We all require access to clean, uncontaminated drinking water, and while we assume that the treated water that flows from our taps is purified, is this always the case?
Some drinking water contaminants have developed a method of survival that enables them to withstand the toughest environmental conditions. During times of severe stress, these parasitic drinking water contaminants are able to form a hard exterior wall, or shell, to protect them from desiccation or other environmental hardships. During this phase, where they are referred to a microbial cysts, their metabolism slows down, and they remain dormant until conditions improve. Once they enter the body of a host and conditions become favorable again, they shed their outer wall and become active. Two common drinking water contaminants found in drinking water include the microbial cysts, Cryptosporidium and Giardia. Both these pathogens are able to withstand lengthy periods outside of the body, where they can resist chemical disinfection due to the protection that the outer casing offers them while they are in the dormant cyst phase of their lifecycle. However, once they enter intestine, gastric juices break down the protective outer wall, allowing the parasites to enter the body and multiply.
Microbial cysts can enter the body through various mechanisms. These include exposure to contaminated feces, handling infected animals, swallowing water during recreation activities in contaminated water, eating uncooked contaminated food, or drinking contaminated water. According to the Centre for Disease Control and Prevention, Cryptosporidium parasites are common drinking water contaminants found throughout the United States and the world, and with an estimated 748,000 cases of Cryptosporidiosis reported in the U.S. every year, it is the highest cause of water borne disease in the United States. The risk is higher in developing countries where water treatment and sanitation standards are inferior, and people travelling to such countries are advised to take precautions. Giardia is another intestinal parasite that forms microbial cysts in order to survive outside the host. The most common method of transmission of these is through drinking contaminated water or swallowing contaminated water during recreational activities.
Life Cycle of Microbial Cysts
Once the microbial cysts are ingested, they enter the small intestine where the exterior wall is shed (excystation) to release the parasites, which rapidly multiply and invade the gut. As the parasites travel along the colon they again form microbial cysts (encystation) before being released from the body in the feces, where they are infectious through person-to-person transmission.
Symptoms of Disease from Microbial Cysts
Ingestion of microbial cysts very often leads to disease, such as cryptosporidiosis from the Cryptosporidium parasite, and giardiasis from Giardia. Symptoms of both these diseases include diarrhea, stomach cramps, nausea, vomiting, dehydration, weight loss, and in the case of cryptosporidiosis, can also include fever. Symptoms typically last for 1-2 weeks, but can persist for up to 30 days, often recurring. According to the Centre for Disease Control and Prevention, people most at risk from serious disease resulting from ingesting microbial cysts are those that have compromised immune systems. This includes individuals suffering with AIDS, and cancer and transplant patients that are being treated with medication that may compromise the immune system. Giardiasis also has the potential to inhibit development and growth in children, and may lead to malnutrition.
Preventing Disease From Drinking Water Contaminants
In order maintain good health and prevent disease as a result of ingesting parasitic microbial cysts, it is essential to practice good hygiene, and to take a few safety precautions, and water purification measures.
- Wash hands thoroughly before eating or preparing food; after using the toilet, changing nappies, or assisting a child or invalid on the toilet; and after handling animals or animal feces.
- Avoid drinking and swallowing contaminated water. Don't swallow water when swimming in public recreational aquatic facilities. Don't drink untreated water from rivers, streams or lakes. Take special precautions when traveling – boil water if there is a chance that if may be contaminated, or drink bottled water.
- Where possible use home filters to filter tap water, to avoid ingesting drinking water contaminants. As both Giardia and Cryptosporidium form dormant microbial cysts, they are able to survive chemical water treatment. Water purification using filtration will in most cases remove drinking water contaminants, including microbial cysts, but there are certain qualities to look for in a water filter. Water purification filters that work on the principle of reverse osmosis will effectively remove microbial cysts, such as Cryptosporidium and Giardia from the water, as will water purification filters that have an absolute pore size of 1 micron or less.