it grows into trophozoites and divides again into 6-30 merozoites. When hemolysis occurs, merozoites travel to other erythrocytes and repeat the cell division. Some merozoites are transformed into gametocytes. When a female Anopheles mosquito bites a person with gametocytes in the bloodstream, these bacteria fertilize to form a zygote that develops into an oocyst, and then implants in the mosquito's stomach. After that, it divides into sporozoites to the salivary glands for the next bites.

Incubation period

P.falciparum: about 7-14 days.

P.vivax and P.ovale: about 8-14 days.

P.malariae: about 18-40 days.

Transmission period

          Mosquitoes that bite humans can be infected as long as the person has gametocytes in their blood. In inadequately treated patients with P.malariae, it may be a source of infection for up to 3 years, or 1-2 years in P.vivax, ot not over 1 year in P.falciparum.

Signs and symptoms

          The signs and symptoms of malaria are not unique. In most cases, symptoms are similar to those of a cold: low fever, headache, body and muscle pain. There may be nausea and loss of appetite as well. These symptoms are short-term for days depending on the incubation period of the infection, type of infection, number of sporozoites infected by the patient, patient's immunity to malaria, and a condition of infected patient that has previously received antimalarial drugs or have already received some malaria medication.

Fever, the hallmark symptom of malaria, consists of three phases: the trembling phase, the heat phase, and the sweating phase. At present, the characteristics of all 3 phases are rarely found. Patients will have a high fever all the time, especially in patients with first time malaria infection. However, in the early stages of malaria infection, the infection may not grow to a mature phase at the same time. This may be the result of being infected at different times and cause many stages of infection. Therefore, hemolysis is not simultaneous. As a result, early malaria patients may have high fevers throughout the day. After a while, simultaneous hemolysis occurs, therefore, the patient was seen to have a fever and chills for a time.

Epidemiology of the disease

         Malaria spreads widely between latitude 640 north and latitude 320 south and covers areas up to 400 m below sea level, such as the Dead Sea, to areas up to 2,600 m above sea level, for example Kenya. Currently up to 2.02 billion people from more than 90 countries are located in the area with a risk of malaria.

•           Malaria falciparum is common in Africa, South America, Asia, and can be found in both tropical and subtropical regions. In cold regions, it is rarely found.

•           Malaria vivax is found in tropical and subtropical Latin America, Turkey, China, and central India. It is rarely found in Africa, especially West Africa.

•           Malaria ovale is common in Africa, especially the Western part of the continent.

•           Malaria malariae is found in both tropical and subtropical regions, especially in East Africa and West India.

In Thailand, the source of malaria is in the border forests of the country, especially around the Thai-Myanmar border and Thai-Cambodian. Provinces that have always seen the highest cases are Mae Hong Son, Tak, Kanchanaburi, Ratchaburi, Prachuap Khiri Khan, Ranong, Sa Kaeo, Trat, and Chanthaburi. In the middle of the country, few cases of malaria were found and no infection was found in Bangkok and its vicinity. Malaria patients are distributed in all age groups, especially in the age group of 10-35 years. The ratio of male patients is about 2 times higher than that of female patients. Patients can be found throughout the year but will be found a lot during the rainy season.

Treatment

          Treatment for malaria is divided into three categories:

Specific treatment

          The specific treatment is schizontocide medication, which can eradicate schizont malaria, asexual stages in red blood cells. Choosing the kind of medicine depends on the efficacy against malaria and the drug resistance characteristics of malaria in different areas.

Treatment of symptoms and complications

          Treatment of symptoms and complications is the treatment of symptoms and other complications that occurred while the patient was still infected with malaria or after the malaria infection, especially in patients infected with falciparum malaria. If patients get treatment late, there will be serious complications.

Prevention of disease transmission

          Prevention of transmission is the use of gametocytocide to kill gametocyte stage of malaria infection.

Details of the use of antimalarial drugs can be found in

Guidelines for Infectious Disease Practice Volume 1. Communicable Diseases. Department of Communicable Disease Control. Ministry of Public Health 2001

Experience in infectious disease in Thailand Infectious Disease Society of Thailand 1999