Cryptosporidium Flashcards
What is Cryptosporidium
- Coccidian protozoan parasite
- Infects animals (sheep/cows) and humans - zoonotic
- Associated with municipal water supplies that cause diarrhoea
- C. parvum causes Cryptosporidiosis and has wide host range
- One of the most common causes of waterborne illness in USA
- C. parvum oocyst is 3um in diameter
What strains of Cryptosporidium is almost exclusively a parasite of humans?
C. hominis
Where is the disease most frequently occurring
USA in states such as Florida, Maine, New Mexico, and North Dakota
What age group does the disease primarily affect?
0-4 years
Outbreaks
1984 - Texas
1987 - Georgia
1988 - Ayrshire
1989 - Swindon
1991 - Pennsylvania/ Isle of Thanet
1992 - Jackson County
1993 - Milwaukee
Overview of Cryptosporidium life cycle
- Thick-walled oocyst exits host
- Contamination of water and food with oocysts
- Thick walled oocyst ingested by host
Life cycle of Cryptosporidium
- Sporozoites are released when oocysts ingested, where they’re freed from oocysts and invade epithelial cells to form trophozoites
- Trophozoites become type I meronts which divide asexually to form merozoites.
- Some type I meronts become type II meronts which leads to sexual stages by forming macrogamonts and macrogamonts which fuse to form zygotes
- Zygotes form thick (80%) or thin-walled oocysts (20%)
- Thin walled oocysts auto infect the same host to form sporozoites
- Thick walled oocysts are released in faeces to infect others
Site of infection
Brush border epithelial cells of small intestine (jejunum).
Cell membrane envelops them but they are intracellular but extracytoplasmic.
Has affected other tissues such as respiratory tract tissues and conjunctiva of the eye.
Infectious dose: < 10 organisms (only 1 needed to initiate)
Cell death is a direct result of parasite invasion, multiplication, and extrusion or
Cell damage could occur through T cell-mediated inflammation, producing microvilli death and Cryptosporidium excess growth
Give some examples of virulence factors from Cryptosporidium
Excystation - Serine protease, aminopeptidases
Adhesion/locomotion - CSL, Gp900, Gp60
Invasion - Cp2, Cpa135
Intracellular multiplication - CpABC, CpATPase2, CpATPase3
Actions of Cryptosporidium
Causes diarrhoea
Less sodium ion absorption and increased chloride ion absorption caused by enterocyte malfunction
Inflammation caused by invasion of muscosa and inflammation of lamina propria leukocytes in stools
Secretion - Bacterial enterotoxins characterized by watery diarrhoea
Symptoms of Cryptosporidium
- Can be asymptomatic
- Incubation period is 2-10 days
- Symptoms include stomach cramps, watery diarrhoea, dehydration, weight loss etc
Immuno-competent individuals - 1-2 weeks
Immuno-compromised individuals - longer
Therapies
None
Immuno-competent individuals recover with fluid/electrolyte replacement
Standard treatment of diarrhoea
AIDS patients - anti-retroviral therapy will reduce oocyst excretion and decrease diarrhoea
Control methods
- Routine testing by utilities
- Drink bottled water
- Educate public
- Wash hands frequently
- Livestock control, management and practices
