Pathogenesis of parasitic infections Flashcards
What is the lifecycle of schistosomiasis
starting with infection with contaminated water
Infected in contaminated water
Snail host is releasing cercariae
Eggs embolise in capillaries, pushed through mucosa into lumen of bladder or intestines and is excreted
Goes on to infect snails
Can develop disease just from exposure to cercariae from animal or bird schistosomes
Require pre-sensitisation
Allergic-type reaction
Cercariae buries through skin and is met with immune response causing rash like lesions
What is the key feature of immune response to schistomasis?
Granuloma formation, eggs become organised in granulomas
Repeated insults and tissue repair leads to fibrosis and organ damage
What is hepato-intestinal schistomiasis infected with?
What can it cause?
Infections with S.mansoni and S.japonicium
Pathology caused by immune response to eggs
Can get fibrosis inside intestine
All caused by host’s immune response, forming granulomas around eggs
Liver damage:
- Fibrotic tissues formed from schistosomiasis
- Can cause enlarged liver and spleen in chronic schistosomiasis
Where does urinary schistosomiasis occur?
What is the first clinical manifestion?
What can it cause in the bladder?
Within mucosa of bladder
Eggs become organised in granulomas if not pushed through mucosa rapidly enough
First clinical manifestation is blood in urine
- Haematuria
Bladder pathology:
- Can cause long term changes due to repeated infection
- End-stage bladder with urinary schistomasiasis looks like carcinoma
Helminths
What is onchocerciasis caused by?
What is it transmitted by?
By a worm, fliarial parasite Onchocherca volvulus, causes blindness.
Pathology:
Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring in skin and eyes
Transmitted by blackflies, long and thin, coil up in fibrous nodules under skin
What skin diseases can onchocerca volvulus cause?
Onchoceral nodules
Acute papular onchodermatitis
Chronic onchodermatitis
Sowda
What eye diseases can onchocerca volvulus cause?
Anterior segment
- Punctuate keratitis
- Acute iridocyclitis
- Sclerosiing keratitis
Posterior segment
- Optic neuritis/atrophy
- Chorlioretinopathy
Punctuate keratitis
- Microfilaria invade corneal stroma and becomes immobilised
- Self-limiting
- Heal
Chorioretinopathy
- Damage to pigment epithelium
- Causes lesion in retinal epithelium
- Repeated damage to pigment epithelium causes you to lose retina
How do ectoparasites like ticks cause disease?
What diseases are transmitted by hard and soft ticks?
Tick bites you and cements itself to your skin, is hard to remove.
Diseases transmitted by hard ticks
- Tick typhus
- Viral encephalitis
- Viral fevers
- Tick paralysis
Soft ticks
- Q fever
- Relapsing fever
Lice are also ectoparasites, what are the different types of lice?
Head lice
- Suck blood from scalp and lay eggs on hair, easy to transmit by close contacts, hats etc
Body lice
- Suck blood from body and lay eggs on clothing
- Uncommon and spread by bodily contact, sharing clothing or bedding
- Shares vector diseases e.g epidemic typhus, trench fever, relapsing fever
Crab or pubic lice
- Broad, flat lice, appear crab like
- Mid and hind legs are stout with very large claws
- Abdominal segments have distinct lateral lobes
- Single species Pthirus pubus, confined to human pubic region
- Bites cause irritation and typical rash
- Spread by close body contact
- No diseases
Botflies don’t directly transmit larvae
Catches mosquito mid-flight, lays eggs on it.
Mosquito goes to warm blooded animal, egg sticks to coat of animal or hatches and invades skin.
Live in burrows under skin, develop into pupas.
Larvae migrate to skin and forms botfly larvae which develops under skin.
Sticks head out skin.
Can be removed by drug that kills it, then squeeze it out, but can’t remove them by squeezing when alive as they have spines that hold them in.
Drugs used to conrol parasite infections
Protozoa
- Tinidazole
- Metronidazole
- Nitazoxanide
- Benzindazole
- Heavy metals (meglumine antimoniate)
Helminths
- Albendazole/mebendazole
- Praziquantel
- Ivermectin
- Diethylcarbamazine
- Pyrantel
Ectoparasites
- Ivermectin
- Benzyl/malathion lotions
What else besides drugs controls parasite infections?
Behaviours
- Education
- Hand washing and hygiene behaviours
Environmental interventions
- Spraying of residual insecticides for household vectors
- Mosquito nets for malaria
- Improved housing
- Swage disposal and portable water
- Drainage of swamps
Poverty reduction
- Micro-financing etc
Why must treatment be given periodically in endemic settings?
Bceuase re-infections are rapid or because the treatment kills larval rather than adult stages.
so treatment will be given every 4/6/12 months for different infections.
