ASSESSMENT OF THE CONVENTIONAL DETECTION OF FECAL CRYPTOSPORIDIUM-SERPENTIS OOCYSTS IN SUBCLINICALLY INFECTED CAPTIVE SNAKES

Fecal specimens of seven captive snakes naturally subclinically infect ed with Cryptosporidium serpentis were monitored for 131 days for the presence and concentration of oocysts. Thirty-three of 81 (41%) of the monoclonal antibody positive stools were read as negative (sensitivit y 59%) by the acid-fast-stained (AFS) fecal smears. Oocyst concentrati ons in the false-negative stools ranged between 6.0 x 10(3)/g to 2.5 x 10(4)/g. The experimentally determined concentration-threshold of ooc yst detection by AFS fecal smear was 3.0 x 10(4)/g. The stool weights did not conform to a normal distribution; the oocyst concentration was significantly correlated with the stool weight (P < 0.01). Due to thi s correlation, stools which constituted less than 0.41% of the snake w eight were classified as negative by the AFS fecal smears. The AFS fec al smear technique should be used exclusively for the determination of Cryptosporidium-positive snakes, but not for diagnosis of snake negat ivity for Cryptosporidium; it should be applied only for larger fecal specimens, such as those which constitute more than 0.41% of snake wei ght. At least five to seven stool samples should be examined by fecal smear in order to determine snake positivity for Cryptosporidium in su bclinical infection.