Actinobacillus pleuropneumoniaeestudio de la inmunidad maternal mediante ensayos inmunoenzimáticos frente a las toxinas RTX (Apx I, II, III y IV) y la proteína de membrana OmpA

Resumen

In this study, the evolution of maternal antibodies against RTX toxins (ApxI, II, III and IV) and against the OmpA protein of Actinobacillus pleuropneumoniae from birth to 10 weeks of life was studied. For this purpose, enzyme-linked immunosorbent assay (ELISA) tests against Apx toxins I, II, III, and IV and OmpA protein were used on 42 piglets from 7 sows from a commercial sow farm positive for the bacterium. Blood serum samples were taken from the sows 24 hours after farrowing and from the piglets 24 hours after farrowing, and then every 7 days until the 10th week of life, to determine the dynamics and duration of these antibodies. Another objective of the present work was to prevent the piglets from being colonised by the bacteria, and thus ensure that the antibodies detected were exclusively due to those transmitted by their mother. To this end, a protocol was carried out consisting of antibiotic treatment of all the sows on the day of farrowing, as well as 11 days after lactation. On the other hand, selected piglets were treated with another antibiotic every 14 days from the second to the sixteenth week of age. This was checked with serum samples taken at 18 weeks of age. On the other hand, the behaviour of these serological tests against ApxI-IV toxins and OmpA protein in A. pleuropneumoniae negative animals was evaluated, analysing the possible presence of antibodies due to other pathogens with ApxI-III toxin production or other antigenically related RTX toxins, or with membrane proteins that could present serological cross-reaction with the tests used. After analysis of the results, it was observed that in all cases the level of maternal antibodies determines the level of antibodies in the piglets at 24 hours. The half-life of these antibodies can be very different depending on the antigen in question, finding half-lives of less than 2-3 weeks in the case of the antibodies against ApxI, ApxIII toxins and the OmpA protein, as well as higher half-lives in the rest, exceeding 5 weeks in the case of ApxII and 8 weeks in the case of ApxIV, with the latter two finding a considerable number of animals with maternal antibodies at 10 weeks of life. Moreover, the amount of maternal antibodies is not homogeneous in all piglets at 24 hours of life. This heterogeneity is influenced by the antibody level of the sow. A high number of animals on the negative farm have been observed with antibodies to ApxII toxin. This fact indicates that antigens that may be present in other bacteria, such as ApxI-III toxins, could lead to serological cross-reactions with ELISA tests against them, thus presenting a low specificity for the detection of A. pleuropneumoniae infections . In negative animals, the concordance observed between the tests for detection of antibodies against ApxIV toxin and against OmpA protein is very high, and the concordance of the test for detection of antibodies against ApxII toxin with respect to the other tests is very low. The best strategy to evaluate the A. pleuropneumoniae status of a farm is the combination of several serological tests against different antigens. Finally, with the established prophylactic protocol, no seroconversion of the animals was detected with any of the tests performed until at least the 18th week, and the success of this protocol to avoid the infection of the animals until approximately the 14th week of age can be established.