Movement of transmigrants and livestock from western Indonesia to southeastern areas of Irian Jaya near the border with Papua New Guinea may pose a risk of introducing
Agile wallabies and pademelons are highly susceptible to infection with T evansi. Wallabies, therefore, have the potential to spread T evansi within New Guinea and Australia if infection is introduced. Mortality is likely to be high thereby acting as an indicator of recent introduction. Histological changes seen in wallabies infected with T evansi are diagnostic for infections occurring in Australia and Papua New Guinea.
Two Ag-ELISAs, an IgG-specific antibody detection ELISA (IgG ELISA) and a card
agglutination test (CATT) for the detection of Trypanasoma evansi infections in buffaloes in
Indonesia, were compared. Diagnostic sensitivity estimates were obtained by testing sera from
139 Indonesian buffaloes which had been found to be infected by parasitological tests.
Diagnostic specificity was estimated by testing sera from 263 buffaloes living in Australia.
Response-operating characteristic curves were constructed, and optimal ELISA cut-off values,
which minimized the number of false–negative and false–positive results, were chosen. The IgG
ELISA had the highest sensitivity (89%) and the CATT had the highest specificity (100%).
There was a significant difference between the sensitivities (71 and 81%), but not between the
specificities (75 and 78%), of the two Ag-ELISAs. The four tests were further compared by
calculation of post-test probabilities of infection for positive and negative test results using a
range of prevalence values, and likelihood ratios. The results suggested that the CATT was the
best test to ‘rule-in’ infection (i.e. the highest probability of infection in test-positive animals)
and the IgG ELISA was the best test to ‘rule-out’ infection (i.e. the lowest probability of
infection in test-negative animals).
SUMMARYThe prevalence and incidence of Trypanosoma e ansi infections in village buffaloes in Central Java were estimated using parasitological tests, two antigen-detection ELISAs (2G6 Ag-ELISA and Tr7 Ag-ELISA), an antibody-detection ELISA (IgG ELISA) and a card agglutination test (CATT). Of 2387 village buffaloes tested in five districts, 4 % (95 % confidence interval [CI] : 3 %, 5 %) were positive with the microhaematocrit test (MHCT), 58 % (95 % CI : 56 %, 60 %) were positive with the 2G6 Ag-ELISA and 70 % (95 % CI : 68 %, 72 %) were positive with the Tr7 Ag-ELISA. An increasing prevalence with age was found and the proportion of positive buffaloes was highest in the over 84 months-old age-group (68 %) with the 2G6 Ag-ELISA and in the 37-60 months-old age-group (78 %) with the Tr7 Ag-ELISA. Parasitaemic buffaloes were found in more than half of the villages visited. Corrected village-specific prevalence values obtained with the two Ag-ELISAs ranged from 0 % to over 100 %, and prevalence differed significantly (P 0n0001) between villages in four of the five districts. Overall, 10 % of buffaloes tested in markets were found to be parasitaemic and 39, 56 and 47 % were found positive with the 2G6 Ag-ELISA, IgG ELISA and CATT, respectively. Incidence rates varied according to the test used and ranged from 0n22 (95 % CI : 0n09, 0n44) to 0n44 (95 % CI : 0n24, 0n76), per animal-year at risk, in two villages. The results highlight the importance of using validated diagnostic tests to obtain accurate estimates of prevalence and incidence. These parameters are needed, for example in mathematical models, for the development and evaluation of different control strategies for T. e ansi infections in buffaloes.
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