Transmission Pathways: Waterborne Disease January 26th, 2010

Categories of disease spread by water Diseases contracted by ingestion of contaminated water Often diarrheal diseases Bacterial, viral, and parasitic diseases Cholera, norovirus, Cryptosporidium The largest burden of these diseases is in countries that lack water infrastructure But they are NOT gone even in countries that have infrastructure

Categories of disease spread by water Diseases spread by contact with contaminated water Bathing, wading Parasitic diseases where pathogen lives naturally in the water Schistosomiasis Leptospirosis

Categories of disease spread by water Diseases spread by contact with contaminated water Recreational waters Example: Cryptosporidium from a spray park Gastroenteritis from a waterpark

Transmission cycles in water The fecal-oral route Exactly what it sounds like! Contamination of drinking water sources by human or animal fecal waste Routes involving vectors Organisms live naturally in the water; they are part of the ecosystem

Sources of Waterborne Disease Excreta from humans and animals Human Shellfish Crops Aerosols Oceans and Estuaries Rivers and Lakes Irrigation Solid Waste Landfills Sewage Land Runoff Recreation Water Supply Groundwater

Surface Water Lakes, streams, rivers Vulnerable to many different kinds of contamination Direct contamination by human and animal fecal waste Animals in and around water Sewage disposal Accidental sewage spills and overflows Runoff Stormwater Agricultural

Groundwater May be safer than surface water in some cases, but still vulnerable to contamination Runoff into unprotected wells High water tables can become contaminated Transport of microbes into wells Failing septic systems Latrines Chemical contamination

Water contamination Inadequate disposal of human feces Partial but inadequate treatment of human fecal waste Use of natural waterways and bodies of water as sites of sewage disposal Example: the Mekong River

Water contamination and waterborne disease Many times, a confluence of events Contamination of source water Lack of treatment barriers Many people in the US drink untreated well water Inadequate treatment barriers Small community water systems may have trouble treating water adequately Even large, sophisticated treatment plants can go wrong Example: Milwaukee Cryptosporidium outbreak

Control of Waterborne Disease Drinking water Multi-barrier approach to treatment Filters Disinfectants

Control of Waterborne Disease Water contact diseases Breaking the chain of transmission Getting rid of vectors Treating infected people Often very difficult to do Preventing water contamination Controlling runoff, sewer overflow, and other sources