5.3 Biliogy of Parasites

Question 1

What are the two types of parasites?

Answer 1

Protozoa (unicellular) and Helminths (multicellular)

Question 2

How are protozoa classified and give an example of each

Answer 2

By motlity 
Flagellate: Giardia 
Pseudopods: entemoeba histolytica 
Ciliates: Balantidium coli 
Coccidians: cryptosoridium

Question 3

How are Helminths classified and give an example

Answer 3

Flatworms

• Trematodes: flukes
• Cestodes: tapeworm

Roundworms (nematodes)

• Blood tissue: Wuchereria boncrofti (elephantitis)
• Intestinal: PInworm, whipworm, hookworm, strongyloides stercoralis, ascaris lumbricodes

Question 4

Define definitive host

Answer 4

parasite matures into adult form and undergoes sexual reproduction

Question 5

Define intermediate host

Answer 5

parasite development occurs but parasite does not reach sexual maturity

Question 6

define paratenic or transport host

Answer 6

parasite remains alive and infective but does not undergo any development

Question 7

define incidental or dead end host

Answer 7

intermediate host that generally does not allow transmission to a definitive host

Question 8

define host sensitivity

Answer 8

range of different hosts in which a parasite can mature

Question 9

What is the process of parasitic disease in general>

Answer 9

Gain entry to the host (exogenous or endogenous)
Replicate/disseminate (intra or extracellular)
Cause damage to the host
Spread to a new victim

Question 10

What factors affect infection, spread, replication and damage

Answer 10

Size

• Protozoa complete lifecycle in humans an usually have low infective dose
• Helminths severity usually related to size

Tissue tropism

Means of evading immune response

Question 11

What are the general consequences of parasitic infection to the host?

Answer 11

Nutritional stress 
Mechanical or physical damage 
secondary infections 
toxicity 
immunopatholgical reactions

Question 12

What is the lifecycle of giardia?

Answer 12

Exposure to stomach acids causes the release of four trophozoites
TZ colonise in small intestine
TZ undergo rapid asexual reproduction
Encystation occurs as transit through large intestine

Question 13

What are the symptoms of giardia?

Answer 13

Asymptomatic 
Chronic diarrhoea 
Epigastric pain 
Nausea and vomiting 
Malabsorption 
Weight loss 
Symptoms typically 6-15 days after exposure

Question 14

What is the pathophysiology of giardia?

Answer 14

Flattening of the villi and inflammation of mucus
Direct damage to intestinal brush border
Alteration of absorption
Alteration of small intestine function
Induction of a host immune response

Question 15

What is the treatment for giardia?

Answer 15

Metronidazole

Question 16

How does entamoeba cause infection?

Answer 16

Cysts and TZ passed in feces
Mature cysts ingested
excystation in the small intestine
trophozite replication in the large intestine
The TZ invade the intestinal wall causing invasive infection (dysentery, colitis, appendicitis)

Question 17

How does cryptosporidium cause infection?

Answer 17

Thick walled oocyst exits host
Contamination of food and water with oocysts
Thick walled oocyst ingested by host

Question 18

What are the symptoms of crytposporodium infection?

Answer 18

In normal adults - gastroenteritis
Immunosuppressed: cholera like illness, chronic diarrhoea illness, intermittent diarrhoea illness, transient diarrhoea illness

Question 19

How do you treat cryptospordium?

Answer 19

In most people rehydration but Nitazoxanide if needed

Question 20

what are the severe forms of malaria?

Answer 20

Plasmodium falciparum and Plasmodium knowlesi

Question 21

What are the clinical features of malaria infection?

Answer 21

Rigors, fevers, sweats
headaches, arthralgia, myalgia

Severe forms: cerebral, aciodsis, renal failure, anaemia, hypoglycaemia, acute respiratory distress syndrome

Question 22

How do flatworms cause infection?

Answer 22

Eggs in feces passed into the environment
Cattle and pigs become infected
oncospheres hatch, penetrate intestinal wall and into circulation and musculature
Humans eat raw or undercooked affected meat