Impact/Purpose:

1) Conduct laboratory evaluations of new methods for detection of protozoan parasites.

2) Determine the infective dose of parasitic protozoa to hosts given a variety of models that will assist in estimating the public health significance at various levels of occurrence.

The work in this task will support CCL2 and 3 and will be completed by 9/05.

Description:

Pathogenic waterborne protozoa (Giardia, Cryptosporidium) have been identified as significant etiological agents in the transmission of waterborne disease. Microsporidians, which are on the Agency's Contaminant Candidate List, are obligate intracellular parasites of invertebrates, fish, laboratory rodents, rabbits, and primates. With the advent of the AIDS epidemic, some species of microsporidians have become fully recognized as emerging agents of human disease. These protozoan parasites are transmitted by the fecal-oral route through contaminated food, fomites, person to person, or water. Since the microsporidian genera of interest localize in the gastrointestinal and urinary tracts, they can challenge wastewater treatment facilities and eventually get into surface drinking water sources. The transmission form is an environmentally resistant spore which ranges in size from 1 to 3 microns in diameter, a size which may allow a proportion of these protozoa to escape removal by traditional flocculation and filtration treatment methods. Other emerging protozoa are also likely causes of waterborne disease. Toxoplasma gondii is a protozoan parasite that has been implicated in causing waterborne disease in North America and elsewhere. Toxoplasmosis is traditionally thought of as a foodborne infection, but may be caused by ingestion of T. gondii oocysts in contaminated water. There are large numbers of individuals with antibodies against T. gondii on serological testing but who do not report symptoms. This suggests that there may be a high asymptomatic infection rate, and that the incidence of T. gondii infections may be under reported. Studies of the biology of this organism show that it can survive exposure to water long enough to be transmitted by this route. In the past several years a number of outbreaks of foodborne cyclosporiasis have occurred in North America. The agent of this disease, Cyclospora cayetanensis, is likely to be a waterborne parasite.

One of the roles of the Biohazard Assessment Research Branch is to determine the exposure of the U.S. population to protozoan disease agents through the waterborne route of infection. Understanding of exposure for the purpose of protecting the population will require a thorough understanding of three elements, parasite incidence, host parasite relationship (infectivity, and virulence), and parasite occurrence. An understanding of the infectivity and virulence of various disease organisms allows for determination of the infectious potential of particular levels of contamination, and for estimation of the probable impact of infection.

There is customer demand for research on waterborne protozoans from the Regions, the Office of Water, and the scientific community in general. This is primarily due to the overriding public health significance of these parasites in the U.S., but also to the prevalence of these parasites in the environment, the pre-existing area of competency of this laboratory using these parasites, and continued customer demand for research on the distribution of these parasites in the nation's waterways. This task addresses children's health, in that children are at high risk of adverse consequences from infections by parasitic diseases. T. gondii is an important cause of birth defects in the U.S., and there is evidence that children borne to infected mothers may suffer serious sequelae even if obvious birth defects are not readily discernable. This task also addresses community health, in that these diseases often occur in epidemics affecting an entire community. Information as to the presence of infectious stages of these organisms in a water supply may assist communities to make informed decisions concerning their public health and infrastructure. Finally, this task addresses contaminated sediments, as these parasites may remain infective for days, months or possibly years under appropriate conditions.

Record Details:

Project Information:

Project IDs: