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

192 Manual of basic techniques for a health laboratorywho 1156Fig. 4.162 Negative reaction in theCATTFig. 4.163 Nonspecific reaction in theCATTNegative reactions (Fig. 4.162)No agglutination is visible. The reaction remains uniform or occasionally slightlydenser in the centre.Nonspecific reactions (Fig. 4.163)A dried-up ring is observed around the edge of the well or small dots or fine threadsare seen.This type of reaction is usually negative. If you are in any doubt about it, repeat thetest using serum or plasma.Note: Discard any unused reconstituted reagents at the end of the day, unless theyhave been refrigerated. They will not keep and may give false results if used thenext day.Other diagnostic tests for African trypanosomiasisIn addition to the tests described above, African trypanosomiasis is also diagnosedin the laboratory by:— examining lymph node aspirates for trypanosomes (see page 183);— testing dried blood collected on filter-paper for IgM and specific antibodies(see page 187);— inoculation of rats or mice with heparinized blood samples (only in specializedlaboratories);— examining CSF specimens for trypanosomes (see section 8.3.3, page 259).Chagas diseaseChagas disease primarily affects children and is characterized by intermittent orcontinual high fever. About 50% of children manifest unilateral swelling of theeyelids (Romaña’s sign). On other areas of the face or body, cutaneous lesions(chagomas) that resemble furuncles occur near the inoculation site. There may begeneralized oedema of the entire body. Enlargement of the liver is common in childrenbut not often seen in adults. The fever can be accompanied by myocarditisand meningitis. The infection of the digestive tract causes vomiting and diarrhoea.Primary infections can often pass unnoticed, but severe infections may be fatal.After the acute phase, a period of latent infection follows (indeterminate phase);this phase is characterized by a low level of parasitaemia and absence of clinicalsymptoms. It can either persist indefinitely or may lead to the chronic form of thedisease. The indeterminate phase is characterized by the presence of specific antibodieswhich can be detected by serological tests, but not by clinical symptoms.Patients suffering from the chronic form of the disease exhibit signs of cardiacinsufficiency. Abnormalities in the electrocardiogram are often apparent although