Comparison of diagnostic tests for Giardia detection in wild ungulates: is ELISA test a good choice?

Giardiasis is one of the most common parasite intestinal infections in humans, wild and domestic animals worldwide, and therefore constitutes a potential zoonotic and zoo-economic risk. However, little information is currently available about its presence or its effect on wildlife populations. Immunofluorescence (IF) is the most widely used assay for Giardia detection, also in wild bovids. In the present study, IF was used as a comparative test in order to evaluate the performance of immunoenzymatic testing (ELISA) as a diagnostic option. Fecal samples were collected from 166 alpine chamois (Rupicapra rupicapra rupicapra), culled during the 2013-2015 hunting season in the Central Italian Alps. Samples were divided into two portions; the first was stored in potassium dichromate (2.5%) and subjected to immunofluorescence analysis (MERIFLUOR® Cryptosporidium/Giardia), while the second was frozen at -20°C and subjected to immunoenzymatic testing. A commercial ELISA kit (RIDASCREEN® Giardia) was used, and the agreement between the analytical approaches was assessed by calculating the Kappa (K) value (EpiTools, Ausvet; CI 95%). A Giardia prevalence of 7.8% (13/166) and 6.6% (11/166) was recorded by IF and ELISA respectively, thus showing a substantial agreement (k-value = 0.73) between the two tests. The ELISA test could therefore represent a good choice and an alternative tool for direct giardiasis diagnosis in wild ungulates because it has several advantages: it is cheaper, can be used to carry out simultaneous screening of numerous samples, and also provides objective spectrophotometer reading and antigen detection. Molecular analyses will make it possible to obtain further data in order to evaluate the actual performances of the ELISA test for Giardia detection, and support its application in a context involving wildlife.