[The serological diagnosis of gastrointestinal nematode infections in cattle]

Ostertagia ostertagi and Cooperia oncophora are widely distributed and are the most important parasites affecting young bovine livestock. Therefore, there is a substantial need for sensitive and specific parameters in support of their diagnosis, especially for sub-clinical disease correlated to production loss. In this review, the value and the application as a diagnostic tool of pepsinogen, gastrin and antibody response are discussed. An increase in pepsinogen or gastrin reflects mucosal damage caused by an Ostertagia infection. Some controversy exists about the level of pepsinogen and gastrin, which may be considered indicative for the diagnosis of clinical and sub-clinical ostertagiasis. Pepsinogen levels between 3,000 tot 4,000 mU tyrosine are regarded indicative for subclinical disease, values in excess of 5,000 mU tyrosine are considered significant for diagnosing clinical disease. For gastrin, it is suggested that based on group means, values of 400 pg/ml are indicative for subclinical parasitic disease in calves with reduced daily weight gain, while threshold levels of > or = 1000 pg/ml gastrin are representative for clinical ostertagiasis. Antibody responses to Ostertagia and Cooperia can be assessed using the enzyme immunoassay (EIA). Until now, mainly crude worm extracts have been used as antigen source in the EIA. They are not species-specific as discussed experiments provide evidence of a close relationship between the onset of parasitic disease and the evolution of the group mean parameters. However, data demonstrate serious variations between animals, which impede a reliable individual diagnosis. For longitudinal epidemiological studies especially pepsinogen and gastrin have proven their value, exhibiting fast fluctuations induced by infection or as a result of treatment. Conversely antibody levels were found to be more stable and therefore are useful in large cross-sectional studies, enabling a rough assessment of the degree of infection.