is caused by the protozoan Cyptosporidium, long recognized as a pathogen in calves, but not known to infect humans until 1976.
Since then, the number of reported cases has been increasing. This; is another example of a disease with particularly serious effects on immunosuppressed individials, including those with AIDS. In otherwise healthy individuals, the organism causes intestinal distress of a short duration. Immune-deficient individuals however suffer from a severe life threateing diarrhoea that may last for months.
Transmission is largely faecal-oral between humans. This is important when considering the impact on a town supplied by an affected water supply.
However, a Zoonosis-type transmission from calves has been observed. Diagnosis is based on microscopic examination of faeces for Cryptosporidium oocysts, and acid-fat staining or fluroscent anti-body tests.
At present there is no reliable treatment. It is now thought that Cryptosporidium may be responsible for up to 30% of diarrhoeal illness in underdeveloped countries. In AIDS patients and other immnunosuppressed persons, Cryptosporidium can caue respiratory and gallblader
infections and may be a major cause of death. The organism, which lives inside the cells lining thee small intestine, can be transmitted through the feaces of cows, rodents, DOGS and CATS. Waterborne and hospital aquired infections have also been reported.
Inside the host cell each Cryptosporidium organism forms four (4) oocysts, each containing four (4) sporozoites. When the the occyst ruptures, sporozoites may infect new cells in the host or be released with the feaces.
Fact Sheets – Micro-organisms 2: Protozoa
No guideline value is set for Cryptosporidium species in drinking water. if detected in an epidemiological or prospective study, action to control this organism may be necessary, and advice should be sought from the relevant health authority.
Until recently, Cryptosporidium was best known as a parasite of pasture animals, but it is now regarded as an important human pathogen. Cryptosporidium that infect mammals are believed to belong to two species, of which C. parvum causes disease in humans. It has a complex life cycle involving intracellular development in the gut wall, with sexual and asexual reproduction. Thick-walled oocysts, shed in faeces, are responsible for transmission.
Pasture run-off and human wastes are the most significant sources of contamination of water. Densities of oocysts have been reported as high as 140 000 per litre in raw sewage and 5800 per litre in surface water. Water-borne outbreaks have occurred in North America and Britain, infecting as many as 400 000 people (Mackenzie et al, 1994) Water is only one of several mechanisms by which the faecal-oral cycle can be completed. Transmission of Cryptosporidium also occurs by direct contact with a human carrier or by contact with infected farm animals and possibly domestic pets.
There is less data on the incidence of infection by Cryptosporidium in Australia than there is for giardiasis. Outbreaks have been recorded in day-care nurseries, presumably spread from person to person (Cruikshank et al., 1988). In South Australia a major outbreak of Cryptosporidium infections was recorded in 1990/91 (Weinstein et al, 1993). Statistical analysis showed that people drinking rainwater were less frequently infected, and the pattern of this outbreak suggested multiple sources of infection. A mixed outbreak of infections by Cryptosporidium and Giardia in Victoria followed contamination of a private water supply by overflow from a septic tank (Lester, 1992).
There is considerable potential for contamination of water in dairying areas. At present, it would be difficult to determine whether infections in such areas can be attributed solely to contact with animals, or whether drinking water might contribute as a vehicle of transmission.
Treatment of drinking Water
Cryptosporidium oocysts are extremely resistant to disinfection, with a significant percentage apparently surviving 24 hour exposure to 1000 rng/L chlorine (Smith et al., 1989). Protection of water catchments from contamination by human wastes and if possible by pasture animals should be a priority. Comprehensive treatment (including filtration) is essential for surface waters that include pasture run-off The small size of Cryptosporidium oocysts (4-6 Em) makes some filtration processes vulnerable to penetration. Operational procedures in water treatment plants should be carefully examined where Cryptosporidium oocysts are present in the raw water to ensure that there is minimal transfer of oocysts to the distribution system.
Method of Identification and Detection
Detection of Cryptosporidium involves concentration of relatively large volumes of water in several stages, fluorescent staining of the concentrated material, and examination using an ultraviolet microscope or an automatic cell counter (Bee et al., 1991). Several Australian laboratories have been developing methods for detecting Cryptosporidium, but processing individual samples is time-consuming and expensive. Routine monitoring for Cryptosporidium is not appropriate, but these methods will become important. in investigating sources of Infection. Prospective studies may also be valuable.
Guarding against Giardia
Although there are many organisms in our water supplies which can infect humans, Giardia Lambia is one of the most cosmopolitan and frequent causes of tummy upsets likely to occur as a result of encounters with the Australian outdoors. Because this common and highly infectious organism thrives in cool water it is often found in high mountain streams, alpine lakes, and even in the local water supplies in cooler regions ‘That is to say, Giardia is present in the waterways of many popular wilderness destinations, and the risk of infection is therefore something of which walkers, cross country skiers and other outdoor adventurers need to be conscious.
Giardia Lambia is a protozoan, a single cell organism which forms a cyst around itself as the organism moves from the small intestine to the outside world. As these cysts are extremely infectious with as few as ten cysts required to infect an adult, and relatively hardy, Giardia has spread widely throughout the world. Because it is transmitted in human faeces, the waterways of many popular bushwalking and other outdoor recreational areas have been contaminated and we can safely predict that more will be affected in time. In some areas of the world particularly developing countries, it is thought that up to 100% of the population have been infected with Giardia by the age of two.
Giardia usually manifests itself with gut symptoms, and though not everyone who is infected with Giardia will become symptomatic a high proportion do. Characteristically symptoms do not appear until 1-3 weeks after infection. The most common early symptoms include abdominal pain, bloating, belching, excessive wind, nausea and vomiting and diarrhea, though the latter may not always be present The acute infection generally lasts in excess of a week. Although any diarrhoea usually settles quickly the-other symptoms may persist for many years, either continuously, or in a relapsing episodic form. Specific treatment is simple and readily available, but unfortunately does nor prevent reinfection. A short course of Flaygl is the most common treatment, and has a cure rate of more than 80%. Other treatments are available for more persistent infection.
As the absolute diagnosis of Giardia can be quite difficult and treatment does not prevent reinfection, it is far better m take steps to avoid infection in the first place, The prevention of infection revolves around a number of simple principles. Firstly, if you are undertaking a relatively short walk, or day walk in a risk area, you can avoid infection simply by carrying all your drinking water from an uncontaminated area. Where the length of a walk makes carrying water impracticable, drinking water should always be boiled, chemically treated or filtered. Five minutes is adequate boiling time to kill Giardia, although it is worth noting that this may not be sufficient to remove other infectious organism. Many commercial sterilizing tablets will adequately deal with Giardia too, although the taste of some iodine based Products may not be to everyone’s liking! A good quality water filter is the third way of eliminating Giardia. It is important to remember when using filtration devices that their effectiveness is contingent on the carrying our of regular filter maintenance, in accordance with the manufacturer’s directions.
Taking these simple precautions and applying some common sense will not only drastically reduce the personal risk of infection, but also slow the rate Of dissemination of this nasty little beasty around the remaining pristine areas of our wilderness