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Medical Microbiology > Parasitology > Flashcards

Parasitology Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What is a parasite?

A

A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host

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2
Q

What are the 3 main classes of parasites that cause disease in humans?

A

There are three main classes of parasites that can cause disease in humans:

  1. Protozoa
  2. Helminths
  3. Ectoparasites
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3
Q

What are protozoa?

A

Protozoa are microscopic, single-celled organisms that can be free living or parasitic in nature

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4
Q

Describe the mechanism of protozoa infections

A

They are able to multiply in humans allowing serious infections to develop from a single organism

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5
Q

How does protozoa transmission occur?

A
  • Protozoa living in blood / tissues are transmitted by an arthropod vector
  • Protozoa living in human intestine can be transmitted via fecal-oral route
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6
Q

How are protozoa classified?

A

Protozoa are classified by mode of movement

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7
Q

Name different classifications of protozoa

A
  • Amoeba: Entamoeba
  • Flagellates: Giardia, Leishmania
  • Ciliates: Balantidium
  • Sporozoa: Plasmodium, Cryptosporidium
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8
Q

What are sporozoa?

A

Protozoa organisms whose adult stage is not motile

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9
Q

Name examples of medically important protozoa infections

A 
Entamoeba histolytica 
Giardia lamblia
Trichomonas vaginalis 
Malaria (Plasmodium spp.) 
Toxoplasma gondii 
Cryptosporidium 
Leishmania spp. 
Trypanosoma cruzi 
Trypansoma brucei (gambiense/rhodesiense)
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10
Q

What are helminths?

A

Helminths are large, multicellular organisms (worms) generally visible to naked eye in adult stages

In adult form, helminths cannot multiply in humans

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11
Q

What are the 3 groups of human parasitic helminths?

A
  1. Nematodes (roundworms)
  2. Trematodes (flukes)
  3. Cestodes (tapeworms)
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12
Q

Outline the clinically significant soil-transmitted helminths

A
  • Ascaris lumbricoides
  • Trichuris trichiura
  • Hookworm spp.
  • Enterobius vermicularis
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13
Q

What are the filarial helminth parasites?

A
  • Wuchereria bancrofti
  • Loa loa
  • Onchocerca volvulus
  • Dracunculus medinensis
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14
Q

Name other medically important helminth parasites

A

Toxocara canis/cati

Trichinella spiralis

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15
Q

Outline trematodes

A
  • Schistosoma mansoni/haematobium/japonicum
  • Clonorchis sinensis
  • Fasciola hepatica
  • Paragonimus spp.
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16
Q

Name some common cestodes

A
  • Taenia saginata
  • Taenia solium
  • Echinococcus granulosus
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17
Q

What are ectoparasites?

A

Blood-sucking arthropods such as ticks, fleas, lice, and mites that attach or burrow into the skin and remain there for relatively long periods of time (e.g., weeks to months).

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18
Q

What are the different types of mites?

A
  • Scabies

* Trombiculid

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19
Q

Describe the different types of ticks

A
  • Hard

* Soft

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20
Q

Name the varying types of lice

A
  • Pediculus humanus capitis
  • Pediculus humanus humanus
  • Pthirus pubis
  • Flies
  • Botflies
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21
Q

What is the significance of parasitic infections?

A

Parasitic infections cause tremendous burden of disease in both tropics and subtropics as well as in more temperate climates

e.g. Malaria kills ~660,000 people each year

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22
Q

What are NTDs?

A

The Neglected Tropical Diseases (NTDs) include parasitic diseases such as lymphatic filariasis, onchocerciasis, and Guinea worm disease, and affect >1 billion people, largely in rural areas of low-income countries.

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23
Q

What are the different types of parasitic hosts?

A

Intermediate – host in which larval or asexual stages develop

Definitive – host in which adult or sexual stage occurs

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24
Q

What are the 2 types of parasitic vectors?

A

Mechanical: no development of parasite in vector

Biological: some stages of life cycle occur

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25
Q

What is a determining factor of parasitic infection presence in humans?

A

Relative wealth is primary determinant of distributions of parasitic infections in humans

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26
Q

How does wealth effect distribution of parasitic infection?

A

Parasitic infections are more common in poorer countries

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27
Q

How does geographical location effect parasitic infection distribution?

A

There are fewer infections in the extreme areas (further North/South and sub-saharan Africa) as climate becomes inhabitable for both humans and parasites

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28
Q

What are the 6 most common NTDs?

A
  • Guinea worm disease
  • Lymphatic filariasis
  • Onchocerciasis
  • Schistosomiasis
  • Soil-transmitted helminths
  • Trachoma
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29
Q

How are parasitic infections transmitted from animals?

A

Many parasite infections are endemic in animal populations but there are limited opportunities for transmission to humans

30
Q

How are parasite transmitted faeco-orally?

A
  • Household sanitation
  • Access to clean water
  • Personal hygiene behaviours
31
Q

How are parasitic infections transmitted from food?

A
  • Animal husbandry
  • Surveillance
  • Regulations and government controls
32
Q

What makes parasitic life cycles so complex?

A

Distributions of vectors and intermediate/definitive hosts

33
Q

What other factors determine spread of parasitic infections?

A
  • Government resources and level of human development/per capita income
  • Education
  • Country-level and regional control programmes
  • Availability of cheap and efficacious treatments
  • Construction and building regulations (eg Chagas)
  • Urban vs. rural residence
  • Environmental sanitation
34
Q

Outline the life cycle of Trypanosoma cruzi (Chagas Disease)

A

Triatomine bug feeds on human at night and defecates - mode of transmission

Parasite enters and multiplies through nerve and muscle cells

35
Q

How many cases of Chagas disease are there currently worldwide?

A

Currently 10m infected in endemic areas

  • 325,000 cases in USA
  • 100,000 cases in Europe
  • 87% in Spain
36
Q

Describe the acute phase of Chagas disease

A

Incubation 1-2 weeks after bite

Trypanosomes in blood

37
Q

Describe the chronic ‘indeterminate’ phase of chagas disease?

A
  • Lifelong infection
  • Generally trypanosomes not detectable but often
    positive for parasite DNA
  • Seropositive
  • 60-70%
  • Normal ECG and X rays
38
Q

Explain what the chronic ‘determinate’ phase of Chagas is?

A

Seropositive
30-40% of infected, 10-30 yrs after infection
5-10% develop chronic

Chagas immediately after acute disease

39
Q

When does acute chagas occur?

A

occurs within 3 weeks Symptoms last 8-10 weeks

40
Q

Outline the signs and symptoms of acute chagas

A 
Generally mild or asymptomatic 
Local swelling (Romaña)
Nodule or chagoma
Fever
Anorexia
Lymphadenopathy
41
Q

What are the rarer symptoms of acute chagas?

A

Hepatosplenomegaly
Acute myocarditis
Meningoencephalitis
Fatality of <5% of symptomatic

42
Q

After how long does chagas become chronic?

A

10-30 years can gradually develop chronic disease

43
Q

What causes chronic chagas to occur?

A

Due to a change in immune response where parasite is recognised again to cause further inflammation
> reactivation of latent infection

44
Q

What are the cardiac consequences of chronic chagas

A

Causes damage to conduction system of the heart leading to arrhythmias

Heart muscle damage (cardiomyopathy) can cause heart to become enlarged

Apical aneurysms are also common as well as strokes due to thrombus formation

45
Q

What % of patients develop digestive problems in chronic chagas?

A

Develops in 10-15% of patients with chronic infections

46
Q

What part of the GI tract is affected by chronic chagas?

A

Oesophagus, rectum and sigmoid colon most affected as peristalsis is impaired

Megacolon presentation: Constipation

47
Q

What are the digestive complications of chronic chagas

A
  • Fecaloma
  • Obstruction
  • Sigmoid volvulus
  • Ulceration
  • Perforation
48
Q

What is acute chagas?

A

Acute illness; (a)symptomatic
Mild illness
Associated with parasite in blood

49
Q

Summarise Indeterminate chagas

A

Immune response determines parasite no
Over couple of years;
- chronic chagas
- cardiac problems

50
Q

What is the pathogenesis of acute chagas?

A

Tissue damage caused by inflammatory response to parasite in nests of amastigotes in cardiac, skeletal and smooth muscle

51
Q

How does the immune system fight acute chagas?

A

Parasite killing by antibodies, activated innate immune response an dTh1 pro-inflammatory cytokines

52
Q

What is the immune response to indeterminate chagas?

A

Regulatory immune response characterised by IL-10 and IL-17

53
Q

What is the pathogenesis of chronic chagas?

A

Chronic inflammatory response to persistent parasites in muscles and nerve cells

54
Q

How does the immune system respond to acute chagas?

A

Autoimmune mechanisms
May vary by parasite strain and tissue tropism
Predominance of Th1 cytokines and CD8+ T cells

55
Q

Outline the strains of visceral leishmaniasis and where they’re found

A

Visceral leishmaniasis

  • Asia: leishmania donovani
  • Middle East / Africa / Asia: L. infantum variants
  • Latin America: L. chagasi
56
Q

Where in the world is cutaneous leishmaniasis commonly found?

A

Largely in Africa & Asia as well as southern Europe

Also present in southern and Latin America

57
Q

Which strains of cutaneous leishmaniasis are found in the ‘old world’?

A

Old world: Mediteranean / Middle East:

  • L. infantum
  • L. major
  • L. tropica
58
Q

Name the strains of cutaneous leishmaniasis found in the ‘new world’

A

New world: Central & South America

  • L. brazilliensis
  • L. amazonensis
  • L. mexicana
59
Q

Describe the lifecycle of leishmaniasis?

A

Caused by sandfly bite transmitting promastigotes

Promastigotes infect macrophages to form nests of amastigotes which are then released

Released amastigotes go on to infect other cells

60
Q

What is the leishmaniasis vector?

A

Vector: Lutzomyia / Phlebotomus

61
Q

How does cutaneous leishmaniasis present in patients?

A

Sandfly bite develops into a papule which spreads to form a lesion which becomes necrotic to forms ulcers

Certain strain of leishmania infects along lymphatic vessels

62
Q

Is immunity developed against leishmaniasis?

A

Children often infected and if they remain in that area they can develop immunity

New strains can reinfect old scars of leishmaniasis to reactivate infection

63
Q

What is the effect of leishmaniasis reinfection?

A

More disseminated forms can occur causing more ulcers

64
Q

What is diffuse cutaneous leishmaniasis?

A

Some individuals are unable to generate an adequate immune response ∴ get packed with parasites

65
Q

What is mucocutaneous leishmaniasis?

A

leishmania developed as a child but later on get stuffy noses as lesions develop around mucosal area - septal destruction occurs

66
Q

Describe the pathogenesis of acute lesions of cutaneous leishmaniasis

A

Tissue damage caused by inflammatory response to presence of parasites in macrophages

Parasite killing by Th1 proinflammatory responses and macrophage killing

67
Q

How does latency develop in cutaneous leishmaniasis?

A

Parasites remain present long-term

Regulatory immune response characterised by balance of Th1 and anti-inflammatory responses

68
Q

What causes a relapse of latent cutaneous leishmaniasis?

A

An alteration in immune response (ie. change in Th1 vs. immune regulation secondary to HIV, malnutrition)

69
Q

Describe the relapse in mucocutaneous leishmaniasis

A

Mucocutaneous disease associated with strong but inadequate inflammatory response to parasites that have metastasized to mucosa

70
Q

When does relapse occur in diffuse cutaneous leishmaniasis?

A

Diffuse cutaneous leishmaniasis associated with uncontrolled parasite replication

71
Q

What is recividans?

A

The recurrence of lesions at old ulcer site

Medical Microbiology (15 decks)

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