Enzyme Immunoassay Detection of Immunoglobulin M and G Antibodies to Cryptosporidium in Immunocompetent and Immunocompromised Persons

Abstract

Cryptosporidium is a parasite of the human gastrointestinal tract and has a worldwide distribution. We developed a sensitive and reproducible enzyme immunoassay for detection of serum IgG or IgM to Cryptosporidium. For IgG, 13 of 15 patients with cryptosporidiosis and 26 of 26 patients with cryptosporidiosis and AIDS were positive, whereas 57 of 60 presumably uninfected individuals were negative. All three IgG-positive presumably uninfected individuals had been potentially exposed. Sensitivity and specificity of this assay was 95%. Patients without AIDS showed an early rise and fall of IgM and later elevation of IgG; some patients with AIDS produced IgM, and all produced IgG. Sera from 9 (20.9%) of 44 Ecuadorian children with diarrhea were positive for both IgM and IgG antibodies; 106 sera from persons with other parasitic illnesses showed a normal distribution for IgG antibody. These ELISA data show that patients without and with AIDS have serum antibody response to Cryptosporidium and suggest that exposure to or infection with Cryptosporidium is common.

Human cryptosporidiosis: detection of specific antibodies in the serum by an indirect immunofluorescence

“…When specific serum IgG and IgM were measured in patients that had oocyst excretion not determined (groups E and H), the prevalence was 4% and 12%, respectively. This finding was quite similar to those of other reports, one employing IIF test 3 and another ELISA 24 , both demonstrating a somewhat higher rate of detection of IgM and IgG in serum samples of patients from a general population with oocyst excretion not determined. The relatively higher than expected IgM frequency could be attributed to a constant antigenic challenge by frequent oocyst ingestion or to a persistent IgM immune response, specific to this parasite.…”

“…Similar findings were reported elsewhere, when only 4 of 26 patients had a positive IgM test by ELISA 24 . This fact could be explained by the low specific IgM response reported in patients with other acute protozoan diseases 24 .…”

“…1B). Sera were considered positive when this characteristic pattern was observed with a 1:10 or greater dilution of the sera for IgG 10,24,25 and with 1:20 or greater dilution for IgM.…”

“…Other sources of oocysts, like ileum from suckling mice infected with Cryptosporidium were also used elsewhere, but visualization of oocysts in this material requires highly trained observers 2 . The ELISA test for both immunoglobulin classes has been described but false positives occurred due to cross-reaction with antibodies from other infections 24 . In the above test, specific absorption studies were used to prove the specificity of the reaction, showing that the approach used provided specific antibody detection.…”

“…Although the host defense mechanisms responsible for controlling Cryptosporidium infections are poorly understood 29 , many studies demonstrated the development of specific serum IgG 7 , IgA 13 , IgM 24 and IgE 3 responses in humans and other animals 16 .…”