Enzyme immunoassay detection of antigen-specific immunoglobulin G antibodies in longitudinal serum samples from patients with cryptosporidiosis

Cryptosporidium parvum is a protozoan parasite that causes diarrheal illnes s in a wide range of mammalian hosts, including humans. Characteristic seru m immunoglobulin G (IgG) antibody responses to antigens in the 27- and 17-k Da size ranges have been shown to develop after infection, and several enzy me-linked immunosorbent assay (ELISA) and Western blot assay formats have b een used to measure these IgG levels in human serum. Using a collection of serial samples from laboratory-confirmed cryptosporidiosis patients, we com pared the results obtained by using two new ELISAs with those obtained with two different Western blot assays. When assayed with the large-format West ern blot, 97% of the 67 patients had a demonstrable antibody response on at least one occasion. The Cp23 ELISA correctly identified 93% of the samples that had a 27-kDa response by Western blot and 100% of the negative sample s. The Triton antigen ELISA detected 77% of the samples that had a 17-kDa r esponse by Western blot and 88% of the negative samples. The sensitivity of the Triton antigen assay was higher for samples collected between 16 and 9 2 days after the onset of symptoms (96%). The minigel-format Western blot d id not compare favorably with the large-format blot for the detection of an tibodies to the 27-kDa antigen (71% sensitivity). A half-life of about 12 w eeks was estimated for antibodies to both the 27- and 17-kDa antigens. We b elieve the Cp23 and Triton antigen ELISAs will be useful in epidemiologic s tudies of the prevalence of Cryptosporidium infection in the population.