The successful use of work oxen in agricultural development of tsetse infested land in Ethiopia

Recent advances in research on draught ruminants

A feeding system, draught cows, disease/work interactions and animal power introduction in a farming system, four areas of recent research on draught ruminants which are important to future development of animal power, are reviewed. A new feeding system for draught animals is described which enables food requirements and the effects of work on live weight and milk production to be calculated.

Recent data on the energy cost of walking are appraised. Research on working cows, mainly in Ethiopia, has shown that undernutrition has a greater effect on milk yield than work, which has a transient effect. The length of the post-partum anoestrous period increases with decrease in body condition. Body-weight loss increases with increasing work load. It is suggested that dairy cows delay conception by 1 day for every day of work done. Work has little effect on food intake or digestive parameters. Although it is associated with an overall increase in food intake of cows, even of un-supplemented forage diets, the increase is not sufficient to meet all the extra energy needs for work. Food intake of both working and non-working cows increases during lactation.

Disease limits the working capacity of draught animals and work can exacerbate disease. These effects were investigated using Trypanosoma evansi in Indonesia and T. congolense in The Gambia. In both studies, infected animals were able to do much less work than non-infected ones and the severity of the effect depended greatly on the strain of trypanosome used. In general, increasing the plane of nutrition did not ameliorate the effects of the disease, nor in the Gambian study did it prevent loss of appetite in infected animals.

The technical and agronomic innovations necessary for the introduction of animal power into an inland valley region of central Nigeria are described and some of the sociological implications discussed.

Some general aspects of the distribution and epidemiology of bovine trypanosomosis in southern Africa

Bovine trypanosomosis occurs in vast areas of southern Africa. Its epidemiology and impact on cattle production is determined largely by the level of interaction between tsetse and cattle. Four situations can be distinguished. First, areas where cattle are absent. Second, zones where cattle have been introduced in game areas but where game is still abundant and constitutes the major source of food for tsetse. Third, areas where, often because of human interference, the density of game animals is low and cattle constitute the main source of food and finally, areas where cattle occur at the edge of tsetse-infested zones. In southern Africa, the impact of the disease on cattle production varies according to the epidemiological circumstances. The disease has an epidemic character with significant impacts on production in areas where cattle have been introduced recently or along the interface between tsetse-infested game areas and tsetse-free cultivated areas. Bovine trypanosomosis has an endemic character, with little impact on production, in areas where tsetse mainly feed on cattle and where the invasion of tsetse is low. Options for the control of bovine trypanosomosis will vary according to the epidemiological circumstance. In particular, the control of tsetse with insecticide-treated cattle will only be effective when a large proportion of feeds are taken from cattle over a large area and when the invasion of tsetse can be reduced sufficiently.

The relationship between the parasitological prevalence of trypanosomal infections in cattle and herd average packed cell volume

The relationship between prevalence of trypanosomal infections (Trypanosoma congolense) and average packed cell volume (PCV) in herds of communally managed adult Angoni breed cattle was investigated in four districts of eastern Zambia. In all areas, regression analyses showed that the herd average PCV decreased with increasing prevalence of trypanosomal infections. The slope of the equation between average PCV and trypanosome prevalence decreased with increasing prevalence of trypanosomal infections. For the same increase in prevalence of trypanosomal infection, the decrease in herd PCV was higher in the areas with low to medium prevalence. Season of sampling also determined the slope of the regression equation. For the same increase in prevalence of trypanosomal infection, the decrease in herd PCV was higher during the dry compared to the rainy season suggesting that trypanosomosis is less well tolerated during the dry season. Results from the study suggest that the relationship between the prevalence of trypanosomal infections and herd average PCV could be a useful tool in the management of trypanosomosis and planning of its control. Reasons for the spatial and temporal variations in the relationship are discussed.

Concentrations of isometamidium chloride (Samorin) in sera of Zebu cattle which showed evidence of hepatotoxicity following frequent trypanocidal treatments

The concentrations of isometamidium circulating in poorly nourished Zebu cattle which showed morbidity, mortality, and biochemical and histopathological evidence of hepatotoxicity, following frequent treatments with isometamidium chloride and diminazene aceturate were investigated using the isometamidium-ELISA. As few as two isometamidium treatments one month apart were associated with significant weight loss, and cattle treated with diminazene aceturate after three or four isometamidium treatments suffered a 50% mortality. Although there were no obvious, marked elevations in isometamidium concentration which might have allowed the use of the ELISA as a predictor of a potential toxicity problem, concentrations did increase significantly with the number of monthly treatments administered, suggesting drug accumulation, and the increases were significantly higher in cattle to which diminazene had also been administered. In cattle treated with both trypanocides, weight loss and serum glutamate dehydrogenase levels were correlated with isometamidium concentrations. These observations, together with the histopathological findings, support the hypothesis that the morbidity and mortality observed were related to the repeated treatment with isometamidium in conjunction with diminazene aceturate, and that the pathogenesis involved a component of hepatic damage. It is therefore recommended that cattle, particularly those under nutritional stress, are not subjected to repeated treatments with isometamidium at intervals as short as one month, and particularly not with concurrent administration of diminazene.

Pharmacology of diminazene: a review

Chemotherapy for trypanosomiasis in domestic livestock depends on only a few compounds, of which several are chemically closely related. Of these compounds, the most widely used therapeutic agent in cattle, sheep and goats is diminazene aceturate. Diminazene was first described in 1955. Subsequently, a substantial body of data has been generated on various pharmacological aspects of the compound. In this review, we consider the current status of knowledge concerning the therapeutic spectrum of diminazene, resistance to diminazene in trypanosomes, and combination therapeutic regimens in which diminazene has been administered together with other compounds. Analytical techniques for diminazene, the pharmacokinetics of diminazene, data concerning diminazene's toxicity, and the different molecular mechanisms by which diminazene may exhibit trypanocidal action are also considered.

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.

Therapeutic activity of isometamidium chloride in Boran cattle against a tsetse-transmitted clone of Trypanosoma congolense with a low level of drug resistance

Experiments were conducted with a clone of Trypanosoma congolense, IL 3580, which exhibited a low level of resistance to isometamidium chloride. Five cattle were treated intramuscularly with isometamidium chloride at a dose rate of 0.5 mg kg-1 body weight (BW) and challenged 28 days later with 5 Glossina morsitans centralis infected with T. congolense IL 3580. All 5 cattle and 15 untreated steers challenged on the same day became parasitaemic by day 15 post-infection. Thus, at a dose of 0.5 mg kg-1 BW, the prophylactic action of isometamidium chloride did not extend to 28 days following treatment. Subsequently, the 20 steers were divided into 4 groups of 5 animals each and treated with isometamidium chloride at one of the following dose rates; 0.5 or 1.0 mg kg-1 BW intramuscularly and 0.5 or 1.0 mg kg-1 BW intravenously (Groups A, B, C and D, respectively). Group A consisted of the 5 animals that had previously been treated with isometamidium chloride. Animals relapsed in all groups except those in Group B, treated intramuscularly with isometamidium chloride at a dose of 1.0 mg kg-1 BW. Four of the 5 animals in Group A, treated intramuscularly with isometamidium chloride at a dose of 0.5 mg kg-1 BW relapsed following a mean interval of 16 days post-treatment. Similarly, infections in all animals in Groups C and D, given intravenous injections of isometamidium chloride at a dose of 0.5 and 1.0 mg kg-1 BW, respectively, were not eliminated as a result of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Trypanosomiasis control in Boran cattle in Kenya: a comparison between chemoprophylaxis and a parasite detection and intravenous treatment method using isometamidium chloride

Two methods of trypanosome control in Boran cattle kept under very high trypanosomiasis risk were compared: the traditional intramuscular isometamidium chloride prophylaxis with a parasite detection and intravenous isometamidium chloride treatment method. The results were related to a control group under diminazene aceturate treatment. Isometamidium chloride at 0.25 mg/kg as routinely used by the ranch was of little benefit by either method, with breakthrough infections occurring as early as one week after treatment. When isometamidium chloride at 1 mg/kg was used, the curative intravenous method appeared to be superior to the intramuscular prophylaxis with regard to cost of drugs and to a 31% higher weight gain over a 30 week period. Weekly infection rates in the intravenous group decreased over time, despite an increasing trypanosomiasis challenge, with a mean interval of 6.4 weeks between treatments as compared with 4.3 weeks in a diminazene aceturate control group. It was concluded that isometamidium chloride given intravenously had not only a very good therapeutic but also a considerable prophylactic effect of not less than four weeks.

Therapeutic and prophylactic activity of isometamidium chloride against a tsetse-transmitted drug-resistant clone of Trypanosoma congolense in Boran cattle

An investigation was conducted on the therapeutic and prophylactic activity of isometamidium chloride (SamorinR) in Boran (Bos indicus) cattle against a Trypanosoma congolense clone, IL 3270. This clone was derived, without drug selection, from a stock originally isolated in Burkina Faso and has previously been shown to be resistant to isometamidium in both cattle and mice using an infection and treatment regimen. A group of 5 cattle were treated intramuscularly with 1.0 mg kg-1 isometamidium chloride and 28 days later challenged with Glossina morsitans centralis infected with T. congolense IL 3270. All 5 cattle and 17 untreated cattle challenged on the same day became parasitaemic by day 16 post challenge, indicating that prophylaxis did not extend to 28 days post treatment. The cattle were then treated with isometamidium chloride at one of the following doses and by different routes of administration; 1.0 or 2.0 mg kg-1 intramuscularly, 0.25, 0.5, 0.75 or 1.0 mg kg-1 intravenously. Infections relapsed in all cattle at an interval of 12-21 days following treatment, with the exception of those treated with 2.0 mg kg-1 intramuscularly in which the development of relapse infections was delayed. Similar studies were also conducted with a highly sensitive clone of T. congolense, IL 1180. Infections in cattle with this clone were eliminated by intravenous treatment with 0.25 mg kg-1 isometamidium chloride or intramuscular treatment with 0.5 mg kg-1 isometamidium chloride. Thus, although intravenous administration of isometamidium eliminated a fully sensitive infection, treatment by this route appeared not to enhance the therapeutic efficacy of the drug in the treatment of a T. congolense clone which expresses a high level of resistance.

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 microliters 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.

Differences in sensitivity of Kenyan Trypanosoma vivax populations to the prophylactic and therapeutic actions of isometamidium chloride in Boran cattle

Isometamidium chloride was administered as a single prophylactic dose of 0.5 mg kg-1 body weight to each of 10 Boran (Bos indicus) steers. At monthly intervals following drug administration, groups of five cattle each were challenged with one of two different Trypanosoma vivax populations transmitted by infected Glossina morsitans centralis; one with a stock (IL 2982) from Galana, Kenya and the other with a stock (IL 2986) from Likoni, Kenya. Prophylaxis was afforded for less than one month against the Galana T. vivax and for one month against the Likoni T. vivax. In a therapeutic study a further 10 Boran steers were similarly infected with either of the T. vivax populations; five steers per population. Eleven days after infection all animals were treated with 0.5 mg kg-1 isometamidium chloride and all were cured. These findings demonstrate that, as defined in the field, the two Kenyan T. vivax populations express a high level of resistance to the prophylactic action of isometamidium yet a low level of resistance to the therapeutic action of the drug. The results also indicate that differences in drug resistance between different isolates play a major role in determining the apparent period of prophylaxis afforded by isometamidium chloride.

Characterization of Trypanosoma congolense serodemes in stocks isolated from Chipata District, Zambia

Six stocks of Trypanosoma congolense were cloned from 17 stocks isolated from Eastern Zambia and used to initiate insect-form in vitro cultures producing metacyclic trypanosomes. Serological assays were then developed using these in vitro-derived metacyclics as a reference collection of antigens. Monoclonal antibodies recognized 8 metacyclic variable antigen types (M-VATs) of one stock, T. congolense TREU 1885, representing 70-80% of that stock's M-VAT repertoire, and in an indirect fluorescent antibody test (IFAT) there were no cross-reactions between them and the metacyclic trypanosomes of the other 5 stocks. Cross-protection assays between the 6 stocks in mice showed that the stocks cultured in vitro were serologically distinct. In order to facilitate serological typing for serodeme characterization, an IFAT was developed using formalin-fixed metacyclic trypanosomes to identify VAT specific immune responses using 21 day post-infection antisera. The cultured stocks reacted only with their homologous antisera thus confirming the results obtained in the cross-protection assays. No cross-reactions were observed with the 6 cloned stocks and antisera against the 11 stocks of T. congolense isolated in the same area at the same time suggesting that these stocks were different from the reference collection of cultured metacyclics. Hence, at least 7 serodemes of T. congolense have been identified from the 17 stocks isolated.

Expression of resistance to isometamidium and diminazene in Trypanosoma congolense in Boran cattle infected by Glossina morsitans centralis

Investigations were conducted on the sensitivity to isometamidium chloride (Samorin) and diminazene aceturate (Berenil) of derivatives of three of the Trypanosoma congolense stocks isolated between 1978 and 1983 from Zebu cattle in the Bobo-Dioulasso region of Burkina Faso. Boran cattle were used in the drug-sensitivity tests and were infected using Glossina morsitans centralis. The results showed that T. congolense stock IL 2466 isolated in 1978 was sensitive to the standard therapeutic dose of isometamidium chloride (0.25 mg kg-1) and of diminazene aceturate (a.i. 3.5 mg kg-1). However, T. congolense stock IL 2468 isolated in 1982 was resistant to both the prophylactic (0.5 and 1.0 mg kg-1) as well as the therapeutic doses of isometamidium chloride (up to 1.0 mg kg-1) although the sensitivity to the therapeutic dose of diminazene aceturate (3.5 mg kg-1) was not affected. The T. congolense stock IL 2856 isolated in 1983 was highly resistant to the therapeutic action of diminazene aceturate (up to 10.5 mg kg-1), as well as to the prophylactic (up to 1.0 mg kg-1) and therapeutic action of isometamidium chloride (up to 2.0 mg kg-1). The infection rates of the drug-resistant stocks of T. congolense in G.m. centralis, when goats were used as reservoir hosts, were as high (range, 22.3-56.3%) as of the drug sensitive stock (49.5%). The resistance trait in the two stocks remained stable after their cyclical development in the tsetse vectors. The rate of transmission of the drug-resistant stocks to mice by the infected tsetse was also high (mean 81.3%).

Recent studies of the biology of Trypanosoma vivax

Recent biological investigations of the African trypanosomes have been moving away from their previous preoccupation with the phenomenon of antigenic variation. The feeling has arisen that antigenic variation, as demonstrated by the Trypanozoon and Nannomonas subgenera of trypanosomes, is too extensive, the number of serodemes too large and the coexistence of different species in many areas too complicated, to allow any immunoprophylaxis based on antibodies to variable antigens. This is, of course, not to rule out possible biochemical intervention in the biosynthesis or export of VSG molecules by trypanosomes. However, in the case of T. vivax, more information is required concerning antigenic variation and coat structure in this organism before these avenues of investigation are discarded. Ways of improving the yield of mature metacyclic trypanosomes in vitro must be found, so that the contribution of metacyclic variable antigens to the induction of immunity in T. vivax infection can be elucidated. The number of bloodstream VATs must be determined (perhaps by genetic rather than serological means), as there is evidence both for VAT exhaustion contributing to the self-cure of infected hosts, and for a possible limit to the number of VATs which can be expressed in infections in Africa. In South America nothing is known of the number of serodemes of T. vivax which exist, although such knowledge is obviously required, especially if immunity to bloodstream variants is the more important mechanism of inducing immunity to this trypanosome and true cyclical transmission is rare in, or absent from, that subcontinent. Further, in a fragile organism, with a coat of suspect integrity, the method of VSG packing and the relative exposure of underlying surface molecules seems to hold out even more hope for an immunological intervention based on cell surface but invariant molecules than is the case with T. brucei or T. congolense, although this is being attempted with the latter species. In T. brucei infections the appearance of the non-dividing stumpy population acts as a stimulus to the induction of humoral immune responses. In ruminants, antibody responses to T. vivax, at least as judged from lysis tests, lag behind the appearance of the different VATs by some days. It would be important to determine, therefore, whether, if late bloodstream forms could be induced more frequently in the ruminant, the speed of anti-VAT responses could be enhanced. Whilst self-cure appears to be relatively common in T. vivax infections, it is unlikely that it results in sterile immunity.(ABSTRACT TRUNCATED AT 400 WORDS)

Natural resistance to African trypanosomiasis

Glossina infected with African trypanosomes infest 10(7) Km2 of intertropical Africa. Ten thousand cases of human sleeping sickness are officially recorded each year and 35 X 10(6) human beings are at risk. Animal trypanosomiasis impedes the use of 7 X 10(6) Km2 of land adequate for cattle raising and constitutes a major constraint to increasing protein production in Africa. Several approaches are used to combat trypanosomiasis (a) vector eradication has been successful in certain defined situations but cannot be realistically extended to the whole area at risk, (b) prophylactic drugs, which are too toxic for humans, are widely used to protect cattle. This practice has led to field resistance to many drugs used in the past (reviewed in Holmes & Scott 1982) and the appearance of resistance to the last available prophylactic drug, isometamidium, is being reported (Bourn & Scott 1978, Küpper & Wolters 1983, Pinder & Authié 1984), (c) the hope for a vaccine has been largely abandoned, in the present state of knowledge, due to the considerable extent of antigenic diversity in trypanosomes (reviewed in Doyle 1977, Turner 1982, Roelants & Pinder 1984), (d) consequently, the possible use of certain West African breeds of cattle, which appear resistant to trypanosomiasis, has been emphasized as a solution to this problem in domestic animals. The analysis of this natural resistance is the subject of the present essay.

Maintaining zebu Maure cattle in a tsetse infested area of Mali

A study was initiated to evaluate two trypanocidal drugs, the prophylactic isometamidium chloride (Trypamidium) and the curative diminazene aceturate (Berenil) as to their potential for long-term maintenance of zebu cattle in a tsetse infested area of Mali. Trypamidium was administered quarterly and Berenil was administered only as animals were found to be positive for trypanosomes. During the 21-month study trypanosomiasis was the most frequently encountered disease in the cattle in the Berenil treatment group with an average of 5.5 reinfections. The predominant trypanosome species encountered was Trypanosoma vivax and the most important vector was Glossina palpalis gambiensis. The results indicate that, even though the direct costs for drugs under the two maintenance regimens were almost identical, the use of Trypamidium resulted in a significantly greater annual weight gain, prevented death loss due to trypanosomiasis and resulted in a herd with a greater market value.

A reassessment of the expected development consequences of tsetse control efforts in Africa

Since the World Food Conference (1974) recommended a long term program of tsetse control, increasing attention of governments and international agencies has focused on the problem. This paper briefly outlines the strategies potentially available for tsetse control operations before assessing the likely consequences of any large scale tsetse control endeavor. The implications for both natural and human systems are shown to be profound and, in many cases, counter-productive to development goals. Suggestions for more appropriate strategies of addressing the tsetse issue are included. The major conclusions of the study are: (1) extreme caution is needed in relating the absence of development to the presence of the tsetse fly; (2) promises of benefits forthcoming with the removal of the tsetse fly must be viewed with skepticism; (3) in some cases a case can be made for retaining the tsetse; (4) fly zone problems can be addressed in many ways other than tsetse removal; (5) the regions most likely to incorporate successful tsetse control efforts will be on the margins of tsetse range, removed from border areas beyond the purvey of tsetse control efforts and within the domain of a stable administrative structure capable of mobilizing planning, funding and personnel; (6) it is important to define the targeted human population for the designed development benefits. Different strategies should be employed in virgin lands, places with people lacking livestock experience and places intended for expanding pastoralist rangelands; (7) the push for tsetse eradication arises from its role as a disease vector, its 'non-political' status as a development target and the strong Western bias toward the role of cattle in the modern agricultural mix.