Pathogenesis of Parasitic Infections Flashcards
Schistosomiasis - list 3 main species
Three main species
• Schistosoma mansoni
• S. haematobium
• S. japonicum
Schistosomiasis; cercarial dermatitis - define
• Exposure to cercariae from
animal or bird schistosomes
Schistosomiasis; cercarial dermatitis - what does it require
• Requires pre-sensitization
Schistosomiasis; cercarial dermatitis - effect
• Allergic-type reaction
Schistosomiasis - key feature of immune response
Key feature of immune response is granuloma formation • Eggs become organized in granulomas • Repeated insults and tissue repair leads to fibrosis and organ damage
Hepato-intestinal schistosomiasis - define and describe cause
• Infections with S.mansoni and S. japonicum • Pathology caused by immune response to eggs
Urinary schistosomiasis - define
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
Helminths: onchocerciasis - define, cause + transmitted by
• Major blinding disease
• Caused by filarial parasite (Onchocerca
volvulus)
• Transmitted by blackflies
Blackfly lifecycle
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
Onchocerciasis - pathology
Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring
in skin and eyes
Onchocerciasis - list skin dieases
Skin disease
• Acute papular onchodermatitis
• Chronic onchodermatitis
• sowda
Onchocerciasis - list anterior eye dieases
Anterior segment:
- Punctate keratitis
- Acute iridocyclitis
- Sclerosing keratitis
Onchocerciasis - list posterior eye dieases
Posterior segment:
- Optic neuritis/atrophy
- Chorioretinopathy
Define tick paralysis
Progressive flaccidity due to a failure of ACh liberation in NM junction
Hard-bodies vs soft-bodies ticks
H = (lxodidae) = carriers of rickettsial, spirochaetal, viral, bacterial + protozoan diseases
S = (omithodorus) = vectors of endemic relapsing fever (caused by borrelia duttoni) + Q-fever
Describe action of sucking head lice
Suck blood from scalp and + eggs on hair
Common + easily spread by close contact, sharing of combs, brushes, hats, etc
Describe action of sucking body lice + examples
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)
Describe cause of sucking lice related to lousiness
Crowded conditions
Long periods without bathing or changing clothes
Describe structure of pthiridae
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
Describe the action of species of pthiridae confined to pubic region
Pthirus pubus:
Bites cause irritation + rash
Spread by close body contact
No diseases
Control of parasite infections - drugs for protozoa
Tinidazole Metronidazole Nitazoxanide Benznidazole Heavy metals (meglumine antimoniate)
Control of parasite infections - drugs for helminths
Albendazole/mebendazole Praziquantel Ivermectin Diethylcarbamazine Pyrantel
Control of parasite infections - drugs for ectoparasites
Ivermectin
Benzyl/malathion lotions
Control of parasite infections - behaviours
Behaviours:
- Education
- Hand washing and hygiene behaviours
Control of parasite infections - environmental interventions
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
Control of parasite infections - importance of long period treatment
• 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
Control of parasite infections - example of long period treatment
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
