Susceptibility of N'Dama cattle to experimental challenge and cross-species superchallenges with bloodstream forms of Trypanosoma congolense and T. vivax.

Susceptibility to Trypanosoma congolense, T. vivax challenge and cross species-superchallenges, and related effects on health and productivity were assessed in N'Dama cattle. Twenty-five N'Dama bulls aged 3-4 years and previously primed with trypanosome infections through natural tsetse exposure over more than one year were used. The experimental herd was divided in five groups each composed of five randomly selected animals. Group 1 was challenged with T. congolense, Group 2 with T. vivax, Group 3 was inoculated with T. congolense followed by a cross-superchallenge with T. vivax, Group 4 was inoculated with T. vivax followed by T. congolense cross-superchallenge. Animals in Group 5 were used as controls. Both T. vivax and T. congolense cross-superchallenges were carried out on Day 14 subsequent to respective initial T. congolense and T. vivax inoculations. All challenges were performed by intradermal needle inoculation of stocks of trypanosome bloodstream forms. In challenged animals (Group 1 to 4), parasitaemia profiles and packed red cell volumes (PCV) were measured for four months. Weight changes were recorded monthly and daily weight gain (DWG) computed. All cattle challenged with T. congolense became parasitaemic. Conversely, one animal in Group 2 and two in Group 3 never displayed patent T. vivax parasitaemia. Both in single (Group 1), initial (Group 3) and cross-superchallenged (Group 4) cattle higher percentage of positive blood samples and higher parasitaemia level were obtained following T. congolense than T. vivax inocula (Group 2, 3 and 4) (P<0.04 or greater). Overall the pre-challenge period, PCV values and DWGs were nearly identical in the five groups. Conversely, over the post-challenge period, cattle singly, initially and cross-superinoculated with T. congolense (Group 1, 3 and 4) displayed lower PCV values and DWGs in comparison with both control animals (Group 5) and with singly T. vivax challenged cattle (Group 2) (P<0.05 or greater). No difference in mean PCV levels and DWGs was found between animals in Group 2 and cattle in Group 5. It was concluded that trypanotolerant N'Dama cattle suffered more from T. congolense and mixed T. congolensel T. vivax infections, while pure T. vivax infection did not produce appreciable negative effects on their health and productivity. Therefore, considering that tsetse and trypanosomosis control campaigns are costly and are justified only when derived economic benefits exceed those of control, and also that an ample mosaic of farming systems exists in West Africa, species-specific trypanosome prevalence and relative impact should be assessed in various cattle populations and breeds differing in trypanosome susceptibility before advising any intervention. Moreover, virulence and related effects of T. congolense and T. vivax endemic stocks on health and productivity in local cattle populations should also be estimated in order to counsel appropriate economic protection measures against trypanosmosis, i.e. vector control and/or strategic use of trypanocidal drugs.     

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

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

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.     

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.     

In vitro erythrophagocytosis by cultured macrophages stimulated with extraneous substances and those isolated from the blood, spleen and bone marrow of Boran and N'Dama cattle infected with Trypanosoma congolense and Trypanosoma vivax

A standard radioactive chromium (51Cr) release assay was used to assess the in vitro phagocytosis and lysis of bovine erythrocytes by cultured splenic, bone marrow and peripheral blood monocyte-derived (PBM) macrophages isolated from healthy and Trypanosoma congolense and T. vivax-infected cattle of the Boran and N'Dama breeds. Recombinant cytokines (rHuTNF-alpha and rBolFN-gamma) and non-acid-dialysed peripheral blood mononuclear cell (PBMNC) culture supernatants stimulated these PBM for enhanced activities. The stimulants caused increases in the rate of erythrocyte phagocytosis and lysis by cultured PBM in a concentration-dependent manner. But very high stimulant concentrations caused deceased in vitro erythrophagocytosis. However, bacterial lipopolysaccharide (LPS) and acid-dialysed PBMNC culture supernatants did not cause any increase in cultured PBM erythrophagocytosis. In vitro erythrocyte phagocytosis and lysis by splenic, bone marrow and peripheral blood monocyte (PBM)-derived macrophages of Boran breed of cattle infected with Trypanosoma congolense increased from 14 days post-infection (DPI) onwards and thereafter maintained at various levels above pre-infection. Cultured splenic macrophages showed the greatest erythrocyte destruction capability while PBM-derived macrophages was the least. The rates of in vitro erythrocyte phagocytosis and lysis were higher with the cultured PBM of the Boran than those of the N'Dama cattle during T. congolense infection. The rate of in vitro erythrocyte destruction was however, similar in both groups of cattle during T. vivax infection. These results correlated positively with the dynamics and degree of anaemia developed by these groups of animals during both T. congolense and T. vivax infections. Cattle infected with T. congolense and T. vivax developed varying degrees of normocytic normochromic anaemia during infection. Boran cattle developed a more severe anaemia, and had to be treated with diminazine aceturate, than N'Dama cattle during T. congolense infection. Both breeds of cattle developed a milder but similar degree of anaemia during T. vivax infection. None of the animals were treated. The results of this study indicated a role of in vivo macrophage stimulatory factors, notably cytokines such as TNF-alpha and IFN-gamma in host's serum, as well as parasite antigens, which may act singly or in concert, in the process of enhanced erythrocyte destruction, hence anaemia by the mononuclear phagocytic system (MPS) during bovine trypanosomosis.     

Comparative studies on N''Dama and zebu cattle following repeated infections with Trypanosoma congolense

Twenty N'Dama and eight zebu cattle were inoculated intradermally with bloodstream forms of a cloned strain of Trypanosoma congolense originating from East Africa. All inoculated cattle became parasitaemic. Zebus showed consistently higher levels of parasitaemia and lower packed red cell volume (PCV) percentages than did N'Damas. Three of the eight zebus required treatment when high numbers of trypanosomes were present in the blood and PCV values dropped below 15 per cent. None of the N'Dama cattle needed treatment. Statistical analysis was performed on the data to assess the variability of parasitaemia and PCV levels before and during infection of the N'Dama cattle. The variation in PCV values was large between individuals during the early stages of the disease and diminished as infection continued. After trypanocidal drug treatment and a recovery period of 14 months, the same animals were inoculated intradermally with T congolense bloodstream forms isolated and cloned in The Gambia. Differences in susceptibility to the ensuing disease were apparent when comparing N'Dama and zebu cattle. Five zebu cattle needed trypanocidal drug treatment, while none of the N'Damas needed drug intervention. Ranking the 20 infected N'Damas according to average PCV levels revealed that the animals responded similarly to both infections.     

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.     

Implications of the re-invasion of Southeast Uganda by Glossina pallidipes on the epidemiology of bovine trypanosomosis

A study to assess the influence of re-invasion of Glossina pallidipes on the epidemiology of bovine trypanosomosis was conducted in Southeast Uganda. A total of 1,992 cattle were screened in villages, with (949) and without G. pallidipes (1043) for trypanosomosis using a combination of the BCT and HCT methods. The prevalence of trypanosomosis (15.5%), Trypanosoma brucei infection (1.4%), T. congolense infection (7.2%), T. vivax infection (5.3%) and mixed infection (1.6%) in cattle in villages with was significantly higher than in those without G. pallidipes: trypanosomosis (7.1%), T. brucei infection (0.6%), T. congolense infection (2.0%), T. vivax infection (3.3%) and mixed infection (1.2%) (overall trypanosome infection, chi2=35.5, d.f.=1, P<0.05; T. brucei infection, chi2=8.06, d.f.=1, P<0.05; T. congolense infection, chi2=22.8, d.f.=1, P<0.05 and T. vivax infection, chi2=6.4, d.f.=1, P<0.05). Infections of Trypanosoma congolense were predominant in cattle in villages with G. pallidipes, while T. vivax infections were predominant in cattle in villages without. In all villages, T. brucei infections were fewer than either T. congolense or T. vivax infections. The risk of transmission of T. brucei, T. congolense and T. vivax infections was 3, 2.7 and 1.6 times, respectively, higher in villages with G. pallidipes than in those without, despite the presence of G. f. fuscipes in either set of villages. The mean PCV (28.27+/-0.41, 95% CI) and mean herd size (3+/-0.46) of cattle in villages with G. pallidipes were significantly (P<0.05) lower than in those in villages without (mean PCV, 29.48+/-0.34; mean herd size, 4+/-0.72). It is evident that presence of G. pallidipes brings about an increase in the prevalence of T. congolense, which causes a more severe disease in cattle than other species of trypanosomes. This is a rare case of a re-invasion of a tsetse species whose disease transmission capability calls for refocusing of the traditional national tsetse and trypanosomosis control strategies to contain it.     

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

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

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.     

Parasitological prevalence of bovine trypanosomosis in Kindo Koisha district,Wollaita zone,south Ethiopia

A cross sectional survey to determine the distribution and prevalence of trypanosomosis was conducted in Kindo Koisha district, in the Wollaita zone in southern Ethiopia. A total of 1 008 adult cattle was examined at eight different localities. Dark field examination of the buffy coat, as well as stained thin blood film examination and packed cell volume (PCV) evaluation were the diagnostic techniques used. The overall prevalence of bovine trypanosomosis was 15 %. Among the positive animals, 108 (71.1%), 43 (28.4%) and 1 (0.6%) were due to Trypanosoma vivax, Trypanosoma congolense and mixed infection (T. vivax and T. congolense), respectively. The infection rate of T. vivax and T. congolense varied significantly (P < 0.01). The mean PCV of the positive and negative animals ranged between 18.3-32.1% and 26.8-33.4%, respectively. The mean PCV of negative animals (28 %) was significantly higher than the mean PCV of positive animals (22.3%) (P < 0.001). There was an inverse association of PCV with the prevalence of trypanosomosis (P > 0.05). The herd average PCV values of each site decreased with increasing proportion of the positive herds of that particular site. Of the diagnostic tests employed, the microhaematocrit buffy coat technique is relatively sensitive and it has an added advantage of indicating the general condition of the animal by haematocrit measurement. In view of the risk of trypanosomosis, a control intervention through the strategic application of appropriate trypanocidal drugs is recommended. A tsetse fly control scheme to reduce host-tsetse fly contact is equally as important as chemotherapy and chemoprophylaxis against trypanosomosis.     

A survival analysis of trypanosomosis diagnostic-test performance under natural infection challenge

Little is known about the time-to-first detection and the time difference (TD) between first parasitological and first serological diagnosis of Trypanosoma spp. infections under natural infection challenge in cattle. The objective of our study was to estimate these measures of "longitudinal aspects" of diagnostic performance and to investigate potential biological factors. Emphasis was on diagnosis at the genus level (Trypanosoma spp.). Twelve N'Dama, 12 Gobra zebu and 12N'DamaxGobra (F1) crossbred cattle (all animals non-infected at the start of the experiment, six male and six female animals in each cohort) were exposed to natural high tsetse challenge in the Niamina East area in The Gambia [Acta Trop. 71 (1998) 57]. The animals were investigated parasitologically (detection of trypanosomes by buffy-coat technique), serologically (detection of T. brucei, T. congolense and T. vivax antigen by enzyme-linked immunosorbent assay (ELISA)) and clinically (packed-cell volume, PCV) over a period of 180 days. The time-to-first detection of trypanosomes, trypanosomal antigen (cut-off as suggested by test supplier) and drop in PCV (subject-based cut-off values) were recorded as outcomes of interest. Thus, incidence was both parasitologically (I(p)), serologically (I(s)) and clinically (I(c)). Recurrent events were not considered. The TD between first parasitological and first serological detection was established as I(s) time minus I(p) time. The effect of breed and sex on the time-to-first detection and on TD was investigated using Cox (proportional hazard) regression and ANOVA, respectively.We found that time-to-first parasitological detection of trypanosomosis in N'Dama animals was significantly longer than in the two other breeds (Cox regression, P=0.002). A similar but less-strong (P=0.063) effect of breed on time-to-first detection of trypanosomal antigen was found, whereas no breed effect was observed for clinical detection (P=0.432). Sex had no effect in all detection systems. The TD varied between -56 and 115 (mean 28). Marked differences among breeds and between sexes were not observed (ANOVA, P=0.8). We suggest that incidence studies are more suitable for detecting risk factors for animal trypanosomosis than prevalence-based (cross-sectional) studies because the latter often result in misinterpretation of factors that increase the survival time with infection as risk factors.     

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.     

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.     

Isometamidium chloride prophylaxis against Trypanosoma congolense challenge and the development of immune responses in Boran cattle

Twenty-four Boran cattle were injected with isometamidium chloride (1 mg/kg bodyweight) to investigate the duration of drug-induced prophylaxis against infection by metacyclic forms of Trypanosoma congolense and to determine if specific antibody responses to the organism were mounted by animals under chemoprophylactic cover. Complete protection against either single challenge by five tsetse flies infected with T congolense, or repeated challenge at monthly intervals by five tsetse flies, lasted for five months. Six months after treatment, two-thirds of the cattle were resistant to challenge, irrespective of whether subjected to single or multiple challenge with trypanosome-infected tsetse flies, or titrated doses of in vitro-cultured metacyclic forms of T congolense (5 X 10(2) to 5 X 10(5) organisms), inoculated intradermally. No animal which resisted infection developed detectable skin reactions at the site of deposition of metacyclic trypanosomes or produced trypanosome-specific antibodies. It was concluded that drug residues effectively limited trypanosome multiplication at the site of deposition in the skin, thus preventing subsequent parasitaemia or priming of the host's immune response.     

The interaction of Trypanosoma congolense and Haemonchus contortus infections in trypanotolerant N'Dama cattle.

The interactions between Trypanosoma congolense and Haemonchus contortus infections were studied in N'Dama calves. A total of 38 N'Dama bulls was divided into four groups and each group infected either with H. contortus 1 week after infection with T. congolense or with T. congolense 4 weeks after infection with H. contortus, or with either infection singly. Parasitological (faecal egg counts, parasitaemia), haematological (packed cell volume, white blood cell counts, albumin) and clinical parameters (body weight change, mortality rate) were compared among the various groups. The results showed a reduced prepatent period and a markedly increased pathogenicity of H. contortus infections in animals with a concurrent T. congolense infection. The most harmful combination was a H. contortus infection 1 week after the T. congolense infection which resulted in a progressive and severe anaemia, accompanied by hypoalbuminaemia, increased weight loss and high mortality. The anaemia induced by dual infections showed a low responsiveness to chemotherapy and in several cases supportive treatment did not help recovery. The results also showed that animals with a concurrent T. congolense and H. contortus infection ran a higher risk of succumbing during the infection, and also during 10 weeks following treatment. Although infections with T. congolense alone produced no clinical signs, they were found to significantly reduce the ability of infected animals to mount a normal response to a subsequent H. contortus infection. It was concluded that the increased H. contortus egg excretion observed in animals infected with both parasites might significantly increase the risk of nematode infections and that the reduced prepatent period might necessitate more frequent anthelmintic treatments. These interactions should, therefore, be considered wherever attempts are made to control these two diseases.     

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.     

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

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

Hypothalamic-pituitary-adrenal axis responsiveness to insulin-induced hypoglycaemia is modified by trypanosome infection in Boran (Bos indicus) cattle.

Ten Boran (Bos indicus) cattle were used to study the stress responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis during trypanosome infection. Five cattle were infected with Trypanosoma congolense IL 1180 by tsetse challenge and five cattle served as controls. All infected animals developed acute trypanosomiasis. Insulin-induced hypoglycaemia (50 per cent of pre-insulin glucose concentration) was used as a stress factor. Acute hypoglycaemia was observed in three infected and three control animals after insulin challenge. Two animals from each group either did not respond or responded slowly. Hypoglycaemia in infected animals completely failed to induce an HPA axis response, while in control animals an HPA axis response was indicated by a significant increase in plasma adrenocorticotrophic hormone (ACTH) and cortisol concentrations (P less than 0.01). The results show that trypanosomiasis in Boran cattle can cause a decrease in the stress responsiveness of the HPA axis as indicated by a blunted ACTH/cortisol response to insulin-induced hypoglycaemia.     

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.