Evaluation of commercial enzyme immunoassay (EIA) and immunofluorescent antibody (FA) test kits for detection of Cryptosporidium oocysts of species other than Cryptosporidium parvum.

A commercial enzyme immunoassay (EIA) (ProSpect Rapid Assay), a direct immunofluorescence antibody (IFA) test for stool testing (MERIFLUOR Cryptosporidium/Giardia), and an indirect IFA test for environmental testing (Hydrofluor-Combo Cryptosporidium/Giardia) were evaluated for detection of low public health risk Cryptosporidium oocyst isolates, and for C. parvum oocyst isolates from human and bovine feces that represent a high public health risk. There was no cross-reactivity of EIA with ova of eight medically important helminths, three Eimeria species oocysts, Sarcocystis cruzi sporocysts, and two Candida sp. isolates. All nine snake oocyst isolates (C. serpentis), two of seven lizard oocyst isolates, one turtle oocyst isolate, two avian oocyst isolates (turkey, C. meleagridis), one C. wrairi oocyst isolate from guinea pigs, one C. muris oocyst isolate from hyrax, one heifer C. muris isolate, and two C. muris-like oocyst isolates from a camel were positive by both IFA tests; six of these 19 oocyst isolates were EIA-positive. There was no difference in the sensitivity and specificity between direct and indirect IFA tests. The sensitivity of the EIA and both IFA tests to the C. parvum oocysts was 100%. The EIA showed less cross-reactivity with the non-C. parvum oocysts (24%) than direct or indirect IFA (76%), and was less sensitive to those isolates (20%) than both IFA tests (63%). A simulated sampling model for high and low public health risk Cryptosporidium oocysts showed that the low risk oocyst isolates may constitute up to 35% of all positive environmental samples by direct or indirect IFA determination, and up to 12% of all EIA positive samples. This study indicates a superiority of direct and indirect IFA and EIA for screening of human-or-bovine-origin fecal specimens, whereas testing of environmental samples may lead to misidentification of medically important isolates. The results demonstrated that the EIA kit can more accurately identify environmental samples containing oocytes pathogenic for humans than both IFA tests. The specificity of commercially available diagnostic kits to C. parvum should be critically examined for cross-species identification before they are recommended or adopted for use in testing environmental samples.