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

4. Parasitology 1595. Add to the test-tube containing the supernatant fluid, without mixing:— 10 drops of 10% acetic acid solution— 5ml of the aminopyrine solution.To prevent mixing, hold the tip of the pipette containing the aminopyrine solutionagainst the inside wall of the test-tube and allow the liquid to run down thewall.6. Add 10 drops of the 10% hydrogen peroxide solution. Do not mix. Let it standfor 1 minute.The results must be read within 5 minutes of adding the hydrogen peroxidesolution.4.6.4 ResultsIf the reaction is positive a red colour appears between the two layersof liquid (Fig. 4.111). Report the results as follows:— pale red = positive reaction (+)— red = strong positive reaction (++)— dark red = very strong positive reaction (+++)— no change in colour = negative reaction (-).4.7 Parasites of the blood and skinParasites that spend all or part of their life cycle in blood or tissueare known as haemoparasites. They include:— species belonging to the genera Brugia, Dirofilaria, Loa,Mansonella, Meningonema, Onchocerca and Wuchereria — responsiblefor filariasis;— Trypanosoma spp. — responsible for trypanosomiasis;— Plasmodium spp. — responsible for malaria.Infection by these parasites and Borrelia spp. can be diagnosed byexamination of stained blood specimens under the microscope.Fig. 4.110 Mixing the stool specimen withdistilled waterFig. 4.111 Chemical test for occult blood instoolsa: Positive reaction; b: negativereaction.4.7.1 FilariaeThere are many species of filariae, but most are parasites of animalsand rarely affect humans. Only eight filarial species have adapted tohumans, and are transmissible between them. Of these, the mostimportant is subperiodic Brugia malayi.The filarial worms inhabit the lymphatic system. The larvae of the adult worms —the microfilariae — invade the blood, and they can be identified in a blood film.The microfilariae of Onchocerca volvulus are normally confined to the skin (seebelow), but sometimes migrate to the eyes (which may result in blindness); theymay also be found in the blood. The main clinical symptoms of lymphatic filariasisare lymphadenopathy and lymphangitis. Attacks of lymphadenopathy lasting severaldays occur at regular intervals, with headache, nausea, swelling of one leg,hydrocoele and sterile abscesses. In advanced cases, elephantiasis of the lower extremitiesmay occur due to obstruction of the lymphatic circulation. Elephantiasisof the scrotum, such as is seen in bancroftian filariasis (caused by Wuchereriabancrofti), is rare in brugian filariasis (caused by Brugia malayi). Infections amongpopulations in regions where bancroftian and brugian filariasis are endemic mayremain asymptomatic.