Anti-Ascaris suum IgG antibodies in fattening pigs with different respiratory conditions.

During their migration through the pig's body, Ascaris suum larvae cause significant damage to the lungs. Little is known about the actual impact of this tissue damage on the occurrence and severity of respiratory problems in industrial pig fattening farms. In this study, we evaluated the link between the serological response to two different A. suum antigen preparations and respiratory or meat inspection outcomes. Two different serological tests were used that measure antibodies against either the A. suum haemoglobin molecule or complete homogenate of the 3rd stage larva that migrate through the lungs. Firstly, serum samples were analysed that were collected from 19 herds in which the cause of acute clinical respiratory symptoms was either Actinobacillus pleuropneumoniae, A. suum, or a miscellaneous cause. This was done to test whether serological results could confirm pathological findings. Secondly, serum samples from 60 herds of finishing pigs with a history of high or low frequency of pleuritis at meat inspection (MI), but without acute respiratory symptoms at the time of sampling, were also submitted for serological evaluation using both tests. Regression models were used to search for potential associations between the proportion of pigs testing seropositive with MI results, in particular pathological changes related to the lungs. The results of both ELISAs were strongly associated (P  < 0.001) with pigs belonging to a herd where the respiratory problems could be attributed to A. suum by histology, indicating that both tests can be used to diagnose clinical respiratory outbreaks due to A. suum. In the herds without acute clinical respiratory symptoms, a positive association was found between the proportion of pigs testing seropositive and the percentage of livers rejected due to milk spots and with whole carcass condemnations. No association was found between Ascaris serology and lung pathology (pneumonia and pleuritis) registered at MI, however, challenging the likely involvement of Ascaris in the development of these lesions.