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PubMed2003

Evaluation of a polymerase chain reaction assay for the diagnosis of bovine trypanosomiasis and epidemiological surveillance in Bolivia.

BACKGROUND: Sporadic outbreaks of bovine trypanosomiasis have been reported in Bolivia since 1996 when T. vivax and T. evansi were identified for the first time by parasitological means. However, comprehensive epidemiological information concerning T. vivax and T. evansi in the country is lacking. Current parasitological and serological diagnostic methods for trypanosomiasis have important limitations either in their sensitivity or specificity, which can result in unreliable data when applied in epidemiological studies. PCR assays are a recently developed procedure that might help to overcome the constraints of parasitological and serological assays. Therefore, the objective of this study was to evaluate PCR assays as a diagnostic tool for epidemiological studies in Bolivia. RESULTS: PCR assays for diagnosis of trypanosome infection in cattle were evaluated for their ability to detect trypanosome DNA in blood spots samples collected from cattle in four different provinces from the Bolivian lowlands and the results compared with those obtained with standard parasitological Micro Haematocrit Centrifugation Technique (MHCT) and stained smears and serological methods (Card Agglutination Test for T. evansi (CATT), and Antibody ELISAs for T. vivax and T. congolense). Kappa agreement analysis showed a significant agreement between PCR assays and results from parasitological methods but there was no agreement when PCR was compared with serological assays. Some samples from T. vivax smear positive animals were negative by PCR, therefore modifications to the PCR assay conditions were undertaken to try to improve agreement between PCR and parasitological assays. Changes in the template DNA concentration or the use of an alternative primer set resulted in improvements in the PCR detection rate, but not all the parasitologically positive samples were detected by PCR. Results from PCR assays for T. vivax and T. evansi were combined with results from parasitological and serological assays to provide information on prevalence rates for the four provinces from where the samples were obtained. CONCLUSION: The present study established evidence of the usefulness of PCR as diagnostic tool for epidemiological studies and confirmed that cattle trypanosomiasis appears to be endemic in several regions of the Bolivian lowlands.

Journal Article↗
PubMed1988

Prevalence of trypanosomiasis in cattle in south-west Zambia.

A trypanosomiasis survey was conducted in South-West Zambia. From a total of 3,346 cattle sampled 342 cattle showed a positive trypanosomiasis parasitaemia. During the survey trypanosome species and PCV values were also recorded. With simple statistical analysis populations with higher and lower prevalence rates were differentiated. The results indicated that the Kwando River Basin Tsetse Fly Belt and the Kafue River Basin Tsetse Fly Belt infested a larger area than originally assumed and that a link-up between both belts occurred or will occur in the near future.

Animals↗
PubMed1984

Tsetse and trypanosomiasis survey of Southern Darfur province, Sudan. II. Entomological aspects.

Atsetse survey of Southern Darfur province, Sudan showed that the distribution of the only species present, Glossina morsitans submorsitans, had not appreciably altered over 10 years. Fly populations are most dense south of the Wadi Umbelasha but light infestations are found in the woodlands north of this riverine system to a latitude of about 10 degrees 15' N. Data are given on host availability which is thought to be the major factor determining tsetse distribution. The relative importance of tsetse and of tabanids as transmitters of bovine trypanosomiasis in the province is discussed. The evidence indicates that tsetse are very much more important and that cattle are most at risk of contracting infections during their dry season southerly migrations to the tsetse belts especially during their "Rushash" migration at first rains. Possibilities of tsetse control are discussed but in the short term trypanosomiasis control is most likely best achieved by chemical prophylaxis/therapy of cattle at risk.

Animals↗
PubMed1992

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.

Animals↗
PubMed1985

African trypanosomiasis in cattle: working with nature's solution.

Both acquired and innate resistance to African trypanosomiasis can occur in cattle. The former raises the possibility of a vaccine against tsetsetransmitted metacyclic trypanosomes which have been shown to have a smaller repertoire of variable antigens than bloodstream parasites. The latter provides two further avenues of approach: firstly, trypanotolerant breeds are being increasingly exploited and improved by conventional management and breeding methods including embryo transfer; secondly, research is being carried out into the factors associated with their innate resistance, i.e., the control of trypanosome growth, the development of effective immune responses and resistance to anaemia. If the mechanisms underlying these factors are identified it might be possible by immunisation, by specific drug treatment or by transfection of appropriate genes to produce highly productive cattle resistant to trypanosomiasis.

Anemia↗
PubMed1997

The daily feeding rate of tsetse (Diptera: Glossinidae) on cattle at Galana Ranch, Kenya and comparison with trypanosomiasis incidence.

At Galana Ranch, south-eastern Kenya, for 2 days each month from January to May 1993. Glossina pallidipes and G. longipennis were sampled around a heifer for 30 min every hour from 06:00 to 19:00. There was a seasonal decline in tsetse abundance; estimates of the total number attracted to the heifer in 1 day ranged from 556 G. pallidipes in January to 0 in May and 122 G. longipennis in February to 27 in May. The number of tsetse estimated to have fed on the heifer in 1 day during peak months was 260 G. pallidipes and 15 G. longipennis. Trypanosome infection rates of tsetse, obtained from trapped flies, suggest that the heifer received 1.1 T. congolense and 2.2 T. vivax-infected bites per day in January but only 0.007 T. congolense and 0.047 T. vivax-infected bites per day in May. These predictions are compared with the observed incidence of trypanosomiasis in a nearby herd of cattle. There was a linear relationship between the estimated daily rate of infected flies feeding on the heifer and the incidence of trypanosomiasis the following month. The slope of this relationship suggests that the transmission efficiencies of T. congolense and T. vivax from tsetse to cattle are 0.84 and 2.36%, respectively, considerably lower than has been reported elsewhere. Possible reasons for this are discussed and it is suggested that previous estimates may be too high.

Animals↗
PubMed1988

A model of tsetse-transmitted animal trypanosomiasis.

The data needed to develop analytical models of trypanosomiasis transmission have become available only recently. By making some simplifying assumptions, models of the dynamics of the disease in vector, cattle and wild mammal populations can be constructed in order to determine criteria for successful disease control by mass and targetted chemotherapy, and by vector control. The heterogeneity in transmission due to tsetse fly feeding preferences and the variability of immunological characteristics among the vertebrate hosts account for differences in prevalence of Trypanosoma vivax and T. congolense, and also lead to an increase in the basic reproductive rates of the parasites and a corresponding decrease in the vector population density threshold for disease eradication or persistence. The long life-span of the vectors relative to the duration of the parasites' developmental period lead to high infection rates in the vector and high values of R0. The efficacy of chemotherapeutic regimes depends on the relationship between treatment rate and the duration of prophylaxis conferred by the drugs used. The model's predictions of the effects of vector control are shown to be in broad agreement with published field data for Mkwaja Ranch, Tanzania. Vector control programmes are frequently blighted by reinvasion, and the implications of this are discussed in terms of a model for fly immigration. With immigration of vectors, the disease is always endemic, though the infection rate in the fly population is modified by the effect of differential mortalities inside and outside the controlled area on cohorts of incubating flies. Sensitivity analysis of the model, using Monte-Carlo methods, enables an assessment of the relative importance of the parameters to be made. The results emphasize the need for studies of the wild animal reservoir to be carried out alongside entomological surveys. The relative accuracy with which field measurements need to be made in order to minimize the uncertainty in predictions of trypanosomiasis prevalence is discussed.

Animals↗
PubMed1992

Application of a monoclonal antibody-based antigen detection enzyme-linked immunosorbent assay (antigen ELISA) for field diagnosis of bovine trypanosomiasis at Nguruman, Kenya.

A monoclonal antibody-based, enzyme immunoassay (antigen ELISA) for the detection of species-specific invariant antigens of Trypanosoma congolense, T. vivax or T. brucei in the serum of infected animals was evaluated as a means of diagnosis using bovine field sera from a trypanosomiasis endemic area, Nguruman, Kenya. Circulating trypanosome antigens were detected in 126 (96.2%) of 131 serum samples from animals with parasitologically confirmed diagnosis: 74.8% were positive for antigens of two or three trypanosome species, while 21.4% tested positive for one trypanosome species. When 70 sera from animals (at Nguruman), which had tested negative for trypanosomes by the buffy coat technique, were tested, 35 (50.0%) of them were shown to be antigen-ELISA positive: 24 (34.3%) showing infection with a single species and 11 (15.7%) with mixed infections. The predominant trypanosome species diagnosed in the two herds by antigen ELISA was T. vivax, which was detected in 133 (82.6%) of the 161 sera that tested positive for antigens, followed by T. congolense in 122 (75.8%) sera, with 109 (67.7%) showing evidence of mixed infections with two or three trypanosome species. In single infections, T. vivax exceeded T. congolense by a ratio of 2:1, with T. brucei accounting for less than 1.0%. Evidence for the specificity of the test was provided by analysis of field sera from 100 cattle, from a trypanosomiasis-free area, infected with other haemoparasites (anaplasmosis, babesiosis and theileriosis), which all tested negative in the assay.

Animals↗
PubMed1993

The FAO/IAEA DGIS Coordinated research programmes on trypanosomiasis diagnosis and animal production in Africa.

During the period 1987-1992, Professor Dick Zwart played a key role in guiding the work of two African research networks established by the Joint FAO/IAEA Division and supported financially by the Netherlands Directorate General of Development Co-operation. These networks brought together staff from African institutes involved in the diagnosis and control of trypanosomiasis and in animal production, with scientists from International Agricultural Research Centres and other advanced research institutions in the Netherlands and elsewhere. Through this approach, the value of recently-developed immunoassay methods was assessed for diagnosing trypanosomiasis and monitoring control programmes, and similar methods were used to monitor animal productivity and ways of improving this on small-holder farms. Furthermore it strengthened the portion together with the functioning of the national agriculture research institutions. This paper outlines the main technical and other accomplishments of these networks.

Africa↗
PubMed1991

Control of tsetse and trypanosomiasis transmission in Uganda by applications of lambda-cyhalothrin.

The pyrethroid insecticide lambda-cyhalothrin was evaluated in field trials against Glossina f.fuscipes and sleeping sickness transmission in Iyolwa sub-county, Tororo District, Uganda. The insecticide was applied selectively to the resting-sites of tsetse, by bush-spraying, using 10% wettable powder (10WP) formulation at an application rate of 11.6 g a.i./ha over an area of 28 km2, or by a 2% Electrodyn formulation (2ED) applied at 0.9 g a.i./ha over 30 km2. In a third trial area of 32 km2, 215 pyramidal traps treated with lambda-cyhalothrin 100 mg/m2 were set. The best impact was obtained with 10WP lambda-cyhalothrin which eliminated tsetse within 1-2 months, whereas G.f.fuscipes persisted at very low density in part of the area treated with 2ED lambda-cyhalothrin. In both treated areas the numbers of human sleeping sickness cases fell to no more than one per month, compared with four to twelve per month previously. The overall rate of cattle trypanosomiasis (T.brucei and T.vivax) was also reduced slightly. Insecticide-treated traps remained fully effective for at least 6 months under field conditions and catches were reduced 20-90-fold. These results in the control of tsetse and trypanosomiasis transmission lead us to recommend lambda-cyhalothrin for tsetse control operations.

Aerosols↗
PubMed1990

Trypanotolerance in cattle and prospects for the control of trypanosomiasis by selective breeding.

Tsetse-transmitted trypanosomiasis is one of the major constraints on the expansion of the livestock and agricultural industries in Africa. The disease affects animals and man, with direct and indirect losses estimated in billions of dollars annually. Because of the phenomenon of antigenic variation, no vaccine is available. Current prophylactic efforts must rely on tsetse control by the use of insecticides and on trypanocidal drugs. However, recent advances in our knowledge of tsetse and trypanosome biology are offering hope for alternative methods of trapping tsetse, new drugs and even vaccination. Possibly of even greater significance is the increasing sense that Africa herself might be able to contribute to the resolution of this problem. Over a period of several thousand years, she has generated cattle, such as the taurine N'Dama and West African Shorthorn breeds of West and Central Africa, that are now known to possess a significant degree of innate resistance to trypanosomiasis and several other important infectious diseases. These cattle are extremely well adapted to the environment and are now recognised as having considerable production potential. The ability to resist the development of anaemia in the face of infection, as assessed by packed red cell volume percent (PCV), has been shown to be correlated with the capacity to be productive, thereby identifying regulation of PCV as a key trait of trypanotolerance. Thus, an estimate of the ability of an infected animal to maintain PCV, following either experimental or field infection, could be used as a method for identifying trypanotolerant individuals. This could provide a means of estimating trypanotolerance heritability, thereby permitting rational breeding programmes to be instituted. Africa may thus provide the answer.

Animals↗
PubMed1991

Laboratory diagnosis of trypanosomiasis.

Although African trypanosomiasis, or sleeping sickness, in humans was largely under control approximately 30 years ago, today most of the historical foci show an alarming increase in the number of cases, particularly those in East and Central Africa. This article describes the epidemiology, clinical features, and diagnostic techniques for both African and American trypanosomiasis.

Animals↗
PubMed1991

Comparative study of clinical signs, haematology and prevalence of trypanosomiasis in Holstein Friesian and White Fulani Zebu cattle exposed to natural infection in a rain forest zone of Nigeria.

A comparison of the symptomatology, haematology and prevalence of trypanosomiasis in Holstein Friesian and White Zebu cattle exposed to natural infections on a ranch in a rain forest zone of Nigeria is presented. 23 (44%) of the adult Friesians had trypanosome infections with a generally heavy parasitaemia. Infection was light in the Friesian calves and the Zebus with infection rates of 2 (6.9%) and 3 (15%) respectively. Trypanosoma vivax was the sole species encountered on the farm. There was a general unthrifty appearance in the adult Friesian herd as well as classical signs of trypanosomiasis. The Friesian calves and Zebus were generally in good conditions with an appearance of good health except one each of the infected animals which showed apparent symptoms of the disease. There was a marked reduction of the red cell values of the infected adult Friesian and Zebu cattle. The red cell values of the uninfected adult Friesians were equally depressed suggesting cryptic infections or that they were cured parasitologically by the recently administered trypanocide. The Friesian calves had normal red cell values for both the infected and uninfected. Leucocyte counts were generally high on the Farm and higher for the infected animals.

Animals↗
PubMed1985

Correlation of serum zinc levels with resistance of cattle to trypanosomiasis.

Zinc, copper and magnesium levels were determined by atomic absorption spectrophotometry in the serum of 32 cattle (Zebus and Baoulés) which were proven to be sensitive to African trypanosomiasis under field challenge and 45 cattle (Baoulés and Ndamas/Baoulés) which were proven to be resistant. Copper and magnesium levels were similar in all animals but zinc levels were higher in sensitive animals (1.50 ppm) than in resistant ones (1.10 ppm) (p less than 10(-5)); the reported normal levels of serum zinc is 1.00 ppm. These differences persisted on repeated measurements and whether individuals were infected with trypanosomes or not. Elevated levels of zinc depressed the stimulation of bovine T cells by trypanosomes in vitro and is reported to inhibit antigen presentation by macrophages. Zinc levels may be an influencial factor determining susceptibility or resistance of West African cattle to trypanosomiasis.

Animals↗
PubMed1987

Epidemiology of animal trypanosomiasis on a cattle ranch in Kilifi, Kenya.

A study of the epidemiology of animal trypanosomiasis was carried out on a 2500 ha cattle ranch, with a history of trypanosomiasis, in the Coast Province of Kenya in 1982. The tsetse survey on the ranch revealed one breeding focus of Glossina austeni in a thicket of approximately 50 ha. Trypanosomes were detected in 20% of the 46 dissected tsetse. During the study period of 9 months, 0.8% of the 3315 samples collected from 2300 Ayrshire X Sahiwal crossbred cattle were found infected with trypanosomes; 32% of 5909 samples collected from the same cattle had a packed cell volume (PCV) of 30% or less. Animals with a PCV of 30% or less were treated with a trypanocide (Berenil, Ethidium or Novidium). Antibody to trypanosomes was detected in 22.1% of the 343 sera collected from the cattle. A sentinel herd of 20 cattle was exposed for 182 days inside the tsetse infested thicket. All animals became infected with Trypanosoma congolense, on average after 53 days; they were subsequently treated with Berenil (6 mg/kg). A second, third and fourth T. congolense infection was diagnosed in 17, 11 and 1 animals, respectively. The cattle were treated similarly with Berenil after each of these infections. T. vivax and T. brucei were not diagnosed in the sentinel cattle. The results suggest that acquired immunity to T. congolense infection did not play a significant role in the sentinel cattle.

Animals↗
PubMed1986

Haematological observations on bovine trypanosomiasis of Holstein-Friesian breed.

Haematological investigation was conducted on 20 cases of bovine trypanosomiasis caused by Trypanosoma congolense and T. vivax in imported Holstein-Friesian cattle using standard techniques. Comparison of the results with the values obtained for clinically normal animals whose blood samples were consistently negative for trypanosomes indicated that natural bovine trypanosomiasis was associated with a significant (P less than 0.001) fall in haemoglobin concentration, packed cell volume and numbers of erythrocytes. Slight reduction in the number of leucocytes, eosinophils, monocytes and basophils was recorded. No significant change (P greater than 0.001) was observed in the number of lymphocytes and neutrophils between naturally infected and control Holstein-Friesian animals.

Animals↗
PubMed1969

Some current problems in the sero-immunology of trypanosomiasis in relation to the epidemiology and control of the disease.

The author draws attention to the need for accurate epidemiological information so that control programmes may be properly orientated and he emphasizes that we are still at a loss in this respect in the case of trypanosomiasis, as we still lack methods to recognize, among the assemblage of natural trypanosome populations with identical morphology, those populations that have the biological capabilities to produce disease in man and his domestic stock.Immunological approaches do, however, show some promise in this respect in that it is possible to relate the antigenic type to particular virulence characteristics, at least in mice. Nomenclature of trypanosome antigenic types requires to be improved and agreed so as to facilitate the integration of the work of different laboratories. Immunological methods have also improved disease survey, and tests such as immunofluorescence, and serum and cerebrospinal fluid IgM estimation, are now available. These tests may be applied conveniently on a large scale and to primitive populations. They powerfully complement the classical parasitological survey methods. Studies on the immunization of animals against trypanosomiasis have not yet yielded any method of practical application but are useful contributions to basic knowledge and have indicated areas in need of special investigation-such as the variety of antigenic types of the main pathogenic trypanosome species circulating in given areas of Africa, the stability of this "spectrum" of antigenic types in time, and the range of distribution in Africa of particular antigenic types.

Africa↗
PubMed1983

African trypanosomiasis in the United States.

African trypanosomiasis of the Rhodesian variety occurred in an American who recently traveled to Tanzania. Skin findings included a fluctuant, indurated, tsetse-fly bite site (chancre) and a fleeting, erythematous, macular eruption. The diagnosis was confirmed by the presence of the organism in peripheral blood smears. The patient's condition responded to intravenous suramin. African trypanosomiasis should be included in the differential diagnosis of patients who have visited areas where this disease is endemic, and in whom the appropriate skin findings are present.

Africa↗