Medical Microbiology: Pathogenesis of Parasitic Infections Flashcards
1
Q
What is Leishmaniasis?
A
- A parasitic disease caused by Leishmania parasites
2
Q
What are the different types of Leishmaniasis?
A
-
Visceral leishmaniasis
- Asia: Leishmania donovani
- Middle East/Africa/Asia: L. infantum variants
- Latin America: L. chagasi
-
Cutaneous Leishmaniasis
- Old world disease: Mediterranean/Middle East - L. Infantum/L. major/L. tropica
- New world disease: Central and South America - L. braziliensis/amazonensis/mexicana
3
Q
Describe the life cycle of Leishmania
A
- Sand fly bites you and transfers promastigote into the body
- Promastigotes invades macrophages
- Inside macrophage promastigotes form nests of amastigotes
- This causes macrophage to burst resulting in release of amastigotes which go on to infect other cells
4
Q
What is the vector for leishmaniasis?
A
- Lutzomyia/Phlebotomus
5
Q
What causes diffuse cutaneous leishmaniasis?
A
- Occurs as a result of someone not being able to produce an adequate immune response to the parasite
6
Q
Describe the pathogenesis of cutaneous leishmaniasis
A
-
Acute lesions
- Due to tissue damage caused by inflammatory response to presence of parasites in macrophages
- Parasite killed by Th1 pro-inflammatory responses and macrophages
-
Latency
- Regulatory immune response which causes parasites to remain dormant long-term
- Characterized by balance of Th1 and anti-inflammatory responses
-
Relapse (rare)
- Alteration in immune response e.g. change in Th1 vs immune regulation due to HIV infection
- Mucocutaneous disease associated with strong but inadequate inflammatory response to parasites that have metastasized to mucosa
- Diffuse cutaneous leishmaniasis associated with uncontrolled parasite replication
7
Q
What are the 3 main species of Helminths that can cause Schistosomiasis?
A
- Schistosoma mansoni
- Schistosoma haematobium
- Schistosoma japonicum
8
Q
Decribe the life cycle of Schistosoma
A
- People exposed to infective stage in contaminated water
- Get infected with cercariae which migrate through the body
- Cercariae fbecome adults in mesenteric system
- Female and male mate and female releases eggs into mucosal epithelium
- Eggs get excreted either through faeces or urine
9
Q
What is cercarial dermatitis?
A
- Allergic type reaction caused by exposure to cercariae from animal or bird schistosomes
- Requires pre-sensitization
10
Q
What is a key feature of the immune response to Schistosomiasis?
A
- Granuloma formation - Eggs from female become organized in granulomas
- Repeated insults and tissue repair leads to fibrosis and organ damage
11
Q
What is Hepato-intestinal schistosomiasis?
A
- Schistosomiasis infection caused by S.mansoni and S. japonicum
- Pathology caused by immune response to eggs - eggs are pushed through intestinal wall and mucosa and are then excreted
- This causes hepatosplenomegaly
12
Q
What diseases/conditions can urinary schistosomiasis cause?
A
- Haematuria - blood in the urine
- Can also lead to bladder cancer due to inflammation of bladder wall caused by eggs
13
Q
What is onchocerciasis?
A
- Major blinding disease caused by filarial parasite (Onchocerca volvulus)
- Transmitted by blackflies
14
Q
Describe the life cycle of Onchocerca volvulus
A
- Blackfly bites you and transmits infectious larvae
- Larvae migrates under the skin and develops into adults
- Male and female adult mate and female releases 1000s of larvae called microfilariae
- Microfilariae get taken up by blackfly and develop in blackfly until they can be trasnmitted themselves
15
Q
What is the vector of Onchocerca volvulus?
A
- Simulium
16
Q
Describe the pathology of Onchocerciasis
A
- Repeated episodes of inflammation due to presence of microfilariae leads to permanent damage and scarring in skin and eyes
17
Q
What diseases/conditions are caused by Onchocerciasis?
A
- Onchocercal nodules - only problematic if around joints
-
Skin disease
- Acute papular onchodermatitis
- Chronic onchodermatitis
- Sowda
-
Eye disease
-
Anterior segment (iris)
- Punctate keratitis
- Acute iridocyclitis
- Sclerosing keratitis
-
Posterior segment (retina)
- Optic neuritis/atrophy
- Chorioretinopathy
-
Anterior segment (iris)
18
Q
What is punctate keratitis?
A
- Condition caused by death of small groups of cells in the cornea as a result of Microfilariae being killed by immune response
19
Q
What is sclerosing keratitis?
A
- Condition caused by repeated inflammation of the cornea
- This results in opacification of the cornea causing blindness
20
Q
Describe the immune response that occurs due to onchocerciasis
A
- Rapid allergic reactions that kill microfilariae in skin
- Activation of mast cells which recruit other immune system cells e.g. eosinophils
-
Acute stage
- Strong TH2 response which produces IL-4 and IL-5
- IL-4 leads to IgE production and IL-5 leads to recruitment and activation of eosinophils
-
Chronic stage
- Host immune response starts to be regulated and shut down
- Modified TH2 response - production of IL-10, TReg cells and IgG4 antibodies
21
Q
How do ticks infect their hosts?
A
- Tick sticks its mouth into skin and releases “cement” which keeps it in the skin
- Once stuck in skin it feeds off blood
- Tick also releases toxins into body which produces a block in motor nerve fibres
22
Q
What are some of the diseases transmitted by hard ticks?
A
- Tick typhus
- Viral encephalitis
- Viral fevers
- Viral haemorrhagic fevers
- Tick paralysis
23
Q
What are some of the diseases transmitted by soft ticks?
A
- Q fever
- Relapsing fever
24
Q
What are some characteristics of head lice?
A
- Suck blood from scalp and lay eggs on hair
- Easily spread by close contact, sharing of combs and brushes etc.
25
What are some characteristics of body lice?
* Suck blood from body and lay eggs on clothing
* Spread via bodily contact, sharing of clothing or bedding
* Can cause vector diseases such as:
* Epidemic typhus
* Trench fever
* Relapsing fever
26
What are some characteristics of pubic lice?
27
Describe the life cycle of the botfly (Dermatobia hominis)
* Mid-flight it grabs a mosquito and lays its eggs on the mosquito
* Mosquito goes on to bite animal, the change in temperature causes eggs to hatch and larvae to invade the skin
28
What is Myiasis?
* Parasitic infestation of the body of a live animal by Botfly larvae (maggots) which grow inside the host while feeding on its tissue
29
What drugs can be used to treat infections caused by different types of parasites?
* Tinidazole has shorter dose regimens compared to other drugs used to treat protozoa infections - 1g once a day for 3 days
* Metronidazole has more adverse reaction and has longer dose course - 1 or 2 week course
* Benznidazole used to treat chagas disease but causes very bad adverse reactions so people can't complete course
* Heavy metals used to treat Leishmaniasis
30
How can parasitic infections be controlled?
* **Behaviours**
* Education
* Introducing Hand washing and hygiene behaviours
* **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
31
Why must treatment of parasitic infections in endemic settings be given periodically over long periods of time?
* Because re-infections are rapid and because the treatment kills larval rather than adult stages
32
Give some examples of treatments of parasitic infections given periodically over a long period of time
* A single dose of albendazole is given to high risk groups such as school children 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
