TRYPANOSOMIASIS
Trypanosomiasis, also known as African sleeping sickness, is an infection endemic to sub-Saharan Africa. It is caused by protozoan parasites called trypanosomes, which are spread by the bite of the tsetse fly. There are two subspecies of trypanosomes that infect humans, each causing a different form of the disease. Trypanosoma brucei rhodesiense, found in eastern and southern Africa, causes an acute illness leading to death within weeks or months. Trypanosoma brucei gambiense, found in western and central Africa, causes a more chronic form of the illness which may last several years. Both forms of sleeping sickness are fatal if left untreated.
It is estimated that approximately 60 million people are at risk for the disease. Accurate assessment of the extent of the disease is made difficult by the remoteness of the areas in which it is found and the variability in the tests used for diagnosis. Trypanosomiasis often occurs focally, so scattered pockets of infection will be found within an endemic region.
Following the bite of an infected tsetse fly, a scab, or chancre, often forms. After an incubation period of days to weeks, the trypanosomes enter the blood and lymphatic systems and multiply. During this stage, patients may experience headaches, fevers, sweating, rash, and malaise. Enlargement of lymph glands occurs, particularly at the back of the neck. The enlarged nodes may be the only visible sign during this phase of the infection. Eventually the trypanosomes will invade the central nervous system, giving rise to neurological symptoms. This stage, aptly called "sleeping sickness," is characterized by headache, apathy, lethargy, and somnolence. Patients may experience personality and cognitive changes, tremors, and coordination problems. They become increasingly wasted and drowsy, and eventually fall into a coma and die. This progression to death usually occurs in months with T. b. rhodesiense and in years with T.b. gambiense.
Diagnosis is made by microscopic identification of the parasite, which may be found in the chancre, lymph glands, blood, or cerebral spinal fluid, depending on the stage of the disease. There are several serologic assays available. The sensitivity and specificity of these tests are variable. They are used mainly for epidemiological surveys, but they do have some clinical utility as well.
The form of treatment depends on whether the central nervous system (CNS) is involved. If the disease has not affected the CNS, suramin or pentamidine may be used. In cases of CNS involvement, melarsoprol is the drug of choice. This is a very toxic drug which may have severe side effects, including a fatal encephalopathy. Another effective medication for the treatment of T. b. gambiense is eflornithine. Unfortunately, this drug is not currently readily available.
Human beings are the main hosts of T. b. gambiense. Control of this infection involves routine screening of at-risk populations, treatment of infected individuals, and control of exposure to tsetse flies, which often inhabit riverine areas. T. b. rhodesiense is found in savannah areas in antelopes, other wild game, and domestic cattle, so control of infection is more complicated and involves the coordination of medical, veterinary, agricultural, entomological, and other services.
BIBLIOGRAPHY
Burri, C. et al. (2000). "Efficacy of New, Concise Schedule for Melarsoprol in Treatment of Sleeping Sickness Caused by Trypanosoma brucei gambiense: A Randomised Trial." Lancet 355:1419–1425.
Neva, F. A., and Brown, W. (1994). Basic Clinical Parasitology. Englewood Cliffs, NJ: Prentice Hall.
Smith, D. H.; Pepin, J.; and Stich, A. H. R. (1998). "Human African Trypanosomiasis: An Emerging Public Health Crisis." British Medical Bulletin 54:341–355.
World Health Organization (1998). "Control and Surveillance of African Trypanosomiasis." World Health Organization Technical Report Series 881(vi):1–114.
—— (2000). "African Trypanosomiasis." WHO Report on Global Surveillance of Epidemic-Prone Infectious Diseases. Geneva: Author.
