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.     

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.     

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.     

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.     

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.     

Response of Trypanosoma vivax and Trypanosoma congolense in zebu cattle in North Cameroon to prophylactic treatment with two formulations of isometamidium

We tested the efficacy of two formulations of isometamidium in a tsetse-infested farm in North Cameroon from 20 August 2000 to 5 January 2001. A total of 90 adult cattle were used in three groups of 30 each corresponding to two treated and one untreated control. Drug efficacies were evaluated in terms of reduction of parasite incidence in the host's blood, maintenance of packed-cell volume (PCV) and weight gains. Both drugs reduced the incidence of parasites even though re-infections 2 weeks after treatment were common. PCV values were similar in both treated groups but higher than in the untreated control. Body weight changes followed a similar trend with the control losing weight from a mean of 427+/-119kg at the beginning to 398+/-93kg in 4 months. Weights increased from 375+/-76 and 396+/-110 to 396+/-69 and 418+/-112kg in the Veridium and Trypamidium groups, respectively. Efficacy was similar between the two formulations of isometamidium in the prophylaxis of bovine trypanosomosis. However, the presence of parasites in some animals barely 2 weeks after treatment suggested that either infections were not cleared or residual drug effects were not sufficient to prevent re-infections.     

Comparative haematological changes following Trypanosoma vivax and T. congolense infections in Zebu bulls

A comparative study of haematological changes subsequent to Trypanosoma vivax and Trypanosoma congolense infections was carried out using 24 Zebu bulls during a period of 12 weeks. Eight bulls were infected with T. vivax, another eight with T. congolense and eight served as controls. Infected bulls developed chronic trypanosomiasis which was characterized by many clinical manifestations including intermittent pyrexia. Elevated rectal temperatures of up to 105 and 106 degrees F were recorded, respectively, in all bulls infected with T. vivax or T. congolense. Mean parasitaemia was higher and more chronic in T. congolense-infected bulls and ranged between means of 0 and 3.06 in all infected bulls. There was a slight and transient drop in packed cell volume (PCV) of T. vivax-infected bulls as against a marked and more chronic drop in T. congolense-infected bulls. Mean PCV of T. vivax- and T. congolense-infected bulls and controls ranged between 28 and 38, 17 and 38, and 31 and 38%, respectively. Haemoglobin (Hb) concentrations also decreased in infected bulls. The decrease was greater and more chronic in the T. congolense-infected bulls. Values ranged between means of 10.47 and 13.84, 5.44 and 14.16, and 10.24 and 14.12 g dl-1 in T. vivax- and T. congolense-infected and control bulls, respectively. Total plasma proteins also decreased in infected bulls; this was more marked in the T. congolense-infected group. Values for T. vivax-infected, T. congolense-infected and control bulls ranged between means of 7.66 and 8.99, 6.26 and 8.81, and 7.94 and 8.78 g dl-1, respectively.2+ that the indigenous T. vivax strains are more     

Adrenal and thyroid dysfunctions in experimental Trypanosoma congolense infection in cattle.

Severe pathological changes were observed in the adrenal and thyroid glands of Zebu (Bos indicus) heifers infected with Trypanosoma congolense. In the adrenal glands, severe inflammatory changes characterised by mononuclear cellular infiltration in the subcapsular areas, zona glomerulosa, zona fasciculata and zona reticularis were observed. In addition, there were hyperaemia, haemorrhage and hyperplasia resulting in increased adrenal weight in the two heifers slaughtered on Days 50 and 70 post-infection (p.i.). In the medullary areas of these two heifers, there was only mononuclear cellular infiltration. In the two heifers slaughtered on Day 113, localised mononuclear cellular infiltration was observed in addition to cortical cell depletion and fibrosis, resulting in reduced adrenal weight when compared with the controls. In the thyroid glands of the infected heifers, gross enlargement of the follicles filled with pale staining colloids were observed in association with squamous metaplasia of the follicular epithelium and fibroplasia. Serum cortisol concentrations showed an appreciable but non-significant increase (P less than 0.05) between Weeks 2 and 6 p.i. in the infected heifers (5.6 +/- 0.86 ng ml-1 vs. 4.4 +/- 0.34 ng ml-1) when compared with the uninfected controls or the pre-infection level. Thereafter, cortisol levels declined though non-significantly throughout the rest of the study. However, there was a steady increase towards normal levels from Week 12 p.i. until the end of the experiment. Changes in the basal serum concentrations of thyroxine (T4) were also measured weekly. There was a progressive decrease in the levels of T4 from the third until the 11th week p.i., when the decrease became significant (P less than 0.05) and remained so until the 16th week when the experiment ended.     

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.     

Susceptibility of African buffalo and Boran cattle to Trypanosoma congolense transmitted by Glossina morsitans centralis

Four African buffalo (Syncerus caffer) and four Boran cattle (Bos indicus) were each exposed to the bites of 10 tsetse flies infected with Trypanosoma congolense. Although both groups of animals became infected, the buffalo showed no clinical signs of trypanosomiasis while the cattle suffered from the disease characterized by pronounced skin reactions, high parasitaemia and severe anaemia. The prepatent periods in the buffalo varied from 18 to 27 days in comparison with 11 to 14 days in the cattle. In the buffalo, skin reactions were only detectable by histological examination of skin biopsies, the peak of parasitaemia was at least a hundredfold below that in cattle and after 54 days parasites were no longer detected. In contrast, the cattle had a continuous high parasitaemia until they were treated with a trypanocidal drug 60 days after infection. Neutralizing antibody to metacyclic trypanosomes appeared in the buffalo during the prepatent period, 15-20 days after infection, whereas in cattle neutralizing antibody was not detected until 10 days after the first peak of the parasitaemia, 25-30 days after infection.     

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.     

Factors influencing the duration of isometamidium chloride (Samorin) prophylaxis against experimental challenge with metacyclic forms of Trypanosoma congolense

The duration of a single isometamidium chloride (Samorin) prophylactic treatment against Trypanosoma congolense ILNat. 3.1 and T. congolense IL 285 was examined in 24 Boran steers with regard to (1) the dose of drug, (2) the level of metacyclic challenge and (3) the influence of infection with an unrelated serodeme at the time of treatment. The cattle were repeatedly challenged at monthly intervals between 2 and 7 months following treatment, either by five infected Glossina morsitans centralis or by intradermal inoculation of 5 X 10(3) or 5 X 10(5) in vitro-derived metacyclic trypanosomes. A dose of 1 mg kg-1 afforded complete protection for 4 months and 0.5 mg kg-1 for 3 months against the two T. congolense serodemes examined, irrespective of the method or weight of challenge. In another group of cattle, which had an established infection at the time of treatment, the duration of chemoprophylaxis against an unrelated serodeme was the same as the other groups which had no previous experience of trypanosome infection. Antibodies to metacyclics did not appear in any of the cattle as long as the chemoprophylaxis was effective. An exception to this was the group challenged with 5 X 10(5) in vitro-derived metacyclic parasites, in which low antibody titres were detected. In all cases these proved to be non-protective. It was concluded that, under the experimental conditions employed, (1) there was a direct relationship between drug dosage and the duration of chemoprophylaxis, (2) the weight of metacyclic challenge did not affect the duration of chemoprophylaxis and (3) when used to treat an existing infection, isometamidium chloride exerted the same degree of chemoprophylactic activity.     

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)     

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.     

Susceptibility and immune responses of zebu and taurine cattle of West Africa to infection with Trypanosoma congolense transmitted by Glossina morsitans centralis

Following tsetse-transmitted infection with Trypanosoma congolense, major differences in development of localised skin reactions, the ability to control parasitaemia, the degree of anaemia and in antibody response to trypanosomes were found between the reputedly trypanotolerant breeds of cattle (N'Dama, N'Dama/Baoule crosses, Baoule) and the trypanosusceptible West African Zebu. The local skin reactions that developed in the Zebu were large and severe while those that occurred in the other breeds were smaller and less severe or mild. The timing of appearance of parasitaemia and the height of the first peaks were similar in all the animals, but the Zebu were less able to control subsequent waves of parasitaemia. Possibly reflecting these events, it was only in the Zebu that significant anaemia developed. Neutralizing antibody against homologous metacyclic trypanosomes developed between 14 to 18 days after infection in all breeds of cattle; however, marked differences were found when antibody to trypanosomes derived from first peak parasitaemias were tested in the Zebu and Baoule. Neutralizing antibody against these parasites appeared in the Baoule on day 24 but were not detected in Zebu until day 51. Furthermore, the antibody titres were 3 log2 higher in the Baoule. It was concluded that the trypanotolerance exhibited by the West African taurine cattle might be related to a) their ability to control trypanosome numbers in the skin and in the bloodstream, an outcome that was possibly brought about by the earlier and superior immune response and b) failure to develop anaemia which might be associated with their capacity to control parasitaemia.     

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.