Use of antigen-detection enzyme immunoassays in assessment of trypanotolerance in N'Dama cattle

Comparative sensitivity of antigen-detection enzyme immunosorbent assay and the microhaematocrit centrifugation technique in the diagnosis of Trypanosoma brucei infections in cattle

Four Boran cattle were infected with Trypanosoma brucei using Glossina morsitans centralis and were left untreated throughout the experimental period of 18 months. During this period, sequential blood samples were collected and examined for the presence of antitrypanosome antibodies and their antigens. Using the buffy coat technique (BCT), trypanosomes were detected in 38 (16.3%) of the 233 blood samples. Unlike the BCT, antigen-detection enzyme-linked immunosorbent assay (Ag-ELISA) diagnosed infections in 189 (81.1%) of the blood samples. These results were supported by the presence of antitrypanosome antibodies in the same samples. Thus Ag-ELISA was 5.5 times more sensitive than the BCT. Towards the end of the observation period, G.m. centralis tsetse were fed on the aparasitaemic cattle to determine whether they still harboured the infection as the persistent antigenaemia seemed to suggest. Bloodmeals from the four cattle were infective to tsetse, thus emphasising the importance of Ag-ELISA in diagnosis of sub-patent infections.

Quantitative phenotyping of N'Dama cattle for aspects of trypanotolerance under field tsetse challenge

Matching animal health and performance data were recorded over the 2 year period from weaning at 10 months of age on 255 N'Dama cattle in a high natural tsetse challenge situation in Zaire. Four parameters that are regarded as possible indicators of trypanotolerance, species of trypanosomes detected, length of time parasitaemic, intensity of parasitaemia (parasitaemia score), and anaemic condition as estimated by packed cell volume (PCV) values, were measured and the relative effects of changes in these parameters on trypanocidal drug requirements and growth were assessed. The effects of species of trypanosome on drug requirements and growth were directly measurable. In the case of the other three indicators, the effects on drug requirements and growth that would be brought about by a change of one standard deviation in each were calculated. This allowed comparison of similar sized changes in these three indicators that are of necessity recorded in dissimilar units. Trypanosoma vivax and Trypanosoma congolense infections had equal effects on the number of trypanocidal drug treatments required, an average of 0.61 treatments being administered to each infected post-weaner. A reduction of one standard deviation (SD) in length of time infected reduced the number of treatments required by 0.23 or 36% and an increase of 1 SD in PCV reduced the number required by 0.27 or 43%. Changes in parasitaemia score were not important. In the case of growth, a T. congolense infection reduced growth by 12.4 g day-1 or 8% more than a T. vivax infection. A reduction of 1 SD in length of time infected increased growth by 9.8 g day-1 or 6.5%, a reduction of 1 SD in parasitaemia score increased growth by 9.0 g day-1 or 6.0%, and an increase of 1 SD in average PCV increased growth by 8.4 g day-1 or 5.6%. The necessity to simultaneously measure the four criteria is clearly indicated by their approximately equal effects on the final performance trait of daily liveweight gain. Thus, absence of information on any of these criteria would significantly affect the accuracy of the estimate of an animal's overall trypanotolerance phenotype in this central African situation and reduce the progress possible in production projects involving N'Dama cattle.

Patterns of Trypanosoma vivax and T. congolense infection differ in young N'Dama cattle and their dams

Trypanosome infection was detected by the dark ground/phase contrast buffy coat microscopic technique in N'Dama cattle in a high natural tsetse challenge situation in Zaire. The data were used to compare the pattern of infection in very young animals and in their dams, and to evaluate how the pattern evolved in calves from birth to maturity, and thereafter in the different age groups represented by their dams. Five hundred and fourteen calves were evaluated at 3 week intervals for an average of 26 months each, over varying periods between birth and 42 months of age. Two hundred and sixty nine dams had matching records from parturition to calf weaning at 10 months. One month after weaning, animals were equally infected with Trypanosoma vivax and Trypanosoma congolense. From then until 42 months, the proportion of time an animal was infected with T. vivax relative to T. congolense gradually decreased. In the dams this trend continued from 4 years to at least 8 years of age by which time T. vivax infection was only one-third that of T. congolense infection. This finding is regarded as strong evidence of the ability of N'Dama cattle, in this region of Africa, to acquire significant control of the development of parasitaemia following T. vivax infection but apparently not following T. congolense infection. Pre-weaner calves, grazing with their dams, appeared to have considerable protection from, or be more resistant to, both T. vivax and T. congolense infections compared with their dams and to their own immediate post-weaning situations.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential of trypanotolerance as a contribution to sustainable livestock production in tsetse affected Africa

Tsetse transmitted trypanosomiasis is possibly the major constraint on livestock and agriculture development in Subsaharan Africa. Control of the disease has been based on vector control as well as on the use of trypanocidal drugs to treat or prevent infection in animals. Both control methods are effective but have proven not to be sustainable. Moreover, the development of a vaccine against trypanosomiasis is unlikely to be successful in the near future. On the other hand, trypanotolerant cattle, like the N'Dama can survive and produce in tsetse affected areas without interventions. This taurine breed has been indigenous to Africa for approximately 7,000 years and forms presently about 6% of the bovine population of Africa. Generally the N'Dama are kept in the rural areas by the small-scale farmer as a multi-purpose animal. Recent studies have defined management characteristics and assessed the production potential at the village level and under ranching conditions of N'Dama cattle exposed to various levels of tsetse challenge. Furthermore, experimental infections showed conclusively the superior resistance to the effects of infection of the N'Dama cattle when compared to zebu cattle and have confirmed that trypanotolerance is innate in N'Dama cattle. Studies have been conducted on development of protective humoral and cellular responses, the regulation of parasite multiplication and control of anaemia. These studies provided tools for identifying components of trypanotolerance. The ability to resist the development of anaemia in the face of infection, has shown to be correlated with the capacity to be productive; moreover, PCV values can serve as selection criterium for trypanotolerance. Subsequently, repeatabilities and heritabilities of trypanotolerance and performance traits were estimated.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of trypanotolerance criteria and their effect on reproductive performance of N'Dama cattle

One thousand and twenty-eight cow-year records were available from 260 N'Dama cows each having at least 2 years of monthly matching health and performance data over a 5-year period under a medium natural tsetse challenge in Gabon. Four hundred and fifty-eight calf/dam pairs were also available where the calf had been reared to weaning, both had monthly matching records and each cow had weaned at least two calves. Evaluations were carried out on effects of, and linkages between, environmental and stress factors, number and species of trypanosome infections, curative drug treatments given, anaemia measured by packed red cell volume (PCV), and performance measured by calf weaning weight, cow calving rate and cow weight change over the lactation period. Major findings were that over the period from calf birth to weaning, while calves and their dams grazing together had similar numbers of trypanosome infections detected, the Trypanosoma vivax: T. congolense ratios were very different: 1:0.7 in calves; 1:2.8 in cows. This indicated that some ability to control the development of parasitaemia following T. vivax infection might be being acquired, from weaning onwards. In cows, relationships between lowest PCV recorded and curative drug treatments given suggested that between 20 and 32% of trypanosome-infected cows were not being identified by the buffy coat parasitological diagnostic technique. The high level of curative treatment given (to 13.7% of cows over the calendar year, and to 40% of calves from birth to weaning) will have tended to reduce the variance and linkages between aspects of infection and PCV values, especially in calves. In calves, the influence of trypanosome infections, in both calf and dam, on their respective PCV values and hence on calf weaning weight was apparent. There was a 0.91 +/- 0.40 kg increase in calf weaning weight for each 1% increase in calf average PCV, and a 0.95 +/- 0.39 kg increase for each 1% increase in cow average PCV. In cows, there was a similar pathway of influence of T. congolense infection through the PCV values to calving rate--not significant with T. vivax infection. There was a 3.3 +/- 0.65% increase in calving rate for each 1% increase in average PCV. Repeatabilities of performance traits were in the normal range. Repeatabilities of numbers of trypanosome infections detected by the buffy coat technique were too low to have any practical significance. Repeatability of average PCV at 0.40 +/- 0.03 could allow PCV when infected to be used as one criterion of trypanotolerance.

Relationships between trypanosome infection measured by antigen detection enzyme immunoassays, anaemia and growth in trypanotolerant N'Dama cattle

Relationships were evaluated between trypanosome infection as measured by antigen detection enzyme immunoassays (antigen ELISA), anaemia as determined by average packed red cell volume (PCV), and animal performance as assessed by daily weight gain in 99 N'Dama cattle in Gabon exposed to natural tsetse challenge at 11.5 months of age and recorded 14 times over a 13 week period. Approximately half the animals were found to be infected for an average of five of the 14 times that they were examined: 38% with Trypanosoma congolense, 13% with Trypanosoma vivax and 49% with a mixed infection. Trypanosoma congolense infections had significant deleterious effects on animal growth, while T. vivax infections did not. Animals found on several occasions to be infected with T. congolense had significantly lower PCV values than those demonstrated to be infected on fewer occasions. No relationship was found between mean optical density (OD) values in antigen ELISA and PCV values. Animals capable of maintaining PCV values, even when antigen ELISA positive on a high number of occasions, grew at the same rate as uninfected animals. Animals that could not maintain PCV values when infected had poorer growth. Antigen ELISA has the potential to increase the efficiency of selection of trypanotolerant N'Dama cattle under tsetse challenge in the field, in three main ways. (1) Accurate identification of trypanosome species, especially in mixed species infections, clarifies relations between infection, anaemia and animal performance. (2) Detection of animals antigenaemic without patent parasitaemia could allow individuals with superior ability to control trypanosome infection to be identified. (3) More accurate measurement of the proportion of time an animal is infected allows more accurate evaluation of its anaemia control capability.