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Pathogens and Pathogenicity > 12. The Pathogenicity of Protozoa - Cryptosporidium > Flashcards

12. The Pathogenicity of Protozoa - Cryptosporidium Flashcards

1
Q

What disease is mainly caused by cryptosporidium infection?

A

Cryptosporidiosis

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2
Q

What factors effect the pathogenicity of cryptosporidium infection?

A

Different virulence among cryptosporidium species and susceptibility if host individuals

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3
Q

What are the symptoms of cryptosporidiosis?

A

Diarrhoea is most common symptom. Vomiting, nausea, abdominal pain and low grade fever is also possible.

Less likely symptoms include myalgia, weakness, malaise, headache and anorexia.

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9
Q

What individuals are particularly susceptible to infection by cryptosporidium species?

A
  • Immunocompromised individuals such as HIV patients.

- Children

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10
Q

How many species of cryptosporidium are identified to infect humans?

A

14

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11
Q

Mention 6 species of cryptosporidium which infect humans.

A
  1. C. parvum
  2. C. hominis
  3. C. meleagridis
  4. C. cuniculus
  5. C. felis
  6. C. canis
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12
Q

What two species of cryptosporidium cause most of human infections?

A

C. parvum

C. hominis

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13
Q

What symptoms are specifically associated with C. hominis and not with other species?

A

Nausea vomiting and malaise

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18
Q

Describe the process of transmission of cryptosporidium species?

A
  1. Direct: Fecal-oral route among and between host species.
  2. Indirect: cryptosporidium contaminated material such as water.
  3. Susceptible individuals (immunocompromised individuals and children) may also become infected by inhalation of oocysts.
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19
Q

What is the reservoir of C. parvum speculated to be?

A

Zoonotic

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20
Q

What is the reservoir for C. hominis speculated to be?

A

Asymptomatic carriage in young children.

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21
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22
Q

What are the 6 developmental phases of the cryptosporidium lifecycle?

A
  1. Excystation
  2. Merogony
  3. Gametogony
  4. Fertilization
  5. Oocyst wall formation
  6. Sporogony
23
Q

What occurs during exycstation?

A

The release of infective sporozoites:

  • Oocysts enter the gastrointestinal tract by ingestion where the low pH of stomach, reducing conditions, pancreatic enzymes, bile salts and temperature function to weaken the structure to release four sporozoites into the intestine.
24
Q

What occurs during merogony?

A

Asexual multiplication within the host cell.

25
Q

What occurs during gametogony?

A

The formation of micro- and macro-gametes.

26
Q

What occurs during fertilization?

A

The union of micro and macro gametes

27
Q

What is the purpose of oocyst wall formation?

A

To produce the environmentally resistant stage responsible for the trnasmission of the infection from one host to another.

28
Q

What occurs during the sporogony phase?

A

The formation of infective sporozoites

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33
Q

Where is the lifecycle of cryptosporidium species completed?

A

Within the host, normally infecting the gastrointestinal tract.

34
Q

What occurs during gametogony?

A

The formation of micro- and macro-gametes.

35
Q

Where is the lifecycle of cryptosporidium species completed?

A

Within the host, normally infecting the gastrointestinal tract.

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37
Q

How does the cryptosporidium species gain entry into the host body?

A
  1. Ingestion of sporulated oocysts containing 4 sporotozoites.
38
Q

Once ingestion has occurred, how are the sporotozoites released from the oocyst?

A
  1. The low pH of the stomach, the reducing conditions, carbon dioxide, temperature, pancreatic enzymes and bile salts of the digestive system weaken the oocysts.
  2. This causes four infective sporozoites to be released into the intestinal tract via a suture in the oocyst wall.
39
Q

How do sporozoites attach to host cells?

A
  1. The released sporozoites glide over intestinal cells facilitated by the attachment properties of the outer pellicle layer binding to host cell membranes.
40
Q

How do sporozoites enter a host cell, once attachment occurs?

A
  1. Rhoptries and micronemes released from the apical complex of the protozoa facilitate adherance and entry into the cell via a parasitophorous vacuole which is confined to the microvillus region of the cell.
41
Q

Describe the replication process of cryptosporidium sporozoites once entry into the host cell has occurred.

A
  1. Within the parasitophorous vacuale, each sporozoite develops into a spherical trophozoite.
  2. Trophozoites undergo asexual division by the process of merogony to form the type I meront containing 8 merozoites.
  3. Merozoites are released form the host cell and continue to infect other gastrointestinal epithelial cells.
  4. Within the second parasitophorous vacuole merogony of the merozoites occurs to form a type II meront containing four merozoites.
  5. Merozoites are again released from the host cell and bind to new host cells where they then proceed to the process of gametogony where micro and macrogamonts are formed.
  6. Microgamonts undertake nuclear division and differentiation to form up to 16 microgametes.
  7. Macrogamonts divide and differentiate into macrogametocytes.
  8. Microgametes are released from the parasitophorous vacuole and locate a unicellular macrogametocyte for fertilization.
  9. The resulting zygote undergoes two asexual cycles of sporogony to produce a thick or thin walled oocyst.
42
Q

What occurs to thick walled oocysts?

A
  1. Thick walled oocysts are released into the gastrointestinal lumen and excreted as infectious particles.
43
Q

What occcurs to thin walled oocysts?

A
  1. Thin walled oocysts are released and cause autoinfection by which the cycle starts again within the same host.
44
Q

How do sporozoites attach to host cells?

A
  1. The released sporozoites glide over intestinal cells facilitated by MUCIN-LIKE GLYCOPROTEINS, THROMBOSPONDIN-RELATED ADHESIVE PROTEINS of the outer pellicle layer binding to host cell membranes.

Other glycoproteins are also known to be important in attachment including:

  • Glycoprotein 900
  • Circumsporozoite-like glycoprotein
  • Many others
45
Q

What occcurs to thin walled oocysts?

A
  1. Thin walled oocysts are released and cause autoinfection by which the cycle starts again within the same host.
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51
Q

What is the chromosome number of cryptosporidium species?

A

8 chromosomes

52
Q

How is cryptosporidium infection speculated to result in its symptoms?

A

Direct damage to epithelial cells by disruption of tight junctions, or release of lactate dehydrogenase.

or indirect injury to the tissue via inflammatory cells and cytokine responses.

53
Q

Why is it difficult to study the pathogenicity and virulence factors of cryptosporidium ?

A

It is difficult to employ in vitro cultivation and reverse genetic techniques with this parasite and as such genes cannot be readily knocked out or knocked down in order to examine their importance.

Pathogens and Pathogenicity (17 decks)

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