This chapter discusses the epidemiology, transmission, pathology, pathogenesis, diagnosis, control and economic impact of Trypanosoma evansi and T. vivax infections in domestic livestock.

Deterministic models were employed to investigate the biology of Trypanosoma evansi infection in the Indonesian buffalo. Models were fitted to two age-structured data sets of infection. The Susceptible-Infected-Susceptible (SIS) model was the best supported description of this infection, although the results of the analysis depended on the serological test used; the Tr7 Ag-ELISA was judged the most reliable indicator of infection. Estimated forces of infection increase with age from 1.2 to 2.0 acquisitions per buffalo per year. The buffaloes would clear infection in an estimated mean time period of 16.8 months (95% CIs: 12.5-25.9 months) since acquisition, either by drug treatment by owners or self-cure. A general discussion on the role of immunity in protozoan infections includes consideration that the fitted SIS model would be consistent with strain-specific immunity. The model may become a useful tool for the evaluation of control programmes.

Sheep peripheral blood mononuclear cells and those depleted of CD8(+) T cells and/or monocytes were stimulated with polyclonal mitogens and specific antigens, and analysed by means of cell proliferation assay procedure to examine whether these cell populations are involved in Trypanosoma evansi-induced immunosuppression. The removal of CD8(+) T cells failed to normalize the proliferative responses of peripheral blood mononuclear cells from infected sheep to concanavalin A stimulation while the depletion of monocytes resulted in full and enhanced response, showing that macrophages are mainly responsible for the suppression. Although the depletion of CD8(+) T cells, monocytes or both restored the responses of the cells to lipopolysaccharide stimulation, the responsiveness of the undepleted cells to this mitogen was significantly higher from day 24 post infection (p<0.01). The results were discussed in relation to current known mechanisms of depressed lymphocyte proliferation in tsetse-transmitted African trypanosome infections.

The prevalence and incidence of Trypanosoma evansi infections in village buffaloes in Central Java were estimated using parasitological tests, two antigen-detection ELISAs (2G6 Ag-ELISA and Tr7 Ag-ELISA), an antibody-detection ELISA (IgG ELISA) and a card agglutination test (CATT). Of 2387 village buffaloes tested in five districts, 4% (95% confidence interval [CI]: 3%, 5%) were positive with the microhaematocrit test (MHCT), 58% (95% CI: 56%, 60%) were positive with the 2G6 Ag-ELISA and 70% (95% CI: 68%, 72%) were positive with the Tr7 Ag-ELISA. An increasing prevalence with age was found and the proportion of positive buffaloes was highest in the over 84 months-old age-group (68%) with the 2G6 Ag-ELISA and in the 37–60 months-old age-group (78%) with the Tr7 Ag-ELISA. Parasitaemic buffaloes were found in more than half of the villages visited. Corrected village-specific prevalence values obtained with the two Ag-ELISAs ranged from 0% to over 100%, and prevalence differed significantly (P[les ]0·0001) between villages in four of the five districts. Overall, 10% of buffaloes tested in markets were found to be parasitaemic and 39, 56 and 47% were found positive with the 2G6 Ag-ELISA, IgG ELISA and CATT, respectively. Incidence rates varied according to the test used and ranged from 0·22 (95% CI: 0·09, 0·44) to 0·44 (95% CI: 0·24, 0·76), per animal-year at risk, in two villages. The results highlight the importance of using validated diagnostic tests to obtain accurate estimates of prevalence and incidence. These parameters are needed, for example in mathematical models, for the development and evaluation of different control strategies for T. evansi infections in buffaloes.

Twenty-four percent of hog deer (Cervus porcinus) that ranged free on a farm in Samut Prakarn province, Thailand, died showing nervous signs between September 1997 and February 1998. The nervous signs shown by most of them included ataxis, paresis of hind limbs, lateral recumbency, excitation and convulsion. Six animals and one carcass were submitted for diagnosis at the National Institute of Animal Health, Bangkok. Trypanosoma evansi was detected in blood and cerebrospinal fluid of four and five animals, respectively. Antibodies to T. evansi were found in all the hog deer by indirect enzyme-linked immunosorbent assay. Histopathological observation revealed a generalised non-suppurative meningoencephalitis affecting the white and grey matter at all levels of the brain. Typically, there were broad perivascular cuffs of mononuclear inflammatory cells, including lymphocytes, and some Mott cells. No trypanosomes were found in any tissue examined by conventional histopathology. However, numerous T. evansi were demonstrated by streptavidine-biotin immunohistochemistry in neuropil and Virchow-Robin spaces of brain in three animals.

Two Ag-ELISAs, an IgG-specific antibody detection ELISA (IgG ELISA) and a card agglutination test (CATT) for the detection of Trypanasoma evansi infections in buffaloes in Indonesia, were compared. Diagnostic sensitivity estimates were obtained by testing sera from 139 Indonesian buffaloes which had been found to be infected by parasitological tests. Diagnostic specificity was estimated by testing sera from 263 buffaloes living in Australia. Response-operating characteristic curves were constructed, and optimal ELISA cut-off values, which minimized the number of false-negative and false-positive results, were chosen. The IgG ELISA had the highest sensitivity (89%) and the CATT had the highest specificity (100%). There was a significant difference between the sensitivities (71 and 81%), but not between the specificities (75 and 78%), of the two Ag-ELISAs. The four tests were further compared by calculation of post-test probabilities of infection for positive and negative test results using a range of prevalence values, and likelihood ratios. The results suggested that the CATT was the best test to 'rule-in' infection (i.e. the highest probability of infection in test-positive animals) and the IgG ELISA was the best test to 'rule-out' infection (i.e. the lowest probability of infection in test-negative animals).

The effects of Trypanosoma evansi on the proliferative responses of ovine peripheral blood leucocytes (PBL) were examined in in vitro cell culture systems. Sheep were vaccinated against pneumonic pasteurellosis with a monovalent Pasteurella haemolytica vaccine and then infected with T. evansi TREU 2143. From 1 week post-infection (p.i.), the PBL were separated and stimulated in cultures with either Concanavalin A (Con A), bacterial lipopolysaccharide (LPS), pasteurella antigen (P.ag), or homologous trypanosome antigen (T.ag). The proliferative responses of the cells to Con A and LPS were significantly (P < 0.001) suppressed by the infection. This suppression was associated with active infection, as treatment of the sheep with a trypanocide restored the proliferative ability of the cells to both mitogens. Similarly, active infection significantly (P < 0.001) suppressed specific responses to P.ag and T.ag but although treatment resulted in full specific proliferative responsiveness to the homologous trypanosome antigen, the same was not true of P.ag, in which the responsiveness of cells from uninfected vaccinated sheep to it were still significantly higher (P < 0.001) than those of cells from infected sheep.

The effects of Trypanosoma evansi on efferent lymphocyte phenotypes draining from a lymph node primed with Pasteurella haemolytica vaccine were studied in sheep. The prefemoral efferent lymphatic ducts of the infected sheep along with those of two uninfected sheep were surgically cannulated. Lymph was collected and lymphocytes recovered from it analysed by two‐colour indirect immunofluorescence staining and cytofluoremetry in a fluorescence activated cell analyser (FACSCAN). The study showed the appearance and persistence of T. evansi in the efferent lymph for a long period of time and the appearance of CD4+CD8+ (double positive, DP) T lymphocytes in the efferent lymph of infected animals. The infection also resulted in increases in CD5+ B cells in the prefemoral efferent lymph. In addition, there were decreases in the output of conventional B cells, CD5+ and CD4+ T cell subsets but large increases in CD8+ cells followed by terminal depletion of all cell subsets. In contrast, inoculation of sheep with pasteurella vaccine antigen alone produced little alterations in the proportions, but large increases in the numbers of all T cell subsets except that of CD8+ cells which also showed little variation; and there was a concurrent increase in the numbers and proportions of efferent B cells. In addition, the abnormal expression of DP and CD5+ B cells did not occur in the uninfected vaccinated sheep. It is concluded that these abnormal changes in the kinetics of efferent lymphocyte phenotypes are likely to play a role in the genesis of the generalized immunosuppression seen in trypanosome‐infected hosts.

The effects of Trypanosoma evansi on the cellular and humoral immune responses of sheep to Pasteurella haemolytica vaccine were studied. Peripheral blood lymphocytes (PBLs) from the sheep were analysed using single and double-colour indirect immunofluorescence staining and flow cytometry to monitor changes in circulating B and T cell subsets. Serum antibody responses were assayed using the enzyme-linked immunosorbent assay technique (ELISA), in addition to measuring local skin reactions at the site of vaccine administration. Results showed significant increases in circulating B cells in all sheep after the primary (p<0.01) and secondary (p<0.001) vaccinations although the increases were much more dramatic in the T. evansi-infected sheep. In addition, infection induced significant increases (p<0.004) both in proportions and numbers of CD5+ B cells with more than 70% of circulating B cells expressing the CD5 antigen and showed significant differences (p<0.01) from those of control sheep in which vaccination alone failed to induce similar increases. Also, infection resulted in significant decreases in CD5+ (p<0.003), CD4+ (p<0.03) and CD8+ (p<0.03) T cell subsets in contrast to their increases in all control animals after vaccination. Moreover, there were significant suppression of both local skin reaction (p<0.005) and serum Ig and IgG1 (p<0.001) antibody responses to the vaccine antigen.

ABSTRACT: The biological characteristics of isolates of T.evansi collected from buffalo in different provinces in North Vietnam was determined in terms of their sensitivity to drugs currently used in the treatment of trypanosomosis. Five isolates were collected from buffalo, cloned and then tested against Trypamidium, Samorine, Naganol and Veriben. All isolates were sensitive to Naganol and Veriben. An isolate from a buffalo in Ha bac province (Hb1) was the least sensitive with trypamidium at a CD80 > 128mg/kg, more than 8 times the CD 100 of the remining isolates (16mg/kg). An antigen‐detection enzyme immunoassay (Ag‐ELISA) based on a T.evansi‐specific monoclonal antibody was evaluated for its ability to detect infections with T.evansi in buffalo. The sensitivity of the Ag‐ELISA was 63% and the specificity 75%. The positive predictive value of this assay was too low to allow identification of individual infected animals on the results of a single test in the districts investigated. For definitive diagnosis, a serial testing protocol was used, where a more specific test, the card agglutination test (CATT) was used initially and any positive samples was then checked by the Ag‐ELISA.

A field study involving 309 horses was undertaken in the provinces of Arsi and Bale in the Ethiopian highlands to investigate the prevalence of Trypanosoma equiperdum infections using enzyme linked immunosorbent assays (ELISAs) for the detection of both trypanosomal antigen and antibody. Adult horses of both sexes were examined for clinical signs of T. equiperdum infection and serum samples were collected for the assays. One hundred and one horses showed the presence of trypanosomal antibodies in their serum and 70 animals showed typical clinical signs of dourine. Nineteen horses showed the presence of trypanosomal antigen. Eight horses were positive for both T. equiperdum antibody and antigen. Blood and genital washes from seven antigenaemic horses were inoculated into mice and rabbits in an attempt to isolate trypanosomes but none became infected.Statistical analysis of the results of the antibody assays indicated that there were significant differences in the distribution of serologically positive horses in the different clinical groupings, with seroprevalence increasing with the severity of the observed clinical signs (P < 0.001). There was also a positive correlation between the presence of circulating trypanosomal antigen and clinical evidence of infection, Although it was not possible to obtain direct parasitological evidence of infection, the results of the serological assays, together with the clinical signs of disease observed in many of the horses, provide strong circumstantial evidence that T. equiperdum occurs in Arsi and Bale provinces of Ethiopia. Furthermore, in view of the large number of horses in Ethiopia and the unrestricted movement of animals throughout the country it is likely that dourine may be more widespread in Ethiopia than is currently realised. The assays used show potential for diagnosis of dourine, but to be widely applied in field situations for the diagnosis and control of dourine in Africa they require further validation of their specificity and sensitivity. (C) 1997 Elsevier Science B.V.

The prefemoral efferent lymphatics of sheep infected with Trypanosoma evansi and inoculated with P. haemolytica vaccine and of those given only the vaccine, were surgically cannulated to study the effects of the infection on the total cellular output and output of blast cells from the node in response to the vaccine. T. evansi delayed and depressed the increases in total cell and lymphoblast outputs. In uninfected sheep, the total cellular output increased and peaked at more than twice the prevaccination values on days 4 and 5 after primary vaccination, but the increases were smaller and peaked on days 6 and 8 after primary vaccination in the infected sheep. The output of lymphoblasts mirrored the total cell output, though it was suppressed to a greater degree by T. evansi. The output of blasts peaked at more than 8 and 14 times the prevaccination values in the uninfected animals after primary and secondary (booster) vaccinations, respectively; but in infected animals, it peaked at twice the prevaccination values after the primary vaccination and showed no increase after booster vaccination until 11 days later. It is concluded that the inhibition of total and blast cell outputs by T. evansi may limit the early systemic dissemination of antigen-specific cells, thus playing a role in the induction of immunosuppression by the parasite.

Intradermal inoculation of sheep with culture-derived metacyclic forms of Trypanosoma congolense resulted in the development of localized skin reactions (chancres) and enlargement of the draining lymph nodes 7 days after infection. Changes in the expression of surface antigens of lymphocytes in lymph leaving the affected skin reactions and in the associated lymph nodes were monitored by cannulating the afferent and efferent lymphatic ducts. Trypanosomes appeared in afferent and efferent lymph 3 to 5 days after infection and persisted even as the chancres regressed. The cellular output in both afferent and efferent lymph increased markedly after the onset of parasitosis. Sequential analysis of the phenotypes of lymphocytes by immunofluorescent staining and flow cytometry revealed that in afferent lymph draining the chancre there was an early response which was due to an increase in T cells, particularly CD4+ and CD8+ cells; however, as the chancres-regressed there was an increase in lymphoblasts and surface immunoglobulin-bearing cells. In contrast, in the efferent lymph, the increase in lymphocytes was due predominantly to a higher number of cells bearing surface immunoglobulins.

Six susceptible Galana and five trypanotolerant Orma Boran (Bos indicus) cattle were infected experimentally with Trypanosoma vivax KETRI 2501 by cyclical transmission using Glossina morsitans morsitans during early and mid-pregnancy. Four pregnant animals, two of each Boran type were used as controls and remained uninfected throughout the study period. Three out of the six infected susceptible Galana Borans aborted, whilst one had a stillborn calf. None of the trypanotolerant Orma Boran cattle aborted and all carried their pregnancies to term. All control animals produced live calves at term. The mechanisms leading to disruption of reproductive function in susceptible Boran cattle were not clear but could involve a number of factors, including anaemia, weight loss and post-infection decline of plasma progesterone levels. It is concluded that infection with T. vivax disrupts maintenance of pregnancy in susceptible Galana Borans but does not affect maintenance of pregnancy in the Orma Boran, demonstrating their tolerance to infection with T. vivax.

Equine Veterinary EducationVolume 8, Issue S2 p. 9-12 Equine trypanosomiasis A. G. Luckins, A. G. Luckins Centre for Tropical Veterinary Medicine, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, Midlothian, Scotland. Biographical details: Currently a Senior Research Fellow at the Centre for Tropical Veterinary Medicine. Is working on the validation of immunoassays for control of T. evansi in buffalo and cattle in South-East Asia and participating in joint FAO/IAEA programme on improving the diagnosis and control of tsetse-transmitted trypanosomiasis in African livestock.Search for more papers by this author A. G. Luckins, A. G. Luckins Centre for Tropical Veterinary Medicine, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, Midlothian, Scotland. Biographical details: Currently a Senior Research Fellow at the Centre for Tropical Veterinary Medicine. Is working on the validation of immunoassays for control of T. evansi in buffalo and cattle in South-East Asia and participating in joint FAO/IAEA programme on improving the diagnosis and control of tsetse-transmitted trypanosomiasis in African livestock.Search for more papers by this author First published: September 1996 https://doi.org/10.1111/j.2042-3292.1996.tb01844.x AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume8, IssueS2September 1996Pages 9-12 RelatedInformation

A study was designed to examine the effect of infection with Trypanosoma vivax KETRI 2501 on the maintenance of pregnancy and postpartum return to reproductive function in susceptible Galana (n = 6) and trypano-tolerant Orma Boran (n = 6) heifers during the third trimester of pregnancy. Of the 12 study animals, 3 Galana and 3 Orma Boran heifers served as controls. One of 3 Galana heifers calved prematurely with subsequent perinatal loss. Of the 2 heifers that produced live calves, 1 calf died shortly after birth, while the other survived. Two of 3 Orma heifers calved prematurely and all 3 calves died shortly after birth. The 6 control heifers produced live calves at term, all of which survived. Infection with T. vivax during the third trimester of pregnancy delayed the resumption of ovarian activity after calving, with the Ormas taking a significantly (P < 0.05) shorter time from calving to ovulation. There was no clear evidence that premature birth was associated with pathological changes in reproductive organs. Results from this study demonstrated that infection with pathogenic T. vivax during late pregnancy influenced the outcome of pregnancy in both susceptible Galana and trypano-tolerant Orma Boran heifers, resulting in premature births, perinatal loss, retained placentae, low birth weights and a prolonged period to the onset of postpartum ovarian activity.

A study was undertaken to investigate the influence of trypanosomosis on the outcome of pregnancy in trypanotolerant Orma Boran (Bos indicus) exposed to natural tsetse challenge in an area of Kenya infested predominantly with Glossina pallidipes. Of 73 pregnant Orma heifers, 58 (79.5%) produced live calves at term, 13 (17.8%) aborted and 2 (2.7%) died of trypanosomosis. Of the 71 surviving animals, 22 (31%) were infected with Trypanosoma vivax , 21 (29.6%) T. congolense, and 26 (36.6%) had mixed infections with T. vivax and T. congolense. These results suggest that in areas of high trypanosomosis risk reproductive function is affected even in trypanotolerant cattle, and that both T. vivax and T. congolense can be responsible for the abortions observed in the field. It is suggested that maintenance of pregnancy in the face of trypanosome challenge was dependent on individual variation among the Orma cattle, but as challenge increased beyond the limits of effectiveness of trypanotolerance, disruption of pregnancy occurred.

In the presence of a trypanocidal drug, trypanosomes which have acquired resistance to that drug have an obvious selective advantage over their drug-sensitive counterparts. In the absence of the drug, the situation probably changes and drugresistant parasites are selected against, otherwise resistance wouldspread much faster than has been observed (Mutugi, 1993). In the present work, the relationship between growth rates of stocks of Trypanosoma evansi and their resistance to suramin was determined in rats. This was to investigate whether differential growth rates of suramin-resistant and sensitive trypanosomes could limit the spread of suramin resistance. One month old male Wistar albino rats weighing between 150 to 200 g were used. The suramin sensitivities of 3 cameline stocks of T. evansi were determined by titration experiments. KETRI 2454 and KETRI 2476 were resistant, in mice, to suramin at a dose rate of 0.005mg/kg but sensitive at 0-01 mg/kg. KETRI 3136 was resistant, in mice, to suramin at 160mg/kg. Two clones from each of stocks of KETR12454 and KETRI 2476 were also included in the study (Table I). By exposing trypanosomes to sub-curative suramin doses in mice, resistance to suramin had been induced in one of the clones from each stock, while the other was its unmodified parent. Thus, KETRI 2454 CL9 was a strain in which resistance was induced starting with KETRI 2454 CL1, a clone of the field isolate KETRI 2454; while KETRI 2476 CL22 was an induced resistant strain from KETRI 2476 CLI, a clone of KETRI 2476. Each stock was infected into groups of 5 rats by intraperitoneal (i/p) injection with approximately 1 x 106 trypanosomes and the onset of parasitaemia in each rat was determined using the haematocrit centrifugation technique (Woo, 1970). Starting the following day, the rats were bled 5 times daily (at 09.00 h, 11.00 h, 13.00 h, 15.00 h and 17.00 h) for 9 days. Parasitaemia was determined by haemocytometer counting. Growth curves of each stock of trypanosomes were obtained by plotting the log trypanosome numbers against the time of bleeding and the increase of parasitaemia on the first day of the first parasitaemic wave was calculated, on the assumption that it would be the time when parasites had least interference from the host's immune response. In each rat, the growth rate of trypanosomes in terms of generation time was calculated using the formula of Topley and Wilson (1955). The mean generation time of each trypanosome stock was then determined and compared using either the Kruskal-Wallis or Mann-Whitney tests. A number of major assumptions were made; namely, that parasites were evenly distributed in the blood, all trypanosomes were capable of multiplying, trypanosome death rate was constant in all the stocks and errors of trypanosome counting were constant.