Swine cysticercosis in the Karangasem district of Bali, Indonesia: An evaluation of serological screening methods

Abstract

A serological assessment was undertaken on pigs from the Kubu and Abang sub-districts of Karangasem on the island of Bali, Indonesia, where earlier studies had detected patients with cysticercosis. Antigens purified from Taenia solium cyst fluid by cation-exchange chromatography were used to evaluate antibody responses in the pigs and the serological tests were also evaluated using sera from pigs experimentally infected with T. solium eggs. A total of 392 serum samples from naturally exposed pigs were tested using an ELISA that could be read based on both a colour change perceptible by the naked eye and an ELISA based on absorbance values. Twenty six (6.6%) pigs were found seropositive by the naked-eye ELISA and were categorized into three groups: strongly positive (absorbance values >0.8, n=6), moderately positive (absorbance values between 0.2 and 0.8, n=7), and weakly positive (absorbance values <0.2, n=13). Necropsies performed on 11 strongly and moderately positive pigs revealed that six strongly positive pigs were infected either solely with T. solium cysticerci (n=3), or co-infected with both T. solium and Taenia hydatigena (n=3). Four moderately positive pigs were infected solely with T. hydatigena. No cysticerci were found in one pig that was moderately positive by the naked-eye ELISA. Two experimentally infected pigs became antibody positive by 6 weeks post-infection, whereas eight control pigs remained negative. An additional 60 pigs slaughtered at authorized abattoirs on Bali were tested using the same ELISA. All 60 pigs were seronegative with no evidence of Taenia infection at necropsy. The results confirm the presence of porcine cysticercosis on Bali and, while the serological responses seen in T. solium infected animals were much stronger than those infected with T. hydatigena, the diagnostic antigens are clearly not species specific. Further studies are necessary to confirm if it is possible to draw a cut off line for differentiation of pig infected with T. solium from those infected with T. hydatigena.

Keywords: Bali; Cysticercosis; ELISA; Indonesia; Necropsy; Pig; Serology; Taenia hydatigena; Taenia solium; Western blot.