Oestrus ovis (Diptera: Oestridae): sheep humoral immune response to purified excreted/secreted salivary gland 28 kDa antigen complex from second and third instar larvae

Abstract

The potential of Oestrus ovis larvae excretory–secretory products (ESP), crude extract, salivary gland contents (SGc) and digestive tube contents (DTc) proteins from O. ovis larvae as antigens in serological assay were analyzed and compared. This study demonstrated that excretory–secretory proteins were produced mainly by digestive tube and salivary gland. The main antigenic component of ESP was a 28 kDa protein complex (pc28) synthesized by the salivary gland ring. After purification, its diagnostic value was estimated by an ELISA using sheep sera sampled in summer ( n=30) and winter ( n=69) in order to investigate the relative importance of wintering hypobiotic first instar larvae on animal responsiveness. ELISA test based on pc28 antigen was compared to a reference ELISA test based on second instar larvae crude extract. After comparison it appeared that the pc28 test was much more specific (87%) and more sensitive (90%) in summer. Anti-pc28 antibody titers were significantly higher in summer than in winter demonstrating the impact of summer developing larvae on the humoral systemic immune response. This data was correlated to the maturation of larvae in summer as the number of larvae at necropsy was significantly higher in winter, when the larval population is only represented by first instar larvae, than in summer. No correlation was observed between the mean antibody titers and the number of larvae.