Trypanosoma congolense: Expression of a heat shock protein 70 and initial evaluation as a diagnostic antigen for bovine trypanosomosis

A 69-kDa immunodominant protein of Trypanosoma congolense was identified as a member of the hsp70 family that is homologous to mammalian BiP. We report here the expression of the gene encoding the T. congolense BiP in a bacterial system. Dot blotting of the truncated recombinant proteins confirmed that BiP antigenicity is mainly located in the C-terminal third of the molecule. A recombinant fragment corresponding to this region was used as an antigen in an indirect ELISA and an initial evaluation of its diagnostic potential for bovine trypanosomosis was performed. The test showed limited sensitivity for detection of primary-infected cattle but was capable of accurately detecting secondary infections. As BiP and its derivatives may be produced at low cost under stable forms allowing standardization of the tests, they warrant further evaluation as antigens fro serodiagnosis of bovine trypanosomosis

A heat shock protein 70 of Trypanosoma congolense as a diagnositic antigen

A 69-kDa antigen of Trypanosoma congolense induces both IgM and IgG in experimentally infected cattle. Cloning and sequencing of the gene coding for this antigen revealed that it belongs to the heat shock protein 70 family (hsp70) and is homologous to mammalian immunoglobulin binding protein (BiP). Due to its high antigenicity, the trypanosome BiP may be useful for developing an antibody-ELISA. Further-more, since defined regions of the molecule are conserved in different species of trypanosomes, while others are specific for T. congolense, it may be possible to develop both a test with broad specificity (pan-trypanosome) and a T. congolense-specific test. In order to assess the diagnostic potential of the trypanosome BiP, seven recombinant fragments were expressed in a bacterial expression system. Preliminary tests were carried out using a recombinant truncated protein (C-25) as the antigen, with forty sera taken during T. congolense experimental infections. All 22 sera from infected cattle gave O.D. values above those given by sera from 18 non-infected cattle. Sera collected sequentially during experimental infections were then compared for their reactivity to a crude lysate or to C-25. The C-25 based assay was of low sensitivity in primary infections, but detected most positive samples during rechallenge infections. The disappearance of anti-C-25 IgG after trypanocidal treatment was faster than that of IgG to a T. congolense crude extract. Although further evaluation of C-25 is required, particularly as regards specificity, this antigen is one of the very few defined candidate antigens for the Development of a standardisable antibody-ELISA

Bovine T-cell responses to defined Trypanosoma congolense antigens during infection

Infections of cattle with tsetse-transmitted Trypanosoma congolense are accompanied by antibody responses to the variable surface glycoprotein (VSG) and to two major invariant antigens, a member of the hsp 70 family and a 33KDa cysteine protease. During primary infection, trypanotolerant N'Dama (Bos taurus) cattle exhibit higher levels of IgG1 to CP than susceptible Borans. Boran cattle, on the other hand, have high levels of IgM to irrelevant antigens. During rechallenge infections, N'Dama cattle have higher levels of IgG1 to hsp70 while Boran cattle exhibit high titres of IgM to this antigen. Although Boran cattle do generate high titres of IgM to hsp70, N'Dama cattle develop higher levels of specific IgG antibody (Authie et al., 1993b). These observations are consistent with a possible dysfunction in isotype switch from IgM to IgG in Boran cattle. Because of the central role of T helper cells in induction of Ig isotype switch, the difference in antibody responses between N'Dama and Boran cattle migh reflect defective T helper cell function in the susceptible breeds during infection. We undertook a study to analyse T-cell function in cattle during infection with T. congolense. T-cell proliferative responses to a recombinant form of the hsp70 (R63), cysteine protease and VSG were measured in a group of Boran cattle following primary challenge with T. congolense. The role of CD4+ and CD8+ cells in the response was also investigated

Trypanotolerance, an option for sustainable livestock production in areas at risk from trypanosomiasis

Trypanosomosis is one of the major constraints on animal production in areas of Africa which have the greatest potential for significant increases in domestic livestock populations and livestock productivity. While the eradication of trypanosomosis from the entire continent is an unrealistic goal, considerable effort has been invested in the control of this disease through the use of trypanocidal drugs, management of the vector and exploitation of the genetic resistance exhibited by indigenous breeds. There is little hope that a conventional, anti-infection vaccine will be produced in the near future. Drug resistance is developing faster than generally thought. The control of the tsetse fly has been attempted over many decades. The decreasing efficacy of available trypanocidal drugs and the difficulties of sustaining tsetse control increase the imperative need to enhance trypanotolerance through selective breeding, either within breeds or through cross-breeding. Trypanotolerance has been defined as the relative capacity of an animal to control the development of the parasites and to limit their pathological effects, the most prominent of which is anaemia. A major constraint on selection for trypanotolerance in cattle, for both within-breed and cross-breeding programmes, has been the absence of practical reliable markers of resistance or susceptibility. Distinct humoral immune response to trypanosome infection is the major feature of bovine trypanotolerance. The role that these responses play in the control of infection or disease is being addressed by ongoing research, but remains a matter of speculation at present. Results in recent years have shown that packed cell volume (PCV) in particular and parasitaemia, the two principal indicators of trypanotolerance, are strongly correlated to animal performance. However, although direct effects of trypanosome infections of PCV and growth are obvious, more sensitive diagnostic methods for reflecting parasite control are required so that individual animals can be categorised reliably for their parasite control capability. One key finding is the major contribution made by each of the indicators evaluated to the overall trypanotolerance variance. Preliminary genetic parameters for PCV provide evidence that trypanotolerance is not only a breed characteristic but is also a heritable trait within the N'Dama population; this brings new opportunities for improved productivity through selection for trypanotolerance. More reliable estimation of genetic parameters of the indicators may well show that these parameters must be handled simulateneously for optimal progress. This would require diagnostics for assessing parasite control capability that identify trypanosome species more accurately, especially in mixed infections. A major advantage of trypanotolerant livestock, particularly N'Dama cattle, is the resistance or adaptation of this breed to many of the important pathogens which prevail in the sub-humid and humid tropics. Research on practical indicators of resistance to these conditions will be required to establish relevant integrated strategies based on disease-resistant livestock. Selective breeding will require the integration of the traits that farmers hold important for their production systems

Exploitation of resistance to trypanosomes and trypanosomosis

While an increasing number of examples of innate resistance to disease are being identified in domestic livestock, resistance to the effect of trypanosomes is one of the best-recognized and most thoroughly investigated. Experimental and field studies reviewed in this chapter are providing the basic tools with which the trypanotolerance trait can be identified and exploited. Comprehensive evaluation of the degree of genetic determination of the different disease resistance traits, their heritability and their genetic correlations with each other and with animal performance traits should allow progress to be made in the Development of breeding programmes and policies. There is increasing recognition that Africa possesses animal genetic resources probably unparalleled in any other continent. Evidence that these resources can provide sustainable and environmentally sound solutions for some of the vast disease problems currently confronting Africa is now being found. Thus, the natural innate resistance possessed by breeds of cattle, such as the N'Dama and the West Africa Shorthorn, to trypanosomosis and to several other important infectious diseases is now accepted as an important component of national and regional disease-control programmes. The fact that these breeds also possess considerable production potential and that their disease-resistance traits could be exploited in crossbreeding offers an unparalleled opportunity to improve livestock production in the vast areas of Africa dominated by the tsetse fly, ticks and helminths, particularly as more market-oriented production evolves. Topics of discussion includes major hindrance to sustainability of livestock production in the tropics; trypanosomosis control; trypanotolerance - a major asset for sustainable livestock production under trypanosomosis risk; biology of trypanotolerance; exploitation of trypanotolerance traits; and multiple attributes of trypanotolerant livestock