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

160 Manual of basic techniques for a health laboratoryMicrofilariae of the following species are found in human blood: Brugia malayi,Brugia timori, Loa loa, Mansonella perstans, 1 Mansonella ozzardi and Wuchereriabancrofti. Table 4.7 shows the geographical distribution of these species.Infections with Loa loa among populations of areas where it is endemic are oftenasymptomatic. Non-residents visiting these areas are susceptible to symptomaticinfection. The initial infection is characterized by a transient, localized, subcutaneousswelling, known as a “Calabar swelling”. Adult worms may migrate across theconjunctiva of the eyes, causing inflammation, but the infection does not causeblindness. Chronic infection may lead to complications such as renal disease,encephalopathy and cardiomyopathy.Infections with Mansonella perstans generally seem to be asymptomatic, but havebeen associated with pruritus, abdominal pain, urticaria and Calabar-like swellings(see above). Infections with Mansonella ozzardi are also generally asymptomatic,but have been associated with lymphadenopathy, pruritus, fever, and pains in theknees and ankles.Microfilariae are transmitted by mosquitoes, flies and midges, which feed on theblood of infected humans. The microfilariae develop into infective larvae whichinvade the mouth parts of the insect.Examination of skin for microfilariae of Onchocerca volvulusA very small piece of the patient’s skin is collected. To see the highly motilemicrofilariae, it is examined as a wet preparation between a slide and coverslipunder the microscope.Materials and reagents●●●●●●MicroscopeMicroscope slidesCoverslipsPasteur pipetteNeedle (for intramuscular or subcutaneous injection), 22-gaugeScalpel or razor blade● Sodium chloride, 0.85% solution (reagent no. 53)●70% Ethanol.Table 4.7 Geographical distribution of filarial wormsSpeciesBrugia malayiBrugia timoriLoa loaMansonella ozzardiMansonella perstansOnchocerca volvulusWuchereria bancroftiGeographical distributionAsiaParts of IndonesiaCentral and West AfricaCentral and South America, CaribbeanCentral and West Africa, Central and South AmericaTropical Africa, Central and South America, parts of ArabiaEndemic in many tropical countries1Previously known as Dipetalonema perstans.