WHO Report on Global Surveillance of Epidemic-prone Infectious Diseases - African trypanosomiasis
Sleeping sickness is one of the few communicable diseases where systematic population screening is necessary, particularly for gambiense sleeping sickness which has a very long almost asympotomatic period. There are several reasons for this including the difficulty of diagnosis which cannot normally be made in remote primary health care facilities (4), the difficulty and high risk of treatment for the late stage, for which special skills are required, and the near impossibility of vector control. Therefore, the control measure most often used for gambiense sleeping sickness is systematic screening of the population to detect all cases, including those in both the first and second stage of disease, and then curing them. Guidelines for sleeping sickness surveillance have been developed by WHO in collaboration with sleeping sickness endemic countries (5).
(4) Serological detection with the CATT test (Card Agglutination Trypanosomiasis Test), is commonly used in screening. However, this test has insufficient specificity (too many false positives) to be used as a definitive diagnosis. Parasitological examinations are sufficiently specific, but are not sensitive enough unless done over a period of several successive days, because the level of parasites in the blood oscillates rapidly. If the blood is taken during the part of the cycle when few parasites are circulating, then a parasitological examination is likely to be negative, even though the disease is present. Appropriate treatment depends on whether or not the parasite has passed the blood/brain barrier. A spinal tap is needed for determining this.
(5) Trypanosomiase Humaine Africaine: Surveillance epidemiologique et systeme d'information geographique (S.I.G), Geneva, World Health Organization, 1996.