Genetic diversity among Trypanosoma brucei rhodesiense isolates from Tanzania.

We compared 19 stocks of Trypanosoma brucei rhodesiense collected in 1991 and 1994 from Tanzania with representative stocks from other foci of Rhodesian sleeping sickness in Zambia, Kenya and Uganda. Stocks were characterized by isoenzyme electrophoresis, restriction fragment length polymorphisms in variant surface glycoprotein genes and random amplification of polymorphic DNA; the banding patterns obtained were coded for numerical analysis. In addition, the Tanzanian stocks were compared by pulsed field gel electrophoresis. Overall the Tanzanian stocks formed a homogeneous group and the predominant genotype isolated in 1991 was still present in the 1994 sample, although at a reduced level. The Tanzanian stocks were distinct from representative stocks from other East African foci. This observation does not support the proposal that there are northern and southern strains of T. b. rhodesiense, but is consistent with the view that T. b. rhodesiense stocks form a mosaic of different genotypes varying from focus to focus in East Africa.

The persistence of genetic homogeneity among Trypanosoma brucei rhodesiense isolates from patients in north-west Tanzania.

Trypanosomes isolated during 1991 from nine patients with Rhodesian sleeping sickness in north-west Tanzania were genetically characterized by electrophoresis of ten enzymes. Eight isolates were allocated to a known zymodeme (Z306); another had an enzyme profile (Z379) not previously encountered. An example of Z306 has been previously isolated in 1971, nearby in a part of Rwanda adjacent to the border with Tanzania; in addition, a closely related isolate, in Z307, was collected in 1959 from a patient in north-west Tanzania. The new zymodeme (Z379) was 94% similar to Z306, and both had a close similarity of 89% to Z307. All these isolates belonged to the zambezi strain group of related zymodemes, and evidence is presented that other examples of the group have been collected from man in Tanzania since 1959. Such apparent long term genetic stability is similar to circumstances further south in an endemic area of Zambia, where 12 examples of Z306 and two of Z307 were acquired over a period of 12 years from patients. The similar genetic homogeneity among trypanosomes in endemic parts of both Tanzania and Zambia contrasted markedly with the heterogeneity described to the north of Tanzania in that different strain groups circulate in epidemic areas of Kenya and Uganda.

The current epidemiology and control of trypanosomiasis and other zoonoses in Tanzania.

The epidemiology and control strategies of African trypanosomiasis, plague, rabies, brucellosis, anthrax and hydatidosis, the most important and well documented zoonotic diseases in Tanzania, have been described. Bovine tuberculosis, tetanus, taeniosis, trichinosis and tungosis are also endemic in some parts of the country but records of their incidences are not available. Initial outbreaks of trypanosomiasis in Tanzania were caused by Trypanosoma gambiense which originated from West Africa and reached Tanzania via Zaire around 1902. T. rhodesiense which is currently responsible for human trypanosomiasis in Tanzania was introduced from Mozambique around 1910 and quickly spread to many parts of the country. The disease is currently prevalent in the western, north and northwestern parts, the southern highlands and southern regions. Over 6000 cases have reported since 1979. Control strategies against sleeping sickness in Tanzania include chemical control of vectors, treatment of patients with trypanocides and avoidance of humantsetse contact. Plague is mostly endemic in central, northern and north-eastern Tanzania. A total of 8161 cases with 1885 deaths have been recorded since 1890. The disease is currently prevalent in Lushoto district where outbreaks have been experienced since 1980, and in Singida district where it has been endemic since 1918. Integrated control measures are currently applied and were possibly responsible for the 1989 decline of outbreaks in the area. Financial constraints which led to deterioration of control activities from July 1989 probably accounted for the severe outbreaks in 1990/91 which spread to other parts of the country. Rabies is endemic country-wide except in Mtwara, Lindi and Zanzibar. Domestic dogs are the principal transmitters and prompt vaccination and destruction of unvaccinated stray dogs are the main control measures. Brucellosis is widely endemic in livestock and potentially so in humans. Destruction of infected animals, immunisation of susceptible ones, proper boiling of milk and its products and chemotherapy are the currently applied control measures against the disease. Anthrax and hydatidosis are sparsely endemic in the country, and they are mostly controlled by appropriate meat inspection and consequent condemnation and proper disposal of the affected meat. Vaccination and treatment of animals are also effective against anthrax.

The baseline susceptibility levels of Chunya Praomys natalensis, the commonest plague reservoir and crop pest in Tanzania, to warfarin.

P. natalensis were live-trapped at Kibwawa (Chunya district) in November 1977 and November 1979. An F3 generation was raised from animals which tolerated 0.025% a.i. warfarin. All three populations were tested using the WHO standard method (WHO/VBC/75.595), with 0.025% warfarin. The populations tested were fully susceptible to the rodenticide, and the latter was well acceptable to the rodents. In this area, warfarin can be successfully used for controlling P. natalensis. Failure to obtain 100% mortality with the 1977-caught wild population was probably due to vigour tolerance. Regular seminars are recommended to train staff in the rodenticide application.