Abstract
BackgroundMycobacterium avium subsp. paratuberculosis (MAP) infections in cattle are generally challenging to detect and cost-effective test strategies are consequently difficult to identify. MAP-specific antibody ELISAs for milk and serum are relatively inexpensive, but their utility is influenced by a number of factors such as herd size, herd composition and diagnostic sensitivity. The sensitivity of the test increases with the age of the tested animal, and therefore the general, or “mean effective sensitivity” (defined as the mean of the sensitivities for all animals within a population, MES), for detecting MAP within a herd is dependent upon the age distribution of the herd. For this study we used a dataset of cattle from 4,259 dairy herds and 4,078 non-dairy herds. The aim was to investigate the MES for groups of cattle considered to be reasonable entities for MAP surveillance and control, in order to assist the decision-makers in planning and optimizing these programs economically. We compared six different groups of cattle (three dairy and three non-dairy) in Denmark by calculating the MES for each herd in each group.ResultsThe distribution of MES showed a large variation within and between groups, and in some groups we found a bimodal distribution of MES. Dairy herds generally showed higher MES than non-dairy herds. Dairy herds in a control programme for paratuberculosis showed a MES similar to all other dairy herds from which animals > 2.0 years were tested (both groups had a median MES = 0.60). For the non-dairy groups, the sensitivity became much higher when animals < 2.0 years and herds with less than 25 cattle were excluded, resulting in a median MES of 0.65.ConclusionThe results showed that MES could indicate the effectivity of testing different cattle groups for MAP, given that the data used are unbiased.
Highlights
Mycobacterium avium subsp. paratuberculosis (MAP) infections in cattle are generally challenging to detect and cost-effective test strategies are difficult to identify
The diagnostic test sensitivity of ELISA for detection of infectious animals has been estimated at approximately 30 % [6], it is affected by the test brand, the chosen cut-off value, and corresponding specificity among other factors, and the sensitivity increases if the animals are tested soon after they begin to shed [7]
The results are useful for optimizing MAP surveillance programs with regards to sensitivity, cost and number of samples to take from different groups
Summary
Mycobacterium avium subsp. paratuberculosis (MAP) infections in cattle are generally challenging to detect and cost-effective test strategies are difficult to identify. Paratuberculosis (MAP) infections in cattle are generally challenging to detect and cost-effective test strategies are difficult to identify. The sensitivity of the test increases with the age of the tested animal, and the general, or “mean effective sensitivity” (defined as the mean of the sensitivities for all animals within a population, MES), for detecting MAP within a herd is dependent upon the age distribution of the herd. The most common diagnostic tests are associated with high costs or low performance, and their sole use in controlling MAP in cattle herds as part of a test-and-cull strategy is not generally advised [2,3,4]. The herd-specific diagnostic sensitivity describes the probability of detecting MAP within a specific herd This will depend on the age distribution within the herd, which may vary between different herds and production types such as dairy
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