[Diagnosis of bovine fascioliasis using serology of pools of sera. Interpretation in field conditions].

The efficacy of a serological test (ELISA with excretory-secretory products of Fasciola hepatica as an antigen) for the diagnosis of bovine fascioliasis was assessed under field conditions using pools of sera from 170 herds. Blood samples were collected from six to ten heifers and from five to ten adults in each herd. In 92 of the herds (Group 1) the animals had not been treated for fascioliasis; in 78 herds (Group 2), a fasciolicide had been used 3 to 6 months earlier. In each herd, three serum pools were examined: aliquots from all the animals sampled in a herd (GM); aliquots from heifers only (PM); and aliquots from the cows only (PM). Individual sera and the pools (GM and PM) were analyzed similarly and the specific antibody titer was calculated by comparison with laboratory standards. The antibody titer for pooled sera were correlated with the proportion of positive sera in the pool (P < 0.0001); but these could not be used to estimate the prevalence of seropositivity in a herd. Diagnosis based on pooled sera was less effective for the detection of low prevalences of seropositivity in Group 2 than in Group 1 because the antibody titer decreases after fasciolicide treatment. Infection was always detected using pooled sera in herds with a prevalence of seropositivity of more than 60% (GM) in Group 1, or with a prevalence of seropositivity of more than 70% in Group 2. The best method for herd diagnosis of fascioliasis was based on the presence of a positive test in either of the two PM groups. Using this method, all infected herds with a prevalence of seropositivity of more than 30% in Group 1, or 50% in Group 2, were accurately detected.