Manual of basic techniques for a health laboratory - libdoc.who.int

4. Parasitology 183African trypanosomiasisAfrican trypanosomiasis occurs in three phases:— the acute phase— the parasitaemic phase— the neurological phase.Two or 3 days after the bite of an infected tsetse fly, a chancre appears at the inoculationsite; it disappears within 2–3 weeks. From the site of the chancre, thetrypanosomes invade the bloodstream, giving rise to occasional episodes of intermittentfever. The most common symptoms of the first or acute phase are headache,sleeplessness, pain in the joints and posterior lymph nodes of the neck, swellingof the eyelids and joints, weight loss and generalized intense itching, especially inthe region of the breast bone. Invasion of the central nervous system causes irritability,paraesthesia, sleeplessness and eventually severe headaches and blurred vision,as well as epileptic attacks, psychotic phenomena, drowsiness, mental lethargyand coma.Trypanosomiasis caused by Trypanosoma brucei gambiense generally has a slow andchronic course. Between the first and second phases, weeks or months can pass,and months or years may elapse between the second and third phases. Trypanosomiasiscaused by T.b. rhodesiense follows a more acute course and the phases areless marked. It may cause death within a few months. Heart complications aremore frequent in trypanosomiasis caused by T.b. rhodesiense, and some patients diebefore reaching the neurological phase.Sources of infection and modes of transmissionAfrican trypanosomiasis is transmitted by tsetse flies (Glossina spp.) and humansare the main reservoir of infection. Pigs, dogs and possibly other animal species canalso harbour the parasite, but their role in spreading the disease is secondary.Transmission occurs when tsetse flies ingest the blood of infected humans oranimals.Examination of lymph node aspirates for Trypanosoma brucei gambienseand T.b. rhodesienseIn patients with African trypanosomiasis trypanosomes are found in the lymphglands in the early stage, i.e. 2–3 weeks after infection. They disappear from theglands within 2–6 months. At a later stage the parasites may infect the central nervoussystem.The standard method of diagnosis of African trypanosomiasis in the early stage isto search for trypanosomes in aspirates from enlarged cervical lymph nodes.PrincipleA drop of fluid from the lymph node is collected with a needle and examined immediatelyas a wet preparation. The trypanosomes, which are motile flagellate protozoa,are easily seen under the microscope.Materials and reagents● Microscope●●●●●Microscope slidesCoverslipsNeedle (for subcutaneous injection), 25-gaugeSyringe, 5 or 10ml (both syringe and needle must be perfectly dry)Tincture of iodine