Evaluation of a milk ELISA for the serodiagnosis of Dictyocaulus viviparus in dairy cows.
ABSTRACT An enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against the bovine lungworm Dictyocaulus viviparus in milk was established. This test is based on recombinant major sperm protein (MSP) as the antigen and ELISA results are expressed as optical density ratio (ODR) values. The cut-off value of the milk ELISA was determined as the arithmetic mean of negative milk samples plus three standard deviations (SD). Specificity and sensitivity were 100% and 97.5%, respectively, using either milk or serum samples as positive control to calculate the ODR. Therefore, the presented recombinant antigen-based ELISA is suitable for routine veterinary diagnosis of exposure to bovine lungworms using milk samples instead of sera. To assess the course of antibody titres following lungworm infection, milk and serum samples from experimentally infected dairy cows were collected over a period of 23-30 weeks in three trials. The milk and serum antibody titre curves showed strong Pearson correlation coefficients in all three trials (Trial 1=0.85; Trials 2 and 3=0.93). In milk D. viviparus-specific antibodies exceeded the cut-off value 30-32 days post-infection (dpi) and remained above this value until day 112-138 post-infection (pi) with an overall detection period of 79-107 days. Treatment with eprinomectin during the pre-patent period prevented larval shedding and the antibody response was eliminated; treatment during patency similarly caused a cessation of larval shedding, but had no effect on the pattern of antibody responses compared to the untreated, infected controls.