Unravelling the phylogenetic relationships of African trypanosomes of suids.

African trypanosomes of the subgenera Nannomonas and Pycnomonas have been recorded from both wild and domestic suids. However, complete descriptions of some of these trypanosomes with regard to host range, pathogenicity, transmission and distribution are still lacking. Neither the recently described Trypanosoma (Nannomonas) godfreyi nor Trypanosoma (Nannomonas) congolense Tsavo have been isolated from mammalian hosts, while Trypanosoma (Pycnomonas) suis remains the rarest of the Salivarian trypanosomes. The only isolate presumed to be of the latter species is maintained at the Kenya Trypanosomiasis Research Institute, Nairobi. We present here the results of characterization of this isolate by morphology, tsetse transmission, the use of species-specific DNA probes and DNA sequence analysis. Morphology in stained blood smears revealed a small trypanosome with a free flagellum. Experimental transmission through Glossina morsitans morsitans showed a developmental cycle typical of subgenus Nannomonas A positive identification was obtained with species-specific PCR primers for T. congolense Tsavo; moreover, the sequence of the SSU rRNA gene was almost identical to that of T. congolense Tsavo on database. In phylogenetic analysis of the SSU rRNA genes of Salivarian trypanosomes, T. congolense Tsavo grouped with T. simiae rather than T. congolense, suggesting that the name T. simiae Tsavo is more appropriate.

Comparison of the isometamidium-based trypanocidal drugs Samorin and Veridium in cattle under field conditions at Nguruman, Kenya.

The trypanocidal activity of two commercially available isometamidium-based products, Samorin (Merial, USA) and Veridium (Sanofi Santé Nutrition Animale, France), used at a dose rate of 0.5 mg kg(-1) bodyweight, was compared in a field trial involving groups of approximately 30 zebu cattle in a trypanosomosis endemic part of south-western Kenya. The trial took place between April 1997 and March 1998 during a time of higher than normal rainfall that resulted in periods of high trypanosome challenge. The trial consisted of five consecutive prophylactic cycles, each of approximately 10 weeks duration. It was demonstrated that there was no significant difference in the prophylactic activity of the two isometamidium-based products, and no significant difference between the relative activity of three different batches of the product Veridium used during the course of the trial. There was some evidence that drug-resistant strains of trypanosomes may have been present, but it was concluded that isometamidium is still an effective trypanocidal drug in this location.

The use of trypanocides and antibiotics by Maasai pastoralists.

Information was collected on the use of veterinary drugs by Maasai pastoralists in an area of Kenya where tsetse flies and trypanosomosis occur. Three herds of cattle were followed for between 4 and 5 years and records were kept of every veterinary drug treatment given by the livestock owners. Almost all treatments were either with the trypanocides homidium or diminazene, or with oxytetracycline by intramuscular injection. The rate of trypanocide use varied between 0.66 and 1.56 treatments per animal per year, while oxytetracycline use was between 0.20 and 1.00 treatments per animal per year. Farmers were injecting these drugs in the absence of veterinary supervision, obtaining their supplies mainly from local village shops or informal traders. Underdosing with trypanocides appeared to be uncommon and the indications were that farmers generally gave the drugs at dosage rates above the recommended standard dose. Accurate information on the dose rates of oxytetracycline could not be obtained, but it was noted that in most cases farmers gave a single injection rather than a course of treatment. In a proportion of cases, trypanocides and antibiotics were mixed together before injection. The farmers administered the drugs when disease was recognized and were rarely using trypanocides as prophylactics. Although necessity forces the livestock owners to obtain and use these drugs without veterinary supervision, there are concerns with regard to the possibility of drug misuse and the development of drug resistance.