Evidence for the occurrence of Trypanosoma brucei rhodesiense sleeping sickness outside the traditional focus in south-eastern Uganda.

The occurrence of Trypanosoma brucei rhodesiense west of the River Nile, in Masindi district in the mid-western part of Uganda, is confirmed. Masindi borders the traditional belt of T. b. gambiense infection in the north-west, Gulu in the north and the Democratic Republic of Congo in the west. Of the 702 persons tested for sleeping sickness in Masindi, 113 (16%) were positive by the card agglutination test for trypanosomiasis (CATT). Trypanosomes were observed in samples of cerebrospinal fluid (CSF) from two (0.3%) of the subjects: a 7-year-old girl, who had been ill for 2 weeks and yet was in good general condition, with three white blood cells (WBC)/microliter CSF; and a 47-year-old woman who had been ill for 8 months, looked sickly, had seven WBC/microliter CSF, but was still able to dig in her gardens. Rats and mice inoculated with blood from the two parasitologically confirmed cases became parasitaemic on day 3 post-inoculation, indicating that the parasites were T. b. rhodesiense. Isoenzyme analysis revealed that the parasites isolated from one of these confirmed cases belonged to a zymodeme (449) which has not been previously observed among isolates from south-eastern or north-western Uganda. Although the isolate shared PGM2 and ICD3 patterns with T. b. gambiense and T. b. rhodesiense, respectively, it did not have the SOD3:5 pattern characteristic of T. b. gambiense. The spread of T. b. rhodesiense beyond its traditional focus and the development of areas where this subspecies and T. b. gambiense are co-endemic will complicate the control of sleeping sickness in Uganda; although the CATT is very useful for the mass screening of populations for T. b. gambiense area, it is not applicable in the detection of T. b. rhodesiense.

Parasitological detection of Trypanosoma brucei gambiense in serologically negative sleeping-sickness suspects from north-western Uganda.

Forty-five parasitologically confirmed cases of sleeping sickness were diagnosed in north-western Uganda using a combination of two or three techniques. Forty of the cases were positive by the card agglutination test for trypanosomiasis (CATT), four were negative and one was not screened by the CATT. Trypanosomes isolated from the four CATT-negative but parasitologically positive cases were propagated for detailed biochemical genetic analysis. The aim was to demonstrate whether these four stocks lacked the LiTat 1.3 gene which encodes the antigen on which the CATT is based. All the DNA extracts isolated from these CATT-negative stocks and from six CATT-positive stocks of Trypanosoma brucei gambiense were targeted for amplification by the three variable-surface-glycoprotein genes thought to be ubiquitous in T. b. gambiense. The LiTat 1.3 gene was shown to be present in all 10 stocks. Trypanosome carriers may be CATT-negative because the CATT is not sensitive enough, because their parasites lack the LiTat 1.3 gene, or because their parasites have this gene but do not express it. The four sleeping-sickness cases who gave negative CATT results in the present study have very important implications in the diagnosis of T. b. gambiense infections using the CATT. Following treatment of the CATT-positive cases, the CATT-negative carriers of the trypanosomes remain as human reservoir hosts for continuous infection of the population. Because CATT-negative individuals are rarely examined further, the general prevalence of parasitologically positive but CATT-negative cases is unclear. This study demonstrates the value of co-ordinated use of serological and parasitological techniques in the diagnosis of Gambian sleeping sickness.