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Microbiology > 6- Pathogenesis of parasitic infections > Flashcards

6- Pathogenesis of parasitic infections Flashcards

1
Q

What are the three main species of schistosomiasis and what areas of the body do they affect?

A

➝ Schistosoma mansoni - hepatic and intestinal
➝ S. haematobium - urinary system
➝ S. Japonicum - hepatic

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2
Q

Describe the life cycle of schistosomiasis?

A

➝ People become exposed to the infective stage in contaminated water
➝ they get infected with cercariae
➝ the cercariae migrate through the body forming adults in the mesenteric system
➝ Schistosoma haematobium forms in the vessels around the bladder
➝ they form adults, the female releases eggs which are pushed through the mucosal epithelium in the faeces or urine which contaminates water and infects snails

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3
Q

How do you get cercarial dermatitis?

A

➝ Exposure to cercariae from animal or bird schistosomes

➝ Requires pre-sensitization​

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4
Q

What type of reaction does cercarial dermatitis?

A

➝ Allergic type reaction

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5
Q

What happens to the eggs of Schistosoma?

A

➝ they become organised in granulomas

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6
Q

What leads to organ damage in schistosomiasis?

A

➝ Repeated insults and tissue repair lead to fibrosis and organ damage

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7
Q

How does hepato-intestinal schistosomiasis occur?

A

➝ Infection with S. mansoni and S. Japonicum

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8
Q

What is pathology caused by in hepato-intestinal schistosomiasis?

A

➝ Immune response to the eggs

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9
Q

How does hepato-intestinal schistosomiasis occur?

A

➝ The adults are in the mesenteric vessels, the eggs are pushed by the immune response through the intestinal wall and through the mucosa

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10
Q

What happens with chronic exposure during hepato-intestinal schistosomiasis?

A

➝ fibrosis in the liver

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11
Q

How do the eggs get into the urine in urinary schistosomiasis?

A

➝ adults live in the vessels around the bladder
➝ they release eggs into the vessels
➝ the eggs get pushed into the mucosa of the bladder and are excreted in the urine

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12
Q

What is a common sequelae to urinary schistosomiasis?

A

➝ there is inflammation in the bladder wall related to the eggs and damage to the bladder wall which leads to cancer

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13
Q

What is a symptom of urinary schistosomiasis in endemic areas and at what age does this occur?

A

➝ haematuria- blood in urine

➝ adolescence

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14
Q

What is onchocerciasis?

A

➝ major blinding disease

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15
Q

What is onchocerciasis caused by?

A

➝ Filarial parasites

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16
Q

What is onchocerciasis transmitted by?

A

➝ blackflies

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17
Q

Where is the female worm found in onchocerciasis?

A

➝ coiled up in fibrous nodules under the skin

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18
Q

What geographical regions is onchocerciasis found in?

A

➝ Equatorial regions of Africa and Central and South America

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19
Q

Describe the life cycle of onchocerciasis?

A

➝ The blackfly bites and transmits L3 infectious larvae
➝ the larvae migrate under the skin and develop into adults which mate
➝ the female releases thousands of larvae called microfilariae which are taken up by the blackfly again

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20
Q

What is the vector of onchocerciasis?

A

➝ Simulium

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21
Q

Why does permanent scarring occur in onchocerciasis?

A

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

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22
Q

Why do you give diethylcarbamazine to patients with onchocerciasis?

A

➝ The parasite downregulates the immune response

➝ the downregulation can be switched off by giving diethylcarbamazine

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23
Q

What type of immune response is there to onchocerciasis?

A

➝ Strong allergic response with a lot of eosinophils that form eosinophilic abscesses

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24
Q

What can you observe clinically in onchocerciasis?

A

➝ Onchocercal nodules- female worms inside
➝ skin disease
➝ eye disease

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25
What 4 skin diseases occur as a result of onchocerciasis?
➝ Acute papular onchodermatitis ➝ Chronic onchodermatitis-with repeated inflammation there is damage to collagen and elastin ➝ sowda
26
What 3 anterior segment eye diseases occur as a result of onchocerciasis?
➝ Punctate keratitis ➝ acute iridocyclitis ➝ sclerosing keratitis
27
What is sclerosing keratitis?
➝ with repeated inflammation there is opacification of the cornea ➝ blindness
28
What is punctate keratitis?
➝ little opacities in the cornea
29
What 2 posterior segment eye diseases occur as a result of onchocerciasis?
➝ Optic neuritis/atrophy | ➝ chorioretinopathy
30
What is chorioretinopathy?
➝ small white spots in the eye where microfilariae are being killed
31
What is optic atrophy?
the retinal vessels are sheathed and there is a pale optic disc
32
In the acute stage of onchocerciasis what chemokines are produced?
➝ Strong Th2 response with the production of IL-4 and IL-5
33
What does IL-4 make?
➝ IgE
34
What does IL-5 do?
➝ Recruits and activates eosinophils
35
In the chronic stage of onchocerciasis what happens to the immune system and what kind of a response is there?
➝ there is a modified Th2 response with production of IL-10 and IgG
36
What 7 diseases do hard ticks cause?
``` ➝ Tick typhus ➝ viral encephalitis ➝ viral fevers ➝ viral haemorrhagic fevers ➝ tularemia ➝ tick paralysis ➝ human babesiosis ```
37
What 2 diseases do soft ticks cause?
➝ Q fever | ➝ relapsing fever
38
What is tick paralysis?
➝ progressive flaccidity due to a failure of acetylcholine liberation in the neuromuscular junction
39
What 5 types of diseases hard bodied ticks (Ixodidae) carriers of?
➝ rickettsial, spirochaetal, viral, bacterial and protozoan diseases
40
What does a tick's toxin cause?
➝ a block in the motor nerve fibres
41
What are soft-bodied ticks (Omithodorus) vectors of?
➝ endemic relapsing fever (caused by Borrelia duttoni) and Q-fever
42
What disease transmitted by ticks is prevalent in the US?
➝ Lyme disease | ➝ via Deer ticks
43
What do head lice do?
⭢ suck blood from scalp and lay eggs on hair
44
What do body lice do?
➝ Suck blood from body and lay eggs on clothing
45
What is the prevalence of head lice and body lice?
➝ head lice- common | ➝ body lice- uncommon
46
How does head lice spread?
➝ easily spread by close contact | ➝ sharing of combs, brushes, hats
47
How does body lice spread?
➝ by bodily contact | ➝ sharing of clothing, bedding
48
What diseases are caused by transmission of body lice?
➝ vector diseases ➝ epidemic typhus ➝ trench fever ➝ relapsing fever
49
What can cause infection with lice?
➝ lousiness related to sanitation ➝ crowded conditions ➝ long period without bathing or changing clothes
50
How are pubic lice different in morphology to body or head lice?
➝ they are broad and flat ➝ appear crab-like ➝ mid & hind legs are stout with very large claws ➝ abdominal segments have distinct lateral lobes
51
What are other names for pubic lice?
➝ Pthiridae | ➝ crab lice
52
What do pubic lice bites cause and how does it spread?
➝ bites cause irritation ➝ typical rash ➝ spread by close body contact- usually sex
53
What do head lice do?
⭢ suck blood from scalp and lay eggs on hair
54
What do body lice do?
➝ Suck blood from body and lay eggs on clothing
55
Describe the lifecycle of the botfly?
➝ Mid-flight the fly lays eggs on a mosquito | ➝ the mosquito bites an animal and the egg hatches and larvae migrate into the skin
56
Where is Dermatobia Hominis (human botfly) common?
Latin America | Brazil, Ecuador
57
Why are botflies hard to extract?
➝ they have spines on the side of their body which anchor into tissue and make them hard to extract
58
What is orbital cavitary myiasis caused by?
➝ cochliomyia hominivorax
59
What 2 drugs are protozoa usually treated with?
➝ tinidazole | ➝ metronidazole (traditional)
60
What is the advantage of tinidazole over metronidazole?
➝ it has a shorter regimen
61
What 3 other drugs can protozoa be treated with?
➝ Nitazoxanide ➝ Benznidazole ➝ Heavy metals (meglumine antimoniate)
62
What is Chagas disease treated with?
➝ Nitazoxanide | ➝ Benznidazole
63
What is leishmania treated with?
➝ Heavy metals (meglumine antimoniate)
64
What 5 drugs are helminths treated with?
``` ➝ albendazole/mebendazole ➝ praziquantel ➝ ivermectin ➝ diethylcarbamazine ➝ pyrantel ```
65
What 2 drugs are ectoparasites treated with?
➝ Ivermectin | ➝ benzyl/malathion lotions
66
What is used to treat nematodes such as schistosomiasis?
➝ praziquantel
67
Why is ivermectin the 'best' drug?
➝ single dose effective against ectoparasites
68
How can you control parasite infections by changing behaviour?
➝ Education | ➝ hand washing and hygiene behaviours
69
How can you control parasite infections by environmental intervention?
``` ➝ Spraying of residual insecticides for household vectors ➝ mosquito nets for malaria ➝ improved housing ➝ sewage disposal and potable water ➝ drainage of swamps ```
70
How can you reduce poverty to control parasite infections?
➝ micro-financing
71
How are parasite infection in endemic areas treated and why?
➝ treatment must be given periodically over long periods of time because re-infections are rapid or because the treatment kills larval and not adult stages
72
What is given to control soil transmitted helminth infections?
➝ Single dose of albendazole is given to high risk groups such as school children every 4 months
73
What is given and how often to control onchocerciasis?
➝ A single dose of ivermectin is given to endemic communities (mass drug administration) every 6 or 12 months
74
What is given and how often to control schistosomiasis?
➝ A single dose of praziquantel is given to endemic communities (mass drug administration) every 6 or 12 months
75
Comment on the distribution of parasites?
They have a worldwide distribution but are found predominantly in tropical regions among populations living in poverty
76
Comment on the treatment of parasitic infections?
Although there are effective treatments for most parasitic infections, limited investment still means limited treatment options (NTD) and problems of drug toxicity for many infections.
77
Overall, how can we control/eliminate parasite infections?
Poverty reduction and education interventions combined with drug treatments will control/eliminate many parasite infections.

Microbiology (11 decks)

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