Cryptosporidium parvum, a single-celled animal, i.e., protozoa, is an obligate intracellular parasite. It has been given additional species names when isolated from different hosts. It is currently thought that the form infecting humans is the same species that causes disease in young calves. Cryptosporidium infects many herd animals (cows, goats, and sheep among domesticated animals). The infective stage of the organism, the oocyst is about half the size of a red blood cell. The sporocysts are resistant to most chemical disinfectants, but are susceptible to drying and the ultraviolet portion of sunlight. Some strains appear to be adapted to certain hosts but cross-strain infectivity occurs and may or may not be associated with illness.
Cryptosporidium is a highly infectious and potentially dangerous parasite, especially when confronted by a weak immune system. When it attaches to the lining of the small bowel, it then multiplies over and over again and attacks the intestine, as a response the body tries to flush it out, this reaction causes diarrhoea. While some is washed away the rest is multiplied, lining the stomach walls. By lining the stomach walls, Cryptosporidium prevents the body from absorbing nutrients out of the body, eventually causes malnutrition and death.
Part of the reason Cryptosporidium is so successful at attacking humans, is because it has a great strategy, it uses water to get to its host, by using water Cryptosporidium is able to affect large populations very quickly, and it is able to spread over large geographical areas. Chlorine kills most stuff in the water, but not even chlorine kills this nasty protozoan. Cryptosporidium has a protected coating which allows it to withstand chlorine based cleaning systems. Ozone treatment reduces the amount of Cryptosporidium in drinking water, but it does not remove all of it. On average there are ten parasites in every 10 gallons of drinking water in Ireland. This concentration rarely causes illness.
In Ireland we have had problems with Cryptosporidium - in 2007 Galway and urban centres around the city were hit with the parasite. The source of the parasite was human and animal waste, the Headford River flowing into Lough Corrib, contained large amounts of raw sewage originally coming from the town of Headford. The area was also surrounded by limestone rock with the scarcity of surface soil and the jointed nature of the rock allowing the waste water to contaminate the underground water. The city of Galway received its water from two treatment plants, one plant was built in the 1970s, while the other was treated in the 1940s. The older plant did not have the filtering technology to remove the parasite. Another contributing factor was that rain in the early months of 2007 which led to the release of large volumes of flood water from the Clare River into Lough Corrib. These floodwaters may have contained overflow liquids from farmyard slurry and septic tanks.
Inhabitants of Galway had to boil their water for months and buy bottled water. Solutions to the problems were rapidly put into operation. These involved creating adequate sewage treatment plants, and installing modern water treatment equipment.
Written by Junior Frog Blog Reporter Lorcan Maule. Submitted for the St. Columba's College Biology Prize 2012.