Tsetse Challenge Research Articles

African animal trypanosomosis (nagana) in northern KwaZulu-Natal, South Africa: Strategic treatment of cattle on a farm in endemic area

African animal trypanosomosis (AAT) is caused by several species of the genus Trypanosoma, a parasitic protozoan infecting domestic and wild animals. One of the major effects of infection with pathogenic trypanosome is anaemia. Currently, the control policies for tsetse and trypanosomosis are less effective in South Africa. The only response was to block treat all infected herds and change the dip chemical to one which controls tsetse flies during severe outbreaks. This policy proved to be less effective as demonstrated by the current high level of trypanosome infections in cattle. Our objective was to study the impacts of AAT (nagana) on animal productivity by monitoring the health of cattle herds kept in tsetse and trypanosomosis endemic areas before and after an intervention that reduces the incidence of the disease. The study was conducted on a farm in northern KwaZulu-Natal which kept a commercial cattle herd. There was no history of any cattle treatment for trypanosome. All cattle were generally in poor health condition at the start of the study though the herd received regular anthelminthic treatment. A treatment strategy using two drugs, homidium bromide (ethidium) and homidium chloride (novidium), was implemented. Cattle were monitored regularly for 13 months for herd trypanosomosis prevalence (HP), herd average packed cell volume (H-PCV) and the percentage of the herd that was anaemic (HA). A total of six odour-baited H-traps were deployed where cattle grazed from January 2006 to August 2007 to monitor the tsetse population. Glossina brevipalpis Newstead and Glossina austeni Newstead were collected continuously for the entire study period. High trypanosomes HP (44%), low average H-PCV (29.5) and HA (24%) were rerecorded in the baseline survey. All cattle in the herd received their first treatment with ethidium bromide. Regular monthly sampling of cattle for the next 142 days showed a decline in HP of 2.2% – 2.8%. However, an HP of 20% was recorded by day 220 and the herd received the second treatment using novidium chloride. The HP dropped to 0.0% and HA to 0.0% by day 116 after the second treatment. The cow group was treated again by day 160 when the HP and HA were 27.3% and 11%, respectively. The same strategy was applied to the other two groups of weaners and the calves at the time when their HP reached 20%. Ethidium and novidium treatment protected cattle, that were under continuous tsetse and trypanosomosis challenge, for up to 6 months. Two to three treatments per year may be sufficient for extended protection. However, this strategy would need to be included into an integrated pest management approach combining vector control for it to be sustainable.

Haematology of N'Dama and West African Shorthorn cattle herds under natural Trypanosoma vivax challenge in Ghana.

Background: Animal trypanosomosis is a major cause of economic loss in livestock production in Africa. A suggested control measure is to use breeds with traits of trypanotolerance. The study examines the effect of natural Trypanosoma vivax challenge on haematological parameters in two trypanotolerant cattle [N'Dama and West African Shorthorn (WASH)] herds. Methods:Trypanosoma vivax-specific primers were used to diagnose T. vivax infection in an N'Dama herd at Cape Coast in southern Ghana and a WASH herd at Chegbani in northern Ghana from May to July 2011 in a cross-sectional study. Levels of haematological parameters comprising packed cell volume (PCV), haemoglobin (Hb) concentration and red blood cell (RBC) and total white blood cell (TWBC) counts; differential WBC counts (neutrophils, lymphocytes, eosinophils, monocytes and basophils); and RBC indices of mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were determined in blood samples and then compared between infected and uninfected cattle. Results: We found that haematological indices for infected and uninfected animals in both breeds were within the normal range. However, the mean PCV values for T. vivax-infected WASH and N'Dama were lower in infected compared to uninfected animals. The difference was significant ( p< 0.05) in N'Dama but not in WASH. Conclusion: Despite the presence of infection by T. vivax, N'Dama and WASH cattle maintained their haematological parameters within acceptable normal ranges, which confirms their trypanotolerant trait. This highlights the need for low-input traditional African farmers in medium, high and severe tsetse challenge areas to be educated on the advantages of N'Dama and WASH breeds to increase their utilization in integrated tsetse and trypanosomosis control programmes.

Haematology of N’Dama and West African Shorthorn cattle herds under natural Trypanosoma vivax challenge in Ghana

Background: Animal trypanosomosis is a major cause of economic loss in livestock production in Africa. A suggested control measure is to use breeds with traits of trypanotolerance. The study examines the effect of natural Trypanosoma vivax challenge on haematological parameters in two trypanotolerant cattle [N’Dama and West African Shorthorn (WASH)] herds. Methods: Trypanosoma vivax-specific primers were used to diagnose T. vivax infection in an N’Dama herd at Cape Coast in southern Ghana and a WASH herd at Chegbani in northern Ghana from May to July 2011 in a cross-sectional study. Levels of haematological parameters comprising packed cell volume (PCV), haemoglobin (Hb) concentration and red blood cell (RBC) and total white blood cell (TWBC) counts; differential WBC counts (neutrophils, lymphocytes, eosinophils, monocytes and basophils); and RBC indices of mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were determined in blood samples and then compared between infected and uninfected cattle. Results: We found that haematological indices for infected and uninfected animals in both breeds were within the normal range. However, the mean PCV values for T. vivax-infected WASH and N’Dama were lower in infected compared to uninfected animals. The difference was significant ( p< 0.05) in N’Dama but not in WASH. Conclusion: Despite the presence of infection by T. vivax, N’Dama and WASH cattle maintained their haematological parameters within acceptable normal ranges, which confirms their trypanotolerant trait. This highlights the need for low-input traditional African farmers in medium, high and severe tsetse challenge areas to be educated on the advantages of N’Dama and WASH breeds to increase their utilization in integrated tsetse and trypanosomosis control programmes.

English

Ethiopia is one of African country with nine regions and two city administration of which five regions were infected with more than one species of tsetse flies. Known species in Ethiopia are five in number namely Glossina pallidipes, G .morsitans, G. fuscipes, G. tachinoides and G. longipennis. Most tsetse transmission is cyclic and begins when blood from a trypanosome-infected animal is ingested by the fly. The clinical feature of the disease follows the level or burdens of tsetse challenge species. The main feature is anemia results in a progressive drop in packed cell volume, a non-specific but useful indicator in endemic areas. The most sensitive rapid method is examining a wet mount of the buffy coat area of a PCV tube after centrifugation, looking for motile parasites. The prevalence of trypanosomosis in enzootic area can be reduced by parasite control, vector control, host resistance protection prophylactic treatment and good husbandry management system. The methods of tsetse fly control involved bush clearing, elimination of game animals on which tsetse feed, and the sterile male technique (sterile insect techniques). Since female tsetse only mates once in a lifetime, this technique is theoretically able to eradicate a targeted tsetse species. Trypanotolerant animals are very important in tsetse fly challenging areas, but most countries did not accept them due to their low production of milk than indigenous breed. In conclusion, prevalence of trypanosomosis is devastating diseases of cattle in Ethiopia with both direct and indirect economic losses. Key words: Bovine, trypanosomosis, nagana, tsetse fly, protozoa.

Protecting cows in small holder farms in East Africa from tsetse flies by mimicking the odor profile of a non-host bovid.

BackgroundFor the first time, differential attraction of pathogen vectors to vertebrate animals is investigated for novel repellents which when applied to preferred host animals turn them into non-hosts thereby providing a new paradigm for innovative vector control. For effectively controlling tsetse flies (Glossina spp.), vectors of African trypanosomosis, causing nagana, repellents more powerful than plant derived, from a non-host animal the waterbuck, Kobus ellipsiprymnus defassa, have recently been identified. Here we investigate these repellents in the field to protect cattle from nagana by making cattle as unattractive as the buck.Methodology/Principal findingsTo dispense the waterbuck repellents comprising guaiacol, geranylacetone, pentanoic acid and δ-octalactone, (patent application) we developed an innovative collar-mounted release system for individual cattle. We tested protecting cattle, under natural tsetse challenge, from tsetse transmitted nagana in a large field trial comprising 1,100 cattle with repellent collars in Kenya for 24 months. The collars provided substantial protection to livestock from trypanosome infection by reducing disease levels >80%. Protected cattle were healthier, showed significantly reduced disease levels, higher packed cell volume and significantly increased weight. Collars >60% reduced trypanocide use, 72.7% increase in ownership of oxen per household and enhanced traction power (protected animals ploughed 66% more land than unprotected). Land under cultivation increased by 73.4%. Increase in traction power of protected animals reduced by 69.1% acres tilled by hand per household per ploughing season. Improved food security and household income from very high acceptance of collars (99%) motivated the farmers to form a registered community based organization promoting collars for integrated tsetse control and their commercialization.Conclusion/SignificanceClear demonstration that repellents from un-preferred hosts prevent contact between host and vector, thereby preventing disease transmission: a new paradigm for vector control. Evidence that deploying water buck repellents converts cattle into non-hosts for tsetse flies—‘cows in waterbuck clothing’.

A Spatio-temporal Model of African Animal Trypanosomosis Risk.

BackgroundAfrican animal trypanosomosis (AAT) is a major constraint to sustainable development of cattle farming in sub-Saharan Africa. The habitat of the tsetse fly vector is increasingly fragmented owing to demographic pressure and shifts in climate, which leads to heterogeneous risk of cyclical transmission both in space and time. In Burkina Faso and Ghana, the most important vectors are riverine species, namely Glossina palpalis gambiensis and G. tachinoides, which are more resilient to human-induced changes than the savannah and forest species. Although many authors studied the distribution of AAT risk both in space and time, spatio-temporal models allowing predictions of it are lacking.Methodology/Principal FindingsWe used datasets generated by various projects, including two baseline surveys conducted in Burkina Faso and Ghana within PATTEC (Pan African Tsetse and Trypanosomosis Eradication Campaign) national initiatives. We computed the entomological inoculation rate (EIR) or tsetse challenge using a range of environmental data. The tsetse apparent density and their infection rate were separately estimated and subsequently combined to derive the EIR using a “one layer-one model” approach. The estimated EIR was then projected into suitable habitat. This risk index was finally validated against data on bovine trypanosomosis. It allowed a good prediction of the parasitological status (r2 = 67%), showed a positive correlation but less predictive power with serological status (r2 = 22%) aggregated at the village level but was not related to the illness status (r2 = 2%).Conclusions/SignificanceThe presented spatio-temporal model provides a fine-scale picture of the dynamics of AAT risk in sub-humid areas of West Africa. The estimated EIR was high in the proximity of rivers during the dry season and more widespread during the rainy season. The present analysis is a first step in a broader framework for an efficient risk management of climate-sensitive vector-borne diseases.

Improvements on restricted insecticide application protocol for control of Human and Animal African Trypanosomiasis in eastern Uganda.

BackgroundAfrican trypanosomes constrain livestock and human health in Sub-Saharan Africa, and aggravate poverty and hunger of these otherwise largely livestock-keeping communities. To solve this, there is need to develop and use effective and cheap tsetse control methods. To this end, we aimed at determining the smallest proportion of a cattle herd that needs to be sprayed on the legs, bellies and ears (RAP) for effective Human and Animal African Trypanosomiasis (HAT/AAT) control.Methodology/Principal findingCattle in 20 villages were ear-tagged and injected with two doses of diminazene diaceturate (DA) forty days apart, and randomly allocated to one of five treatment regimens namely; no treatment, 25%, 50%, 75% monthly RAP and every 3 month Albendazole drench. Cattle trypanosome re-infection rate was determined by molecular techniques. ArcMap V10.3 was used to map apparent tsetse density (FTD) from trap catches. The effect of graded RAP on incidence risk ratios and trypanosome prevalence was determined using Poisson and logistic random effect models in R and STATA V12.1 respectively. Incidence was estimated at 9.8/100 years in RAP regimens, significantly lower compared to 25.7/100 years in the non-RAP regimens (incidence rate ratio: 0.37; 95% CI: 0.22–0.65; P<0.001). Likewise, trypanosome prevalence after one year of follow up was significantly lower in RAP animals than in non-RAP animals (4% vs 15%, OR: 0.20, 95% CI: 0.08–0.44; P<0.001). Contrary to our expectation, level of protection did not increase with increasing proportion of animals treated.Conclusions/significanceReduction in RAP coverage did not significantly affect efficacy of treatment. This is envisaged to improve RAP adaptability to low income livestock keepers but needs further evaluation in different tsetse challenge, HAT/AAT transmission rates and management systems before adopting it for routine tsetse control programs.

Bovine trypanosomosis prevalence at the edge of Hluhluwe-iMfolozi Park, KwaZulu-Natal, South Africa.

The northern KwaZulu-Natal (NKZN) region of South Africa is the southern limit of the African tsetse belt. Entomological information on Glossina brevipalpis and Glossina austeni was generated following the outbreak of trypanosomosis in cattle in 1990. However, these data have not been supported by parallel studies on epidemiology of the disease and therefore there has been no control policy in place. This study presented the first intensive investigations to address the epidemiology of trypanosomosis in NKZN. Tsetse abundance, trypanosome herd average prevalence (HAP), herd average anaemia (HAA) and herd average packed cell volume (HA-PCV) were investigated at three communal diptanks located at the edge of Hluhluwe-iMfolozi Park by monthly sampling from June 2006 - November 2007. Seasonal trypanosome surveys were conducted at seven other communal diptanks. Glossina brevipalpis prevalence was high at two of the diptanks, Mvutshini and Ekuphindisweni, but low at Ocilwane, whilst G. austeni was only collected from Mvutshini. This high and low tsetse challenge presented different disease scenarios. Cattle at Mvutshini and Ekuphindisweni had the highest HAP of 12.3% and 8.9% respectively, both significantly different (p = 0.001) from the HAP obtained from cattle at Ocilwane (2.9%). These two cattle herds also had the highest HAA, 27.7% and 33.4% respectively, whilst cattle at Ocilwane had the lowest, 11.1% (p = 0.001). Conversely, cattle at Ocilwane had the highest HA-PCV, ranging between 29.0% and 32.0%, whilst cattle at Mvutshini and Ekuphindisweni had the lowest HA-PCV (24.0% - 29.0%). By combining the data from the three diptanks (1318 observations), 62.0% of the infected cattle were found anaemic, compared to 20.0% in the uninfected group. Trypanosome seasonal surveys showed that cattle at all the seven diptanks were infected with trypanosomes; mean HAP, HAA and HA-PCV of 10.2%, 46.6% and 23.7%, respectively. This study generated information on the epidemiological factors related to the wide spread of trypanosome-infected cattle and tsetse flies. Trypanosomosis is a disease of economic importance impacting the livelihood of resource-poor farmers in NKZN.

Trypanosome infection rate of Glossina pallidipes and trypanosomosis prevalence in cattle in Amaro Special District of Southern Ethiopia

The survey was conducted in Amaro Special District, Southern Ethiopia in 2010. It was initiated to determine the trypanosome infection rate, population density of Glossinaspecies and prevalence of trypanosomosis in cattle. Glossina pallidipes was the only species of tsetse found in the study area during the study period. A total of 202 flies were dissected. The overall infection rate of G. pallidipes was 6.93%, among which 1 (0.49%) was male and 13 (6.43%) female flies. The prevalence was significantly higher (c2 = 99.82; P = 0.00) in female flies than male flies. In determination of tsetse flies population density, flies were trapped using baited stationary traps, and other biting flies were estimated in relation to altitude levels and vegetation types. Higher proportion of tsetse flies was caught in the riverine vegetation type followed by savanna and bush areas. Blood samples from 561 randomly selected cattle of both sex and different age groups were collected and examined with conventional haematological and parasitological techniques. Out of the total examined animals, 74 (13.19%) cattle were infected with trypanosomes. Most of the infections were due to Trypanosomacongolense (78.37%) followed by Trypanosoma vivax (12.13%), mixed infections of T. congolense and T. vivax (8.1%) and the rest were Trypanosoma brucei (1.35%). There was no statistically significant difference (P > 0.05) in infection between male and female, and altitude levels. Mean packed cell volume (PCV) value of parasitaemic and aparasitaemic animals was significantly (P < 0.05) different. Diagnosis of trypanosomosis in tsetse or domestic livestock is a basic requirement for epidemiological studies as well as for planning and implementing control operations. Therefore, the results of this study should be used to define the strategy of disease control in places where tsetse and trypanosomosis challenge were reported. Key words: Cattle, apparent fly density, Glossina pallidipes, Infection rate,Trypanosomosis, Southern Ethiopia.

The effect of El Nino on trypanosome infection in cattle in Dar es Salaam, Tanzania: A retrospective field report

A retrospective study was carried out to assess the effect of El Nino on trypanosome infection in cattle. Trypanosome infection was monitored in free grazing dairy cattle before and after El Nino in Dar es Salaam. The study involved 49 smallholder dairy herds with a total of 570 dairy cattle. Trypanosomes were identified by microscopic examination of Giemsa- stained blood smears. The rate of trypanosome infection after El Nino in each location with figures before El Nino in brackets were 24.8% (8.0%) in Makongo juu, 28.0% (8.7%) in Madale, 35.6% (14.9%) in Bunju, and 0.5% (4.9%) in Beach areas. The results also indicated that cattle exposure to tsetse challenge was higher in high altitude parts of Dar es Salaam compared to low-lying areas after El Nino. The observation suggests that El Nino phenomenon influenced tsetse redistribution in many tsetse endemic areas and the increase in infection rate after El Nino was a result of increase in tsetse fly population. It is recommended that the effect of weather changes be taken into consideration when offering animal health and extension services on trypanosomosis control. Key words : Dar es Salaam, El Nino, dairy cattle, trypanosomes, tsetse fly

Field trial of a synthetic tsetse-repellent technology developed for the control of bovine trypanosomosis in Kenya

We conducted a field trial among Maasai cattle-keepers in Nkuruman and Nkineji areas of Kenya to evaluate the effectiveness of a synthetic tsetse-repellent technology developed for the control of trypanosomosis in cattle. The technology was a repellent (2-methoxy 4-methylphenol) emitted from dispensers attached to collars worn by cattle. Treatment was allocated at the herd level to ensure adequate protection of all the animals in a herd, with measurements of effectiveness conducted at the individual-animal level. The trial began in April 2005 and ran for 16 months including a baseline phase of 4 months. We recruited 12 herds in each area using a restricted random-sampling technique and distributed them equally into intervention (repellent) and control groups. Sample size was determined using a formal power calculation. Effectiveness or minimal worthwhile difference was defined as a 50% reduction in the incidence of trypanosome infection in the treated versus control group (effectiveness below which the technology was considered by experts as not viable compared to existing control techniques). All the animals in the recruited herds were screened monthly (buffy-coat technique) for trypanosome infections. The analysis followed the principle of intention-to-treat by which subjects are analysed according to their initial treatment assignment, regardless of the mechanical performance of the device. Crude and adjusted effects of the technology were 23% ( p < 0.001) and 18% ( p = 0.08) reduction in the infection incidence in the treatment compared to the control groups, respectively. The impact of the technology estimated in this study did not achieve the threshold of 50% reduction in the trypanosome infection incidence set a priori to indicate effectiveness ( p < 0.001). We therefore concluded that the prototype repellent technology package was not sufficiently effective in reducing trypanosome infection incidence under natural tsetse challenge to merit commercial development.

Experimental estimation of challenge of a natural population of &lt;i&gt;Glossina palpalis palpalis&lt;/i&gt; R-D (Diptera:Glossinidae) on cattle in the southern Guinea Savanna, Nigeria

The challenge posed by Glossina palpalis palpalis Robineau-Desvoidy 1830 to cattle was studied in a riverine forest of Manchok, Kaduna State, Nigeria. The challenge was estimated indirectly from entomological parameters using the number of flies biting the host and the proportion of flies that are potentially infective. Trypanosome infection rates of 26% and 24.3% were recorded in flies sampled from several sites in the dry and wet seasons. From the 134 flies that landed to bite, it was estimated that each animal received an estimated 11 and 15 mean bites per day in the dry and wet season respectively out of which approximately 3 and 4 harbour infections. This means that each animal host received an estimated total infective bite of about 15 (range 0.5-4.1/hr) and 19 (range 0.9-6.6/hr) during the dry and wet seasons, equivalent to 2.96 and 3.8 infective bites per day. Of the estimated infective bites, 12.6 and 2.2 were due to T. vivax Ziemann 1905 and T. congolense Boaden 1904 received during the dry season while 17.3 and 1.5 were received during the wet season. Activity of flies started at 09.00hr during the wet season and one hour later during the dry season. For both seasons, diurnal activity was less pronounced in the early morning (06.00-11.00hr) than mid (11.00-15.00hr) and late afternoon (15.00-18.00hr), and so was the number of potentially infective bites. The number of potentially infective flies feeding per day (06.00-18.00hr) was higher and more consistent during the wet season than in the dry season but the difference was not significant (P>0.50).The results suggest a high tsetse challenge in the area which is exacerbated by several factors including the synchronized activity of the flies and grazing herds, frequency of visit to riverine habitats of the vector and duration of contact between vector and host. Key words: Tsetse fly challenge, Trypanosoma vivax, T. congolense, cattle, Nigeria

Evaluation of the Cost-Effectiveness of Pyramidal, Modified Pyramidal and Monoscreen Traps for the Control of the Tsetse Fly,Glossina fuscipes fuscipes, in Uganda

Several trap designs have been used for sampling and control of the tsetse fly, Glossina fuscipes fuscipes, Newstead (Diptera: Glossinidae) based on preferences of individual researchers and program managers with little understanding of the comparative efficiency and cost-effectiveness of trap designs. This study was carried out to evaluate the cost-effectiveness of four commonly used trap designs: monoscreen, modified pyramidal and pyramidal, relative to the standard biconical trap. The study was performed under high tsetse challenge on Buvuma Island, Lake Victoria, Uganda, using a 4 × 4 Latin square design replicated 3 times, so as to separate the trap positions and day effects from the treatment effect. A total of 12 trap positions were tested over 4 days. The monoscreen trap caught significantly higher numbers of G. f. fuscipes (P<0.05) followed by biconical, modified pyramidal and pyramidal traps. Analysis of variance showed that treatment factor was a highly significant source of variation in the data. The index of increase in trap catches relative biconical were O.60 (pyramidal), 0.68 (modified pyramidal) and 1.25 (monoscreen). The monoscreen trap was cheaper (US$ 2.61) and required less material to construct than pyramidal trap (US$ 3.48), biconical and the modified pyramidal traps (US$ 4.06 each). Based on the number of flies caught per meter of material, the monoscreen trap proved to be the most cost-effective (232 flies/m) followed by the biconical trap (185 flies/m). The modified pyramidal and the pyramidal traps caught 112 and 125 flies/m, respectively.

Heterogeneity in the trypanosomosis incidence in Zebu cattle of different ages and sex on the plateau of eastern Zambia

On the plateau of eastern Zambia, trypanosomosis is endemic. Glossina morsitans morsitans Westwood (Diptera: Glossinidae), the only tsetse species present, is almost entirely dependent on livestock as its source of food with cattle being the most preferred host. To determine if tsetse challenge is distributed equally over the various age categories and sexes within a cattle herd, a longitudinal study of trypanosomosis incidence was conducted during the rainy season. A total of 354 head of cattle consisting of 40% oxen, 30% cows, 15% young stock, 13% calves and 2% bulls were sampled for three consecutive months and their infection statuses determined using the PCR–RFLP technique as diagnostic method. Results indicated that there were significant differences (P<0.001) in the proportion of infected animals between the various categories. In oxen, the risk of infection was 5.6 times higher than in calves. Those results suggest heterogeneity in the challenge by tsetse flies and are in line with entomological observations on the feeding preference of tsetse on cattle. The implications of these results for the control of trypanosomosis in Eastern Province and other epidemiologically related areas are discussed.

Response of four indigenous cattle breeds to natural tsetse and trypanosomosis challenge in the Ghibe valley of Ethiopia

A comparative study on the response of four indigenous cattle breeds of Ethiopia, namely Abigar, Horro, Sheko and Gurage, to natural challenge of trypanosomosis in the Tolley–Gullele area of the Ghibe valley has been undertaken from August 2000 until August 2004. Fifty female yearlings each of Horro, Sheko and Abigar and 31 of the Gurage were purchased from their natural habitats and introduced in to medium to high tsetse–trypanosomosis challenge area of the Ghibe valley. While the natural habitats of first three breeds are naturally infested with tsetse flies and trypanosomosis, that of the Gurage is known to be very minimal, if any, and hence the Gurage breed was used in this study as the known susceptible breed. During the study animal health, production performance and tsetse fly situation were monitored monthly. The Sheko breed has manifested very significantly ( p < 0.001) high overall average packed cell volume (PCV) values (25%) compared to that of Abigar (24%), Horro (23%) and Gurage (22%). It also had the lowest mean trypanosome prevalence rate of 9% against 23% of Horro, 26% of Abigar and 27% of Gurage, and the least number of Berenil ® treatments (1.36) compared to Abigar (4.0), Horro (4.6) and Gurage (6.7). While the Abigar manifested high sensitivity and frequent death to PCV depression, the Horro showed strong resilience to PCV depression and better response to Berenil ® treatment assistance. At this stage the Sheko breed was also found to be equal to the other breeds in its reproductive performance. These results need to be substantiated with further in-depth investigation including immune response, animal behavior and environmental influences.

Parasitoses des chèvres Naines de l’Afrique de l’Ouest et de ses croisements avec la race Saanen dans un système d’agriculture zéro-pâturage en Gambie

L’étude a concerné l’élevage de 20 chèvres Naines de l’Afrique de l’Ouest (NAO) et 15 croisements Saanen x NAO au sein d’un système d’agriculture zéro-pâturage intensif dans une zone peu à moyennement infestée de mouches tsé-tsé en Gambie. Pendant une période d’une année, des échantillons ont été prélevés mensuellement pour déterminer le nombre d’oeufs d’helminthes, le nombre d’oocystes de coccidies par gramme de matières fécales, les valeurs de l’hématocrite et les trypanosomoses des chèvres. Des nombres élevés d’oocystes ont été trouvés pendant la période de septembre à décembre, entraînant une mortalité présevrage de 20 p. 100 chez les deux races. Les animaux ont été modérément infestés par les helminthes du milieu de la saison des pluies jusqu’au début de la saison sèche. Des trypanosomoses n’ont été détectées ni chez les NAO ni chez les chèvres croisées lors de l’utilisation de la technique du buffy coat. Les poids moyens à la naissance des chevreaux et des NAO ont été respectivement de 2,4 et 2,0 kg. Le taux de croissance des chevreaux croisés a été significativement plus élevé que celui des chevreaux de race locale. Les taux de croissance présevrage des chevreaux croisés et des NAO ont été respectivement de 114,75 et 65,57 g/jour, tandis que les taux de croissance postsevrage ont été de 58,82 et 36,41 g/jour. Le taux de croissance rapide des chèvres croisées comparé à celui des NAO indique que l’élevage de croisements Saanen x NAO dans un système zéropâturage peut accroître la productivité. Une hygiène stricte dans les abris des chèvres est cependant indispensable pour éviter l’apparition de foyers de coccidiose.

TRANSITION MODELS TO ASSESS RISK FACTORS FOR NEW AND PERSISTENT TRYPANOSOME INFECTIONS IN CATTLE—ANALYSIS OF LONGITUDINAL DATA FROM THE GHIBE VALLEY, SOUTHWEST ETHIOPIA

The objective of this study was to apply transition models to distinguish between factors associated with both incident and persistent trypanosome infections. Data collected from 1561 cattle were analyzed from a long-term study involving 8 herds in which both trypanosome infections (a total of 56,931 cattle sampling-months) and tsetse (Glossina spp.) challenge were monitored monthly from March 1986 to March 1998. Both pour-on and insecticide-target tsetse control programs and mass treatment with diminazene aceturate before tsetse control were associated with significant decreases in both incidence and persistence of trypanosome infection relative to noncontrol periods, as were seasonal and sex effects. The magnitudes of the effects were, however, often different for new and persistent infections. For persistence of infection, there were 2 trends. In general, the duration of infection increased during the study, despite the regular treatment with diminazene aceturate. The transition model had 2 major benefits. The first was to identify an increasing duration of infections with time, taking into account other factors associated with increasing infection risk. The second was to highlight different patterns in the effects of certain factors on new and persistent trypanosome infections.

Differences in susceptibility to trypanosome infection between Nkedi Zebu and Ankole cattle, under field conditions in Uganda

A cross-sectional study was conducted in tsetse-infested areas of Soroti district in Uganda, with the aim of assessing the response of the Nkedi Zebu and Ankole breeds of cattle to trypanosome infection. Overall, 1215 Nkedi Zebu and 260 Ankole cattle kept under similar levels of tsetse challenge were examined for trypanosome infection, using the Buffy-coat technique and haematocrit centrifugation, and had their packed-cell volumes (PCV) measured. As expected, the infected cattle, whether of the Nkedi Zebu (26.7% v. 29.6%; P < 0.05) or Ankole breeds (24.9% v. 29.1%; P < 0.05), had significantly lower mean PCV than the uninfected. In the Nkedi Zebu cattle, the prevalence of trypanosome infection was lower (7.9% v. 10.8%; P > 0.05) and the overall mean PCV was significantly higher (29.4% v. 28.7%; P < 0.05) than in the Ankole. Compared with the Ankole, Nkedi Zebu cattle appear to be less susceptible to (detectable) trypanosome infection and to the trypanosome-attributable lowering of their PCV.

Evaluation of isometamidium levels in the serum of sheep and goats after prophylactic treatment against trypanosomosis

Isometamidium chloride has been used for the control of trypanosomosis in animals for over 36 years, but recently there have been reports of prophylaxis failure under natural conditions. In this study, use of the drug for prophylactic purpose against trypanosomosis in small ruminants was investigated. Forty-two sheep and 44 goats were divided into four treatment groups. Groups 1 and 2 were treated with isometamidium chloride (Samorin, Rhone Merieux, Lyon, France) at 3-month intervals while groups 3 and 4 were used as controls. All the animals were exposed to natural tsetse challenge and monitored for serum isometamidium levels and anti-trypanosome antibodies. Seven days after drug administration, isometamidium levels were significantly higher in goats 13.7+/-0.07 ng/ml than in sheep 6.2+/-0.06 ng/ml. However, the elimination half-life in the sheep was 14.2+/-0.92 days and was significantly higher (P> 0.05) than that of the goats 12+/-0.5 days. This study established that isometamidium metabolism differs between sheep and goats and this difference may have important implications in high tsetse challenge areas.

Field studies of drug-resistant cattle trypanosomes in Kénédougou Province, Burkina Faso

Field studies were conducted to assess the occurrence of resistance to isometamidium chloride and diminazene aceturate in trypanosomes infecting cattle in Kénédougou Province of Burkina Faso. Forty-five of the 166 villages in Kénédougou were randomly sampled and visited to assess livestock numbers, trypanosomosis risk, and tsetse challenge. The proportion of cattle infections associated with drug-resistant trypanosomes was assessed in the nine villages with the highest trypanosome infection prevalence and one village with a confirmed history of drug-resistant infections. These studies showed that resistance to both isometamidium and diminazene was widespread. However, there was considerable variation between villages in drug-resistance parameters, with the proportion of treated cattle with trypanosome infections 3 months after isometamidium prophylaxis varying from 6.9 to 63.8% and the proportion of cattle having infections 2 weeks after treatment with diminazene varying from 0 to 36.8%. The demonstration of widespread resistance to both isometamidium and diminazene has important implications, as administration of trypanocides is the most commonly employed method to control trypanosomosis in this area.