Pathogenesis of Parasitic Infections Flashcards
Leishmaniasis - what is it?
a protozoa
2 types of this disease: visceral and cutaneous
Leishmaniasis: life cycle
-fairly simple life cycle
- sand fly bites you and transmits a promastigote
- promastigote invades immune cells, e.g. neutrophils and macrophages
- inside the macrophage it forms nests of amastigotes
- the cells eventually burst and release amistogotes, which can infect other cells or be taken up by a sand fly at another blood meal and transmitted to someone else
what is the vector of leishmaniasis?
Sand-flies
they are very common in tropical regions and tend to affect poorer households - housing not up to standard
they love feeding on chickens as a source of blood, and they are small enough to get through mosquito nets.
what type of infection is leishmaniasis?
largely a zoonotic infection - the reservoir are rodents and animals like sloths, but humans can become infected, as can domestic dogs
domestic dogs being infected then paves the way for urban transmission
clinical forms of leishmaniasis?
Cutaneous leishmaniasis:
- papule gradually spreads into a lesion - the centre becomes necrotic and you get ulcer formation
- if these people move to a different area, and are exposed to a different strain of Leishmania, they can get it again
Diffuse cutaneous Leishmaniasis:
- some individuals aren’t able to generate an adequate immune response so they get packed full of parasites
- uncontrolled parasite replication
Mucocutaneous leishmaniasis:
- everyone is infected as a child and have a scar
- strong but inadequate inflammatory response to parasites that have metastasized to mucosa
- small % of individuals, years later, start to get a stuffy nose and then it becomes more marked, lesions around the mucosal area
- break down of nasal septum region
Pathogenesis of cutaneous leishmaniasis
Acute lesions
• Presence of parasites in macrophages cause tissue damage due to the Th1 pro inflammatory responses, which kill both the parasite and macrophage
Latency
• Parasites remain present long-term, there is a regulatory immune response characterized by balance of Th1 and anti-inflammatory responses (tnf beta, IL10)
Relapse (rare)
• Alteration in immune response (change in Th1, HIV, malnutrition) may trigger relapse
does leishmaniasis go away?
never goes away
-the leishmania parasites can linger, and may reactivate at other sites in the body due to situations, eg. malnutrition or stress
Recividans?
recurrence of lesions at old ulcer site
Helminths - what important infections do they cause?
schistosomiasis
onchocerciasis
Schistosomiasis (worm infections): geography
3 main species:
- Schistosoma mansono – affects hepatic and intestinal system
- S. Haematobium – affects urinary tract
- S. japonicum – affects hepatic and intestinal system, found in Asia
Schistosomiasis: Life cycle
people become exposed to the infective stage in contaminated water – they get infected with cercarae.
cercarae migrate through the body forming adults in the mesenteric system (manosono and japonicum in the intestinal mesenteric system, haemabotium in the vessels around the bladder)
the female and male mate, female releases lots of eggs which are pushed through the mucosal epithelium and leave via the faeces, which enter the water system and infect snails
Cercarial dermatitis?
allergic reaction to the presence of cercariae in the water source
- Exposure to cercariae from animal or bird schistosomes
- Requires pre-sensitization
- Allergic-type reaction
key feature of the immune response is granuloma formation
-eggs become organised in granulomas, and repeated insults and tissue repair leads to fibrosis and organ damage
Hepato-intestinal schistomiasis
- Infections with S.mansoni and S. japonicum
- Pathology caused by immune response to eggs
- adults are in the mesenteric vessels
- the female releases thousands of eggs which go into the intestines through the capillaries, and are pushed by the immune response through the intestinal wall through the mucosa, and are then excreted
-chronic inflammation over a long period of time will cause fibrosis, splenamegaly and hepatomegaly
Urinary schistomiasis
- adults live in the vessels around the bladder and release eggs into those vessels which are pushed through the mucosa of the bladder and excreted into the urine
- in endemic areas, what is quite common at puberty is haematuria – peeing blood
- because of inflammation in the bladder wall related to the eggs, you get damage to the bladder walls which can lead to the development of cancer
Helminths: onchocerciasis?
river blindness - major blinding disease
- caused by a filarial parasite called Onchocerca volvulus
- transmitted by blackflies
- female worm is long, coiled up into tight bundles in fibrous nodules found under the skin
complex life cycle:
- black fly bites you and transmitter infectious larvae
- the larvae migrate under the skin and develop into adults
- male and female adults mate and the female release thousands on larvae called microfilariae, and are taken up by the black fly and can be transmitted