Re-visiting the detection of porcine cysticercosis based on full carcass dissections of naturally Taenia solium infected pigs

Abstract

Background: Taenia solium is a neglected zoonotic parasite. The performances of existing tools for the diagnosis of porcine cysticercosis need further assessment, and their shortcomings call for alternatives. The objective of this study was to evaluate the performance of tongue palpation and circulating antigen detection for the detection of porcine cysticercosis in naturally infected pigs of slaughter age compared to full carcass dissections (considered the gold standard). Additionally, alternative postmortem dissection procedures were investigated. A total of 68 rural pigs of slaughter age randomly selected in the Eastern Province of Zambia were dissected. Dissections were conducted on full carcasses (or half carcass in case cysticerci were already detected in the first half), including all the organs. Total cysticercus counts, location and stages were recorded and collected cysticerci were identified morphologically and molecularly. All sera were analysed with the B158/B60 antigen detecting ELISA (Ag-ELISA).

Results: Key findings were the high occurrence of T. solium infected pigs (56%) and the presence of T. solium cysticerci in the livers of 26% of infected animals. More than half of the infected carcasses contained viable cysticerci. Seven carcasses had T. hydatigena cysticerci (10%), out of which five carcasses were co-infected with T. hydatigena and T. solium; two carcasses (3%) had only T. hydatigena cysticerci. Compared to full carcass dissection, the specificity of the Ag-ELISA to detect infected carcasses was estimated at 67%, the sensitivity at 68%, increasing to 90% and 100% for the detection of carcasses with one or more viable cysticerci, and more than 10 viable cysts, respectively. Tongue palpation only detected 10% of the cases, half carcass dissection 84%. Selective dissection of the diaphragm, tongue and heart or masseters can be considered, with an estimated sensitivity of 71%, increasing to 86% in carcasses with more than 10 cysticerci.

Conclusions: Depending on the aim of the diagnosis, a combination of Ag-ELISA and selective dissection, including investigating the presence of T. hydatigena, can be considered. Full carcass dissection should include the dissection of the liver, kidneys, spleen and lungs, and results should be interpreted carefully, as small cysticerci can easily be overlooked.

Keywords: Antigen ELISA; Cysticercosis; Dissection; Liver; Pig carcass; Taenia solium; Tongue palpation.

Fig. 1

Overview of the T. solium cysticercosis infection level (total number of (viable) cysticerci; log₁₀-transformed; total number of cysticerci indicated with black circles and number of viable cysticerci with grey circles) and Ag-ELISA ratio (OD/cut-off; indicated with x) per pig (n = 68). Ag-ELISA ratios in black and red indicate T. hydatigena negative and positive animals, respectively. The dashed horizontal line indicates the cut-off value for a positive ELISA result, i.e. ratio = 1

Fig. 2

Relation between Ag-ELISA ratio and the total number of cysticerci (log₁₀-transformed; n = 38 T. solium positive animals; indicated in black) and the total number of viable cysticerci (n = 22 confirmed T. solium infected carcasses with viable cysticerci; indicated in grey). The curves represent the median spline plots, which use the cross medians to fit a cubic spline. Stata/IC 14.1 (StataCorp, College Station, TX, USA)