Dynamics of porcine humoral responses to experimental infections by Spanish Trichinella isolates: comparison of three larval antigens in ELISA.

Five groups of six helminth-free pigs of the Iberian and Landrace x White breeds were each experimentally-infected randomly at a dose of 150 larvae per kg, body weight with one of the five Trichinella isolates, coded as Gm-1, Co-77, Laso, C-76 and Mad-83. These isolates were selected from the two Trichinella species (T. spiralis and T. britovi) so far identified in the Iberian Peninsula. Specific antibodies against the infections were measured on days -14, 0, 6, 16, 20, 27, 34, 49, 63 and 82 post-infection (p.i.), in a comparative indirect ELISA assay using three different antigens prepared from the muscle stage of the parasite. The antigens were a crude saline larval extract (CSLE), excretory-secretory (ES) and surface stripped cetyl-trimethyl ammonium bromide detergent (CTAB) products. Over all, the dynamics of antibody responses were very similar for infections with the five different isolates, although a significant delay in positive and maximum antibody titres was seen in the group infected with C-76, the isolate exhibiting a marked low infectivity to domestic mammals. ELISA with the crude antigen was more sensitive (positive antibody titres appeared between days 6 and 16 p.i.) than with the ES and CTAB preparations (positive titres appeared between days 16 and 20 p.i.). For infections with the C-76 isolate, positive titres appeared between days 16 and 20 p.i. with the CSLE antigen and, on day 27 p.i. with the ES and CTAB antigens. Little cross-reactivity with other common porcine helminth infections appeared only when ELISA was carried out with CSLE and CTAB antigens.