Evaluation of an ELISA for the routine diagnosis of Dictyocaulus viviparus infections in cattle.

An enzyme-linked immunosorbent assay (ELISA) that detects antibodies against Dictyocaulus viviparus in experimentally and naturally infected cattle was evaluated for its sensitivity, specificity, the moment of seroconversion and persistence of the anti-D. viviparus response and precision. The first three parameters were compared with those of an indirect haemagglutination assay (IHA). Specificity and sensitivity of both assays were assessed in sera collected from calves experimentally infected with pure isolates of D. viviparus, Ostertagia ostertagi, Cooperia oncophora, Nematodirus helvetianus, Ascaris suum or Fasciola hepatica, and from parasite-naive calves. The specificity of both the ELISA and IHA was very high, 99.2% and 99.6%, respectively. The sensitivity of the ELISA (100%) was significantly higher than that of the IHA (78.1%). In experimentally infected cattle, D. viviparus-specific antibodies were first detected with the ELISA between days 28 and 42 post-infection (p.i.), whereas the IHA only became positive between days 42 and 70. With the ELISA, antibody levels persisted until day 168 p.i. The IHA remained positive until the end of the experiment (day 196). None of the vaccinated animals were seropositive with the ELISA, whereas 25% of the calves were seropositive with the IHA. The seroprevalence of D. viviparus infections was determined in a field study with 467 sera from cattle of 64 herds; 227 (48.6%) of the animals were seropositive with the ELISA whereas only 38 (8.1%) scored positive with the IHA. To determine the precision of the ELISA, a total of five laboratories participated in trials, in which panels of strong positive, positive, and weak positive candidate sera were tested blind according to an international (International Standard ISO 5725, 1986) standard procedure. The repeatability and reproducibility of the ELISA were 0-16% and 14-26%, respectively. After these promising results it was decided to introduce this ELISA in 1995 as a routine test in all Animal Health Services in the Netherlands, replacing the IHA and faecal examinations for lungworm.