60. Parasitology Flashcards Preview

Clinical Pathology > 60. Parasitology > Flashcards

Flashcards in 60. Parasitology Deck (9)
Loading 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.

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

1) Protozoa
2) Helminths
3) Ectoparasites.

2
Q

What are protozoa?

A
  • Protozoa are microscopic, single-celled organisms that can be free- living or parasitic in nature.
  • They are able to multiply in humans allowing serious infections to develop from a single organism.

• Transmission:

  • 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
3
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.
  • There are three main groups of helminths that are human parasites:

1) Nematodes (roundworms)
2) Trematodes (flukes)
3) Cestodes (tapeworms)

4
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).

5
Q

Parasites- general comments

A

•Parasites often have complex life cycles
•Type of host
- Intermediate – host in which larval or asexual stages develop
- Definitive – host in which adult or sexual stage occurs
•Vectors
- Mechanical when no development of parasite in vector
- Biological when some stages of life cycle occur

6
Q

Determinants of parasite infections

A

Depends on mode of transmission and opportunities for transmission

FAECO-ORAL

  • Household sanitation
  • Access to clean water
  • Personal hygiene behaviours

FOOD

  • Animal husbandry
  • Surveillance
  • Regulations and government controls

COMPLEX LIFE CYCLE
- Distributions of vectors and intermediate/definitive hosts

OTHERS

  • 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
7
Q

Phases of disease

A

•Acute

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

•Chronic ‘indeterminate’

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

•‘Determinate’ Chronic disease

  • Seropositive
  • 30-40% of infected 10-30 years after infection
  • 5-10% develop chronic Chagas immediately after acute disease
8
Q

Chronic Chagas

A

CARDIAC

  • Damage to the conduction of the heart – arrhythmias
  • Damage to the heart muscle ~ cardiomyopathy
  • Apical aneurysms and thrombus formation

DIGESTIVE

  • Damage to the NS of the gut, and it starts to swell
  • megacolon ~ Constipation
9
Q

Chagas pathogenesis

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.

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

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

Decks in Clinical Pathology Class (62):