11. Parasitic Diseases Flashcards
1
Q
What is a parasite?
A
- An organism that lives upon or within another living organism at whose expensive it gains some advantage
2
Q
What is an ectoparasite?
A
- Parasite that lives on surface of host
e. g. ticks, louse, scabies
3
Q
What is an endoparasite?
A
- Parasitic organism that lives within the host
4
Q
What are parasitic diseases?
A
- Can be caused by many organisms including:
- Viruses
- Bacteria
- Fungi/yeast/algi
- protozoa
- helminths
- anthropods
- Particularly prevalent in developing countries
5
Q
What are protozoa?
A
- Single-celled eukaryotes
- Have different modes of transmission
e. g. Plasmodium- malaria
e. g. Toxoplasma- toxoplasmosis
e. g. trypanosoma- African sleeping sickness
6
Q
What are zoonoses?
A
- Animal diseases that are transmissible to humans
- Transfer can be direct or indirect
- Natural reservoir of the infectious agent is an animal
- 70% of pathogens that affect humans are zoonotic
e. g. protozoa and helminths
7
Q
What is malaria?
A
- Arguably most important parasitic pathogen: kills many children
- Caused by protozoan parasites of the genus Plasmodium
- Class: apicomplexa- specialised for invasion and intracellular growth (in this case invasion of liver and red blood cells)
- Limited drugs and no vaccine
8
Q
What is toxoplasmosis?
A
- Disease caused by protozoan parasite: Toxoplasma gondii (a type of Apicomplexa)
- One of the most common infections in the world (but few infected people are symptomatic)
- Primary host (species in which the adult (sexual) for or parasite occurs) is the cat
- Transmission:
Primary host: cats spread oocytes into environment through feces
Intermediate host: pigs, sheep goat etc. eat from soil and ingest oocytes where they mature and form cysts
Humans: ingest cysts from infected meat or through ingestion of cat feces
9
Q
What is the pathogenesis of Toxoplasmosis?
A
Process:
- Ingestion of cycts
- Cysts activated in gut and penetrate intestinal epithelium
- Toxoplasma invade multiple cell types including phagocytes and other tissue cells
- Develop into tissue cysts to avoid immune recognition/clearance
- Can cross placenta to fetus
Symptoms:
Healthy individuals:
- Acute systemic inflammatory response involving flu like symptoms but often no symptoms at all
- Chronic: due to tissue cysts
- Possbily linked to psychiatric disorders
Immunocomprimisied/pregnant individuals:
- severe pathogenic consequences
- fetal abnormalities
10
Q
How is Toxoplasmosis diagnosed?
A
- Serology (testing for toxoplasmosa antibodies)
- PCR
- Blood test
- Histology (detection of tissue cysts)
- Difficult to determine if infections are acute or chronic
11
Q
What is the treatment and prevention for toxoplasmosis?
A
Treatment: Healthy people: - usually none Pregnant/immunocomprimised: - antibiotics
Prevention:
- gloves when gardening
- hygiene around cats
- washing hands properly
- cooking meat thoroughly
- no vaccine
12
Q
What are trypanosomes?
A
- A type of protozoan parasite
- Class: kinetoplastida
- Transmitted by insect vectors
- Causes:
African trypanosomiasis (ASS)- African sleeping sickness: T. brucei
American Chagas’ disease: T. cruzi
13
Q
Describe African Trypanosomiasis
A
- Caused by 3 species of Trypanosoma brucei
- These protozoa have a kinetoplast which is a DNA containing granule located in base of flagella
1. T. b. brucei (doesn’t infect humans)
2. T. b. gambiense (causes West African sleeping sickness)
3. T. b. rhodesiense (causes East African sleeping sickness)
Transmission:
- All forms transmitted via Tsetese flies
- Primary host: Tsetse fly; they reproduce in gut of fly and enter saliva and are transmitted to humans via bites
- They replicate extracellularly (different from apicomplexa which are intracellular)
14
Q
What are the stages of ASS pathogenesis?
A
Stage 1:
- Trypanosomes multiply in tissue around bite causing inflammation
- Trypanosomes enter blood stream and lymphatic system
- Causes low grade fever, swollen lymph nodes and toxic symptoms (at this stage T. b, rhodesiense has more severe symptoms)
Stage 2:
- Characterised by progressive anemia and kachexia (wasting of the body)
- Due to extremely high levels of TNF-a
Stage 3:
- Trypanosomes infect CNS (still are extracellular)
- Causes sleeping sickness and severe dementia
- Stage 3 occurs much easlier in EASS (T. b. Rhodesciense
15
Q
Why is African sleeping sickness so deadly?
A
- They are extracellular pathogens and produce a strong antibody response but constantly undergo antigenic variation of surface coats
- This occurs through the expression of different VSGs (variant surface glycoproteins)
- They switch VSG expression and thus surface protein coat under immune pressure
