Ecology, Environment and Conservation Paper

ASIAN CLAMS (CORBICULA FLUMINEA) AS BIOINDICATORS OF CRYPTOSPORIDIUM CONTAMINATION IN LAGUNA DE BAY, PHILIPPINES

Vachel Gay V. Paller, Renz L. Salumbre and Christian Paul P. de la Cruz

Abstract

Members of the genus Cryptosporidium are ubiquitous waterborne parasites causing diarrhea and have resulted in considerable morbidity among human and animal hosts. Freshwater Asian clams (Corbicula fluminea) collected from Laguna Lake were examined for the presence of Cryptosporidium oocysts employing sucrose-phenol flotation and Kinyoun acid fast staining procedure. This study revealed the presence of viable forms (morphotype-1a) of Cryptosporidium oocysts in clams, with potential to infect humans upon ingestion. Out of the total 45 pooled-clam samples, nine pools (20%) were found positive for the presence of oocysts. The mean abundance was four oocysts per gram. In terms of temporal variability, both prevalence and abundance were higher during rainy month periods (26% and six oocysts/g) relative to drier months (11% and one oocyst/g). Results of exact logistic regression analysis showed that both rainfall and water clarity appeared to have significant associationwith the occurrence of oocysts in clams. The chance of a pooled-clam sample being contaminated with Cryptosporidium oocysts increased by 8% when heavy rainfall occurred several days prior to clam collection and decreased by 7% as water clarity increased. Dissolved oxygen, water temperature, and water pH were not significantly associated with the occurrence of oocysts in clams. Nevertheless, it appeared that increasing water temperature and water pH decreased the chance by 22% and 48%, respectively; whereas, increasing dissolved oxygen increased the odds by twentynine percent (29%). Results of this study indicated Cryptosporidium contamination in Laguna Lake using C. fluminea as potential bioindicators.