Utility of IgM Titers With IgG and C-Reactive Protein Quantitation in the Diagnosis of Suspected Encephalitozoon Cuniculi Infection in Rabbits

The objective of this study was to evaluate the utility of measuring IgM, IgG, and C-reactive protein (CRP) levels in rabbits with suspected Encephalitozoon cuniculi (ECUN) infection. Serum samples from 130 pet rabbits were submitted from veterinary clinics within the United States. Participating veterinarians completed a questionnaire that was used to classify rabbits as either non-ECUN suspect (n = 36) or suspected of having ECUN infection (n = 94). An enzyme-linked immunosorbent assay was used to detect IgG and IgM titers against ECUN. In addition, an immunoturbidimetric assay was used to detect CRP. In all, 50% of non–ECUN-suspect rabbits were IgG positive vs 95% of ECUN-suspect rabbits. When comparing the results from the 2 groups, higher titers of IgM and IgG and elevated CRP levels were observed in the ECUN-suspect group (P < 0.05). When examined alone, the positive predictive values of IgM, IgG, and CRP varied from 88% to 90%. The use of combinations of these tests decreased the sensitivity of the diagnostic panel but increased the specificity—resulting in a positive predictive value ranging from 92% to 100%. These data suggest that the use of multiple immunological tests appears helpful in diagnosing ECUN in rabbit patients exhibiting clinical signs consistent with infection.