Trypanosoma evansi in Indonesian buffaloes: evaluation of simple models of natural immunity to infection

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.

Effects of the depletion of CD8(+) T cells and monocytes on the proliferative responses of peripheral blood leucocytes from Trypanosoma evansi-infected sheep

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 occurrence of Trypanosoma evansi in buffaloes in Indonesia, estimated using various diagnostic tests

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 < or = 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.

Detection of Trypanosoma evansi in brains of the naturally infected hog deer by streptavidine-biotin immunohistochemistry

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.

Evaluation of antigen detection and antibody detection tests for Trypanosoma evansi infections of buffaloes in Indonesia

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).

Changes in peripheral blood lymphocyte subpopulations and parasite-specific antibody responses in Trypanosoma evansi infection of sheep

This paper reports on changes in the lymphocyte composition of the peripheral blood in sheep infected with Trypanosoma evansi. In addition, parasite-specific IgG1 and IgM antibody responses were monitored using a double-sandwich enzyme-linked immunosorbent assay (ELISA) technique. Eight sheep were infected with 2 x 10(6) T. evansi TREU 2143. The infection was characterised by chronicity and ended in self-cure in two of the sheep. These two sheep were designated group A, whereas the other six sheep, which remained parasitaemic until treated, were designated group B. Analysis of the peripheral blood lymphocytes (PBLs) by indirect immunofluorescence staining and flow cytometry revealed significant alterations in the numbers of T- and B-cell subsets detected in all infected sheep. In group A, whereas the numbers of CD8+ cells decreased, CD4+ cells showed marginal decreases, remaining at or above pre-infection figures and resulting in increase in the CD4:CD8 ratio. In group B, CD8+ cells showed few marginal decreases, being at or above pre-infection figures most of the time, whereas CD4+ cells decreased significantly from day 26 post infection (p.i.) such that the CD4:CD8 ratio decreased. Infection also resulted in significant increases (P < 0.001) as of day 26 p.i. in circulating B-cells in group B as shown by the numbers of sIg+, CD45R+, CD1+ and major histocompatibility complex (MHC) II+ cells. The increases, however, were moderate and biphasic in group A. T. evansi-specific IgM and IgG1 antibody isotypes were detected in all infected sheep, but their levels were significantly higher in group A than in group B (IgM P < 0.05; IgGI P < 0.01). In addition, although an initially higher level of IgM response was subsequently replaced by a higher level of IgG1 response in group A, this was never the case in group B until after drug treatment.

Adaptation and validation of antibody-ELISA using dried blood spots on filter paper for epidemiological surveys of tsetse-transmitted trypanosomosis in cattle

The indirect enzyme-linked immunosorbent assay (ELISA) for the detection of anti-trypanosomal antibodies in bovine serum was adapted for use with dried blood spots on filter paper. Absorbance (450 nm) results for samples were expressed as percent positivity, i.e. percentage of the median absorbance result of four replicates of the strong positive control serum. The antibody-ELISA was evaluated in Zambia for use in epidemiological surveys of the prevalence of tsetse-transmitted bovine trypanosomosis. Known negative samples (sera, n = 209; blood spots, n = 466) were obtained from cattle from closed herds in tsetse-free areas close to Lusaka. Known positive samples (sera, n = 367; blood spots, n = 278) were obtained from cattle in Zambia's Central, Lusaka and Eastern Provinces, diagnosed as being infected with Trypanosoma brucei, T. congolense, or T. vivax using the phase-contrast buffy-coat technique or Giemsa-stained thick and thin blood smears. For sera (at a cut-off value of 23.0% positivity) sensitivity and specificity were 86.1 and 95.2%, respectively. For bloodspots (at a cut-off value of 18.8% positivity) sensitivity and specificity were 96.8 and 95.7%, respectively. The implications of persistence of antibodies following treatment or self-cure are discussed.

Proliferative responses of peripheral blood leucocytes of sheep infected with Trypanosoma evansi

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.

Drug sensitivity of Trypanosoma evansi and the use of immunoassays in diagnosing infections with T. evansi in buffaloes in Vietnam

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 > 128 mg/kg, more than 8 times the CD 100 of the remaining isolates (16 mg/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.

Increase in CD5+ B cells and depression of immune responses in sheep infected with Trypanosoma evansi

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.

Induction of CD4+CD8+ double positive T cells and increase in CD5+ B cells in efferent lymph in sheep infected with Trypanosoma evansi

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 use of enzyme linked immunosorbent assays to investigate the prevalence of Trypanosoma equiperdum in Ethiopian horses

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 antibody assays indicated that there were significant differences in the distribution of serologically positive horses in the different clinical groupings, with seropositivity 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 validation of their specificity and sensitivity.

Effects of Trypanosoma evansi on the output of cells from a lymph node draining the site of Pasteurella haemolytica vaccine administration

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.

The effect of trypanosoma vivax infection on late pregnancy and postpartum return to cyclicity in boran cattle

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.

Haematological changes in sheep experimentally infected with Trypanosoma evansi

Sheep were infected with 2 x 10(6) Trypanosoma evansi TREU 2143 through the external jugular vein. The parasite kinetics as well as the effects on body temperature, packed cell volume (PCV), erythrocyte counts and total and differential white blood cell counts were monitored twice weekly for 3 months. The results showed that T. evansi produced a chronic form of the disease in sheep characterised by low-level and often cryptic parasitaemia, with self-cure occurring in two cases; mild anaemia as evidenced by decreases in PCV and erythrocyte counts; and significant (P < 0.02) leucocytosis by day 22 post infection (p.i.). The leucocytosis was a result of marked lymphocytosis whose significant rises (P < 0.02) parallelled the rises in total white blood cell (TWBC) counts. These changes were less obvious in the animals that underwent self-cure. We conclude that T. evansi produces pathological changes in the peripheral blood of sheep similar to those produced by its tsetse-transmitted counterparts. It would thus appear that the sheep/T. evansi model is suitable for long-term study of the immunopathology of pathogenic trypanosomes since the sheep is easily available, easy to handle and a natural host to all pathogenic trypanosomes.

The effect of trypanosomosis on pregnancy in trypanotolerant Orma Boran cattle

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.

The effect of experimental infection of Boran cattle in early and mid-pregnancy with Trypanosoma vivax

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 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.

Trypanosomosis research at the Centre for Tropical Veterinary Medicine (CTVM) 1970 to 1995

This review covers aspects of research work carried out on animal trypanosomes at the Centre for Tropical Veterinary Medicine (CTVM) during the last 25 years. The review covers work on antigenic variation, tissue culture, drug resistance, immunology, biochemistry and pathology of Trypanosoma brucei, T. congolense, T. gambiense and T. evansi. It is not intended as an exhaustive review of the subject but focuses on certain aspects of these areas which are presented in relation to work carried out within the broader scientific community.

Trypanosoma congolense infection in sheep: cellular phenotypes in lymph and lymph nodes associated with skin reactions

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.

Differences in cloning and sub-cloning success rates in four stocks of Trypanosoma evansi and variation in suramin resistance of the clones

Four Trypanosoma evansi stocks with sensitivity to suramin in mice ranging from 0.05 to 160 mg kg-1 were cloned and sub-cloned and the sensitivity of the clones determined. The results suggest that it is easier to clone and sub-clone trypanosome stocks which are sensitive to suramin than those that are resistant to the action of the drug. The clones obtained from the four stocks had sensitivities to suramin which were similar to or different from the parent stocks. These results are important in view of the development of resistance for, in the presence of suramin, these resistant yet heterogeneous populations would provide the material from which selective processes could operate. These observations also suggest that the maintenance and spread of suramin-resistant trypanosomes might be curtailed by their comparative inability to establish themselves in a new host.

Trypanosoma congolense infection in sheep: ultrastructural changes in the skin prior to development of local skin reactions

Events occurring in the skin of sheep prior to development of Trypanosoma congolense-induced local skin reactions (chancres) were studied using electron microscopy. Three days after infection, few trypanosomes were present in the dermal collagen. However, these parasites were more abundant 5 days after infection, and were also found in dermal lymphatics and in the connective tissue matrix between collagen bundles. Mast cells in the skin obtained 5 days after infection showed evidence of degranulation. These events may play a role during the induction phase of trypanosomal chancres.

Early stages of infection with Trypanosoma congolense: parasite kinetics and expression of metacyclic variable antigen types

Trypanosoma congolense develops in the skin of sheep at the site of inoculation of metacyclic trypanosomes, forming a chancre containing large numbers of parasites. By cannulating the afferent and efferent lymphatic ducts draining the skin and regional lymph node, the progressive development and migration of trypanosomes from the chancre was monitored and the expression of metacyclic antigen types (M-VATs) was determined. The kinetics of development of parasitosis in the afferent and efferent lymph was similar. Trypanosomes were detected in lymph 5 to 6 days after the inoculation of cultured metacyclic trypanosomes, at the same time as the chancre first appeared in the skin. The numbers of trypanosomes in the lymph reached their peak levels 8 to 10 days post infection and thereafter numbers fell, although there were still parasites in the lymph after the chancre had regressed. Trypanosomes in the afferent lymph expressed mainly M-VATs and the absolute numbers of four M-VATs which were monitored increased up to 9 days post infection. There was a fall in numbers by day 10, but 92% of the trypanosomes in the afferent lymph continued to express M-VATs. In contrast, trypanosomes from the efferent lymph were found not to express M-VATs suggesting that a major switch in VAT expression occurs in the lymph node. Specific antibody responses, measured by neutralization tests, were evident 16 to 20 days after infection in afferent lymph but only low levels of antibodies were found in efferent lymph.

Efficacy of Cymelarsan in Friesian Holstein calves infected with Trypanosoma evansi

Two studies on the efficacy of mel Cy (Cymelarsan, Rhone Merieux, France) for the treatment of cattle infected with Trypanosoma evansi were carried out with groups of 5 Friesian Holstein calves infected with an Indonesian stock of T. evansi and treated 14 days after infection. In the first study 3 groups were injected subcutaneously with Cymelarsan at dose rates of 0.125, 0.25 and 0.50 mg/kg and in the second study 2 i/m at 0.50 and 0.75 mg/kg. The response to treatment was monitored parasitologically by daily microhaematocrit centrifugation technique and weekly mouse inoculation. Enzyme linked immunosorbent assays were used to monitor trypanosomal antibodies and trypanosomal antigens in serum samples collected weekly. Relapse infections occurred in all the groups given the drug s/c whilst all the animals treated i/m remained parasitologically negative up to 80 days after treatment. Results from serological assays, however, suggested the possible persistence of trypanosome infection in the animals treated at a dose rate of 0.50 mg/kg i/m although trypanosomes could not be demonstrated parasitologically. A dose rate of 0.75 mg/kg administered i/m is recommended, therefore, for the treatment of T. evansi infection in Friesian Holstein cattle.

Experimental induction of suramin-resistance in cloned and uncloned stocks of Trypanosoma evansi using immunosuppressed and immunocompetent mice

Suramin-resistance was experimentally induced in cloned or uncloned T. evansi populations using both immunosuppressed and immunocompetent mice by administration of subcurative doses of the drug. The highest level of resistance achieved was 3,000 fold using cloned trypanosomes in immunosuppressed mice. In the absence of suramin, suramin-resistance in T. evansi was observed to be stable for ten passages in mice. The results obtained in this study imply that induction of suramin resistance is by a mutational event followed by selection of resistant mutants by the presence of the drug. Immunosuppression of animals by heavy parasite burden or stressful conditions in conjunction with underdosing may therefore play an important role in the development of drug resistance under field conditions.

Oestrus in the British white goat: timing of plasma luteinizing hormone surge and changes in behavioural and vaginal traits in relationship to onset of oestrus

Length of oestrus and timing of the LH surge was measured in six British White does, housed with a vasectomized buck (experiment 1). The following breeding season, pulsatile LH release during the cycle was measured in eight does and the pattern of behavioural and vaginal traits in relation to onset of oestrus (time 0) determined (experiment 2). In experiment 1, the interval to first oestrus after introduction of the buck on 1st October was 10.3 +/- 3.0 days (n = 6) but in experiment 2, when the buck was put in on 1st September, first oestrus occurred after 39.3 +/- 3.4 days in 7/8 does and 7 days in 1/8 does indicating that adequate exposure to short days is needed before the buck can initiate ovarian activity. LH pulse frequency increased from 0-1 pulses/8 h to 3 pulses/8 h after luteolysis, with no change in pulse amplitude, suggesting that progesterone regulates LH pulse frequency. Mean LH values rose from basal to 102.1 +/- 7.8 ng/ml, 12 +/- 1.5 h after the onset of oestrus, which was 16.3 +/- 1.7 h in length. Does sought out the buck and displayed tail wagging, bleating and restlessness from -60 h to +36 h relative to the onset of oestrus (time 0). The incidence of these activities rose at -12 h and peaked at 0 h. Tail wagging, but not bleating or restlessness, also increased in intensity at 0 h, as did the intensity with which the doe actively sought out the buck. Vulval redness and swelling and onset of a clear thin vaginal discharge were first observed 1-2 days before oestrus, becoming maximal on day 0. It was concluded that onset of frequent tail wagging was the most useful trait for detecting onset of oestrus.

Variability of in vitro culture characteristics, including metacyclic trypomastigote production, in different stocks of Trypanosoma congolense

Six cloned stocks of Trypanosoma congolense, isolated from the same area of Eastern Zambia, were maintained in vitro as insect form cultures producing infective metacyclic trypanosomes. Although the same general culture conditions were applied, different handling regimes were required for optimum growth of each stock. During primary isolation, many differences were found in the culture characteristics of the stocks. The time taken for cytoadherence to occur varied from 14 to 62 days, while the interval between attachment and the appearance of infective metacyclic trypanosomes ranged from 9 to 94 days. There was a 10-fold difference in the numbers of metacyclic forms produced by different stocks. Time in culture appeared to have little effect on the production of metacyclic forms, and it is probable that in vitro characteristics of T. congolense depend on the genetic constitution of individual stocks or clones.

Multiplication of Trypanosoma evansi at the site of infection in skin of rabbits and cattle

Local skin reactions (chancres) developed at the sites of inoculation with Trypanosoma evansi in rabbits and calves. Trypanosomes multipled in the dermal collagen and, in the rabbit, were present in large numbers by 7 days after infection. Thereafter, however, numbers decreased and few parasites were observed by 11 days after infection. The presence of trypanosomes in the skin caused an extensive inflammatory reaction with disruption of collagen, oedema, necrosis of the skin and increases principally in neutrophils and lymphocytes. In calves, similar changes were observed although there were fewer trypanosomes present in the chancre and the cellular involvement was less extensive than that seen in the rabbit. This early extracellular proliferative phase of development of T. evansi may be of importance in naturally transmitted infections both in the initial establishment of the parasite in the mammalian host and in enabling the parasite to increase the numbers of antigenic variants expressed before the parasites invade the general circulation.

Trypanosoma congolense: re-expression of a deleted metacyclic variable antigen type in vivo and in vitro

The expression of variable antigen types (VATs) was determined among dividing populations of T. congolense growing in vivo in rabbit chancres and in vitro on bovine aorta endothelial cell monolayers. Experiments were performed in which a single metacyclic VAT (M-VAT) was deleted from a cultured metacyclic population by neutralisation with a monoclonal antibody and complement. Subsequent expression of the deleted M-VAT and two unrelated M-VATs was determined by an indirect immunofluorescent antibody test. The deleted M-VAT was re-expressed both in vivo and in vitro and the proportions of unrelated M-VATs were not markedly affected by the neutralisation of this single M-VAT. In addition, an overall similarity was observed between M-VAT expression and re-expression in vivo and in vitro.

Immunohistology of lymph nodes draining local skin reactions (chancres) in sheep infected with Trypanosoma congolense

Marked enlargement of lymph nodes draining local skin reactions (chancres) occurred in sheep following intradermal inoculation of cultured metacyclic forms of Trypanosoma congolense. Histologically, these lymph nodes were characterized by follicular hypertrophy and hyperplasia, compression and relative reduction of the paracortical areas and expansion of the medullary regions. Immunohistochemical staining with monoclonal antibodies to ovine lymphocyte subsets and Fc receptor (FcR) bearing macrophages, revealed increased expression of B cells (CD45R+), major histocompatibility complex (MHC) Class II, FcR+ macrophages, and CD1+ cells in the cortical and paracortical areas. The paracortical areas were found to be sparsely populated by CD5+, CD4+ and CD8+ cells, while the medullary areas contained numerous CD8+ cells and FcR+ macrophages. FcR+ macrophages were also present in cortical trabecular and subcapsular sinuses. As the chancre regressed, lymph node reactivity also subsided and fewer B cell follicles were observed and there was decreased expression of CD45R+ and MHC Class II+ cells.

Trypanosoma evansi infection in cattle, buffaloes and horses in Indonesia

Cattle, buffaloes and horses in several areas of Indonesia were examined for evidence of infection with Trypanosoma evansi by the microhaematocrit centrifugation technique (MHCT) and an enzyme-linked immunosorbent assay (ELISA) for detection of antibodies to T. evansi. Evidence of infection was found in animals at each sampling site although differences were seen in prevalence rates between sites. Prevalence rates in buffalo were usually higher than in cattle in the same area while in horses they were much lower than in cattle or buffalo. An age-dependent prevalence rate was seen in buffalo and cattle with the highest rates seen in animals older than 2 years. These results concur with the view that T. evansi infection is widespread throughout most of the livestock-producing areas of Indonesia. The apparent lack of any obvious disease owing to T. evansi infection in the sampled animals suggests that a form of stability exists in most endemic areas which serves to ameliorate the effect of T. evansi infection and has an immunological basis linked to the parasite's limited antigenic diversity.

Cellular phenotypes in Trypanosoma congolense infected sheep: the local skin reaction

Mononuclear cell subpopulations in local skin reactions (chancres) in sheep infected with metacyclic forms of Trypanosoma congolense were studied by indirect immunoperoxidase staining using a panel of monoclonal antibodies (MoAbs) specific for ovine leucocyte subsets. Morphometric analysis revealed significant increases in numbers of cells expressing CD5, CD4, CD8, CD45R (mainly B cells), major histocompatibility complex (MHC) class II antigens, Fc receptors (FcR) on macrophages (VPM32) and FcR on B cells and macrophages (VPM33) from five days post-infection. B cells which also expressed MHC class II were found mainly in dense aggregates. The CD4/CD8 ratios were raised over pre-infection levels at 5-7 days post-infection. In sheep which had been infected, treated with trypanocidal drugs and then challenged with an heterologous serodeme of T. congolense, changes in cellular phenotype kinetics were similar to those seen in the skin in primary infections. Sheep superinfected with either an homologous or an heterologous, T. congolense serodeme showed only mild cellular infiltration and slight increases in various cellular phenotypes at the sites of inoculation.

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

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

Stability of metacyclic variable antigen types (M-VATs) during the early stages of infection with Trypanosoma congolense

Expression of nine metacyclic variable antigen types (M-VATs) of Trypanosoma congolense in chancres from infected rabbits was determined using monoclonal antibodies raised against metacyclic forms of trypanosomes. Trypanosomes present in chancres 7-9 days post infection expressed M-VATs present in metacyclic populations of the parasites. The majority of M-VATs expressed showed little proportional change from those observed on metacyclic trypanosomes during this period although expression of one M-VAT increased, and another decreased. Although trypanosomes in chancres continued to express M-VATs, other VATs, not present in the M-VAT repertoire were also expressed and neutralization tests showed that new VATs appeared by 7 days after infection. In infected sheep neutralizing antibodies against M-VATs were detected by day 14 in lymph from efferent lymphatics draining lymph nodes in the region of chancres. Neutralizing antibodies directed against metacyclics were also present in the serum by day 14 and were still detectable for up to 35 days post infection. Hence, it is likely that in the vertebrate host the trypanosomes multiplying in the skin at the site of tsetse bit express all M-VATs characteristic of that particular serodeme, enabling the host to develop immunity to all antigen types present in the M-VAT repertoire.

Evaluation of enzyme immunoassays in the diagnosis of camel (Camelus dromedarius) trypanosomiasis: a preliminary investigation

Three enzyme immunoassays were used for the serodiagnosis of Trypanosoma evansi in camels in the Sudan in order to evaluate their ability to discriminate between infected and non-infected animals. Two assays were used for the detection of trypanosomal antibodies, one using specific anti-camel IgG conjugate and another using a non-specific Protein A conjugate. The third assay detected the presence of trypanosomal antigens using anti-T. evansi antibodies in a double antibody sandwich assay. Inspection of the frequency distribution of assay results suggested that the ELISA for circulating trypanosomal antibodies using specific antisera and the ELISA for circulating antigens can distinguish between non-infected camels and infected camels exhibiting patent infections or not. The ELISA using Protein A conjugate to bind non-specifically to camel immunoglobulin did not appear to discriminate between infected and non-infected animals.

Interference in the establishment of tsetse-transmitted Trypanosoma congolense, T. brucei or T. vivax superinfections in goats already infected with T. congolense or T. vivax

An interference phenomenon that delays superinfection with a trypanosome species different from that used for the initial infection has been found to occur in goats. Following tsetse transmission of Trypanosoma brucei to goats already infected with T. congolense, there was a delay in chancre development, as well as in the appearance of T. brucei and anti-T. brucei antibodies in the blood when compared to previously uninfected goats. However, there was no delay in the establishment of a tsetse-transmitted superinfection with T. vivax in goats already infected with either T. congolense or in animals already infected with a different serodeme of T. vivax.

Trypanosoma evansi in Asia

Trypanosoma evansi has the widest geographical range of all the pathogenic trypanosome species and infects domesticated livestock in many countries of South America, Africa and Asia. In spite of this wide distribution, T. evansi has been less intensively investigated than the African tsetse-transmitted trypanosomes and there is correspondingly less information available on the incidence and economic importance of the disease that it causes. Many of the new techniques in immunology and molecular biology, which have provided much fundamental information on the tsetse-transmitted trypanosomes, have yet to be applied to T. evansi. Interest in T. evansi is increasing and a Working Group has now been established to coordinate and promote future research (Box 1). T. evansi is an important aetiological agent of disease in the livestock of Asia; this article evaluates both the historical perspective and our current knowledge of the epidemiology and pathology of T. evansi in this region.

Hyalomma anatolicum anatolicum: the role of humoral factors in the acquisition of host resistance

A significant degree of resistance to Hyalomma anatolicum anatolicum can be adoptively transferred to naive recipients with immune serum from rabbits repeatedly infected with adult H. a. anatolicum. Ticks fed on recipients of immune serum took longer to become engorged and showed a significant decrease (P less than 0.01) in engorgement weight and oviposition compared with ticks that fed on recipients of normal serum. A direct correlation between resistance and anti-saliva IgG antibodies was indicated by a progressive increase in the degree of resistance and IgG antibody titres following successive tick infestations. Challenge feeding sites on actively sensitised hosts and recipients of immune serum revealed significantly greater infiltration of basophils and eosinophils compared with feeding sites on recipients of normal serum. However, both the degree of resistance and the accompanying cutaneous basophil and eosinophil responses in recipients of immune serum were considerably weaker than those induced by active tick feeding, thus suggesting that nonhumoral (cell-mediated) mechanisms might also be involved in acquired host resistance to H. a. anatolicum.

Analysis of trypanosome variable antigen types in cultures of metacyclic and mammalian forms of Trypanosoma congolense

Cultured metacyclic forms of Trypanosoma congolense display a characteristic repertoire of metacyclic variable antigen types (M-VATs) similar to that exhibited in vitro in the tsetse fly. There appeared to be no change in expression of M-VATs in cultures of two stocks of T. congolense even after several passages, cryopreservation or long-term cultivation in vitro. Metacyclic forms transformed into mammalian forms when transferred to cultures of bovine aorta endothelial cells and whilst one stock retained expression of M-VATs without change even after 4 months, the other stock underwent antigenic variation within 14 days of transfer. Analysis of the M-VAT composition of mammalian forms of this stock using monoclonal antibodies showed that although the proportion of mammalian forms expressing certain M-VATs declined considerably, trypanosomes expressing one M-VAT increased proportionally to comprise 50% of the population. In contrast, only small changes were seen in antigen expression in cultures of metacyclic trypanosomes from which mammalian-form cultures were derived. It was possible to produce in vitro, loss and reacquisition of variable antigen surface coat, similar to the differentiation process occurring when bloodstream trypanosomes are ingested by the tsetse fly and eventually develop into metacyclic forms.