Sources of protozoa and amoeba in drinking water
Drinking water supplies that depend on surface or ground water are subject to contamination by enteric waterborne pathogens. The detection of these pathogens (and other indicator organisms) may indicate fecal contamination of water. These pathogens can originate from leaking sewer lines, septic systems, or improperly protected well heads that allow contaminated surface water to drain into the aquifer along the outer well casing. Contaminated ground water represents approximately half of the waterborne disease outbreaks documented in the United States every year.
Organisms of particular concern with respect to water contamination include waterborne pathogenic human enteric viruses, such as Adenovirus, Rotavirus, Hepatitis A, and Norovirus; enteric bacteria, such as the pathogenic strain of Escherichia coli 0157:H7, Salmonella, Campylobacter, Vibrio cholerae and Shigella spp.; protozoan pathogens, such as Cryptosporidium and Giardia; and, the recently reported amoeba Naegleria fowleri. These organisms present a human health risk to those who ingest the water. Typical symptoms associated with an infection include acute gastroenteritis, severe cramping, abdominal pain, dehydration and diarrhea.
Although all of the above mentioned organisms pose a risk to human health, viral contaminants are typically considered more of a threat to groundwater than bacterial or protozoan contaminants for two reasons. First of all, because of the small size of viruses, they typically can be transported further into the aquifer than bacteria and can eventually reach the groundwater. Secondly, viruses are thought to be more persistent in the environment than their bacterial counterparts and require greater disinfection procedures to render them inactive.
Cryptosporidium and Giardia
Microorganisms transmitted by the fecal-oral route are referred to as enteric pathogens because they infect the gastrointestinal tract. One specific group of enteric pathogens is called protozoa. All protozoa rely on water, and they are most commonly observed in freshwater and marine habitats, although some are terrestrial in moist soils and others are exclusively found in the gastrointestinal tracts of animals. Diseases caused by protozoa that are transmitted by contaminated drinking water are considered waterborne diseases. Common protozoa, such as Cryptosporidium and Giardia, are extremely hardy and can survive chlorine disinfection that is commonly practiced at conventional water treatment plants. These organisms can enter the environment via human and animals wastes and have been found in marine water and bathing beaches in the vicinity of sewage outfall locations. Additionally, cattle are known to harbor these organisms, and consequently agricultural land runoff has been shown to contaminate surface water.
The pathogenic protozoan parasites, Cryptosporidium and Giardia, are significant microbial contaminants in the U.S. and have been found in surface waters and filtered drinking water supplies. Cryptosporidium and Giardia produce environmentally resistant oocysts and cysts, respectively, which allow the parasites to survive in water for extended periods of time. Many waterborne outbreaks of cryptosporidiosis and giardiasis have been reported in North America. Increases of microbial pathogens in lakes and streams due to heavy rainfall events/flooding can lead to breeches in the treatment process and have occasionally resulted in community outbreaks of gastroenteritis. Another source of outbreaks could be due to a breakdown in the water treatment process, such as coagulation, filtration, or disinfection.
Naegleria fowleri is a protozoan amoeba found in soil environments but more frequently in ground and surface waters. Because Naegleria is commonly found in warmer temperatures, states in the Southwest are particularly prone to its presence. In a recent study in Arizona of 188 drinking water systems and individual household wells, the waterborne amoeba Naegleria fowleri was reported in 29 cases (personal communication, C. Gerba 2009). Biodegradable oils used to lubricate ground water pumps may act as a food source for bacteria and other organisms. Research has indicated that N. fowleri, may feed upon bacteria growing in wells, thus allowing them to persist in the environment. Although it is alarming that this waterborne pathogen is currently being found in wells in warmer climates, infections occur only by immersion in the water and do not occur as a result of drinking contaminated water.
Potential health effects of protozoa and amoeba in drinking water
Cryptosporidium and Giardia have become the leading cause of gastroenteritis outbreaks associated with treated recreational water venues (e.g., swimming pools, water parks, water slides, wave pools, interactive fountains), accounting for approximately 60 percent of the outbreaks reported to the Centers for Disease Control and Prevention (CDC) during 1995-2004. During 2006 and 2007, considerable increases in the number of Cryptosporidium and Giardia outbreaks were reported to the CDC. The availability of the first drug to combat Cryptosporidium illness has likely increased the chance that healthcare providers test for the protozoan when a patient has diarrhea. Additionally, improvement of Cryptosporidium tracking systems has also led to the investigation of more cases, and consequently more outbreaks have been identified.
Alternatively, Naegleria causes acute primary amoebic meningoencephalitis in infected individuals. According to the Centers for Disease Control (CDC), Naegleria infects people by entering the body through the nose. This can occur when people use warm freshwater or untreated ground water for activities like swimming or diving. The amoeba travels up the nose to the brain and spinal cord where it destroys the brain tissue. Symptoms are said to mimic a hangover and include a head ache as well as stiffness of the back and neck.
Testing drinking water for protozoa and amoeba
The microbial quality of drinking water is regulated in the U.S. by the Total Coliform Rule (TCR) and the Surface Water Treatment Rule (SWTR). According to the SWTR, a minimum treatment level of 99.9 percent removal (3-log reduction) of Giardia and 99.99 percent removal (4-log reduction) of enteric viruses is required. Cryptosporidium was listed as a potential contaminant of concern under the Safe Drinking Water Act in 1987 and then was included in an Interim Enhanced Surface Water Treatment Rule (IESWTR) in 1998, requiring the removal of 99.9 percent (3-log reduction) of oocysts. However, there are still no regulations in the U.S. that specifically address Cryptosporidium in potable supplies. Recently, the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) was promulgated by U.S. Environmental Protection Agency (EPA), which requires drinking water source monitoring for Cryptosporidium oocysts.
Currently, testing is very limited for Naegleria in both public and private systems as no water quality regulations exist. With this in mind, proper maintenance of private systems is the best measure that can be done to alleviate human exposure to this pathogen. Reducing the use of biodegradable oils used to lubricate ground water pumps that may act as a food source for bacteria and other organisms will in turn reduce your risk of this pathogen.
Options for protozoa and amoeba in drinking water
Unlike most waterborne pathogens, such as bacteria and enteric viruses, Cryptosporidium and Giardia oocysts and cysts are very resistant to chlorine disinfection, which is commonly used to treat surface and ground waters. Because infected individuals shed oocysts for approximately one week after symptoms resolve, there is an increased risk of future outbreaks. Lack of awareness and failure to reduce transmission of these protozoan parasites using alternative water-sanitizing technologies make future Cryptosporidium and Giardia outbreaks inevitable. While substantial regulatory efforts have been directed at drinking water, there has not been a corresponding effort to regulate public recreational water facilities. Alternative water-sanitizing techniques that have proven successful for the disinfection of protozoa include the use of ozone and ultra-violet (UV) light as disinfectants.
Alternatively, Naegleria is highly susceptible to chlorination and as such is recommended as an adequate disinfection technique.