Pathogenesis of Parasitic Infections Flashcards
Which parasite causes schistosomiasis?
Helminths
What are the 3 main species of Schistosomiasis?
- Schistosoma mansoni
- S. haematobium
- S. japonicum
Outline where and what effect S. japonicum has
- Asia
- Hepatic & intestinal system
Outline effects of S. haeatobium
- Sub-saharan Africa
- Urinary tract
Where and what does S. mansoni effect?
- Latin America, Sub-saharan Africa
- Hepatic & intestinal system
Outline the life cycle of schistosomiasis
- Exposed to infective stage in contaminated water
- Cercariae migrate through body
- Adults form in mesenteric system
- Eggs lain and pushed through mucosal epithelium
- Excreted in faeces/urine
What is Cercarial Dermatitis?
Schistosomiasis exposure to cercariae from animal or bird schistosomes
Requires pre-sensitization - allergic type reaction
Describe the immune response to schistosomiasis
key feature of immune response is granuloma formation of eggs
Th2 delayed type hypersensitivity
What does repeated exposure of schistosomiasis cause?
Repeated insults and tissue repair leads to fibrosis and organ damage
What causes Hepato-intestinal schistosomiasis?
Infections with S.mansoni and S. japonicum
Pathology caused by immune response to eggs
How does S.mansoni and S.japonicum effect the hepatic and intestinal space?
When infected, adults present in mesenteric vessels
Females release 1000’s of eggs - travel through intestine to capillaries and pushed into intestinal wall through mucosa due to immune response and excreted
What does chronic schistosomiasis (mansoni + japonicum) exposure cause?
Chronic exposure leads to inflammation repair and fibrosis
Typical pipe stem fibrosis seen in advanced schistosoma liver disease ⇒ secondary hepato-splenomegaly
How does urinary schistosomiasis occur?
Adults live in vessels surrounding bladder and release eggs there
Eggs pushed through bladder mucosa and excreted in urine
How is urinary schistosomiasis diagnosed?
urine tests show haematuria to diagnose schistosomiasis
> Very common in adolescence in endemic areas
What causes haematuria in urinary schistosomiasis?
Damage due to inflammation caused by the eggs in bladder wall commonly leads to secondary development of cancer
What is onchocerciasis?
Major binding disease
Caused by worm infection; filarial parasite (onchocerca volvulus)
Transmitted by backflies
What is the vector of onchocerciasis?
Simulium
Where is onchocerciasis (river blindness) common?
Present in equatorial regions of Africa and Central and South America
Outline the life cycle of onchocerciasis
- Blackfly bite transmits infectious larvae
- Larvae migrates under the skin
- Develops into adults and mate to release 1000s of eggs (microfilariae)
- Microfilariae taken up by blackfly
How does onchocerciasis lead to blindness?
Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring in skin and eyes
Outline the different forms of Onchocerciasis clinical disease
- Onchocercal nodules
- skine disease
- Eye disease
Describe the skin disease of onchocerciasis
- Acute papular onchodermatitis
- Chronic onchodermatitis
- Sowda
Outline the 2 types of eye disease associated with onchocerciasis
Anterior segment
- Punctate keratitis
- Acute iridocyclitis
- Sclerosing keratitis
Posterior segment
- Optic neuritis/atrophy
- Chropretinopathy
Describe what acute papular onchodermatitis looks like
Looks like an acute papular rash but looking closely at skin shows microfilariae surrounded by inflammatory response; characterised by eosinophils