CRYPTOSPORIDIUM and GIARDIA

Cryptosporidium parvum causes a disease called Cryptosporidiosis. Until 1993 few people had heard of it. It was first recognised in 1976. It is spread by putting something in the mouth that has been contaminated with the stool of an infected person or animal.

Municipal water can be contaminated with cryptosporidium. It enters the body as a cyst, and through its process, becomes a trophazoite, which attaches itself to the wall of the intestine, where it reproduces.

Symptoms appear 2-10 days after infection by the parasite. Some people have no symptoms, others have diarrhea, headache, cramps, nausea, vomiting and low grade fever.

Cryptosporidium can become life-threatening in persons with suppressed immune systems, particularly very young and the elderly. Childcare centres in USA are known to have increased risk. The routine stool examination used for most parasites usually fails to detect Cryptosporidium. Specific tests need to be carried out to detect it. (from www.cdc.gov.)

GIARDIA

(Extract from report of Dennis D. Juranbek, Chief, Epidemiology Activity Parasitic Disease Branch of Parasitic Diseases Centres for Disease Control (PDC) (www.flash.net/~bhphiker).

Giardia lambla is a one-celled parasite which causes the disease Giardiasis. Symptoms may include diarrhea, abdominal cramps, bloating, weakness, fatigue, headaches.

It can cause mild fever and vomiting, and it can be symptomless. Sometimes diarrhea does not occur, while other symptoms do. Many infections persist for 1-2 months. Chronic infections persist for years. Although infection after the ingestion of only one Giardia cyst is theoretically possible, the minimum number of cysts shown to infect a human is 10.

They divide every 12 hours, which means if a person swallowed only one cyst, reproduction at this rate would result in one million parasites 10 days later, and one billion by day 15. They can survive in water as cold as 4 degrees C for at least 2 months, and are killed if water is boiled for one minute.

It is clear from the number of waterborne outbreaks of Giardia that have occurred in communities where chlorine was employed as a disinfectant, that the amounts of chlorine used routinely for municipal water treatment is not effective against Giardia cysts.

These observations have been confirmed in laboratory and experimental conditions. Data reports to PDC indicate that Giardia is the most frequently identified cause of diarrhea outbreaks associated with drinking water in the United States.

Waterborne epidemics are a relatively frequent occurrence. Giardia is the parasite most commonly identified in stool specimens submitted to State laboratories for parasitologic examination.

Newcomers in the battle against waterborne Giardiasis includes a variety of filters. Until more published experimental data becomes available about the methods and results of tests employed to evaluate their efficiency, a consumer should look for a few common sense things, when selecting a filter.

The first thing to consider is the filter media. Filters relying on ordinary Carbon or silver impregnated Carbon should be avoided, because they are not intended to prevent, destroy or repel microorganisms. Their principal use is to remove undesirable chemicals, odours and very large particles of dirt and rust.

Some filters rely on chemicals such as iodine-impregnated resins to kill Giardia. While properly designed and manufactured filters of this type have been shown to kill many species of bacteriant virus present in human faeces, their efficiency against Giardia cyst is less well established... long contact time (several hours) may be needed in some situations.

The so-called micro-strainer types of filter are the true filters. Theoretically, a filter having a pore size of less than 6 microns might be able to prevent Giardia cysts of 8-10 microns in size from passing. One to three micron range is more effective. Less than one micron is most advisable.

Keep in mind that even sparkling clear mountain streams can be contaminated. You should choose a 'strainer'type filter that is certified to be 'absolute' 1 micron (or 0.5 micron). 'Nominal' one micron is not as reliable. The smallest parasites are viruses. Ordinary filters do not remove viruses. Viruses are 100 times smaller than bacteria, but need a host cell to survive.

Giardiasis is contracted mostly by poor personal hygiene, contact with an infected person, and from water.