Factors associated with persistence of African animal trypanosomiasis in Lango subregion,northern Uganda

African animal trypanosomiasis (AAT) continues to inflict heavy losses on livestock production especially cattle in terms of decreased production and productivity in Uganda. AAT is a disease complex caused by tsetse fly-transmitted Trypanosoma brucei brucei, Trypanosoma brucei rhodesiense, Trypanosoma congolense, and Trypanosoma vivax. The disease is most important in cattle but also known to cause serious losses in pigs, camels, goats, and sheep. Several control measures including live bait technology, mass treatment of cattle with trypanocidal drugs, and deployment of tsetse traps have been used in the past 10 years, but the problem still persists in some areas. This necessitated an exploration of the factors associated with continued trypanosome infections in cattle, which are also known reservoirs for the zoonotic trypanosomiasis. A structured questionnaire was administered to 286 animal owners from 20 villages purposively selected from Lira, Kole, and Alebtong districts of Lango subregion to obtain information on the factors associated with persistence of infection. Over 50% of the respondents reported trypanosomiasis as a major challenge to their livestock. Land ownership (P = 0.029), type of livestock kept (P = 0.000), disease control strategy employed (P = 0.000), source of drugs (P = 0.046), and drug preparation (P = 0.017) were associated with persistent AAT infection. We recommend continued farmer sensitization on the threat of AAT and the available prevention and control options. The use of isometamidium chloride for prophylaxis against trypanosomiasis is highly recommended. There is also a need to foster qualified private veterinary drug supply in the region.

     

A comparative longitudinal study of bovine trypanosomiasis in tsetse-free and tsetse-infested zones of the Amhara Region, northwest Ethiopia

A study was conducted to determine the incidence of trypanosome infections in cattle in tsetse-free and tsetse-infested zones of the Amhara Region of northwest Ethiopia. A total of six sentinel herds were established and the cattle observed during a period of 8 consecutive months. The prevalence of seropositive cattle was high in both the tsetse-free and tsetse-infested zones. The average monthly incidence of trypanosome infection, determined using molecular diagnostic tools, was 20.9% and 25.7% in the tsetse-free and the tsetse-infested zones, respectively. In the tsetse-free, Trypanosoma vivax was responsible for 90.9% of the cattle trypanosome infections. In the tsetse-infested zone, Trypanosoma congolense and T. vivax contributed almost equally to the trypanosome infections in cattle. Trypanosome infection, regardless of species, resulted in anaemia as evidenced by a significant decrease in the packed cell volume of the infected animal. The outcome of this longitudinal study suggests that control of trypanosomiasis in the Amhara Region cannot be achieved by tsetse control alone. Supplemental measures to include drug therapy and biting fly control are discussed.     

Prevalence and source of trypanosome infections in field-captured vector flies (Glossina pallidipes) in southeastern Zambia

The prevalence of trypanosome infections in tsetse flies, Glossina pallidipes, collected from Chiawa and Chakwenga in Zambia with endemic trypanosomosis was assessed by polymerase chain reaction (PCR). Out of the 550 G. pallidipes, 58 (10.5%) flies were found to harbor trypanosome DNA. Infection rates of tsetse with Trypanosoma vivax universal, Trypanosoma congolense savannah, T. congolense forest and T. congolense kilifi were 4.2% (23/550), 4.7% (26/550), 1.1% (6/550) and 1.6% (9/550), respectively. To determine the mammalian hosts of T. congolense and T. vivax infections from the tsetse flies, mammalian mitochondrion DNA of blood meal in these flies were analyzed by PCR and subsequent gene sequence analysis of the amplicons. Sequence analysis showed the presence of cytochrome b gene (cyt b) of 7 different mammalian species such as human, elephant, buffalo, goat, warthog, greater kudu and cattle. Goats which were main livestock in these areas were further examined to know the extent of its contribution in spreading the infection. We examined the prevalence of trypanosome infections in the domestic goat population in 6 settlements in Chiawa alone. Of the 86 goats sampled, 4 (4.6%), 5 (5.8%), 4 (4.6%) and 4 (4.6%) were positive for T. vivax universal, T. congolense savannah, forest and kilifi, respectively. These findings showed that the host-source of trypanosome infections in vector fly give a vital information about spread of infection. The result of this study will certainly contribute in elucidating more the epidemiology of trypanosomosis.     

The transmissibility of Trypanosoma congolense seems to be associated with its level of resistance to isometamidium chloride

In large parts of Africa the control of livestock trypanosomiasis relies on the use of trypanocidal drugs. Resistance against the available compounds is developing rapidly in the trypanosome population. The effect of the development of drug resistance on the fitness of the trypanosome is not well known. To determine the effect of the development of resistance to isometamidium chloride on the trypanosome's transmissibility, transmission experiments were conducted. Use was made of three isogenic clones of Trypanosoma congolense with different susceptibility to the drug. The infection rate in Glossina morsitans morsitans differed significantly between clones and was significantly higher in tsetse flies infected with the T. congolense clone with the highest level of drug resistance.     

Prevalence and incidence of bovine trypanosomosis on the Adamaoua plateau in Cameroon 10 years after the tsetse eradication campaign

Between March 2004 and February 2005, the monthly incidence of trypanosome infections was measured in cattle from nine sentinel herds in the Adamaoua province of Cameroon. Three herds of 20 cattle each were kept on the plateau which has been cleared from tsetse flies about 10 years ago, three other herds were grazing in the tsetse infested valley whereas the last three were herded in the buffer zone. The cross-sectional study showed that the initial trypanosomosis prevalence was 1.8, 5.2 and 2.0% on the plateau, in the buffer zone and the valley, respectively. During the longitudinal study, the trypanosomosis incidence was high in the valley (3.7-20%) and the buffer zone (1.8-13.4%), whereas it was significantly lower (0-2.1%) on the plateau. Tsetse flies, mainly Glossina morsitans submorsitans and a few G. tachinoides, were caught in the valley and the buffer zone, but none on the plateau. The data indicate a low trypanosomosis risk on the plateau. Further entomological studies, however, are required to clarify the origin of the trypanosome infections on the plateau.     

Susceptibility of buffaloes, cattle and goats to infection with different stocks of Trypanosoma vivax transmitted by Glossina morsitans centralis

A comparison was made of the susceptibility of buffaloes, cattle and goats to infection with Trypanosoma vivax transmitted either by Glossina morsitans centralis or by syringe inoculation. Three different isolates of T vivax (two from East Africa, one from West Africa) were used to compare skin reactions, parasitaemia, anaemia and the development of trypanosome-specific antibodies in buffaloes, cattle and goats. African buffaloes reared in captivity in an area free from trypanosomiasis proved to be highly resistant to infection with the three stocks of T vivax tested, irrespective of whether infection was by tsetse transmitted metacyclic forms or by intradermal or intravenous inoculation of bloodstream forms of the parasite. The bites of 19 tsetse infected with a West African T vivax stock did not cause local skin reactions, detectable bloodstream infections or antibody responses in two buffaloes. Following the bites of 120 tsetse flies infected with the same stock, two different buffaloes showed no local skin reactions, but had detectable bloodstream infections without showing signs of anaemia. Cattle and goats infected in a similar way showed severe local inflammatory skin reactions, high levels of parasitaemia and severe anaemia. The two East African stocks of T vivax caused no local skin reactions and only a transient parasitaemia in buffaloes following tsetse-transmitted infection or intradermal inoculation of bloodstream forms. On the other hand, cattle and goats infected with the East African stocks showed high parasitaemias but local skin reactions only occurred in the goats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth and Mortality in Sheep and Goats under High Tsetse Challenge in Kenya

Trypanosomosis is a major impediment to livestock production and economic development in those areas of Africa where it is endemic. Although small ruminants appear to perform better than cattle in various agro-ecological zones, the importance of trypanosomosis has not been extensively investigated in these livestock. This study was designed to investigate the prevalence of trypanosomosis in sheep and goats in an endemic area and to evaluate the performance of different breeds under high tsetse challenge and the potential role of chemoprophylaxis in the control of the disease. The results showed that tsetse flies feed readily on small ruminants, and that these animals are susceptible to trypanosomosis. The Small East African goats acquired fewer infections than the Black Head Persian and Dorper sheep used in the study. In both sheep and goats, chemoprophylaxis with isometamidium chloride (Samorin, Rhone Merieux, Annecy, France) was protective, resulting in fewer infections and higher body weight gain. Trypanosomosis caused anaemia in both sheep and goats, and animals whose PCV fell below 15% rarely recovered, even with trypanocidal drug treatment. The peak transmission period was between 1 and 3 months after the peak tsetse fly density, which raises the possibility of effective strategic prophylaxis.     

The distribution and epidemiology of bovine trypanosomosis in Malawi

A survey to update the distribution and clarify the epidemiology of bovine trypanosomosis in Malawi was conducted between 1995-97. Use was made of parasitological and serological (anti-trypanosomal antibody-detection Enzyme-Linked Immunosorbent Assay (ELISA) diagnostic methods. Trypanosomal infections were detected in cattle sampled adjacent to known tsetse foci. The distribution of cattle with anti-trypanosomal antibodies indicated that the distribution of bovine trypanosomosis was more widespread than the parasitological prevalence data suggested. This is attributed to the seasonal movement of tsetse (mainly Glossina morsitans morsitans and G. pallidipes) from its prime habitat and the presence of localized foci of G. brevipalpis. The odour-baited, insecticide-treated, target barriers along the edge of Kasungu National Park and the Nkhotakota Game Reserve appeared to be effective in preventing tsetse from moving outside the game areas and contacting cattle. The anti-trypanosomal antibody-detection ELISA proved to be a useful tool in establishing the distribution of bovine trypanosomosis. Moreover, the distribution and prevalence of cattle with anti-trypanosomal antibodies was instrumental in clarifying the epidemiology of bovine trypanosomosis in Malawi. The anti-trypanosomal antibody-detection ELISA had high sensitivity in detecting Trypanosoma congolense infections. In parasitologically negative animals, the average packed cell volume was higher in those that had no anti-trypanosomal antibodies. The packed cell volume decreased with increasing antibody titre.     

Apparent lack of a domestic animal reservoir in Gambiense sleeping sickness in northwest Uganda

The role played by domestic animals in the transmission of gambiense Human African Trypanosomosis remains uncertain. Northwest Uganda is endemic for Trypanosoma brucei gambiense. Of the 3267 blood samples from domestic animals in four counties examined by hematocrit centrifugation technique (HCT), 210 (6.4%) were positive for trypanosomes. The prevalence of animal trypanosomosis was estimated at 13.8% in Terego County, 4.2% in East Moyo County, 3.1% in Koboko County, and zero in West Moyo County. The trypanosome infection rates varied from 0.2% in goats, 3.5% in dogs, 5.0% in sheep, 7.5% in cattle, to 15.5% in pigs. DNA was extracted from the blood samples by Chelex method, Sigma and Qiagen DNA extraction Kits. A total of 417(12.8%) DNA samples tested positive by polymerase chain reaction (PCR) using T. brucei species specific primers (TBR) indicating that the DNA was of Trypanozoon trypanosomes while 2850 (87.2%) samples were TBR-PCR negative. The T. brucei infection rates based on TBR-PCR were highest in pigs with 21.7%, followed by cattle (14.5%), dogs (12.4%), sheep (10.8%), and lowest in goats with 3.2%, which indicated that pigs were most bitten by infected tsetse than other domestic animals. TBR-PCR detected 6.3% more infected domestic animals that had been missed, and confirmed the 6.4% cases detected by HCT in the field. Statistical analysis done using one-way ANOVA Kruskal-Wallis test (Prism version 5.0) showed no significant difference in trypanosome infections among domestic animals using both HCT and TBR-PCR techniques in the different counties (Confidence Interval of 95%, p-values >0.05). All the 417 trypanosome DNA samples were negative by PCR using two sets of primers specific for the T. b. gambiense specific glycoprotein gene and serum resistance associated gene of T. b. rhodesiense, indicating that they were probably not from the two human infective trypanosomes. Polymerase chain reaction using primers based on ribosomal internal transcribed spacer-1 region (ITS-PCR) resolved the 417 DNA of trypanosome samples into 323 (77.5%) as single trypanosome infections due to T. brucei and 39 (9.4%) mixed infections but missed detecting 55 (13.1%) samples, possibly because of the low sensitivity of ITS-PCR as compared to TBR-PCR. The 31 mixed infections were due to T. brucei (T.b) and T. vivax (T.v); while 8 mixed infections were of T. congolense (T.c) and T. brucei but no mixed trypanosome infections with T. congolense, T. brucei, and T. vivax were detected. Statistical analysis done using one way ANOVA Kruskal-Wallis test (Prism version 5.0) to compare single and mixed trypanosome infections showed no significant difference in trypanosome infections due to single (T.v, T.b, T.c) and mixed (T.v+T.b; T.v+T.c; T.b+T.c; T.v+T.b+T.c) trypanosome species among domestic animals in the different counties using ITS-PCR technique (Confidence Interval of 95%, p-values >0.05). It was concluded that domestic animals in northwest Uganda were probably not reservoirs of T. b. gambiense and there was no infection, as yet, with T. b. rhodesiense parasites.     

内蒙古巴彦淖尔市畜禽寄生虫病调查

为了查清巴彦淖尔市辖区内畜禽寄生虫的感染、分布情况、流行与危害程度,提高防治效果,开展了本次畜禽寄生虫感染调查。调查采取生前临床检查、血液学检查、动物解剖、收集虫体、分类鉴定等方法,在全市7个旗、县、区,共66个乡镇选取羊386只(其中绵羊238只、山羊148只)、牛12头、骆驼8峰、猪11头、马驴8匹、鸡16只、兔10只,于实验室内解剖收集虫体,进行分类鉴定。调查结果显示,羊感染内外寄生虫53个种,牛、骆驼26个种,马属动物39个种,猪8个种,鸡5个种,兔7个种;畜禽寄生虫病在巴彦淖尔市较为普遍,感染率较高,危害也较为严重。本次调查不仅为我市进一步防治畜禽寄生虫病提供了依据,而且也对其他地区防治寄生虫病及寄生虫感染具有参考价值和指导作用。     

Endemic type of animal trypanosomiasis is not associated with lower genotype variability of Trypanosoma congolense isolates circulating in livestock

In order to verify whether the low impact on livestock production in endemic areas is related to a low number of trypanosome strains circulating in livestock, 37 Trypanosoma congolense isolates collected from cattle in 11 sites in an endemic trypanosomiasis area in Eastern Zambia were characterised for genotype variability using a modified amplified fragment length polymorphism technique (AFLP). Isolates were further cloned to evaluate the occurrence of mixed infections in individuals. The results obtained revealed a high genotype diversity (94.6%) among these isolates. Apart from one site, all isolates gave different AFLP profiles in each of the sites. When clones were compared, three (8%) of the 37 isolates had mixed infections. These results indicate the circulation of a high number of strains in this trypanosomiasis endemic area despite the low impact the disease has on livestock production.     

Methods for the rapid appraisal of African animal trypanosomosis in the Gambia.

A technique for the rapid field assessment of African animal trypanosomosis (AAT) was developed during studies in the Gambia. This involved gathering indigenous information from rapid-appraisal questionnaires addressed to local informants, the results of single tsetse surveys and evaluations of the prevalence of trypanosome infections in village cattle. Local informants included livestock owners and herdsmen and trained personnel such as livestock assistants. The answers to the questionnaires were weighted in order to translate them into semi-quantitative ranked estimates (zero, low, medium, high or very severe) of the severity of AAT problems. A similar ranking was also defined for tsetse and prevalence data in the Gambia. The three assessment methods generally gave complementary results leading to similar conclusions about the severity of tsetse-trypanosomosis problems in a survey area; inconsistencies usually suggested that additional information was needed. The rankings of AAT intensity were used to develop management guidelines for minimising the impact of AAT at different levels through control interventions or improved livestock management. The methodology was designed to provide reliable, up-to-date and cost-effective assessments of AAT problems. Emphasis was placed on the importance of the involvement, priorities and perceptions of village livestock owners and herdsmen in making these assessments.     

Tsetse challenge, trypanosome and helminth infection in relation to productivity of village Ndama cattle in Senegal

Data on tsetse fly, and on village Ndama cattle collected over a 4-year period in southern Senegal, were analysed. A total of 431 Ndama cattle in four herds of three villages in the Upper Casamance area of southern Senegal were monitored monthly. Glossina morsitans submorsitans and Glossina palpalis gambiensis are present in the study area. Mean tsetse apparent density was 5.4 flies/trap/day. Trypanosome (Trypanosoma congonlense and Trypanosoma vivax) infection rate in flies was 2.4 (s.e. 0.37)%. Tsetse challenge index was 17.3 (s.e. 4.18). Mean monthly trypanosome prevalence in cattle was 2.5 (s.e. 0.51)%. Highest trypanosome prevalence occurred during the dry season, and animals less than 1-year old were more frequently infected than older animals. The linear relationship between the log10+1 tsetse challenge and the arcsine of the trypanosome prevalence was significant only when mean monthly values of these variables over the 4-year period were used with tsetse challenge preceding infection rate by 3 months. Mean monthly prevalence of strongyle, Strongyloides spp., Toxocara spp. and coccidia were 34.4 (s.e. 0.60), 2.1 (s.e. 0.18), 1.2 (s.e. 0.45) and 15.6 (s.e. 0.47)%, respectively. Calf mortality rate at 1,6 and 12 months of age was 2.1 (s.e. 2.1), 5.2 (s.e. 2.8) and 12.2 (s.e. 3.3)%, respectively. Calving interval (584 s.e. 58 days) was not influenced by trypanosome status of the cow during lactation. Calving interval was shorter by 167 days when the calf died before 1 year of age in comparison to calving intervals for which the calf survived beyond one year. Live weight at birth, 6 and 12 months of age were 15.8 (s.e. 0.54), 48.1 (s.e. 2.56) and 71.1 (s.e. 5.44) kg, respectively. Mean lactation length, total and daily milk offtake were 389 (s.e. 16) days, 231 (s.e. 15) litres and 0.69 (s.e. 0.037) litres, respectively. Trypanosome infection during lactation did not have a significant effect on the amount of milk extracted for human consumption nor did trypanosome status affect calf growth.     

Estimation of tsetse challenge and its relationship with trypanosomosis incidence in cattle kept under pastoral production systems in Kenya

In an on-farm trial conducted amongst the Maasai pastoralists in Nkuruman and Nkineji areas of Kenya between April 2004 and August 2005 designed to evaluate the effectiveness of a synthetic tsetse repellent technology, we assessed the relationship between tsetse challenge and trypanosomosis incidence in cattle. Six villages were used in each area. Each of these villages had a sentinel cattle herd that was screened for trypanosomosis on monthly basis using buffy coat technique. Animals found infected at each sampling were treated with diminazene aceturate at 7 mg kg(-1) body weight. Treatments administered by the owners over the sampling intervals were recorded as well. Tsetse flies were trapped at the time of sampling using baited stationary traps and apparent tsetse density estimated as flies per trap per day (FTD). A fixed proportion (10%) of the flies was dissected and their infection status determined through microscopy. Blood meals were also collected from some of the flies and their sources identified using enzyme-linked immunosorbent assay (ELISA). Tsetse challenge was obtained as a product of tsetse density, trypanosome prevalence and the proportion of blood meals obtained from cattle. This variable was transformed using logarithmic function and fitted as an independent factor in a Poisson model that had trypanosomosis incidence in the sentinel cattle as the outcome of interest. The mean trypanosomosis incidence in the sentinel group of cattle was 7.2 and 10.2% in Nkuruman and Nkineji, respectively. Glossina pallidipes was the most prevalent tsetse species in Nkuruman while G. swynnertoni was prevalent in Nkineji. The proportions of tsetse that had mature infections in the respective areas were 0.6 and 4.2%. Most tsetse (28%) sampled in Nkuruman had blood meals from warthogs while most of those sampled in Nkineji (30%) had blood meals from cattle. A statistically significant association between tsetse challenge and trypanosomosis incidence was obtained only in Nkuruman when data was pooled and analyzed at the area but not at the village-level. In the later scenario, lagging tsetse challenge by 1 month improved the strength but not the significance of the association. These findings show that when the spatial unit of analysis in observational studies or on-farm trials is small, for instance a village, it may not be possible to demonstrate a statistically significant association between tsetse challenge and trypanosomosis incidence in livestock so as to effectively control for tsetse challenge.     

High prevalence of Trypanosoma brucei gambiense group 1 in pigs from the Fontem sleeping sickness focus in Cameroon

To understand the importance of domestic pigs in the epidemiology of human trypanosomiasis, PCR was used to identify trypanosome populations in 133 pigs from the Fontem sleeping sickness focus of Cameroon. The results from this study show that 73.7% (98/133) of pigs from the Fontem area carry at least one trypanosome species. Trypanosoma vivax, T. brucei s.l. and T. congolense forest were found in 34.6% (46/133), 40.0% (53/133) and 46.0% (61/133) of the pigs respectively. T. simiae and T. congolense savannah were not identified in these animals. The use of repeated DNA sequences detected T. b. gambiense group 1 in 14.8% (15/101) of the pigs. Such pigs can be possible reservoir hosts for T. b. gambiense group 1 and contribute to the maintenance of the disease in the area. Mixed infections were revealed in 35.3% (47/133) of the pigs. Furthermore, we observed that under natural conditions, 52.4% (11/21) of the pigs from the Fontem focus carry mixed infections with T. b. gambiense group 1. No significant difference was observed between the percentage of T. b. gambiense group 1 single and mixed infections, and between the prevalence of this trypanosome in pigs from villages with and without sleeping sickness patients.     

Seasonal prevalence of bovine trypanosomosis in a tsetse-infested zone and a tsetse-free zone of the Amhara Region, north-west Ethiopia

During a period of four consecutive years, trypanosomosis surveys were conducted in a tsetse-infested and tsetse-free area of the Amhara Region of north-west Ethiopia. In each study area randomly selected communal cattle were sampled and their blood was investigated using parasitological diagnostic methods. At the same time the population of biting flies was sampled. The monthly average prevalence of trypanosome infections in cattle did not differ significantly between study areas. In both study areas, the prevalence of trypanosome infections was highest during the long rainy season. Trypanosome infections were mainly due to Trypanosoma vivax and they significantly reduced the average packed cell volume and the body condition of the animals. The monthly prevalence of infection was correlated with the density of biting flies, such as Tabanidae and Stomoxys spp., in the preceding month suggesting an important role of mechanical transmission in the epidemiology of trypanosomosis in both areas.     

Impact of tsetse and trypanosomiasis control on cattle herd composition and calf growth and mortality at Arbaminch District (Southern Rift Valley, Ethiopia)

The effect of tsetse/trypanosomiasis control on cattle herd composition and growth and mortality of calves in tsetse controlled (by Southern Tsetse Eradication Project (STEP)) and uncontrolled blocks in southern Ethiopia was assessed. Structured questionnaire was used to interview 182 households to estimate cattle herd composition and calf mortality. Calves were bled to examine the presence of trypanosomes by the buffy coat technique. Forty NGU traps were deployed and fly catches determined. A case-control study was performed on 40 calves for 6?months to estimate calve growth parameters. Accordingly, the mean cattle herd size was lower in tsetse-controlled block than in the uncontrolled block, whereas the relative number of calves in a herd tend to be higher in the tsetse-controlled block (P?=?0.06). While there was no report of cattle mortality in tsetse-controlled block, 16.48?% of the respondents have lost calves in tsetse-uncontrolled block in 1?year time. The prevalence of trypanosome positive calves was 2.95?% for uncontrolled block but no positive case in tsetse-controlled block. The apparent densities of flies/trap/day in tsetse-uncontrolled block were 30-fold higher than in tsetse-controlled block (P?相似文献   

Protective efficacy of isometamidium chloride and diminazene aceturate against natural Trypanosoma brucei, Trypanosoma congolense and Trypanosoma vivax infections in cattle under a suppressed tsetse population in Uganda

The protective efficacy of isometamidium chloride (ISMM) and diminazene aceturate (DIM) against Trypanosoma brucei, Trypanosoma congolense and Trypanosoma vivax infections in cattle under a suppressed tsetse population was assessed in southeast Uganda. A total of 66 and 57 trypanosome-infected cattle were treated with ISMM and DIM, respectively together with 177 trypanosome-free animals not treated were followed for 12 months, checked every 4 weeks. There was no statistical difference in the mean time to infection with any trypanosome species in animals treated with ISMM or DIM. However, the mean time to trypanosome infection was significantly longer for treated animals than controls. The mean time to infection with each of the three trypanosome species differed significantly, with the average time to T. vivax infection the lowest, followed by T. congolense and then T. brucei. The protective efficacy of DIM was as good as that of ISMM; implying curative treatments against trypanosomosis are sufficient for combination with tsetse control. Isometamidium chloride or DIM had the highest impact on T. brucei and T. congolense infections in cattle.     

Estimation of trypanosomal status by the buffy coat technique and an antibody ELISA for assessment of the impact of trypanosomosis on health and productivity of N'Dama cattle in The Gambia

The buffy coat/dark ground phase contrast technique (BCT) and an indirect antibody enzyme immunoassay (ELISA) were employed to assess the trypanosomal status of 32 N'Dama cattle, aged 19-28 months, exposed to natural challenge of Glossina morsitans submorsitans and G. palpalis gambiensis. Prior to the start of the investigation animals experienced 9-16 months of tsetse challenge in the study area. Blood and corresponding serum samples were examined monthly for a period of 8 months for patent parasitaemia by BCT and presence of Trypanosoma vivax and T. congolense antibodies by ELISA. In the ELISA, the reactivity of sera to anti-trypanosomal antibodies was expressed in percent positivity (pp). Packed cell volumes (PCV) and body weights were also recorded monthly, and daily weight gain (DWG) computed to assess the impact of trypanosomal status on health and productivity. During the study period, the overall parasitaemic trypanosome prevalence was 3% (6/199), while the serological prevalence was 54.7% (109/199). Both diagnostic tests revealed a predominance of T. vivax over T. congolense infections in N'Dama cattle. Sensitivity of the immunoassay was 83.3%. In T. vivax-parasitaemic cattle, antibodies persisted for 4-6 months after the parasite was detected by BCT. A significantly higher overall mean PCV level was observed in blood samples obtained from cattle found, in any particular month, negative by BCT and ELISA, compared with those blood samples from animals responding serologically positively for anti-trypanosome antibodies. Likewise, mean DWG was significantly higher in cattle found negative for both tests in comparison to animals presenting detectable anti-trypanosome antibodies and those detected positive by both tests. A significant negative relationship was observed between pp values and PCV levels in animals seropositive for T. vivax and/or T. congolense. Similarly, a negative relationship was observed between DWGs and pp values. PCV levels were significantly positively correlated with DWGs. It was concluded that serological screening could provide useful information complementary to that obtained by the use of BCT not only to assess more accurately the trypanosomal status of cattle populations, but also to evaluate the effects of trypanosome infection on animal health and productivity and estimate the trypanosomosis risk.     

Evaluation of a preliminary title to protect zero-grazed dairy cattle with insecticide-treated mosquito netting in Western Kenya

The incidence of trypanosome infection was monitored in dairy cattle during a 6-month trial in Busia and Teso districts, western Kenya, to assess the efficacy of insecticide-treated netting for protection against tsetse flies. Frequently, the fragile netting did not last longer than 2 months because of destruction by strong wind or animal movements. Also, many farmers let their cattle graze freely outside the units during the day, despite technical advice, resulting in exposure of the free-ranging animals to habitats suitable for tsetse and thereby an increased risk of trypanosome infections. The trial groups thus comprised 34 animals from 11 dairy units that were continuously protected, and 153 animals from 46 dairy units that were partially protected. The control group consisted of 162 animals in 42 unprotected units. The phase-contrast buffy-coat technique was used for parasitological monitoring. The mean hazard rate for trypanosomes was significantly lower in protected cows, with a value of 0.007 as opposed to 0.02 for the control animals. Mean packed cell volumes (PCV) were significantly higher in protected cattle (29.7%) than in unprotected ones (27.6%). Farmers with protected animals also reported fewer nuisance flies and mosquitoes in their compounds.