Water and public health

Question 1

Describe the features of cryptosporidium spp

Answer 1

• Single genus of unicellular protozoan parasites
• Forms environmentally robust oocysts
• C. parvum also causes diarrhoea in young animals, especially calves & lambs
• Adult animals asymptomatic
• C. hominis appears to be exclusive to man

Question 2

Describe the life cycle of Cryptosporidium

Answer 2

• Sporulated oocysts, containing 4 sporozoites, are excreted by the infected host through faeces
• Following ingestion by a suitable host, excystation occurs. The sporozoites are released and parasitize the epithelial cells of the GIT
• In these cells, usually within the brush border, the parasites undergo asexual multiplication (schizogony or merogony) and then sexual multiplication (gametogony) producing microgamonts (male) and macrogamonts (female).
• Upon fertilization of the macrogamonts by the microgametes that rupture from the microgamont, oocysts develop and sporulate in the infected host.

Question 3

How is Cryptosporidium transmitted?

Answer 3

Transmission mainly through ingestion of faecally contaminated water (e.g., drinking or recreational water) or food (e.g., raw milk) or following direct contact with infected animals or people.

Question 4

Describe the two different types of oocyst produced by the zygotes for cryptosporidium

Answer 4

• Thick-walled oocysts are excreted from the host into the environment
• Thin-walled oocysts are involved in the internal autoinfective cycle and are not recovered from stools.

Question 5

Describe the infective stage of Cryptosporidium

Answer 5

Oocysts are infectious upon excretion, thus enabling direct and immediate fecal-oral transmission. Extracellular stages have been reported, but their relevance in the overall life cycle is unclear.

Question 6

What are the clinical signs of Cryptosporidium in humans?

Answer 6

• Nausea, vomiting
• Watery diarrhoea, dehydration
• Weight loss
• Stomach cramps, fever
• 3 weeks, usually self limiting
• Immunocompromised

Question 7

What requirement for Cryptosporidium monitoring was introduced in 1999?

Answer 7

The requirement to monitor drinking water for Cryptosporidium oocysts

Question 8

Describe the survival of Cryptosporidium oocysts in water

Answer 8

• Increased raw water turbidity – higher risk of Cryptosporidium oocysts presence
• Oocysts survive very well in raw water, run off, effluents – very resistant to chlorine

Question 9

Where are possible source of Cryptosporidium in meat production premises

Answer 9

natural spring, a reservoir, a well or a borehole

Question 10

How is water treated for Cryptosporidium?

Answer 10

• Flocculation (colloids suspended as flakes), sedimentation, filtration,
• then addition of chlorine or fluorine
• ozone treatment or UV light chlorination (aims to eliminate Cryptosporidium).

Question 11

What is the most significant pathogen in public water supplies?

Answer 11

Cryptosporidium spp