Abstract
The bulk milk enzyme-linked immune sorbent assay (ELISA) is a rapid and inexpensive method of assessing herd exposure to pathogens that is increasingly being used for the diagnosis of parasite infections in dairy herds. In this paper, with the dairy herd health veterinarian in mind, we review the principles of the assay and the recent literature on the potential role of bulk milk ELISA for the diagnosis of ostertagiosis, fasciolosis, parasitic bronchitis due to cattle lung worm and neosporosis. It is generally accepted that assay results reflect exposure to the parasite rather than the presence of active infection. Bulk milk ELISA can be a useful tool for the veterinary practitioner as a component of a herd health monitoring programme or in the context of a herd health investigation. It can also play a role in regional or national surveillance programmes. However, the results need to be interpreted within the context of the herd-specific health management, the milk production pattern and the parasite life cycle.
Highlights
This review paper emerged from discussions within the Animal Health Ireland (AHI) Technical Working Group for Parasite Control which identified a need to seek as much scientific clarity as possible in relation to the usefulness of bulk milk testing for parasite infections within the Irish dairy herd
If most individual antibody levels are only just above the cut-off, bulk milk results might be negative even if more than 15% of animals are infected. In spite of these drawbacks, bulk milk enzyme-linked immune sorbent assay (ELISA) testing is considered an effective tool in tracking N. caninum prevalence at herd level [68], since control measures for the disease currently focus on minimising the seroprevalence within herds [23]
Investigative protocols are employed to identify the cause and appropriate control strategies implemented. The effects of these controls on farm performance are monitored and the cycle begins again (Figure 1) [82]. This concept is central to all aspects of herd health management including parasite control
Summary
This review paper emerged from discussions within the Animal Health Ireland (AHI) Technical Working Group for Parasite Control which identified a need to seek as much scientific clarity as possible in relation to the usefulness of bulk milk testing for parasite infections within the Irish dairy herd. If most individual antibody levels are only just above the cut-off, bulk milk results might be negative even if more than 15% of animals are infected In spite of these drawbacks, bulk milk ELISA testing is considered an effective tool in tracking N. caninum prevalence at herd level [68], since control measures for the disease currently focus on minimising the seroprevalence within herds [23]. Since no effective treatment is available to prevent either abortion or transplacental transmission, the only management practice open to the farmer is not to breed from seropositive animals It is to be expected, that selective breeding together with restricting canine access would, over time, lead to a reduction in antibody levels in the bulk milk sample of a herd, but to our knowledge there are no published records. Further surveillance and monitoring may lead to models associating climate with levels of Neospora occurrence
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