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Spud's Down to Earth Advice on...

CRYPTOSPORIDIUM PARVUM

Cryptosporidium parvum is a microscopic single-celled parasite that causes diarrhoea in humans and cattle, the illness being termed cryptosporidiosis. During the past 2-3 decades, Cryptosporidium parvum has become recognised as one of the most common causes of waterborne disease in the UK. Infection is mostly associated with consumption of contaminated water; however, raw fruits & vegetables and raw milk have been implicated in infections.

Life Cycle

Sporulated oocysts, containing 4 sporozoites, are excreted by the infected host through faeces and possibly other routes such as respiratory secretions. Transmission of Cryptosporidium parvum occurs mainly through contact with contaminated water (e.g., drinking or recreational water). Following ingestion (and possibly inhalation) by a suitable host, excystation occurs. The sporozoites are released and parasitise epithelial cells of the gastrointestinal tract or other tissues such as the respiratory tract. In these cells, the parasites undergo asexual multiplication and then sexual multiplication producing microgamonts (male) and macrogamonts (female). Upon fertilization of the macrogamonts by the microgametes, oocysts develop that sporulate in the infected host. Two different types of oocysts are produced, the thick-walled, which is commonly excreted from the host, and the thin-walled oocyst, which is primarily involved in autoinfection. Oocysts are infective upon excretion, thus permitting direct and immediate faecal-oral transmission.

Note that oocysts of Cyclospora cayetanensis, another important coccidian parasite, are unsporulated at the time of excretion and do not become infective until sporulation is completed.

Incubation Period & Duration

Incubation Period
2 - 14 days.

Duration
Cryptosporidiosis is usually a self-limiting infection. In persons with healthy immune systems, the symptoms may last for 1 - 2 weeks.

Symptoms

The most severe symptoms are shown in the young. The infection is characterised by:

severe watery diarrhoea
abdominal cramps
fever
loss of appetite & weight loss

In immunocompromised patients, cryptosporidiosis can contribute to death.

Sources/Associated Foods

The reservoir of Cryptosporidium spp. is the gastrointestinal tract of humans and animals, particularly farm and other domesticated animals. As millions of cryptosporidia can be released in a bowel movement from an infected human or animal, the main consequent source is faecally-contaminated water.
Additionally, Cryptosporidium spp. could occur, theoretically, on any food touched by an infected food handler.
Fertilising salad vegetables with manure is another possible source of human infection.
Infection is frequently associated with foreign travel.

Spread

Transmission routes are:

the consumption of contaminated water and food
contact by animal-to-human (e.g. farm visits) or human-to-human (particularly in households and nurseries)
recreational exposure to contaminated water or land

Swallowing the parasite in any of the following ways may lead to infection:

Accidentally putting something into your mouth or swallowing something that has come into contact with faeces of a person or animal infected with Cryptosporidium
Swallowing recreational water contaminated with Cryptosporidium
Eating uncooked food contaminated with Cryptosporidium
Accidentally swallowing Cryptosporidium picked up from surfaces (such as bathroom fixtures, changing tables, nappy buckets, or toys) contaminated with faeces from an infected person.

The incidence of cryptosporidiosis is higher in (young) child day care centres that serve food, due to the potential for spread from nappy changing activities.

Control

Good personal hygiene
Practice good hygiene (especially hand washing) and protect others by not swimming if you are experiencing diarrhoea (essential for children in nappies) or for at least 2 weeks after diarrhoea has stopped. This latter advice is because you can still contaminate water after your symptoms have ended. Indeed, outbreaks of cryptosporidiosis among recreational water users have been caused via this route.
Note: Cryptosporidium can be spread in a chlorinated pool because it is resistant to chlorine and, as such, can live for days in these pools.
Avoid water that might be contaminated

do not swallow recreational water
do not drink untreated water from lakes, rivers, springs, ponds, and streams
do not drink untreated water during community-wide outbreaks of cryptosporidiosis caused by contaminated drinking water
do not use untreated ice or drinking water when travelling in countries where the water supply might be unsafe.

Avoid food that might be contaminated

wash and/or peel all raw vegetables and fruits before eating
use safe, uncontaminated water to wash all food that is to be eaten raw
avoid eating uncooked foods when travelling in countries with minimal water treatment and sanitation systems
cook food thoroughly

Take extra care when travelling
If you travel to developing countries, you may be at a greater risk for Cryptosporidium infection because of lower standards of water treatment and food sanitation. Travellers should avoid the following items which could be contaminated with Cryptosporidium:

unprocessed foods, in particular raw fruits and vegetables
tap water, or ice made from tap water
unpasteurised milk or dairy products
items purchased from street vendors.

Steaming-hot foods, fruits you peel yourself, bottled and canned processed drinks, and hot coffee or hot tea are probably safe.

Exclusion/Return to Work Parameters

Cases in risk groups 1- 4 not to return until 48 hours after first normal stool.

[Group 1 - food handlers; Group 2 - health care workers; Group 3 - children under 5 in nurseries etc.; Group 4 - older children and adults who may find it difficult to implement good standards of personal hygiene]

Additional Information

On average, between 1986 and 2003 there were 4552 cases of cryptosporidiosis in England and Wales each year. One Department of Health estimate was that 2% of diarrhoea could be due to Cryptosporidium.
Infection is patchy in England and Wales, but testing of the population indicates wider prevalence. In the US, population exposure has been estimated at 80%.
Can get big outbreaks associated with contaminated water supplies e.g. Milwaukee, USA (1993) - 400,000 cases; Swindon (1989) - 500 cases.
The infective dose appears to be less than 10 organisms.
It is an obligate intracellular parasite, the intracellular stages causing severe tissue alteration.
There are indications that hosts can become lifetime carriers of the parasite.
The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine- based disinfectants.
The adult organism is usually non-motile and has a complex life cycle, with alternating asexual & sexual phases. Asexual reproduction means it can autoinfect the host without going outside it.The infective stage is the oocyst (spore) which is very small (3 microns, half the size of a red blood cell). Development goes from oocyst to sporozoites to merozoites and, by sexual reproduction, a zygote which then sporulates within the gut to produce 80% thick-walled and 20% thin-walled oocysts [the former are excreted and the latter autoinfect the host as part of an asexual phase].
Oocysts are resistant to chlorine and other common/traditional methods of disinfection [ozone may be effective however] and can survive well in the environment if cold and moist.
Oocysts are sensitive to heat (max. 60^oC), drying and U/V light.
It is currently thought that the form infecting humans is the same species that causes disease in young calves (50% of which shed oocysts).

Useful Links:

Library Item: Cryptosporidium in Water Supplies - 1st Report

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Friday 10 September 2010