Infectivity and virulence in a serodeme of Trypanosoma vivax

The course of infection by a mouse-adapted Trypanosoma vivax was studied. Serological variants were isolated from sheep and their infectivity and virulence were studied in mice and sheep. Isolates obtained in the early stage of the infection were highly virulent while isolates obtained at the terminal stage of the infection were found to be extremely virulent in both mice and sheep. Trypanosoma vivax organisms isolated in between these series of parasitaemias were of low to moderate virulence in both groups of animals. The degree of virulence exhibited by each isolate was closely related to the viability of the organisms. The success of making clones was equally found to be related to the virulence of the isolates.     

Effect of isometamidium on Trypanosoma congolense infectivity

Isometamidium chloride (Samorin, RMB, England) is a widely used and highly effective trypanocide for the treatment of bovine trypanosomiases. However, the appearance of isometamidium-resistant populations of T. congolense in Africa makes it necessary to develop methods for the rapid and reliable detection of drug resistance in the laboratory. Currently available tests are time-consuming and/or expensive. In the present study, the short-term in vitro incubation of trypanosomes in a range of isometamidium concentrations and the infectivity of the parasites in mice has been assessed. A series of T. congolense isolates were used which were known to differ in their in vivo sensitivity to the drug. The results showed a close correlation between the known level of resistance and the capability of trypanosomes to remain infective after incubation in isometamidium. Thus isolates displaying a high level of resistance in vivo remained infective following incubation in higher concentrations of drug. This assay may provide a simple and reliable method for detecting drug resistance in T. congolense.     

Trypanosoma congolense infection in two dogs

Trypanosomiasis, caused by Trypanosoma congolense, was diagnosed for the first time in Israel in two boxer dogs imported from Kenya. The dogs developed clinical signs two days after arrival and succumbed to the disease within four days. The major clinical and clinicopathological findings included anaemia, haemorrhages, lymphadenomegaly, hepatosplenomegaly and neurological signs. Histopathology showed lymphocytic-plasmacytic infiltration in the skin, brain, meninges, kidney and liver.     

Effect of strains of mice and challenge dose on the infectivity and virulence of Trypanosoma vivax

Factors influencing the infectivity and virulence of clone-derived Trypanosoma vivax for mice were investigated using a titration technique capable of recognizing differences in magnitude of about 10-fold. Marked differences were observed in the susceptibility and duration of infection in four inbred strains of mice after low dose (10(2.2)ID63) challenge. Only mild differences in survival period were observed when challenge doses of 10(3.2) and 10(4.2)ID63 per mouse were used. In all tests, Balb/C mice were most susceptible while CBA mice were most resistant. Long survival of infected mice was highly correlated with frequent occurrence of remission of parasitaemia. Infectivity of T. vivax isolates varied during the course of an infection, being high at the early stages of the infection and very low at later stages.     

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。     

Diminazene aceturate residues in the tissues of healthy, Trypanosoma congolense and Trypanosoma brucei brucei infected dogs

The tissue distribution and residue profile of diminazene aceturate was investigated in healthy dogs and in dogs infected with Trypanosoma congolense and Trypanosoma brucei brucei. The drug was administered at 3.5 mg/kg i.m. and tissue samples were taken post mortem from the animals at 48, 72, 120, 168 and 240 h after injection. The drug was distributed to various organs and tissues of the body with the highest concentrations occurring in liver and kidney. Higher drug levels were obtained in the tissues of healthy dogs compared with trypanosome infected animals except in the brain. The levels of residues in the healthy animals were significantly different (P less than 0.05) from those of the infected dogs. The drug residues were still detectable in the tissues of the animals 10 days after drug administration.     

Two enzymically distinct stocks of Trypanosoma congolense

Two stocks of Trypanosoma congolense, isolated from a sheep and a goat on the Kenyan coast, were found to be distinctly different from 112 other stocks of the same species after comparing, by isoenzyme electrophoresis, trypanosomes originating from various parts of Africa. The results show a marked genetic distinction that may be of epidemiological or taxonomic significance.     

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.     

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.     

Interference between drug-resistant and drug-sensitive stocks of Trypanosoma congolense in goats

A study was undertaken in goats to investigate the ability of two unrelated stocks of Trypanosoma congolense, one of which is highly sensitive to isometamidium chloride and one which is drug-resistant, to become established in the presence of an existing infection with the other stock. The goats, which were initially infected with the sensitive strain and were then challenged with the resistant strain, were cured by treatment at 0.1 mg kg-1 isometamidium, indicating that the resistant stock did not establish an infection. Goats initially infected with the resistant stock, which were then challenged with the sensitive stock, experienced temporary remission of infection followed by relapse after treatment at 0.1 mg kg-1 isometamidium. In contrast, the goat infected only with the resistant stock remained parasitaemic following treatment at 0.1 mg kg-1. This suggests that superinfection with the sensitive stock resulted in the establishment of infection, which suppressed the resistant stock to below the limit of detection of the method used. These observations suggest that isometamidium-resistant stocks may be less viable than sensitive strains, and could explain the relative scarcity of isometamidium resistant in the field.     

Prevalence of mixed Trypanosoma congolense infections in livestock and tsetse in KwaZulu-Natal, South Africa

Trypanosoma congolense causes the most economically important animal trypanosomosis in Africa. In South Africa, a rinderpest pandemic of the 1890s removed many host animals, resulting in the near-eradication of most tsetse species. Further suppression was achieved through spraying with dichlorodiphenyltrichloroethane (DDT); however, residual populations of Glossina austeni and G. brevipalpis remained in isolated pockets. A total of 506 of these tsetse flies were captured in the Hluhluwe-iMfolozi Park, the St Lucia Wetland Park and Boomerang commercial farm. The polymerase chain reaction (PCR) was used to determine the infection rate and frequency of mixed infections of these flies. Additionally, 473 blood samples were collected from cattle at communal diptanks and a commercial farm in the area and each one examined by the haematocrit centrifugation technique (HCT). Furthermore, buffy coats from these blood samples were spotted onto FTA Elute cards and the DNA extracted from each one tested using 3 separate PCRs. The HCT revealed the presence of trypanosomes in only 6.6% of the blood samples; by contrast, species-specific PCR detected trypanosome DNA in 50% of the samples. The species-specific PCR detected trypanosome DNA in 17% of the tsetse flies, compared with the nested PCR targeting rDNA which detected trypanosome DNA in only 14% of the samples. Over time, the transmission of Savannah-type T. congolense and Kilifi-type T. congolense as mixed infections could have an impact on disease manifestation in different hosts in the area.     

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.     

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.     

Depressed immunoconglutinin responses in calves experimentally infected with Trypanosoma congolense

Contrary to expectation, immunoconglutinin levels failed to rise significantly in calves infected with Trypanosoma congolense. In addition, it was shown that trypanosome infection appeared to inhibit the immunoconglutinin response to Brucella abortus strain 19. The possible reasons for these findings are discussed.