Pathogenesis of Parasitic Infections

Question 1

Schistosomiasis - list 3 main species

Answer 1

Three main species
• Schistosoma mansoni
• S. haematobium
• S. japonicum

Question 2

Schistosomiasis; cercarial dermatitis - define

Answer 2

• Exposure to cercariae from

animal or bird schistosomes

Question 3

Schistosomiasis; cercarial dermatitis - what does it require

Answer 3

• Requires pre-sensitization

Question 4

Schistosomiasis; cercarial dermatitis - effect

Answer 4

• Allergic-type reaction

Question 5

Schistosomiasis - key feature of immune response

Answer 5

Key feature of immune response is
granuloma formation
• Eggs become organized in granulomas
• Repeated insults and tissue repair leads to fibrosis and
organ damage

Question 6

Hepato-intestinal schistosomiasis - define and describe cause

Answer 6

• Infections with
S.mansoni and S.
japonicum
• Pathology caused by
immune response to
eggs

Question 7

Urinary schistosomiasis - define

Answer 7

Urinary schistosomiasis is a disease caused by infection of people with the parasitic worm Schistosoma haematobium.

worms live in BVs around person’s bladder = releases eggs which are released in the person’s urine

Question 8

Helminths: onchocerciasis - define, cause + transmitted by

Answer 8

• Major blinding disease
• Caused by filarial parasite (Onchocerca
volvulus)
• Transmitted by blackflies

Question 9

Blackfly lifecycle

Answer 9

BF takes (genus simulium) takes blood = L3 lavae enter bite

Adults in subcutaneous nodule = prod unsheathed microfilariae (found in skin/lymph + in peripheral blood, urine + sputum)

BF takes blood meal

MF penetrate BF’s midgut + migrate to thoracic muscles

L1-L3 lavae

Migrate back to head + BF’s proboscis

Repeat

Question 10

Onchocerciasis - pathology

Answer 10

Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring
in skin and eyes

Question 11

Onchocerciasis - list skin dieases

Answer 11

Skin disease
• Acute papular onchodermatitis
• Chronic onchodermatitis
• sowda

Question 12

Onchocerciasis - list anterior eye dieases

Answer 12

Anterior segment:

• Punctate keratitis
• Acute iridocyclitis
• Sclerosing keratitis

Question 13

Onchocerciasis - list posterior eye dieases

Answer 13

Posterior segment:

• Optic neuritis/atrophy
• Chorioretinopathy

Question 14

Define tick paralysis

Answer 14

Progressive flaccidity due to a failure of ACh liberation in NM junction

Question 15

Hard-bodies vs soft-bodies ticks

Answer 15

H = (lxodidae) = carriers of rickettsial, spirochaetal, viral, bacterial + protozoan diseases

S = (omithodorus) = vectors of endemic relapsing fever (caused by borrelia duttoni) + Q-fever

Question 16

Describe action of sucking head lice

Answer 16

Suck blood from scalp and + eggs on hair

Common + easily spread by close contact, sharing of combs, brushes, hats, etc

Question 17

Describe action of sucking body lice + examples

Answer 17

Suck blood from body + lay eggs on clothing

Uncommon + spread by bodily contact, sharing of clothing or bedding

Vector dieases (epidemic typhus, trench fever, relapsing fever)

Question 18

Describe cause of sucking lice related to lousiness

Answer 18

Crowded conditions

Long periods without bathing or changing clothes

Question 19

Describe structure of pthiridae

Answer 19

Pthiridae (crab lice, pubic lice)

• Broad, flat lice that appear crab-like
• Mid + hind legs are stout with very large claws
• Abdominal segments have distinct lateral lobes

Question 20

Describe the action of species of pthiridae confined to pubic region

Answer 20

Pthirus pubus:

Bites cause irritation + rash
Spread by close body contact
No diseases

Question 21

Control of parasite infections - drugs for protozoa

Answer 21

Tinidazole
Metronidazole
Nitazoxanide
Benznidazole
Heavy metals (meglumine antimoniate)

Question 22

Control of parasite infections - drugs for helminths

Answer 22

Albendazole/mebendazole
Praziquantel
Ivermectin
Diethylcarbamazine
Pyrantel

Question 23

Control of parasite infections - drugs for ectoparasites

Answer 23

Ivermectin

Benzyl/malathion lotions

Question 24

Control of parasite infections - behaviours

Answer 24

Behaviours:

• Education
• Hand washing and hygiene behaviours

Question 25

Control of parasite infections - environmental interventions

Answer 25

Environmental interventions: * Spraying of residual insecticides for household vectors * Mosquito nets for malaria * Improved housing * Sewage disposal and potable water * Drainage of swamps * Poverty reduction * Micro-financing, etc

Question 26

Control of parasite infections - importance of long period treatment

Answer 26

• For many parasite infections in an endemic settings, treatment must be given periodically over long periods of time because re-infections are rapid or because the treatment kills larval rather than adult stages

Question 27

Control of parasite infections - example of long period treatment

Answer 27

For example: • a single dose of albendazole is given to high risk groups such as schoolchildren up to every 4 months to control STH infections. • a single dose of ivermectin is given to endemic communities (mass drug administration) every 6 or 12 months to control onchocerciasis • a single dose of praziquantel is given to endemic communities (mass drug administration) every 6 or 12 months to control schistosomiasis