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Medical Microbiology > Pathogenesis of Parasitic Infections > Flashcards

Pathogenesis of Parasitic Infections Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Which parasite causes schistosomiasis?

A

Helminths

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2
Q

What are the 3 main species of Schistosomiasis?

A
  • Schistosoma mansoni
  • S. haematobium
  • S. japonicum
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3
Q

Outline where and what effect S. japonicum has

A
  • Asia

- Hepatic & intestinal system

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4
Q

Outline effects of S. haeatobium

A
  • Sub-saharan Africa

- Urinary tract

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5
Q

Where and what does S. mansoni effect?

A
  • Latin America, Sub-saharan Africa

- Hepatic & intestinal system

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6
Q

Outline the life cycle of schistosomiasis

A
  1. Exposed to infective stage in contaminated water
  2. Cercariae migrate through body
  3. Adults form in mesenteric system
  4. Eggs lain and pushed through mucosal epithelium
  5. Excreted in faeces/urine
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7
Q

What is Cercarial Dermatitis?

A

Schistosomiasis exposure to cercariae from animal or bird schistosomes

Requires pre-sensitization - allergic type reaction

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8
Q

Describe the immune response to schistosomiasis

A

key feature of immune response is granuloma formation of eggs

Th2 delayed type hypersensitivity

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9
Q

What does repeated exposure of schistosomiasis cause?

A

Repeated insults and tissue repair leads to fibrosis and organ damage

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10
Q

What causes Hepato-intestinal schistosomiasis?

A

Infections with S.mansoni and S. japonicum

Pathology caused by immune response to eggs

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11
Q

How does S.mansoni and S.japonicum effect the hepatic and intestinal space?

A

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

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12
Q

What does chronic schistosomiasis (mansoni + japonicum) exposure cause?

A

Chronic exposure leads to inflammation repair and fibrosis

Typical pipe stem fibrosis seen in advanced schistosoma liver disease ⇒ secondary hepato-splenomegaly

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13
Q

How does urinary schistosomiasis occur?

A

Adults live in vessels surrounding bladder and release eggs there
Eggs pushed through bladder mucosa and excreted in urine

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14
Q

How is urinary schistosomiasis diagnosed?

A

urine tests show haematuria to diagnose schistosomiasis

> Very common in adolescence in endemic areas

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15
Q

What causes haematuria in urinary schistosomiasis?

A

Damage due to inflammation caused by the eggs in bladder wall commonly leads to secondary development of cancer

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16
Q

What is onchocerciasis?

A

Major binding disease
Caused by worm infection; filarial parasite (onchocerca volvulus)
Transmitted by backflies

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17
Q

What is the vector of onchocerciasis?

A

Simulium

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18
Q

Where is onchocerciasis (river blindness) common?

A

Present in equatorial regions of Africa and Central and South America

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19
Q

Outline the life cycle of onchocerciasis

A
  1. Blackfly bite transmits infectious larvae
  2. Larvae migrates under the skin
  3. Develops into adults and mate to release 1000s of eggs (microfilariae)
  4. Microfilariae taken up by blackfly
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20
Q

How does onchocerciasis lead to blindness?

A

Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring in skin and eyes

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21
Q

Outline the different forms of Onchocerciasis clinical disease

A
  • Onchocercal nodules
  • skine disease
  • Eye disease
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22
Q

Describe the skin disease of onchocerciasis

A
  • Acute papular onchodermatitis
  • Chronic onchodermatitis
  • Sowda
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23
Q

Outline the 2 types of eye disease associated with onchocerciasis

A

Anterior segment

  • Punctate keratitis
  • Acute iridocyclitis
  • Sclerosing keratitis

Posterior segment

  • Optic neuritis/atrophy
  • Chropretinopathy
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24
Q

Describe what acute papular onchodermatitis looks like

A

Looks like an acute papular rash but looking closely at skin shows microfilariae surrounded by inflammatory response; characterised by eosinophils

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25
Q

How does the immune system respond to acute papular ochodermatitis?

A

Myocelles activated; immediate hypersensitive immune response recruits eosinophils ⇒ delayed response to kill and destroy microfilariae

26
Q

How does chronic onchodermatitis occur?

A

Chronic onchodermatitis occurs with repeated inflammation causing skin elastin and collagen damage
=> leads to aged appearance

27
Q

What causes punctate keratitis?

A

Microfilariae can infect the cornea of the eye -> punctate keratitis

28
Q

What are the clouded patches in the eye seen in punctate keratitis?

A

Fluffy patterns visible in cornea shows where microfilariae are being destroyed by the immune response

29
Q

What is sclerosing keratitis?

A

Repeated episodes of inflammation over long periods of time causes opacification of cornea due to chronic inflammation ⇒ leads to eventual blindness

30
Q

What is chorioretinopathy?

A

complete damage of retina

31
Q

Describe the presentation of chorioretinopathy

A

Small white spots present very early on in eye - where microfilariae have been destroyed by inflammatory response

32
Q

How does chrioretinopathy lead to blindness?

A

Chronic inflammation causes damage to retinal pigment epithelium which causes overlying neuronal cells to also die

Choroid (structure under retina) now visible as retina and macula is destroyed ⇒ blindness

33
Q

What is optic atrophy?

A

Microfilariae enter optic nerve - typical of onchocerciasis

34
Q

What are the effects of inflammation in optic atrophy

A

Sheathing of retinal vessels caused by inflammation

Pale optic disc seen in optic atrophy - post inflammatory optic atrophy causes blindness in onchocerciasis

35
Q

Describe the acute response to onchocerciasis

A

In acute responses there are rapid allergic reactions where microfilariae die in skin:

Myocelles activated which recruit other immune cells; eosinophils causing eosinophilic abscesses

36
Q

Which inflammatory cells are active in an acute response to onchocerciasis?

A

strong Th2 and allergic response (IL-4; IgE, IL-5; recruits & activates eosinophils)

37
Q

What happens in a chronic response to onchocerciasis?

A

In chronic episodes of inflammation, the immune response begins to shut down; host immune cell is regulated

38
Q

Which inflammatory immune cells are responsible for chronic response to onchocerciasis?

A

modified Th2 response (IL-10, T reg cells and IgG4

39
Q

Why do chronic onchocerciasis patients not produce an apparent immune response?

A

Someone with chronic infection produces no apparent immune response due to microfilariae presence in skin

40
Q

What is the significance of ticks?

A

Ticks act as important vectors for infections

41
Q

How do ticks spread infection?

A

Mechanical injury by bite; Stick mouth parts into the skin and forms a cement which keeps it in to feed off blood

42
Q

What is tick paralysis?

A

The progressive flaccidity due to a failure of acetylcholine liberation in neuromuscular junction
Ticks toxin produces a block in the motor nerve fibres

43
Q

What diseases are caused by Hard-bodied ticks?

A 
Hard-bodied ticks (ixodidae) 
carriers of rickettsial, spirochetal, viral, bacterial and protozoan diseases:
- tick typhus
- Viral encephalitis
- Viral fevers
- Viral hemorrhagic fevers
- Tularemia
- Tick paralysis 
- Human babesiosis
44
Q

What diseases are caused by soft-bodied ticks?

A

Soft-bodied ticks (omithodorus)

vectors of endemic relapsing fever (caused by borrelia duttoni) and Q-fever

45
Q

What is the effect of head lice?

A

Suck blood from scalp and lay eggs on hair

Common and easily spread by close contact, sharing of combs, brushes, hats, etc.

46
Q

What is the mechanism of action of body lice?

A

Suck blood from body and lay eggs on clothing

47
Q

How common are body lice?

A

Uncommon and spread by bodily contact, sharing clothes and bedding

48
Q

Which diseases do body lice spread?

A

Vector diseases (epidemic typhus, trench fever, relapsing fever)

49
Q

What increases risk of ectoparasite infection?

A

Lousiness related to sanitation

  • Crowded conditions
  • Long periods without bathing or changing clothes
50
Q

What are pthirus?

A

Pthirus (crab lice, pubic lice)

- sucking lice

51
Q

Describe the structure of pthirus

A

Broad, flat lice; appear crab like
Stout mid and hind legs, large claws
Abdominal segments with distinct lateral lobes

52
Q

Where do pthirus infect?

A

Single species (pthirus pubus), confined to human pubic region

  • Bites cause irritation & typical rash
  • Spread by close body contact (sexual intercourse)
  • No diseases
53
Q

Outline the lifecycle of botflies

A
  1. Botfly mid flight lays eggs on a mosquito
  2. Mosquito bites animal and egg hatches due to temp change
  3. Larvae enters skin
54
Q

Where are myiasis causing botflies commonly found?

A

Common in central and latin america

More common in tropical areas of countries - coastal and amazon areas as well as the highlands

55
Q

How do botflies cause infection?

A

Botfly sticks head out of lesion, and has spines that stick to surrounding tissue making it difficult to remove

56
Q

What drugs are used to control protozoa infections?

A
  • Tinidazole
  • Metronidazole
  • Notazoxanide
  • Benznidazole
  • Heavy metals (meglumine antimoniate)
57
Q

What drugs are administered for helminth infections?

A
  • Albendazole / Mebendazole
  • Praziquantel
  • Ivermectin
  • Diethylcarbamazine
  • Pyrantel
58
Q

What drugs are available for ectoparasite infections?

A
  • Ivermectin

- Benzyl/malathion lotions

59
Q

Compare and contrast protozoa medications

A

Tinidazole has advantage of shorter dose regimens (e.g. 1g)

Metronidazole has longer course of dose and isn’t well tolerated

Benznidazole used to treat Chagas disease however has very nasty adverse effects; peripheral neuropathy and dermatitis - many patients don’t complete the course

60
Q

How can behaviours effect control of parasitic infections?

A

Education

Hand washing and hygiene behaviours

61
Q

What environmental interventions can prevent spread of parasitic infections?

A 
Spraying residual insecticides (household vectors) 
Mosquito nets (malaria)
Improved housing 
Sewage disposal and potable water
Swamp drainage
62
Q

How should treatments be administered in endemic areas of parasite infections?

A

For many parasite infections in an endemic settings, treatments must be given periodically over long periods of time because re-infections are rapid, and treatments kill larvae rather than adult stages

Medical Microbiology (15 decks)

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