Bruikbaarheid van een Tankmelk ELISA voor het aantonen van longwormuitbraken

Abstract

Infections of the bovine lungworm Dictyocaulus viviparus are the main cause for respiratory disease in (young) cattle. Increasing numbers of clinical lungworm infections are being seen in herds of adult dairy cows in the Netherlands. Serological testing is one of the methods being used to diagnose these infections. Recent studies have suggested the detection of antibodies with an enzyme-linked immunosorbent assay (ELISA) in milk samples instead of sera as a possible tool to diagnose lungworm infections. To assess the value of the detection of antibodies in bulk milk in order to diagnose clinical outbreaks, 16 affected and 21 non-affected (control) herds of adult cattle have been sampled on faeces, sera and bulk milk. Two types of ELISA using two different antigens from adult worms (the ‘Hannover’ ELISA based on a recombinant Major Sperm Protein; the ‘GD’ ELISA based on a specific low molecular weight antigen) were tested. The results were said to be positive or negative in relation to a set cut-off value expressed as Optical Density Ratio (ODR). The ‘Hannover’ ELISA exhibited a sensitivity and specificity of 50% and 90,5% for detecting outbreaks using a cut-off value of 0,493. The ‘GD’ ELISA showed a sensitivity and specificity of 100% and 28,6% using a cut-off value of 0,07. Although both ELISA’s could not satisfactory distinguish affected herds from non-affected herds, they were predictive of the % seropositivity of the individual animals in the herd. In addition, a national survey has been executed to estimate the prevalence of outbreaks in herds in the Netherlands. In October of 2010 305 dairy farms were sampled on bulk milk in order to assess the level of lungworm antibodies. 60 farmers were contacted and asked whether clinical signs of lungworm were or had been present during the current season. Using the ‘GD’ ELISA 81% of the 305 herds was positive for antibodies. Out of 60 herds, 4 had experienced clinical signs of lungworm (6,7%). Out of these 4 bulk milk samples, 3 samples originated from a group of 20 samples with an ODR between 0,24 – 0,37 (15%). Apparently, the results of the ELISA reflect a kind of seroprevalence and do not in any way show a prevalence in clinical outbreaks of lungworm.