Parasites

Question 1

Describe the basic properties of parasites.

Answer 1

Unicellular, animal-like microbes. Facultative anaerobes. Most are motile. Acquire nutrition by pinocytosis or phagocytosis. Enters host via a specialized site/structure.

Question 2

What are the routes of transmission?

Answer 2

Fecal-oral (Intestinal), sexually transmitted (Urogenital Tract) and insect vectors (Blood and Tissue).

Question 3

What are the two life cycle forms of parasites?

Answer 3

Trophozoite (motile, metabolically active, multiplies by replication) and Cyst (non motile, passed in feces, resistant to hostile environment, does not multiply).

Question 4

Name the protozoal parasites.

Answer 4

1. Entamoeba histolytica
2. Giardia lamblia
3. Balantidium coli
4. Cryptosporidium parvum
5. Cyclospora cyatenensis
6. Trichomonas vaginalis

Question 5

1. Entamoeba histolytica

Answer 5

Moves via pseudopodia. May invade the colon and cause bloody diarrhea (Amoebic dysentery). Also cause liver abscess. Reproduces asexually.

Question 6

2. Giardia lamblia

Answer 6

Moves via flagella. Reproduces asexually. Lives in the small intestine and results in malabsorption.

Question 7

3. Balantidium coli

Answer 7

Large and moves via cilia. Reproduces asexually. lives in the colon of pigs, humans and rodents and can lead to colonic ulceration.

Question 8

4. Cryptosporidium parvum

Answer 8

Non motile. Reproduces sexually. Prevalent in immunocompromised patients.

Question 9

5. Cyclospora cyatenensis

Answer 9

Non motile. Reproduces sexually. Takes over the small intestine mucosa and may cause diarrhea for several weeks.

Question 10

6. Trichomonas vaginalis

Answer 10

Moves via flagella. Reproduces asexually. Sexually transmitted.

Question 11

Extra -intestinal/Blood and tissue protozoal parasites

Answer 11

1. Plasmodium spp.
2. Leishmania spp.
3. Trypanosoma: Cruzi and Brucei
4. Toxoplasma gondii

Question 12

1. Plasmodium spp.

Answer 12

Non motile. Reproduces sexually and asexually. Causes Malaria via the Anopheles mosquito. Four species infect humans.

Question 13

2. Leishmania spp.

Answer 13

Moves via flagella. Transmitted via sand flies. Can lead to visceral, cutaneous and mucocutaneous leishmaniasis.

Question 14

3. Trypnosoma

Answer 14

Haemoflagellates.
In Africa- Causes sleeping sickness. Transmitted via the Tsetse fly
in South Amercia - Causes Chaga’s disease. Transmitted via the Reduviid bug

Question 15

4. Toxoplasma gondii

Answer 15

Transmitted through the ingestion of oocysts from cat feces. Infection can lead to severe manifestations or neonatal toxoplasmosis.

Question 16

Other Protozoal Parasites

Answer 16

1. Naegleria fowleri

2. Acanthamoeba spp.

Question 17

1. Naegleria fowleri

Answer 17

Free living amoeba found in freshwater. Causes very rare/fatal brain infection. rapidly progressing primary acute meningoencephalitis.

Question 18

2. Acanthamoeba spp.

Answer 18

Free living amoeba found in environmental water sources. Contaminates fluid used to clean contact lenses, but may also come from dust or swimming. Infection results in keratitis.

Question 19

Describe metazoan parasites (Helminths)

Answer 19

Eukaryotic. Multicellular. Have digestive, circulatory, nervous, excretory and reproductive systems. Have bilateral symmetry, a head, tail and tissue differentiation (endo-, meso- and ectoderm). 
Free living. Acquire nutrition from the host. Reproduces sexually and asexually. Produces large number of eggs per day. 
Two(2) groups:
1. Nemathelminthes (Roundworms)
                -Nematodes
2. Platyhelminthes (Flatworms)
                -Trematoda (Flukes)
                -Cestoda (Tapeworms)

Question 20

Symptoms associated with Nematodes

Answer 20

Lungs (Larvae)

   - Asthma or pneumonia like 
   - Cough, shortness of breath, wheezing

Intestines (Adult worms)

   - Diarrhea, or bloody stool
   - Nausea, vomiting, abdominal pain
   - Severe infections: malnutrition, weightloss

Question 21

1. Nematodes (general features)

Answer 21

Have cylindrical bodies and complete digestive tracts.?Have separate male and female sexes which mate. The eggs typically have a characteristic shape, cell wall density and operculum on one or both ends.

Question 22

1. Nematodes (Types)

Answer 22

Intestinal

i) Ascaris (Roundworm)
ii) Enterobius (Pinworm)
iii) Trichuris (Whipworm)
iv) Ancylostoma and Necator (Hookworms)
v) Strongyloides

Tissue

vi) Toxocara
vii) Trichinella

viii) Filarial worms

Question 23

i) Ascaris (Roundworm)

Answer 23

World wide distribution. Found in conditions of poor hygiene. Adult worm lives in intestine. Causes eosinophilia.

Question 24

ii) Enterobius (Pinworm)

Answer 24

Prevalent in cold and temperate climates (rare in tropics) . Found mainly in children.

Question 25

iii) Trichuris (Whipworm)

Answer 25

Transmitted via the soil; warm and humid. Can cause diarrhea, rectal prolapse and anemia.

Question 26

iv) Ancylostoma and Necator (Hookworms)

Answer 26

Major cause of anemia in the tropics.

Question 27

v) Strongyloides

Answer 27

Inhabits the small bowel. Infection is more severe in immunocompromised persons.

Question 28

vi) Toxocara

Answer 28

Worldwide infection of cats and dogs. Infection occurs when humans ingest embryonated eggs from dog/cat feces.

Question 29

vii)Trichinella

Answer 29

Associated with consumption of infected and unfrozen or poorly cooked meat.

Question 30

viii) Filarial worms

Answer 30

Onchocerca volvulus Transmitted by Simulium spp (black fly). Causes visual impairment, blindness and severe itching of skin. Wuchereria bancrofti Major cause of lymphatic filariasis. Brugia malayi Causes lymphatic filariasis.

Question 31

2. Trematodes (General features)

Answer 31

Have a dead end digestive system. Have more than 1 host (a mollusk and a vertebrate). They are generally hermaphrodites.

Question 32

2. Trematodes (Classes)

Answer 32

i) Fasciolopsis buski (Intestinal fluke) ii) Paragonimus westermani (Lung fluke) iii) Fasciola hepatica (Liver fluke) iv) Clonorchis sinensis (Chinese liver fluke) v) Schistosoma spp. (Blood flukes)

Question 33

i) Fasciolopsis buski (Intestinal fluke)

Answer 33

Common parasite of pigs and humans in Southeast Asia. One of the largest trematodes and lives in upper intestine. Chronic infection leads to inflammation, ulceration and haemorrhage of the small intestine.

Question 34

ii) Paragonimus westermani (Lung fluke)

Answer 34

Widespread in Far East and Southeast Asia. Acquired through ingestion of infective metacercariae in raw or pickled crustaceans.

Question 35

iii) Fasciola hepatica (Liver fluke)

Answer 35

Parasite of sheep. Humans infected when they ingest metacercariae that have encysted. Adult trematode lives in the intrahepatic bile ducts of the liver. Can lead to severe anemia in humans.

Question 36

iv) Clonorchis sinensis (Chinese liver fluke)

Answer 36

Widespread in China, Japan, Korea and Taiwan. Acquired by ingestion of infective metacercariae in raw or pickled fish.

Question 37

v) Schistosoma spp. (Blood flukes)

Answer 37

Free living (cercariae). Have a characteristic spine. Hermaphrodites. Unsual flukes because they are acquired through skin penetration.