Tsetse Challenge Research Articles

The distribution of the tsetse flies Glossina morsitans submorsitans and G. palpalis gambiensis (Diptera: Glossinidae) in The Gambia and the application of survey results to tsetse and trypanosomiasis control

AbstractA country-wide survey of the distribution of tsetse flies Glossina morsitans submorsitans Newstead and G. palpalis gambiensis Vanderplank was carried out in The Gambia, during 1989–1990, using box traps at 1654 sites over an area of 10,000 km2 The general distribution of tsetse had changed little during the last 45 years. G. m. submorsitans was present in dry, canopied woodland throughout most of the country, but was absent from an area south of the River Gambia stretching from the coast to some 100 km inland. G. p. gambiensis occurred in evergreen forest and woodland near the coast, and in riparian habitats along the length of the River Gambia and its major tributaries. Nowhere in the country was more than 20 km from tsetse-infested areas. Five major foci of G. m. submorsitans infestation were identified. Demographic, climatic and environmental factors affect tsetse populations in The Gambia, but it is expected that these foci of infestation will persist for at least the next 5–10 years. The numbers of tsetse trapped, expressed as relative densities, were used to assess the extent and severity of losses from trypanosomiasis to different categories of livestock. Survey results such as these could be used to assess whether control measures to reduce tsetse challenge are likely to be economically viable by using techniques such as insecticide-impregnated targets, pour-ons or chemotherapy.

Seroepidemiological survey of cattle trypanosomiasis in coastal savanna zone of Ghana

Animal trypanosomiasis causes severe losses in livestock production as a result of poor growth, weight loss, low milk yield, reduced capacity to work, infertility and abortion, even in cases of chronic low level infections (Trail et al., 1985; Anon., 1988). In Ghana, very few outbreaks of trypanosomiasis have been reported, although tsetse flies are present (Aryee et al., 1991). This has been attributed to the predominance of trypanotolerant breeds in the country. However, trypanosome infection among trypano-tolerant animals may result in poor health, which may lower their resistance to other diseases and parasites (ILCA, 1979b). There is evidence that in the face of increased tsetse challenge, the productivity of tolerant animals e.g., Ndama, falls as a result of stunting, wasting, abortion and death (Trail et al., 1984). Farmers in Ghana are increasingly showing a preference for zebu cattle and as these animals are introduced into high tsetse challenge areas, it is likely that trypanosomiasis will assume greater importance (Aryee et al., 1991). There are few reports of trypanosome infections in the Northern, Upper West, Ashanti, Western and Greater Accra Regions (Aryee et al., 1991) and none so far reported from Central Region, where the present study was conducted. The objective of the survey was to investigate the prevalence of bovine trypanosomiasis in Winneba District in the Coastal Savanna Zone of Ghana to assess the importance of trypanosomiasis on livestock development in that area and also help in the formulation of any necessary control measures. Winneba district lies between longitudes 0°30 ' and 0°45'W and latitudes 5°15 ' and 5°40 ' N in Ghana. It is in humid coastal ecozone with a thicket and grassland type of vegetation. Four locations, namely Animal Breeding Station (AHPD) (Location I), Kojoku (Location II), Kasoa (Location III) and Domiebra (Location IV) were chosen, since they are important cattle rearing areas. The district has one of the highest concentrations of cattle in the coastal savanna zone of Ghana. In 1988, 86% of the cattle in Central Region were found here (Enchill, 1989). In location I, Sanga and West African short horn breeds predomi-

Epidemiology of bovine trypanosomiasis in the Ghibe valley, southwest Ethiopia 1. Tsetse challenge and its relationship to trypanosome prevalence in cattle

In this, the first of a series of papers on the epidemiology of bovine trypanosomiasis in the Ghibe valley, southwest Ethiopia, the tsetse populations and their relationships to the prevalence of trypanosome infections in cattle are described. The tsetse challenge to cattle at two sites in the area was estimated as the product of tsetse relative density and the trypanosome infection rate in flies. The proportion of feeds taken by tsetse from cattle was also considered. Three tsetse species were detected in the area, Glossina pallidipes, G. fuscipes and G. morsitans submorsitans. A significant correlation ( r=0.60, P<0.001) was observed between the mean monthly estimates of tsetse challenge due to G. pallidipes and the prevalence of trypanosome infections in cattle the following month at one site, whilst at the other, no significant relationship was observed ( P=0.08). The tsetse density at both sites showed seasonal changes which were related to the monthly rainfall. Finally, variations in tsetse density appeared to be the main factor responsible for variation in tsetse challenge and thus trypanosome prevalence in cattle.

Epidemiology of bovine trypanosomiasis in the Ghibe valley, southwest Ethiopia. 2. Factors associated with variations in trypanosome prevalence, incidence of new infections and prevalence of recurrent infections

An average of 840 East African Zebu cattle from nine herds in the Ghibe valley, southwest Ethiopia were monitored from January 1986 to April 1990. Each month blood samples were collected for analysis of packed red cell volume (PCV) and detection of trypanosomes. Animals found to be parasitaemic and with a PCV less than 26% were treated with diminazene aceturate at a dose of 3.5 mg/kg body weight. The majority of infections were associated with Trypanosoma congolense (84% of infections in adult cattle and 71% in cattle less than 24 months of age), and the mean percentage of adult animals detected parasitaemic 1 month after treatment of an infection with T. congolense was 27%. In order to assess possible existence of drug resistance, a model was applied which allowed monthly incidences of new infections to be distinguished from recurrent infections. This model showed that the monthly incidence of new infections of T. congolense in adult cattle increased significantly from 11% in 1986 to 24% in 1989 following a concomitant increase in the tsetse challenge. The corresponding increase in overall prevalence of T. congolense was from 17% to 38% and the mean prevalence of recurrent infections increased significantly from 6% to 14%. These findings ruled out the possibility that the high prevalence of trypanosome infections in cattle was due only to a high tsetse challenge and pointed to the existence of T. congolense populations which expressed resistance to diminazene. There were variations associated with season, herd, age and sex in the incidence of new infections, prevalence of recurrent infections and relapse to treatment.

Measurement of trypanotolerance criteria and their effect on reproductive performance of N'Dama cattle

One thousand and twenty-eight cow-year records were available from 260 N'Dama cows each having at least 2 years of monthly matching health and performance data over a 5-year period under a medium natural tsetse challenge in Gabon. Four hundred and fifty-eight calf/dam pairs were also available where the calf had been reared to weaning, both had monthly matching records and each cow had weaned at least two calves. Evaluations were carried out on effects of, and linkages between, enviromental and stress factors, number and species of trypanosome infections, curative drug treatments given, anaemia measured by packed red cell volume (PCV), and performance measured by calf weaning weight, cow calving rate and cow weight change over the lactation period. Major findings were that over the period from calf birth to weaning, while calves and their dams grazing together had similar numbers of trypanosome infections detected, the Trypanosoma vivax: T. congolense ratios were very different: 1:0.7 in calves; 1:2.8 in cows. This indicated that some ability to control the development of parasitaemia following T. vivax infection might be being acquired, from weaning onwards. In cows, relationships between lowest PCV recorded and curative drug treatments given suggested that between 20 and 32% of trypanosome-infected cows were not being identified by the buffy coat parasitological diagnostic technique. The high level of curative treatment given (to 13.7% of cows over the calendar year, and to 40% of calves from birth to weaning) will have tended to reduce the variance and linkages between aspects of infection and PCV values, especially in calves. In calves, the influence of trypanosome infections, in both calf and dam, on their respective PCV values and hence on calf weaning weight was apparent. There was a 0.91 ± 0.40 kg increase in calf weaning weight for each 1% increase in calf average PCV, and a 0.95 ± 0.39 kg increase for each 1% increase in cow average PCV. In cows, there was a similar pathway of influence of T. congolense infection through the PCV values to calving rate — not significant with T. vivax infection. There was a 3.3 ± 0.65% increase in calving rate for each 1% increase in average PCV. Repeatabilities of performance traits were in the normal range. Repeatabilities of numbers of trypanosome infections detected by the buffy coat technique were too low to have any practical significance. Repeatability of average PCV at 0.40 ± 0.03 could allow PCV when infected to be used as one criterion of trypanotolerance.

Hypothalamic-pituitary-adrenal axis responsiveness to insulin-induced hypoglycaemia is modified by trypanosome infection in Boran ( Bos indicus) cattle

Ten Boran ( Bos indicus) cattle were used to study the stress responsiveness of the hypothalamic-pituitary-adrenal ( HPA) axis during trypanosome infection. Five cattle were infected with Trypanosoma congolense IL 1180 by tsetse challenge and five cattle served as controls. All infected animals developed acute trypanosomiasis. Insulin-induced hypoglycaemia (50 per cent of pre-insulin glucose concentration) was used as a stress factor. Acute hypoglycaemia was observed in three infected and three control animals after insulin challenge. Two animals from each group either did not respond or responded slowly. Hypoglycaemia in infected animals completely failed to induce an HPA axis response, while in control animals an HPA axis response was indicated by a significant increase in plasma adrenocorticotrophic hormone ( ACTH) and cortisol concentrations (P<0·01). The results show that trypanosomiasis in Boran cattle can cause a decrease in the stress responsiveness of the HPA axis as indicated by a blunted ACTH/cortisol response to insulin-induced hypoglycaemia.

Relationships between trypanosome infection measured by antigen detection enzyme immunoassays, anaemia and growth in trypanotolerant N'Dama cattle

Relationsips were evaluated between trypanosome infection as measured by antigen detection enzyme immunoassays (antigen ELISA), anaemia as determined by average packed red cell volume (PCV), and animal performance as assessed by daily weight gain in 99 N'Dama cattle in Gabon exposed to natural tsetse challenge at 11.5 months of age and recorded 14 times over a 13 week period. Approximately half the animals were found to be infected for an average of five of the 14 times that they were examined: 38% with Trypanosoma congolense, 13% with Trypanosoma vivax and 49% with a mixed infection. Trypanosoma congolense infections had significant deleterious effects on animal growth, while T. vivax infections did not. Animals found on several occasions to be infected with T. congolense had significantly lower PCV values than those demonstrated to be infected on fewer occasions. No relationship was found between mean optical density (OD) values in antigen ELISA and PCV values. Animals capable of maintaining PCV values, even when antigen ELISA positive on a high number of occasions, grew at the same rate as uninfected animals. Animals that could not maintain PCV values when infected had poorer growth. Antigen ELISA has the potential to increase the efficiency of selection of trypanotolerant N'Dama cattle under tsetse challenge in the field, in three main ways. (1) Accurate identification of trypanosome species, especially in mixed species infections, clarifies relations between infection, anaemia and animal performance. (2) Detection of animals antigenaemic without patent parasitaemia could allow individuals with superior ability to control trypanosome infection to be identified. (3) More accurate measurement of the proportion of time an animal is infected allows more accurate evaluation of its anaemia control capability.

Trypanosomiasis in cattle in Gambia: Incidence, prevalence and tsetse challenge

The incidence of trypanosome infections, measured by a Berenil Index in experimental herds of 10 Zebu and 10 N'Dama cattle, was compared with tsetse challenge and with the prevalence of parasitaemia in local N'Dama at three villages in Gambia. Tsetse challenge was more strongly correlated with the incidence of parasitaemia in the Zebu than in the N'Dama. There was a strong correlation between prevalence and incidence of infection in the N'Dama. There was no correlation, however, between prevalence of infection in cattle and tsetse challenge unless the data were offset by 3–5 months. The Berenil Index in the Zebu increased at about twice the rate as in the N'Dama under corresponding levels of challenge. It is concluded that whereas incidence of infection in susceptible animals is best measured independently, it can, under stable conditions, be inferred from an assessment of tsetse challenge.

Use of antigen-detection enzyme immunoassays in assessment of trypanotolerance in N'Dama cattle

Antigen-detection enzyme immunoassays (ELISA) were used for the diagnosis of Trypanosoma vivax, T. congolense and T. brucei in N'Dama cattle in Gabon, Central Africa. The assays are based on monoclonal antibodies which recognise trypanosome antigens specific for each of the three species and animals were termed ‘antigenaemic’ when found positive by this technique but not found parasitaemic by the buffy coat technique. 148 one-year-old animals were exposed to a medium natural tsetse challenge and an average of 6 assays per animal were carried out over a 92-day period. Blood samples were routinely examined 11 times over this period and 28% of animals were detected as parasitaemic by the buffy coat technique. 90% of these were antigen-ELISA positive. More importantly, 40% of the animals with negative parasitological findings were also found to be antigenaemic. Parasitaemic animals with above-average packed-red-cell volume percent (PCV) values had 32% higher daily weight gains than those with below average, while antigenaemic animals showed no significant linkage between PCV values and weight gain. Thus only the 28% of animals with detectable parasitaemias could have been used for selection decisions based on PCV values. Antigenaemic animals grew at the same rate as negative animals and had 22% superior growth rates to parasitaemic animals. When antigenaemic animals were classified as having more ability to control parasite growth than parasitaemic animals, a significant sire effect suggested some possibility of a degree of genetic control being involved. Thus the ELISA could offer a practical possibility for selection of trypanotolerant animals based on infection criteria.

Pathogenicity of tsetse-transmitted Trypanosoma congolense for waterbuck ( Kobus defassa) and Boran cattle ( Bos indicus)

Five waterbuck ( Kobus defassa) and four Boran cattle ( Bos indicus) were infected with Trypanosoma congolense IL2895 using Glossina morsitans morsitans. At the same time, two waterbuck and two cattle were inoculated intravenously with bloodstream forms. With both methods of challenge, cattle had short prepatent periods followed by a continuous high parasitaemia. All cattle became severely anaemic and had to be treated with trypanocidal drugs to prevent death. In contrast, tsetse and intravenous challenge of waterbuck resulted in a long prepatent period, followed by brief, intermittent levels of low parasitaemia, and eventual selfcure. Waterbuck did not become anaemic, even during short bouts of parasitaemia which in general were very low. Both cattle and waterbuck developed parasite-specific antibodies, but some waterbuck failed to develop neutralizing antibodies. These results suggest that the ability of the waterbuck to resist trypanosome infection may not be mediated entirely by antibody-dependent immune processes.

Therapeutic effect of Berenil and Samorin in mice infected with four trypanosome populations isolated from Zambian cattle

Four populations of Trypanosoma congolense and Trypanosoma brucei brucei were isolated from cattle under different management practices and environments in Zambia. All four isolates had varied responses to both diminazene aceturate (Berenil®) and isometamidium chloride (Samorin®) as curative drugs in infected mice. Trypanosomes from a traditionally managed herd in a high-tsetse-challenge area had the strains most resistant to Berenil, with maximum curative dose of 45 mg kg −1 body weight. Another isolate from a high-tsetse-challenge area was evidently resistant both to Berenil at 40 mg kg −12and to Samorin at 4 mg kg −1. The strains most susceptible to both Berenil and Samorin were from a commercially managed herd of cattle under medium tsetse challenge. They responded to recommended cattle standard doses of 3.5 mg kg −1 or 7 mg kg −1 Berenil and to as little as 0.25 mg kg −1 Samorin. It is evident that trypanosome strains resistant to Berenil and/or partially resistant to Samorin exist, and that both T. congolense and T.b.brucei are implicated.

An analysis of survey measurements of tsetse challenge to trypanotolerant cattle in relation to aspects of analytical models of trypanosomiasis

The recent development of analytical models of trypanosomiasis has increased the general applicability of models to the strategic control of the disease. An analysis of detailed data on tsetse abundance and infection rates and trypanosome prevalence in village-based trypanotolerant cattle over 4 years in The Gambia showed that seasonal patterns of abundance in Glossina morsitans-infested areas were consistent, and that the rates of trypanosome infection remained relatively unchanging. However, there were two distinct seasonal trypanosome prevalence patterns in cattle, with peaks occurring either in May/June/July or November/December. The peaks of trypanosome prevalence therefore occurred either 4 months before or after the times of peak challenge from G. morsitans, not 1 or 2 months after as predicted by analytical models. In G. palpalis-infested areas there was little seasonal variation in abundance or trypanosome infections, but peak trypanosome prevalence still occurred mostly in June/July. Despite the incongruity between the months of peak prevalence and challenge, the overall annual prevalence rates and tsetse challenge indices showed a significant linear relationship. It is concluded that existing analytical models need to be refined to take into account trypanotolerance and the various influences on the expression of this trait.

Development of an enzyme-linked immunosorbent assay for the detection and measurement of the trypanocidal drug isometamidium chloride in cattle

An enzyme-linked immunosorbent assay ( elisa) was developed to measure accurately levels of the trypanocidal drug isometamidium in the serum of treated cattle. The assay requires only 5 Id of test serum, is sensitive to a level of 0·5 pg ml −1 and is highly specific. Cross reactivity does not occur with the two other widely used trypanocidal drugs diminazene aceturate and homidium bromide. Serum drug levels are detectable for up to six months in cattle after a single dose of 1 mg kg −1 intramuscularly, the maximum period under field conditions for which effective prophylaxis can be maintained against tsetse challenge. Application of the assay will aid the rationalisation of treatment campaigns and assist in assessing the occurrence of drug-resistant trypanosome populations.

Glossina fusca group tsetse as vectors of cattle trypanosomiasis in Gabon and Zaire

1. The significance of Glossina fusca group tsetse flies as vectors of cattle trypanosomiasis was examined using biconical traps to survey tsetse populations at one site in Gabon and two sites in Zaire. 2. Mean trypanosome infection rates in G.tabaniformis Westwood over the study period ranged from a minimum of 8.9% at one site to a maximum of 17.7% at another. The mean infection rate in G.nashi Potts was 6.0%. 3. Up to 49% of bloodmeals of G.tabaniformis were from cattle. Trypanosome prevalence in cattle where G.tabaniformis appeared to be the main vector was 9.5% and 5.4% at the Mushie and OGAPROV ranches, respectively. 4. A highly significant positive correlation was found between tsetse challenge and trypanosome prevalence in N'Dama cattle across sites. Tsetse challenge was defined as the product of tsetse relative densities, trypanosome infection rates in the flies and the proportion of feeds taken by them from cattle. Thus, G.tabaniformis can be an important vector of pathogenic Trypanosoma species in cattle.

Effect of trypanosome infection, control of parasitaemia and control of anaemia development on productivity of N'Dama cattle

One hundred and forty six calving interval records were built up from 64 N'Dama cows maintained for 3.5 years under a high natural tsetse challenge in Zaire. Matching health and performance data were recorded monthly to allow simultaneous evaluation of the effects of different criteria of trypanotolerance represented by time detected parasitaemic, parasitaemia score and packed red cell volume percent (PCV) on reproductive performance, calf weaning weight and cow productivity. Control of development of anaemia, measured by PCV value during trypanosome infection, had the major effect on all three performance traits. The repeatability of this criterion (0.33) was almost equal to that of calf weaning weight, indicating PCV measurement might be suitable for identification of more trypanotolerant animals. Simultaneous evaluation of the relative effects of control of development of anaemia in both the pre-weaner calf and its dam, on calf performance, suggested that its measurement in an animal might be feasible at an early post-weaner stage. Guidelines for work to develop practical field tests for trypanotolerance involving post-weaners maintained for varying lengths of time in high natural challenge situations are suggested.

Relationships between tsetse challenge and trypanosome prevalence in trypanotolerant and susceptible cattle

The relationships between estimates of tsetse challenge and trypanosome prevalence in trypanotolerant and susceptible cattle were examined at sites of the African Trypanotolerant Livestock Network. Estimates of tsetse challenge were determined as the product of tsetse relative densities, their trypanosome infectionTates and the proportions of feeds taken by them from cattle. Trypanosome prevalence in both trypanotolerant and susceptible breeds of cattle was estimated from monthly examination of groups of ear-tagged cattle. Regression equations between estimates of trypanosome prevalence and tsetse challenge were fitted using an arcsin transformation of trypanosome prevalence and a log10 transformation of tsetse challenge. Highly significant relationships between estimates of tsetse challenge and trypanosome prevalence were found for sites with trypanotolerant cattle (P < 0.0001) and sites with susceptible cattle (P < 0.01). Mean trypanosome prevalence at a given level of tsetse challenge was at least twice as high in susceptible as in trypanotolerant cattle. The slopes of the regression lines for the two groups of cattle were significantly different (P < 0.05). The results confirm the superior ability of trypanotolerant cattle to withstand tsetse challenge in the field. The curves obtained for the two groups of cattle illustrate the necessity in tsetse control campaigns for a major reduction of tsetse populations to take place before significant decreases in trypanosome incidence in livestock can be achieved.

Tsetse and human trypanosomiasis challenge in south eastern Uganda

Pyramidal traps (8000) have been set up against Glossina fuseipes fuseipes to control Trypanosoma rhodesiense in Busoga. In order to understand the pattern of tsetse/human contact, the collection of data on the density, spatial distribution and mobility of flies has been related to the dynamics of human trypanosomiasis in Busoga. As for T. gambiense, few reasonable correlations between global fly densities and incidence of the disease have been found. However, field observation with a recording time of seasonal variations of movements of people and animals associated with particular habitats, remains the key to understanding the transmission of the disease.

Bovine trypanosomiasis in southern Tanzania: investigation into the incidence of infection and duration of chemoprophylaxis.

Before implementing chemoprophylaxis to control bovine trypanosomiasis it is essential to have epidemiological data upon which to base control regimes. A study was conducted under natural tsetse challenge with two groups each of 12 calves grazing their first season. Group 1 received isometamidium treatments prophylactically at intervals during the rainy season and calves in group 2 were treated individually with diminazene as they become infected with trypanosomes. Infections were first detected in the unprotected calves and indicated that the onset of challenge was approximately four weeks after the rainy season began. Trypanosoma vivax accounted for 21 of the 30 infections detected in blood smears, and although one infection remained unspeciated, the remaining eight were T. congolense. It was concluded that a prophylactic regime beginning one month after the start of the rains with repeat treatments of isometamidium at 1 mg/kg at intervals of 10 weeks could be expected to give good control of trypanosomiasis at this location.

Susceptibility of goats to tsetse-transmitted challenge with Trypanosoma vivax from East and West Africa.

To determine if, as is the case with Trypanosoma brucei and T. congolense, serodemes of T. vivax could be distinguished on the basis of immunity to the metacyclic stages of the parasite, attempts were made to immunize goats by infection with infected tsetse, followed by chemotherapy or eventual 'self-cure'. Thirty goats were infected by tsetse with either clones or stocks of T. vivax from East or West Africa. Twenty-four goats were treated with diminazene aceturate (Berenil, Hoechst A.G.) 2-6 weeks after infection and 6 goats were allowed to self-cure. Infection, followed by treatment, induced immunity to a first homologous challenge by infected tsetse in only 2 of 24 goats (one immune to the East African stock, and the other to a clone of the West African stock). Immunity to a clone of the East African stock was induced in 3 or 4 animals after a second infection and treatment and in the fourth animal of the group following a third infection and treatment. One of 2 goats infected with the clone of the East African stock was immune to challenge at 16 weeks, following self-cure without treatment, and 1 of 4 goats infected with the parent stock was similarly immune when challenged at 40 weeks post-infection. Goats susceptible to infection with East African T. vivax showed evidence of partial immunity by delayed pre-patent periods and depressed parasitaemias after challenge. Goats infected with the relatively more virulent West African T. vivax were, however, completely susceptible to infection after homologous challenge, and showed only a slight delay in pre-patent period. A similar result was obtained in a further 8 goats primed and challenged by large numbers of tsetse (20 or 100 infected tsetse/goat) with the West African T. vivax. In further experiments using a very short treatment interval, infections following challenge were clearly shown to be the result of a lack of immunity rather than relapse following treatment. Lytic antibody activity to cultured metacyclic trypanosomes could not be detected during infection but such activity against bloodstream forms was detected after 2 weeks of infection. It is suggested that the primary reason for the erratic induction of immunity to T. vivax employing this methodology is the low number of metacyclics transmitted by infected tsetse, and thus poor antigenic stimulus encountered by goats upon tsetse challenge.

Comparative epidemiology and control of trypanosomes

Tsetse-transmitted trypanosomiasis in man and domestic livestock is a major constraint to livestock and socio-economic development in Africa. Analysis of the limited number of databases on matching animal health and productivity available for cattle in tsetse-infested areas of Africa has provided new information about the value of current methods of controlling the disease. It was established that the trypanotolerant breeds of cattle, namely N'Dama and West African Shorthorn, were much more productive than originally believed, despite their small stature, and, as a result, could be considered for livestock development programmes in tsetse-infested regions. Moreover, in areas of low tsetse challenge, it was shown that the strategic use of therapeutic trypanocidal drugs allowed the maintenance of high levels of productivity in dairy cattle and demonstrated genotype and acquired differences in treatment requirements. On the other hand, the use of a prophylactic drug regime allowed beef cattle to be reared to an economically acceptable level of productivity in an area where tsetse challenge was high that animals rapidly succumbed if left untreated. These results show that the current methods available for the control of animal African trypanosomiasis can be effective if properly applied.