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Parasitology Flashcards

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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
What is a determining factor of parasitic infection presence in humans?
Relative wealth is primary determinant of distributions of parasitic infections in humans
26
How does wealth effect distribution of parasitic infection?
Parasitic infections are more common in poorer countries
27
How does geographical location effect parasitic infection distribution?
There are fewer infections in the extreme areas (further North/South and sub-saharan Africa) as climate becomes inhabitable for both humans and parasites
28
What are the 6 most common NTDs?
- Guinea worm disease - Lymphatic filariasis - Onchocerciasis - Schistosomiasis - Soil-transmitted helminths - Trachoma
29
How are parasitic infections transmitted from animals?
Many parasite infections are endemic in animal populations but there are limited opportunities for transmission to humans
30
How are parasite transmitted faeco-orally?
* Household sanitation * Access to clean water * Personal hygiene behaviours
31
How are parasitic infections transmitted from food?
* Animal husbandry * Surveillance * Regulations and government controls
32
What makes parasitic life cycles so complex?
Distributions of vectors and intermediate/definitive hosts
33
What other factors determine spread of parasitic infections?
* 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
Outline the life cycle of Trypanosoma cruzi (Chagas Disease)
Triatomine bug feeds on human at night and defecates - mode of transmission Parasite enters and multiplies through nerve and muscle cells
35
How many cases of Chagas disease are there currently worldwide?
Currently 10m infected in endemic areas - 325,000 cases in USA - 100,000 cases in Europe - 87% in Spain
36
Describe the acute phase of Chagas disease
Incubation 1-2 weeks after bite | Trypanosomes in blood
37
Describe the chronic 'indeterminate' phase of chagas disease?
- Lifelong infection - Generally trypanosomes not detectable but often positive for parasite DNA - Seropositive - 60-70% - Normal ECG and X rays
38
Explain what the chronic 'determinate' phase of Chagas is?
Seropositive 30-40% of infected, 10-30 yrs after infection 5-10% develop chronic Chagas immediately after acute disease
39
When does acute chagas occur?
occurs within 3 weeks Symptoms last 8-10 weeks
40
Outline the signs and symptoms of acute chagas
``` Generally mild or asymptomatic Local swelling (Romaña) Nodule or chagoma Fever Anorexia Lymphadenopathy ```
41
What are the rarer symptoms of acute chagas?
Hepatosplenomegaly Acute myocarditis Meningoencephalitis Fatality of <5% of symptomatic
42
After how long does chagas become chronic?
10-30 years can gradually develop chronic disease
43
What causes chronic chagas to occur?
Due to a change in immune response where parasite is recognised again to cause further inflammation > reactivation of latent infection
44
What are the cardiac consequences of chronic chagas
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
What % of patients develop digestive problems in chronic chagas?
Develops in 10-15% of patients with chronic infections
46
What part of the GI tract is affected by chronic chagas?
Oesophagus, rectum and sigmoid colon most affected as peristalsis is impaired Megacolon presentation: Constipation
47
What are the digestive complications of chronic chagas
- Fecaloma - Obstruction - Sigmoid volvulus - Ulceration - Perforation
48
What is acute chagas?
Acute illness; (a)symptomatic Mild illness Associated with parasite in blood
49
Summarise Indeterminate chagas
Immune response determines parasite no Over couple of years; - chronic chagas - cardiac problems
50
What is the pathogenesis of acute chagas?
Tissue damage caused by inflammatory response to parasite in nests of amastigotes in cardiac, skeletal and smooth muscle
51
How does the immune system fight acute chagas?
Parasite killing by antibodies, activated innate immune response an dTh1 pro-inflammatory cytokines
52
What is the immune response to indeterminate chagas?
Regulatory immune response characterised by IL-10 and IL-17
53
What is the pathogenesis of chronic chagas?
Chronic inflammatory response to persistent parasites in muscles and nerve cells
54
How does the immune system respond to acute chagas?
Autoimmune mechanisms May vary by parasite strain and tissue tropism Predominance of Th1 cytokines and CD8+ T cells
55
Outline the strains of visceral leishmaniasis and where they're found
Visceral leishmaniasis - Asia: leishmania donovani - Middle East / Africa / Asia: L. infantum variants - Latin America: L. chagasi
56
Where in the world is cutaneous leishmaniasis commonly found?
Largely in Africa & Asia as well as southern Europe | Also present in southern and Latin America
57
Which strains of cutaneous leishmaniasis are found in the 'old world'?
Old world: Mediteranean / Middle East: - L. infantum - L. major - L. tropica
58
Name the strains of cutaneous leishmaniasis found in the 'new world'
New world: Central & South America - L. brazilliensis - L. amazonensis - L. mexicana
59
Describe the lifecycle of leishmaniasis?
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
What is the leishmaniasis vector?
Vector: Lutzomyia / Phlebotomus
61
How does cutaneous leishmaniasis present in patients?
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
Is immunity developed against leishmaniasis?
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
What is the effect of leishmaniasis reinfection?
More disseminated forms can occur causing more ulcers
64
What is diffuse cutaneous leishmaniasis?
Some individuals are unable to generate an adequate immune response ∴ get packed with parasites
65
What is mucocutaneous leishmaniasis?
leishmania developed as a child but later on get stuffy noses as lesions develop around mucosal area - septal destruction occurs
66
Describe the pathogenesis of acute lesions of cutaneous leishmaniasis
Tissue damage caused by inflammatory response to presence of parasites in macrophages Parasite killing by Th1 proinflammatory responses and macrophage killing
67
How does latency develop in cutaneous leishmaniasis?
Parasites remain present long-term | Regulatory immune response characterised by balance of Th1 and anti-inflammatory responses
68
What causes a relapse of latent cutaneous leishmaniasis?
An alteration in immune response (ie. change in Th1 vs. immune regulation secondary to HIV, malnutrition)
69
Describe the relapse in mucocutaneous leishmaniasis
Mucocutaneous disease associated with strong but inadequate inflammatory response to parasites that have metastasized to mucosa
70
When does relapse occur in diffuse cutaneous leishmaniasis?
Diffuse cutaneous leishmaniasis associated with uncontrolled parasite replication
71
What is recividans?
The recurrence of lesions at old ulcer site

Medical Microbiology (15 decks)

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