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Fundamentals of P > Parasitology > Flashcards

Parasitology 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 three main classes of parasites that can 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 freeliving or parasitic in nature.

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4
Q

Protozoa - ability in humans

A

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

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5
Q

Protozoa - describe transmission

A

Protozoa living in the human intestine can be transmitted by the fecal-oral
route

Protozoa living in blood or tissues are transmitted by an arthropod vector

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6
Q

Protozoa are classified by

A

Protozoa are classified by mode of movement

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7
Q

Protozoa - list types with examples

A 
Amoeba, e.g. Entamoeba
Flagellates, e.g. Giardia, Leishmania
Ciliates e.g. Balantidium
Sporozoa – organisms whose adult stage is not motile
e.g. Plasmodium, Cryptosporidium
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8
Q

List 9 medically important protozoa infections

A
  • Entamoeba histolytica
  • Giardia lamblia
  • Trichomonas vaginalis
  • Malaria (Plasmodium spp.)
  • Toxoplasma gondii
  • Cryptosporidium
  • Leishmania spp.
  • Trypansoma cruzi
  • Trypansoma brucei (gambiense/rhodesiense)
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9
Q

What are helminths?

A

Helminths are large, multicellular organisms (worms) generally visible
to the naked eye in their adult stages. In their adult form, helminths
cannot multiply in humans.

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10
Q

The three main groups of helminths that are human parasites

A

There are three main groups of helminths that are human parasites:

  1. Nematodes (roundworms)
  2. Trematodes (flukes)
  3. Cestodes (tapeworms)
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11
Q

List 4 soil-transmitted helminths and name what group of helminths they are in

A

Nematodes:

  • Soil-transmitted helminths
  • Ascaris lumbricoides
  • Trichuris trichiura
  • Hookworm spp.
  • Enterobius vermicularis
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12
Q

List 4 filarial parasites and name what group of helminths they are in

A

Nematodes:

  • Wuchereria bancrofti
  • Loa loa
  • Onchocerca volvulus
  • Dracunculus medinensis
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13
Q

List 4 trematodes

A

Trematodes:

  • Schistosoma mansoni/haematobium/japonicum
  • Clonorchis sinensis
  • Fasciola hepatica
  • Paragonimus spp.
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14
Q

List 3 cestodes

A

Cestodes:

  • Taenia saginata
  • Taenia solium
  • Echinococcus granulosus
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15
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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16
Q

Medically important ectoparasites

A

Mites:
• Scabies
• Trombiculid

Ticks:
• Hard
• Soft

Lice:
• Pediculus humanus capitis
• Pediculus humanus 
   humanus
• Pthirus pubis

Flies:
• Botflies

17
Q

Parasitic infections - effect on disease in terms of climate + give example

A

• Parasitic infections cause a tremendous burden of disease in both the
tropics and subtropics as well as in more temperate climates. Malaria
kills ~660,000 people each year.

18
Q

The Neglected Tropical Diseases (NTDs) include parasitic diseases
such as

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.

19
Q

Parasites - Type of host

A

Type of host
• Intermediate – host in which larval or asexual stages develop
• Definitive – host in which adult or sexual stage occurs

20
Q

Parasites - Type of vectors

A

Vectors
• Mechanical when no development of parasite in vector
• Biological when some stages of life cycle occur

21
Q

Relative wealth is primary determinant of

A

Relative wealth is primary determinant of distributions

of parasite infections in humans

22
Q

Determinants of parasite infections

A
  • Faeco-oral
  • Food (Animals, government controls)
  • Complex life cycles (distributions of vectors and intermediate/definitive hosts)
  • Resources
  • Education
  • Regional/national control programmes
  • Treatments (efficacy/cost)
  • Constr./building regulations
  • Residence - urban/rural
  • Environmental sanitation
23
Q

Life cycle of Trypansoma cruzi

A
  1. Triatomine bug takes a blood meal = passes metacyclic trypomastigotes in feces - enter wound/mucosal membranes)
  2. Metacyclic trypomastigotes penetrate various cells at bite site - inside they transform into amastigotes
  3. Amastigotes multiply by binary fission in infected cells
  4. IntraC A → TM = burst out of cell into bloodstream
  5. Triatomine bug takes blood meal = TM ingested
  6. Epimastigotes in midgut
  7. Multiply in midgut
  8. Metacyclic TM in hind gut

Repeat

24
Q

Chagas - describe acute phase

A

• Acute
– Incubation 1-2 wks after bite
– Up to months after transfusion
– Trypanosomes in blood

25
Q

Chagas - describe ‘interdeterminate’ chronic phase

A 
Chronic ‘indeterminate’
• Lifelong infection
• Generally trypanosomes not
detectable but often positive for
parasite DNA
• Seropositive
• 60-70%
• Normal ECG and X rays
26
Q

Chagas - describe ‘determinate’ chronic phase

A 
‘Determinate’ Chronic disease
– Seropositive
– 30-40% of infected 10-30 years
after infection
– 5-10% develop chronic Chagas
immediately after acute disease
27
Q

Chagas - describe acute symptoms

A 
• Generally mild or
asymptomatic
• Local swelling (Romaña)
• Nodule or chagoma
• Fever
• Anorexia
• Lymphadenopathy
28
Q

Chagas - describe effect on digestive system

A

Develops in 10-15% of patients with chronic
infections
• Esophagus, rectum, and sigmoid colon most
affected

29
Q

Chagas - describe effect on colon

A

Presentation
– Constipation

• Complications
– Faecaloma
– Obstruction
– Sigmoid volvulus
– Ulceration
– Perforation
30
Q

Chagas pathogenesis - for acute

A

Acute
• Tissue damage caused by inflammatory response to parasite in nests of
amastigotes in cardiac, skeletal, and smooth muscle
• Parasite killing by antibodies, activated innate immune response and Th1 pro- inflammatory cytokines

31
Q

Chagas pathogenesis - for interdeterminate

A

Indeterminate

• Regulatory immune response characterized by IL-10 and IL-17

32
Q

Chagas pathogenesis - for chronic

A

Chronic
• Chronic inflammatory response to persistent parasites in muscle and nerve
cells
• Autoimmune mechanisms
• May vary by parasite strain and tissue tropism
• Predominance of Th1 cytokines and CD8+ T cells

33
Q

Leishmaniasis: life cycle

A

Sandfly bites into mammalian skin
Promastigote engulfed by histiocyte
Replicate by binary fission
Amastigotes present in histiocyte also amastigotes released and taken up by fly

34
Q

Pathogenesis of cutaneous leishmaniasis for acute lesions

A

Acute lesions
• Tissue damage caused by inflammatory response to presence of parasites in
macrophages
• Parasite killing by Th1 pro-inflammatory responses and macrophage killing

35
Q

Pathogenesis of cutaneous leishmaniasis for latency

A

Latency
• Parasites remain present long-term. Regulatory immune response characterized by
balance of Th1 and anti-inflammatory responses

36
Q

Pathogenesis of cutaneous leishmaniasis for relapse

A

Relapse (rare):

Alteration in immune response (i.e change in Th1 vs. immune regulation secondary
to HIV, malnutrtition) may trigger relapse:

• Mucocutaneous disease associated with strong but inadequate inflammatory response to
parasites that have metastasized to mucosa
• Diffuse cutaneous leishmaniasis associated with uncontrolled parasite replication.
• Recividans – recurrence of lesions at old ulcer site.

Fundamentals of P (62 decks)

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