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

194 Manual of basic techniques for a health laboratoryNucleus: large, central and red.Kinetoplast: large and round granule, dark red or purple, near the posteriorextremity.Undulating membrane: narrow, reddish-pink.Flagellum: pink, extending beyond the undulating membrane.Fig. 4.165 Appearance ofTrypanosomarangeli in thickblood filmsIdentification of Trypanosoma rangeli in thick blood films (Fig. 4.165)Length: 25–35mm.Shape: only slender forms, with tapering extremities.Nucleus: red, near the central part of the cell body.Kinetoplast: small, like a dark red dot, far away from the posterior extremity.Undulating membrane: visible, narrow.Flagellum: extending beyond the undulating membrane.4.7.4 Leishmania spp.Leishmaniasis is a group of diseases caused by infection with parasitic protozoa ofthe genus Leishmania. It can affect the skin (cutaneous leishmaniasis), mucousmembranes (mucocutaneous leishmaniasis) and the reticuloendothelial system (visceralleishmaniasis or kala-azar).The incubation period is generally from 2 to 6 months, but can vary from 10 daysto several years. In some patients a primary lesion forms several months before theother symptoms appear. Amastigotes of the Leishmania spp. multiply slowly inmacrophages near the site of inoculation. Some infected macrophages enter thebloodstream and reach the viscera, where the amastigotes multiply rapidly.Clinically, the early phases of visceral leishmaniasis are characterized by chronicirregular fever, cough, diarrhoea and bleeding of the mucous membranes and secondaryinfections. Later, progressive enlargement of the spleen, liver and, occasionally,the lymph nodes, weight loss and — in some patients — patchyhypopigmentation of the skin occur.Cutaneous leishmaniasis is characterized by skin ulcers, which may be single ormultiple. In certain forms of cutaneous leishmaniasis plaques, papules or nodulesmay appear in different parts of the body.The clinical symptoms of leishmaniasis may be similar to those found inschistosomiasis, chronic malaria and chronic leukaemia.Sources of infection and modes of transmissionThe epidemiology of the disease has unique features in each region and varies fromone geographical area to another.● In the Americas, infection is spread to humans by the bite of the phlebotominefly Lutzomyia longipalpis. The vector feeds on dogs, wild animals and, less frequently,humans; it can be found both outside in the countryside and insidedwellings. The disease occurs mainly in rural areas.● In India, humans are the main reservoir.● In the Mediterranean basin and the Gulf area, dogs are the main reservoir, andthe vectors are various species of the genus Phlebotomus.● In Sudan, wild rodents and carnivores have been found to be reservoirs.Transmission can take place inside dwellings, which constitute microfoci ofinfection.