Diagnostic Performance Characteristics of Serum Chemistry in the Detection of Cysticercus fasciolaris in Brown Rats (Rattus norvegicus)

Aim: Brown rats (R. norvegicus), a natural intermediate host for Cysticercus fasciolaris, are widely distributed in Grenada. C. fasciolaris causes cysts in a number of organs, but with greater frequency in the liver. The purpose of this study was to investigate the alterations of serum chemistry particularly serum proteins and activity of liver enzymes associated with liver cysts in brown rats infected with C. fasciolaris, as well as to assess their performance in the diagnosis of Cysticercus fasciolaris.

Study Design: In this cross sectional study, 170 brown rats were anesthetized and blood was obtained directly from the heart and collected in red-top tubes. The rats were then euthanized, and dichotomously classified as positive or negative for Cysticercus fasciolaris based on the presence or absence of Cysticercus fasciolaris-associated cysts, grossly and/or histopathologically.

Methodology: For both groups of rats (positive or negative), the concentrations of each specific protein (g/dL), selected liver and pancreatic enzymes (U/L), metabolic waste products (mg/dL) and electrolytes (mg/dL) were measured using Vet Test (IDEXX, USA). Cut-off points for test values of liver enzymes were set at 2-fold or greater than upper reference limit. For all other analytes, test values that were outside the reference interval were considered to be diagnostically relevant. In order to determine the diagnostic performance and agreement between liver enzymes and Cysticercus fasciolaris-associated liver cysts, predictive values and Cohen’s kappa statistics, respectively were calculated.

Results: The activity of AST significant increased among the infected brown rat population. The sensitivity and specificity of AST in detecting Cysticercus fasciolaris in brown rats was 76% and 59%, respectively. The positive and negative predictive values of AST were (80%) and (35%) respectively. Based on Cohen’s kappa, AST showed good agreement to gross/histopathology [0.4, 95% CI 0.16 – 0.53, SEkappa 0.42] in the detection of Cysticercus fasciolaris-associated liver cysts.

Conclusion: AST is the most reliable enzyme in detecting Cysticercus fasciolaris in brown rats, and thus C. fasciolaris should be included among the differential diagnoses whenever increased serum activity of AST are observed in brown rats.