Congolense Infection Research Articles

Tumor Necrosis Factor (TNF) Receptor–1 (TNFp55) Signal Transduction and Macrophage‐Derived Soluble TNF Are Crucial for Nitric Oxide–MediatedTrypanosoma congolenseParasite Killing

Control of Trypanosoma congolense infections requires an early cell-mediated immune response. To unravel the role of tumor necrosis factor (TNF) in this process, 6 different T. congolense strains were used in 6 different gene-deficient mouse models that included TNF(-/-), TNF receptor-1 (TNFp55)(-/-), and TNF receptor-2 (TNFp75)(-/-) mice, 2 cell type-specific TNF(-/-) mice, as well as TNF-knock-in mice that expressed only membrane-bound TNF. Our results indicate that soluble TNF produced by macrophages/neutrophils and TNFp55 signaling are essential and sufficient to control parasitemia. The downstream mechanism in the control of T. congolense infection depends on inducible nitric oxide synthase activation in the liver. Such a role for nitric oxide is corroborated ex vivo, because the inhibitor N(G)-monomethyl-l-arginine blocks the trypanolytic activity of the adherent liver cell population, whereas exogenous interferon- gamma that stimulates nitric oxide production enhances parasite killing. In conclusion, the control of T. congolense infection depends on macrophage/neutrophil-derived soluble TNF and intact TNFp55 signaling, which induces trypanolytic nitric oxide.

Cytokine mRNA Profiles in Bovine Macrophages Stimulated with Trypanosoma congolense

It is known that different breeds of cattle display differential susceptibilities to Trypanosome congolense infections, and that N'Dama cattle remain more productive after infection than Boran cattle which are more susceptible to T. congolense. Macrophages from both breeds were cultured in vitro and the expressions of a number of cytokines and iNOS mRNA were analyzed using real time RT-PCR after stimulation with antibody-opsonized trypanosomes. No significant difference was seen between the responses of the two breeds. However, RNA levels of TNF-alpha in the IFN-gamma-primed macrophages were about 100-fold higher than those in the non-primed macrophages. A significant ten-fold decrease was seen for the anti-inflammatory cytokine IL-10. These results indicate that priming of the cells with IFN-gamma cause a serious shift toward an inflammatory response.

Preliminary evaluation for anti-trypanosomal activity of aqueous stem bark extract of <i> Crossopteryx febrifuga</i> in <i>Trypanosoma congolense</i> - infected rats

Aqueous stem bark extract of Crossopteryx febrifuga was evaluated for anti-trypanosomal activity in rats. Twenty four rats divided into four groups (A, B, C, D) of six animals per group were used. Infection with T. congolense was established after a pre-latent periods of 10 and 11 days for curative (Group B) and prophylaxis (Group A) studies respectively. Both Group A and Group B were treated orally with 1500mg/kg of the crude extract for five consecutive days. Parasitemia, Packed Cell Volume (PCV), Red Blood Cells (RBC) counts and Differential leucocytes (WBC) counts were monitored throughout the studies. Phytochemical analysis of the crude aqueous extract was also carried out. Anaemia developed with establishment of infection in all the groups. Analysis of PCV, RBC and Differential WBC counts showed no significant difference (P>0.05) between treated and untreated animals. The crude extract contains saponins, tannins, reducing sugars, volatile oils and alkaloids as phytochemicals. It showed no significant prophylaxis or curative against T. congolense infection in rats as traditionally claimed. Although the plant may be used locally in combination with other plants or ingredients or even other orthodox drugs, further work is needed to fully assess the claim of the use of Crossopteryx febrifuga stem bark in the management or treatment of animal trypanosomiasis. Journal of Pharmacy & Bioresources Vol. 2(2) 2005: 111-115

Bovine Transcriptome Analysis by SAGE Technology during an Experimental Trypanosoma congolense Infection

In central and sub-Saharan Africa, trypanosomosis is a tsetse fly-transmitted disease, which is considered as the most important impediment to livestock production in the region. However, several indigenous West African taurine breeds (Bos taurus) present remarkable tolerance to the infection. This genetic capability, named trypanotolerance, results from numerous biological mechanisms most probably under multigenic dependences, among which are control of the trypanosome infection by limitation of parasitemia and control of severe anemia due to the pathogenic effects. Today, some postgenomic biotechnologies, such as transcriptome analyses, allow characterization of the full expressed genes involved in the majority of animal diseases under genetic control. One of them is serial analysis of gene expression (SAGE) technology, which consists of the construction of mRNA transcript libraries for qualitative and quantitative analysis of the entire genes expressed or inactivated at a particular step of cellular activation. We developed four different mRNA transcript libraries from white blood cells on a N'Dama trypanotolerant animal during an experimental Trypanosoma congolense (T. congolense) infection: one before experimental infection (ND0), one at the parasitemia peak (NDm), one at the minimal packed cell volume (NDa), and the last one at the end of the experiment after normalization (NDf). Bioinformatic comparisons in bovine genomic databases allowed us to obtain more than 75,000 sequences, among which are several known genes, some others are already described as expressed sequence tags (ESTs), and the last are completely new, but probably functional in trypanotolerance. The knowledge of all identified named or unnamed genes involved in trypanotolerance characteristics will allow us to use them in a field marker-assisted selections strategy and in microarrays prediction sets for bovine trypanotolerance.

Pathogenicity of <i>Trypanosoma congolense</i> infection following oral calcium chloride administration in rats

Eighty healthy adult albino rats of both sexes weighing 180-200g were used in two experiments to study the effects of oral calcium chloride treatment on the pathogenicity of Trypanosoma congolense infection. Experiment 1 was terminated at the peak of parasitaemia while experiment II was allowed to run a full course. In each experiment, forty rats were divided into four groups of 10 rats each, namely: A, uninfected untreated control; B, treated uninfected control; C, infected untreated and D, treated infected. Aqueous solution (10%) of CaCl2 was administered daily using stomach tube to each rat at 100mg/kg in groups B and D from 7 days before infection to the end of the study. Each rat in groups C and D was infected by intraperitoneal injection of 1x106 trypanosomes in phosphate buffered saline solution (pH 7.4) diluted donor rat blood. The infected untreated group exhibited higher (P< 0.05) parasitaemia, more severe anaemia and hepatic and renal damage than the infected treated group. In conclusion, oral calcium chloride treatment in rats seemed to reduce the pathogenicity of T. congolense infection by delaying the onset of parasitaemia and reducing the levels of parasitaemia, accompanied anaemia as well as organ damage. Keywords: rats, Trypanosoma congolense, calcium chloride treatment, pathogenicity African Journal of Biomedical Research Vol. 8(3) 2005: 197-201

BENEFICIAL EFFECT OF ERYTHROPOIETIN ADMINISTRATION ON MURINE INFECTION WITH TRYPANOSOMA CONGOLENSE

The effect of erythropoietin treatment on Trypanosoma congolense infection in mice was studied. Survival rates of mice were dramatically improved by treatment with recombinant human erythropoietin (r-hu-EPO; 5,000 U/kg) when infected with 1,000 cells of T. congolense IL3000 (P < 0.05). All the untreated mice infected with T. congolense IL3000 died by day 9 of infection; however, 100%, 50%, and 25% of the mice treated with r-hu-EPO for 8 days survived to day 20, day 40, and day 60 of the parasitical infection, respectively. Anti-8-hydroxy-2'-deoxyguanosine antibody, a biomarker for oxidative damage of DNA, yielded positive reactions in the cytoplasm of the parasites recovered from the mice treated with r-hu-EPO. These results, taken together, indicate that erythropoietin administration is effective for the treatment of T. congolense infection.

Interferon‐γ and Nitric Oxide in Combination with Antibodies Are Key Protective Host Immune Factors duringTrypanosoma congolenseTc13 Infections

The control of chronic Trypanosoma congolense trypanosomiasis was analyzed using several gene-deficient mouse strains. First, interferon (IFN)-gamma receptor (IFN-gamma-R)-deficient mice were used to show that IFN- gamma -mediated immune activation is crucial for parasitemia control. Second, infections in major histocompatibility complex (MHC) class II-deficient mice indicate that this molecule is needed for initiation of IFN- gamma and subsequent tumor necrosis factor (TNF) production. Downstream of IFN-gamma-R signaling, inducible NO synthase (iNOS)-dependent trypanosome killing occurs, as is shown by the hypersusceptible phenotype of iNOS-deficient mice. Besides proinflammatory responses, B cells and, more specifically, immunoglobulin (Ig) G antibodies are crucial for parasite killing. Hence, parasitemia control is abolished in B cell-deficient mice, whereas IgM-deficient mice control the infection as efficiently as do wild-type mice. In addition, splenectomized mice that have a normal IgM response but an impaired IgG2a/3 response fail to control T. congolense infection. Collectively, these results suggest that host protective immunity against T. congolense is critically dependent on the combined action of the proinflammatory mediators/effectors IFN- gamma , TNF, and NO and antiparasite IgGs.

Experimental African Trypanosomiasis: A Subset of Pathogenic, IFN-γ-Producing, MHC Class II-Restricted CD4+ T Cells Mediates Early Mortality in Highly Susceptible Mice

Infections of highly susceptible BALB/c mice with virulent strains of Trypanosoma congolense or Trypanosoma brucei result in rapid death (8 days). We have previously shown that this mortality is IFN-gamma dependent. In this study we show that IFN-gamma is produced predominantly by CD3+Thy1.2+TCRbeta+CD4+ T cells shortly before the death of infected mice. Mortality may therefore be dependent on IFN-gamma-producing CD4+ T cells. Surprisingly, infected CD4+/+ and CD4-/- BALB/c mice have similar parasitemia and survival time. In infected CD4-/- mice, the production of both IFN-gamma and IL-10 is very low, suggesting that both cytokines are predominantly produced by CD4+ T cells and that the outcome of the disease might depend on the balance of their effects. Infected BALB/c mice partially depleted of CD4+ T cells or MHC class II function have lower parasitemia and survive significantly longer than infected normal BALB/c mice or infected BALB/c mice whose CD4+ T cells are fully depleted. Partial depletion of CD4+ T cells markedly reduces IFN-gamma secretion without a major effect on the production of IL-10 and parasite-specific IgG2a Abs. Based on our previous and current data, we conclude that a subset of a pathogenic, MHC class II-restricted CD4+ T cells (Tp cells), activated during the course of T. congolense infection, mediates early mortality in infected BALB/c mice via excessive synthesis of IFN-gamma. IFN-gamma, in turn, exerts its pathological effect by enhancing the cytokine release syndrome of the macrophage system activated by the phagocytosis of parasites. We speculate that IL-10-producing CD4+ T cells might counteract this effect.

Efficiency and limits of the Serial Analysis of Gene Expression (SAGE) method: Discussions based on first results in bovine trypanotolerance

Post genomic biotechnologies, such as transcriptome analysis, are now efficient enough to characterize the full complement of genes involved in the expression of specific biological functions. One of them is the Serial Analysis of Gene Expression (SAGE) technique. SAGE involves the construction of transcript libraries for a quantitative analysis of the entire set of genes expressed or inactivated at particular stages of cellular activation. Bioinformatic comparisons in hosts and pathogens genomic databases allow the identification of several up- and down-regulated genes, ESTs and unknown transcripts directly involved in the host–pathogen immunological interaction mechanisms. Based on the first results obtained during an experimental Trypanosoma congolense infection in trypanotolerant cattle, the efficiency and limits of such a technique, from the data acquisition level to the data analysis level, is discussed in this analysis.

Transmissibility of Trypanosoma brucei during its development in cattle

Recent outbreaks of Trypanosoma brucei rhodesiense sleeping sickness in Soroti District of eastern Uganda have demonstrated the important role cattle can play as reservoirs of this parasite. To clarify the epidemiological importance of the cattle reservoir, experiments were conducted to determine the ease with which T. brucei is transmitted during the course of its development in Friesian cattle. The development of T. brucei in cattle is characterized by an acute phase with high levels of parasitaemia and a decline in PCV. The acute phase is followed by a chronic phase during which the PCV remains low but stable and the parasitaemia is low. Parasites are often difficult to detect using parasitological diagnostic tools during this chronic phase. Challenge of chronically infected cattle with T. congolense results in a sudden increase in the T. brucei parasitaemia. Despite significant differences in parasitaemia, the proportion of tsetse flies that developed metacyclic infections after a first bloodmeal on the infected cattle did not differ significantly between the acute and chronic phases or the phase of mixed T. b. brucei/T. congolense infection. This suggests that, throughout the observation period, the parasitaemia was above the threshold above which infection rates of tsetse are independent of the parasitaemia. The repercussions of the research findings for the understanding of the epidemiology, spread and the control of T. b. rhodesiense sleeping sickness are discussed.

Influence of an experimental Trypanosoma congolense infection and plane of nutrition on milk production and some biochemical parameters in West African Dwarf goats

The interactions of trypanosomosis and plane of nutrition on health and productivity of multiparous and primiparous West African Dwarf (WAD) does were studied in a multi-factorial experiment including diet (supplementation or basal diet) and infection (infected or control). Experimental does were infected with Trypanosoma congolense at the beginning of the second week post-kidding and monitored for 16 weeks after infection. Trypanosome infection significantly reduced packed cell volume (PCV) (control: 30.1 ± 0.3% versus infected: 22.2 ± 0.3%; P < 0.0001). Regardless of infection, the drop in PCV from the pre-infection period to the end of the experiment was more severe in animals under restricted diet (interaction diet × period, P < 0.001). Trypanosome parasitaemia tended to be higher in the supplemented group than in the basal diet group ( P > 0.05) and multiparous animals had a higher parasitaemia (score: 2.6 ± 0.1) than primiparous animals (score: 2.2 ± 0.1) ( P < 0.05). Trypanosome infection as well as dietary supplement had a significant effect on lactation length. Milk off-take from trypanosome-infected does was significantly lower than that from the uninfected control group (17.5 ± 3.2 l versus 35.5 ± 3.2 l, P < 0.001) and there was a positive effect of plane of nutrition (supplemented: 32.8 ± 3.2 l and basal diet: 20.2 ± 3.5 l, P = 0.01). The drop in milk off-take due to trypanosome infection was more severe in the supplemented group (control: 46.7 ± 4.7 l versus infected: 18.9 ± 4.2 l) than in the group receiving a basal diet (control: 24.2 ± 5.0 l versus infected: 16.1 ± 4.7 l) (interaction infection × diet, P = 0.04) due to the number of does from the supplemented group that were withdrawn from the experiment. The effect of trypanosome infection on doe's live-weight was only noticeable during the first 8 weeks of lactation and there was no significant effect on offspring growth rate unless the mother died. Plasma total protein (TP), albumin and cholesterol concentrations were significantly reduced by the infection but were significantly increased by supplementation. Supplemented does had a higher level of cholesterol and a tendency for a higher parasitaemia. Does of high parity also had a higher cholesterol level than primiparous does and, based on the number of animals that were withdrawn from the experiment, they showed a lower resistance to the infection.

Protective efficacy of isometamidium chloride and diminazene aceturate against natural &lt;i&gt;Trypanosoma brucei&lt;i/&gt;, &lt;i&gt;Trypanosoma congolense&lt;i/&gt; and &lt;i&gt;Trypanosoma vivax&lt;i/&gt; 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.

Use of the Serial Analysis of Gene Expression (SAGE) Method in Veterinary Research: A Concrete Application in the Study of the Bovine Trypanotolerance Genetic Control

New postgenomic biotechnologies, such as transcriptome analyses, are now able to characterize the full complement of genes involved in the expression of specific biological functions. One of these is the Serial Analysis of Gene Expression (SAGE) technique, which consists of the construction of transcripts libraries for a quantitative analysis of the entire gene(s) expressed or inactivated at a particular step of cellular activation. Bioinformatic comparisons in the bovine genomic databases allow the identification of several up- and downregulated genes, expressed sequence tags, and unknown functional genes directly involved in the genetic control of the studied biological mechanism. We present and discuss the preliminary results in comparing the expressed genes in two total mRNA transcripts libraries obtained during an experimental Trypanosoma congolense infection in one trypanotolerant N'Dama animal cow. Knowing all the functional genes involved in the trypanotolerance control will permit validation of some results obtained with the quantitative trait locus approach, to set up specific microarrays sets for further metabolic and pharmacological studies, and to design field marker-assisted selection by introgression programs.

Susceptibility of TNF-α-deficient mice to Trypanosoma congolense is not due to a defective antibody response

C57BL/6 mice deficient in one or two copies of the gene for tumor necrosis factor alpha (TNF-α) were more susceptible to Trypanosoma congolense infection than their resistant, wild-type counterparts. The number of TNF-α genes was correlated with the capacity to control parasitaemia and with survival time. Absence of TNF-α resulted in a diminished capacity to form germinal centres in lymph nodes and spleen. Since germinal centres are involved in antibody production and affinity maturation, the susceptibility of the TNF-α-deficient mice could have been due to this secondary defect. Despite the lack of the germinal centres, the antibody responses to internal and exposed trypanosome antigens and to non-trypanosome antigens were not significantly different. Also the relative avidities measured in infected sera did not significantly differ between the two mouse strains. These data suggest that the role of TNF-α in control of T. congolense was not due to its role in the development of an antibody response.

The secretion of acute phase proteins and inflammatory cytokines during Trypanosoma congolense infection is not affected by the absence of the TNF-α gene

Tumor necrosis factor-α (TNF-α) plays a role in the host’s defence against infections with African trypanosomes. It helps to control the blood stream form of the parasite and in Trypanosoma congolense infections, it also prolongs survival. The mechanisms by which this cytokine can influence parasitemia and survival are unknown. Therefore, the levels of acute phase proteins and other inflammatory cytokines were monitored in trypano-tolerant wild-type and TNF-α-deficient mice during a T. congolense infection. The titres of ceruloplasmin (CP), α1-acid glycoprotein (AGP) and serum amyloid P (SAP) increased and reached their peaks at 11 days post-infection, when the first peak of parasitemia was observed. No significant differences were observed in the acute phase protein profiles between the two mouse strains. Also the profiles of serum titres of IFN-γ, IL-1α, IL-6 and IL-10 were not significantly different. Our present results indicate that acute phase protein and cytokine responses can be induced in the absence of TNF-α during a T. congolense infection in mice, and that the susceptibility of the TNF-α-deficient mice is not due to modulation of expression of these molecules.

Trypanosoma congolense infections: antibody-mediated phagocytosis by Kupffer cells.

Immunohistochemical double-label technique was used to detect trypanosomal antigen in macrophages. Immunoglobulin (Ig)M as well as IgG2a monoclonal antibodies (mAb) specific for the variant surface glycoprotein (VSG) mediated phagocytosis of Trypanosoma congolense variant antigenic type (VAT) TC13 by macrophages [bone marrow-derived macrophage cell line from BALB/c (BALB.BM)] in vitro. Administration of these IgM or IgG2a antibodies to BALB/c mice 30 min after injection of 3 x 10(8) T. congolense mediated phagocytosis of trypanosomes by Kupffer cells of the liver within 1 h. Plasma levels of the monokines interleukin (IL)-1beta, IL-10, and IL-12p40 were significantly increased 6-48 h after phagocytosis. In BALB/c mice infected with 10(3) T. congolense, a small degree of phagocytosis of trypanosomes by Kupffer cells, mediated by actively synthesized antibodies, was detected as early as 5 days after infection. Phagocytosis of trypanosomes was dramatically enhanced on day 6. Concomitantly, the Kupffer cells trippled in size. In BALB/c mice infected for 6 days, treatment with IgM or IgG2a mAb specific for T. congolense VSG led to clearance of VAT TC13 parasitemia but did not prevent death at the second parasitemia of a different VAT. We conclude that IgM as well as IgG antibody mediate phagocytosis of trypanosomes by Kupffer cells.

Effects of an experimental Trypanosoma congolense infection on the reproductive performance of West African Dwarf goats

Thirty-six West African Dwarf (WAD) goats were used to assess the effects of an experimental Trypanosoma congolense infection on their reproductive system. Estrous cycles were synchronised and when confirmed pregnant ( n=31), the does were randomly allocated into control and trypanosome-infected groups. After infection, the animals were carefully observed till parturition. Trypanosome infection caused an increase of rectal temperature, a significant drop in PCV (infected: 23.3±0.3%; control: 28.5±0.4%; P<0.0001) and abortions in 27.8% of the infected does. Kids born from infected does had a lower birth weight than kids born from control goats (0.9±0.1 kg versus 1.6±0.1 kg; P<0.0001). Eight out of 13 kids (61.5%) that were born alive from infected does died during their first week of life. Plasma pregnancy-associated glycoprotein (PAG) and progesterone concentrations were lower in the infected animals than in the controls. In general, PAG concentration in does which aborted dropped before abortion. Our results revealed that artificial T. congolense infection affected reproductive performance of WAD goats with abortions, premature births and perinatal losses being observed. Neither transplacental transmission of T. congolense nor histopathological lesions of the placenta could be demonstrated.

The effect of high oral magnesium chloride supplementation on the pathogenicity of &lt;i&gt;Trypanosoma brucei brucei&lt;/i&gt; and &lt;i&gt;T. congolense&lt;/i&gt; infections in rats

Eighty healthy adult albino rats of both sex weighing 200-240 grams were used to assess the effect of high oral Magnesium chloride (100mg/kg body weight) supplementation on the pathogenicity of T. b. brucei (Basa strain) or T, congolense (Gboko strain) infections. Two studies were carried out and the rats were divided into 4 groups of 10 rats each (per study) namely; Group A (uninfected, unsupplemented control), Group B (uninfected and supplemented with Magnesium chloride), Group C (T.b. brucei or T. congolense infected, 1x10 6 trypanosomes and supplemented), Group D (T.b. brucei or T, congolense infected, 1x10 6 trypanosomes and unsupplemented). Each rat in groups B and C received approximately 0.2ml of MgCl2 intragastrically daily for 10 days before and during the course of the infection. The prepatent period and survival times were shorter (P Key words: Magnesium chloride; Supplementation; Trypanosomes; Pathogenicity; Rats. Trop. Vet. Vol. 21: (3) 152-159 (2003)

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.

The effects of trypanosomosis on sperm morphology in Zebu x Friesian crossbred bulls.

Detailed studies of sperm morphological abnormalities were carried out on 12 Zebu x Friesian crossbred bulls used in a study of the effects of trypanosomosis. Four bulls were infected with T. vivax, another four with T. congolense, while four served as controls. The infected bulls developed chronic trypanosomosis. All the bulls initially had very low sperm morphological abnormalities that were within acceptable limits for fertile animals. After infection there was a rapid and progressive increase in all sperm abnormalities. Spermatozoa of infected bulls were highly deformed with multiple morphological defects. Mean percentage pre-infection baseline values prior to infection for acrosomal, sperm-head, detached heads, proximal cytoplasmic droplets, distal cytoplasmic droplets, sperm-tail, midpiece and total sperm morphological defects ranged between 0.1 +/- 0.1 for acrosomal and 8.3 +/- 3.2 for total morphological abnormalities in the semen of the bulls. All the infected bulls developed sperm morphological abnormalities of more than a mean of 40.0% from the 4th week after infection until the end of the investigation and were considered unfit for breeding. At 7 weeks post-infection (PI) until the end of the study (12 weeks PI), the controls had a mean of less than 5% sperm morphological defects, while the infected bulls had 100%. Mean percentage values of sperm morphological defects throughout the duration of the investigation for control bulls were low and within the normal range for fertile bulls. These values differed significantly (p<0.001) from the elevated values of the infected bulls. The results show that trypanosomosis due to T. vivax or T. congolense infection can render Zebu x Friesian crossbred bulls unfit for breeding within a very short time. The resultant infertility could be of economic importance in trypanosomosis-endemic sub-Saharan Africa where Zebu x Friesian crossbred bulls are kept.