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.     

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

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

The transmission of mixed Trypanosoma brucei brucei/T. congolense infections by tsetse (Glossina morsitans morsitans)

Laboratory experiments and field observations clearly show that tsetse flies can be carriers of mixed trypanosome infections. Question remains how easy it is for the tsetse fly to acquire such a mixed infection during the first bloodmeal. This is of particular importance in the epidemiology of Trypanosoma brucei s.l., often a cryptic infection and difficult to transmit to non-teneral tsetse flies. To determine the transmission rate of T. brucei as part of a mixed infection, teneral Glossina morsitans morsitans were fed once on cattle with a mixed (Trypanosoma brucei brucei/Trypanosoma congolense) or single (T. brucei) infection. Of the 140 flies fed on animals with a mixed infection and examined 30 days later, 4 had a metacylic T. brucei infection, 29 a T. congolense infection and 13 a mixed T. brucei/T. congolense infection. There was no significant difference between the transmission rate of T. brucei as a single or as part of a mixed infection. The high proportion of mixed T.b. brucei/T. congolense infections was explained best by a model implying that if a fly is refractory to T. congolense, it is also refractory to T.b. brucei and vice versa. Hence, results suggest that the transmission of T.b. brucei is affected mainly by the vectorial capacity of flies and not by concurrent trypanosome infections in the host.     

Susceptibility of West African Dwarf goats and WAD x Saanen crosses to experimental infection with Trypanosoma congolense

West African Dwarf goats (WADs) and their Saanen crosses were experimentally infected with Trypanosoma congolense. No significant differences were found between trypanosome parasitaemia and antibody response of the crossbred and WAD goats. Neither the WAD goats nor the Saanen crosses were able to control the drop in PCV following trypanosome infection. The level of anaemia caused by the trypanosome infection was similar in the two breeds during the trial. Based on these findings, no difference in tolerance or susceptibility to T. congolense could be demonstrated between the WAD goats and their Saanen crosses. Although the weight of all goats increased during the trial, the crosses gained significantly more weight than the WAD goats. The trypanosome infection reduced the growth rate of both breeds, but this reduction was not statistically significant. Crossbreeding trypanotolerant WADs with trypanosusceptible Saanen goats might, therefore, be an effective means of increasing productivity.     

Performance of enzyme-linked immunosorbent assays for detection of antibodies against T. congolense and T. vivax in goats

Indirect ELISAs using denatured antigen preparations of Trypanosoma (T.) congolense (TcAGd) and T. vivax (TvAGd) for detection of anti-trypanosome antibodies in bovine serum (I-TAB ELISAs), were adapted for serodiagnosis in goats. The diagnostic proficiency, the cross-reactivity with sera from heterologous trypanosome infections and the operational performance of the assays were evaluated on experimentally trypanosome-infected goats. The I-TAB ELISA (TcAGd) detected antibodies in all T. congolense infected goats (100% overall sensitivity) from 2 to 4 weeks post-infection (p.i.) until the end of the experiments. Specificity tested on 92 uninfected goats was 96.7%. Extensive cross-reactions of I-TAB ELISA (TcAGd) with sera from T. vivax or T. brucei infected goats were observed. The I-TAB ELISA (TvAGd) detected antibodies in 5 of the 6 T. vivax infected goats, specificity tested on uninfected goats was 100%. Cross-reactivity with sera from T. congolense or T. brucei infected goats remained limited. Infecting species identification based on the highest percent positivity (PP) in both systems, correctly identified all T. congolense infections, but misidentified in 2/19 occasions a T. vivax infection as a T. congolense infection. In the absence of T. brucei specific antigen coated plates, T. brucei infections were identified in, respectively, 7/9 and 2/9 occasions as T. congolense or T. vivax infections. Acceptable inter-plate repeatability was observed. The implications of results and technical requirements for ongoing applied research are discussed.     

Occurrence of human serum-resistant Trypanosoma congolense in goats and sheep in Nigeria

An assessment of the role of dogs, goats and sheep as reservoir hosts of African trypanosomes infective for humans (sleeping sickness) was carried out in Nigeria during a 2-year study period. Twelve stocks of Trypanosoma (Trypanozoon) brucei, 10 stocks of Trypanosoma congolense and 11 stocks of Trypanosoma vivax were isolated from a total of 699 animals, comprising 286 sheep, 221 goats and 192 dogs. The potential infectivity of the isolates for man was tested in vitro using the blood incubation infectivity test. None of the T. brucei group was resistant to the trypanocidal action of human serum; three of the T. congolense group were resistant to human serum. A parallel study of the trypanocidal action of test serum on authenticated T. brucei brucei and T. brucei gambiense showed that the human serum behaved as expected. The possibility is discussed that T. congolense might produce infections in man and should, therefore, be handled carefully both in the laboratory and by veterinarians in the field.     

Development of Trypanosoma congolense, T vivax and T brucei in the skin reaction induced in goats by infected Glossina morsitans centralis: a light and electron microscopical study

The development and distribution of Trypanosoma congolense, T vivax and T brucei in the skin of goats was examined after the animals were bitten by infected Glossina morsitans centralis. Following the tsetse bite, the trypanosomes in the skin multiplied, reaching maximum numbers when the skin reaction (chancre) of the host attained its maximum size. In goats infected with T vivax and T brucei, trypanosomes were observed circulating in the blood before the peak of the chancre, while in T congolense-infected goats microscopically detectable parasites were found in blood only during the decline of the chancre. In contrast to T vivax, large numbers of T congolense and T brucei parasites were found in the skin following tsetse-transmitted infection. Ultrastructural differences were observed in T congolense and T brucei indicating an intracutaneous transformation from metacyclic to blood stream forms. T congolense forms in the skin reactions had a well developed secretory reticulum, small mitochondria and lacked large lipid inclusions compared to metacyclic and blood stream forms. The intracutaneous forms of T brucei had smaller mitochondria, the glycosomes were of more uniform size and the rough endoplasmic reticulum was less developed than in metacyclic or blood stream forms.     

Analysis of host genetic factors influencing African trypanosome species infection in a cohort of Tanzanian Bos indicus cattle

Trypanosomosis caused by infection with protozoan parasites of the genus Trypanosoma is a major health constraint to cattle production in many African countries. One hundred and seventy one Bos indicus cattle from traditional pastoral Maasai (87) and more intensively managed Boran (84) animals in Tanzania were screened by PCR for the presence of African animal trypanosomes (Trypanosoma congolense, Trypanosoma vivax and Trypanosoma brucei), using blood samples archived on FTA cards. All cattle screened for trypanosomes were also genotyped at the highly polymorphic major histocompatibility complex (MHC) class II DRB3 locus to investigate possible associations between host MHC and trypanosome infection. Overall, 23.4% of the 171 cattle tested positive for at least one of the three trypanosome species. The prevalence of individual trypanosome species was 8.8% (T. congolense), 4.7% (T. vivax) and 15.8% (T. brucei). The high prevalence of T. brucei compared with T. congolense and T. vivax was unexpected as this species has previously been considered to be of lesser importance in terms of African bovine trypanosomosis. Significantly higher numbers of Maasai cattle were infected with T. brucei (23.0%, p=0.009) and T. congolense (13.8%, p=0.019) compared with Boran cattle (8.3% and 3.6%, respectively). Analysis of BoLA-DRB3 diversity in this cohort identified extensive allelic diversity. Thirty-three BoLA-DRB3 PCR-RFLP defined alleles were identified. One allele (DRB3*15) was significantly associated with an increased risk (odds ratio, OR=2.71, p=0.034) of T. brucei infection and three alleles (DRB3*35, *16 and *23) were associated with increased risk of T. congolense infection. While further work is required to dissect the role of these alleles in susceptibility to T. brucei and T. congolense infections, this study demonstrates the utility of FTA archived blood samples in combined molecular analyses of both host and pathogen.     

Immunosuppressive effect of Trypanosoma congolense and Trypanosoma vivax on the secondary immune response of cattle to Mycoplasma mycoides subsp mycoides.

Trypanosoma congolense and T vivax infections in cattle were shown to have a suppressive effect on the secondary humoral immune response to M mycoides. The trypanosome infections caused an involution of the thymus. The secondary response was biphasic in nature and was unrelated to infection with trypanosomes.     

Immunosuppression in bovine trypanosomiasis: studies with louping-ill vaccine.

The antibody response to louping-ill virus vaccine was examined in mice infected with Trypanosoma brucei and T congolense, and in Ethiopian cattle experimentally infected with T brucei, T congolense and T vivax. In mice the antibody response was completely suppressed, while in cattle infected with T congolense and T vivax the antibody response to the vaccine was only 10 per cent that of uninfected animals. In contrast, the response of cattle infected with T brucei was not significantly reduced, and this was attributed to their relatively light and transient parasitaemias. Trypanocidal chemotherapy (diminazine aceturate) administered on the same day as vaccination largely restored the competence of the immune response of both mice and cattle infected with T congolense. The use of such drugs should be considered when cattle are vaccinated in trypanosome endemic areas.     

PCR-RFLP using Ssu-rDNA amplification: applicability for the diagnosis of mixed infections with different trypanosome species in cattle

The use of a single restriction fragment length polymorphism (RFLP)-PCR assay which is able to characterise all important bovine trypanosome species was evaluated for the detection of mixed infections with Trypanosoma brucei brucei, Trypanosoma theileri, Trypanosoma congolense and Trypanosoma vivax. Results showed that mixed infections are detectable at a minimum ratio of 2%/98% of standardised DNA solutions with a concentration of 10 ng ml(-1). All mixed infections gave clear profiles that could be easily differentiated except with T. theileri and T. congolense where the T. theileri band was concealed by the T. congolense profile.     

Trypanosome infection rate in cattle at Nguruman, Kenya

Trypanosome infection rate in cattle at Nguruman was investigated in a study conducted in 1984-1986. Shifting pastoralism significantly reduced trypanosome infections in cattle. The cattle were more heavily infected with Trypanosoma congolense (16.5%) than Trypanosoma vivax (4.95%) and Trypanosoma brucei (0.19%). Trypanosoma theileri was observed only once among the cattle examined. Mixed trypanosome infections in cattle were observed to be 2.75% and 0.014% for T. congolense/T. vivax and T. congolense/T. brucei, respectively. The duration of infection in the cattle was 55 days for T. congolense and 79 days for T. vivax. High infections in cattle were observed 2 months after the rains, which were concomitant with high tsetse densities.     

Differential kinetic activities of glycerol kinase among African trypanosome species: phylogenetic and therapeutic implications

African trypanosome species are causative agents for sleeping sickness in humans and nagana disease in cattle. Trypanosoma brucei can generate ATP via a reverse reaction with glycerol kinase (GK) when alternative oxidase (AOX) is inhibited; thus, GK is considered to be a crucial target for chemotherapy combined with AOX. However, the energy metabolism systems of African trypanosome species other than T. brucei are poorly understood. Thus, GK genes were surveyed from genome databases and cloned by PCR from T. vivax and T. congolense. Then, recombinant GK proteins (rGK) of T. vivax, T. congolense and T. brucei were expressed and purified. Kinetic analysis of these rGK proteins revealed that the K(m) values of T. congolense rGK for ADP and G-3-P substrates were lower than those of T. vivax and T. brucei. The expression level of GK molecules was highest in T. congolense cells and lowest in T. vivax cells. Based on these results, effective combination dosages of ascofuranone, a specific inhibitor of AOX, and glycerol, an inhibitor of the GK reverse reaction, were determined by using in vitro-cultured trypanosome cells.     

Heligmosomoides polygyrus and Trypanosoma congolense infections in mice: effect of immunisation by abbreviated larval infection.

Concurrent African trypanosome and gastrointestinal helminth infections are prevalent in sub-humid savannah where they are endemic. However, acquired resistance in animals varies with their responder status and exposure. As a guide to study in the definitive hosts, the effects of Trypanosoma congolense infection on the development and maintenance of homologous Heligmosomoides polygyrus resistance were investigated in outbred TO mice. These mice were immunised by abbreviation of larval infection. Immune or naive mice were either infected with 500 infective larvae (L3) of H. polygyrus and/or 10(4) bloodstream forms of T. congolense or were not infected. The outcome of infection was monitored by routine parasitological and immunological techniques for 30 days after the day of the T. congolense infection. Significantly more immune mice concurrently infected with both parasites survived than did immune mice in which H. polygyrus was superimposed on a 10-day-old T. congolense infection. Although all the mice in this latter group died before the end of the experiment, larval immunisation prolonged their survival, relative to similarly treated naive mice. The antibody titres to H. polygyrus in the sera of immune mice challenged with H. polygyrus alone were significantly higher than those of immune mice concurrently infected with both parasites but the levels of protection obtained were comparable. It is concluded that T. congolense may not completely block the strong acquired resistance induced by abbreviated H. polygyrus larval infection in TO mice but is capable of interfering with protective responses, especially if the trypanosome infection occurs prior to H. polygyrus challenge infection.     

伊氏锥虫、马媾疫锥虫、布氏锥虫、刚果锥虫的18S rDNA部分序列测定与系统发育关系

对伊氏锥虫（Trypanosoma evansi）：新疆株（XJCA）、湖北株（HBM）、云南株（YNB）、广东株（GDB2）；马媾疫锥虫（Trypanosoma equiperdum）、布氏锥虫（Trypanosoma brucei）、刚果锥虫（Trypanosoma congolense）提取基因组DNA，根据已报道的伊氏锥虫株18SrDNA基因序列设计合成引物，用PCR扩增了锥虫虫株基因组DNA,伊氏锥虫新疆株、湖北株、云南株、广东株、布氏锥虫、刚果锥虫均为373bp的片段；马媾疫锥虫为372bp的片段，PCR产物经电泳鉴定后用试剂盒回收纯化，纯化后PCR产物经连接、转化后测序，将测得的序列用DNAMAN软件分析并与国外已发表的相应序列进行了同源性比较，并绘制了系统发育进化树。结果与国外AJ009153、AJ223564、D89527株同源性达到99％～100％，与另外11株同源性75％。本研究为锥虫分子流行病学研究及分类研究打下基础。     

Pathological changes in male genitalia of cattle infected with Trypanosoma vivax and Trypanosoma congolense

Samples for histological studies were taken from the genitalia of 14 bulls (five infected with Trypanosoma vivax, five with T. congolense and four uninfected control animals), slaughtered 12, 22 or 30 weeks post-infection. Infection with Y58 strain of T. vivax and strain 2295 of T. congolense caused various grades of lesions in the male reproductive organs, especially the testes and epididymides. T. congolense produced more severe degenerative changes than T. vivax. It is concluded that in long-standing cases, the result of trypanosome infection is either serious infertility or even sterility.     

Therapeutic effect of Berenil and Samorin in mice infected with four trypanosome populations isolated from Zambian cattle

Four populations of Trypanosoma congolense and Trypanosoma brucei brucei were isolated from cattle under different management practices and environments in Zambia. All four isolates had varied responses to both diminazene aceturate (Berenil) and isometamidium chloride (Samorin) as curative drugs in infected mice. Trypanosomes from a traditionally managed herd in a high-tsetse-challenge area had the strains most resistant to Berenil, with maximum curative dose of 45 mg kg-1 body weight. Another isolate from a high-tsetse-challenge area was evidently resistant both to Berenil at 40 mg kg-1 and to Samorin at 4 mg kg-1. The strains most susceptible to both Berenil and Samorin were from a commercially managed herd of cattle under medium tsetse challenge. They responded to recommended cattle standard doses of 3.5 mg kg-1 or 7 mg kg-1 Berenil and to as little as 0.25 mg kg-1 Samorin. It is evident that trypanosome strains resistant to Berenil and/or partially resistant to Samorin exist, and that both T. congolense and T. b. brucei are implicated.     

Studies on the influence of non-steroidal anti-inflammatory drugs upon trypanosomiasis in goats and sheep

The non-steroidal anti-inflammatory drug (NSAID) flurbiprofen caused a rise in parasitaemia in goats infected with Trypanosoma vivax, Trypanosoma congolense and Trypanosoma brucei. All trypanosome-infected goats treated with flurbiprofen showed many dividing trypanosomes. This also included the short-stumpy forms of T. brucei. In T. vivax-infected goats flurbiprofen treatment resulted in 100% mortality in the acute and chronic stages of the infection. The increase in parasitaemia of T. brucei infected goats, treated with flurbiprofen, was not associated with an increase in mortality. The increase in parasitaemia of T. congolense-infected goats, treated with flurbiprofen, tended to be associated with a somewhat higher mortality but this was statistically not significant. The significant rise in parasitaemia could be reproduced in T. brucei-infected sheep without, however, killing the animals. Two other NSAIDs were also studied. Suprofen caused a rise in parasitaemia and 100% mortality when given to goats in the acute stage of T. vivax infection. Results with flunixin meglumine, when tested in T. brucei infected goats, were not conclusive.     

Recirculation of Trypanosoma brucei brucei in cattle after T. congolense challenge by tsetse flies

The effect of challenging cattle, chronically infected with Trypanosoma brucei brucei, with T. congolense on the development of the T. b. brucei infection was investigated. For this purpose, nine experimental animals were first infected with T. b. brucei through the bites of infected tsetse flies. Once the T. b. brucei had developed into a chronic infection, that was difficult to detect using routine parasitological diagnostic tools, seven of the experimental animals were challenged by tsetse flies infected with T. congolense. Two of the animals infected with T. b. brucei were kept as control. The infection with T. congolense resulted in a sudden increase in the parasitaemia of T. b. brucei. In the T. b. brucei control animals, on the other hand, the parasitaemia remained below the level of detection. The epidemiological repercussions of this increase in the parasitaemia of T. b. brucei after infection with T. congolense are discussed.     

Prevalence and incidence of trypanosomosis in horses and donkeys in the Gambia

In a study of the prevalence and incidence of trypanosomosis in horses and donkeys in two regions of the Gambia, surveys were carried out at Niamina east and Bansang south with a high and low to moderate tsetse challenge, respectively. Eleven horses and 67 donkeys were sampled monthly from August 1997 to September 1998. Blood samples were examined for trypanosomes using the buffy-coat (BC) method and polymerase chain reaction (PCR). Three primer sets were used, specific for either Trypanosoma vivax (TVW), Trypanosoma congolense (GOL) or Trypanosoma brucei (ORPHON5J).The BC results showed that the prevalence (August 1997) and the average monthly incidence (September 1997-1998) of trypanosome infections in horses (45.5 and 16%, respectively) were significantly higher than in donkeys (6.2 and 9%, respectively). Using PCR, the number of detected cases was seven times higher than using the BC. T. congolense was the most frequently observed species, followed by T. vivax and T. brucei. This study confirms earlier observations by other authors that donkeys, which are exposed to a similar tsetse challenge as horses, are significantly less infected with trypanosomes than the latter.