Intro to Parasitology and Parasites of medical importance Flashcards
What are medically important parasites?
(a) Protozoa
(b) Worms (helminths):
- Nematodes (roundworms)
- Cestodes (tapeworms)
- Trematodes (flukes)
What is a Parasite?
Organisms, animals or plants that live on or in a host and draws nutrients directly from it, benefiting at the expense of the host
- The parasite offers nothing to the relationship, creating an arrangement which may be neutral or harmful, but never positive
- Some parasitic relationships are harmless, while in other cases a parasite can damage or kill its HOST
- Para (beside) Sitos (food)
- Ectoparasites / Endoparasites
Which parasites are unicellular and which are multicellular?
Unicellular→ Protozoa
Multicellular→ Helminths
What are the 2 main groups of medically important parasites and their common locations?
- PROTOZOA (systemic / gastrointestinal)
- HELMINTHS (worms) (systemic / gastrointestinal)
Gastrointestinal Parasites have two main stages?
Active stage
Infective stage
What are the properties of the active and infective stage of protozoa?
• Protozoa
(A)Active eg. TROPHOZOITE: causes disease / symptoms
(B)Infective eg. PROTOZAN CYST: dormant, resting stage; excreted in faeces; contaminates vegetation and water
What are the properties of the active and infective stage of helminths?
(A)Active eg. ADULT WORM, LARVAE: causes disease / symptoms
(B)Infective eg. WORM EGGS: contains larvae; excreted in faeces;
contaminates vegetation and water
LARVAL STAGE: dormant in the tissue and organs of birds, mammals and fish
What are the main features of a worm?
mouth-cutting plates
intestine
ovary
larva (3mm)
What is a Parasite Host?
•Organism eg. human that harbours a parasite (eg protozoa, worm) providing nourishment and shelter
What are the two types of host?Save
(a) DEFINITIVE HOST: supports the sexually mature, reproducing adult parasite
(b) INTERMEDIATE HOST: supports the immature or non-reproductive forms of a parasite (larval stage)
How does protozoa’s utilisation of a host differ from that of worms?
•Some parasites (eg protozoa) utilise a definitive host only whilst others (eg worms) may utilise one (or more) intermediate hosts before maturing in its definitive host
Transmission of Gastrointestinal Parasites to Humans: Environomental contamination
Protozoan cysts+ Worm eggs→Environmental Contamination→
Consumption of contaminated water, fruits/ vegetation
+ Fruits / veg washed with contaminated water
+ Shellfish feeding on contaminated water
Transmission of Gastrointestinal Parasites to Humans: Intermediate Host Infection
Worm larval stage (present in the ‘meat’ of the intermediate host→ Intermediate Host Infection→ Consumption of contaminated undercooked beef /pork /fish and squid
ie Consumption of the intermediate host
Classify parasites of medical importace based on cellularity, reproduction and hosts
What are the general Characteristics of Protozoa?
- Unicellular
- Eukaryotic (membrane bound organelles)
- Asexual reproduction (mainly): Produces daughter
cells with DNA identical to parent protozoan
-Size: varies 10-150µm (visualised by light microscopy)
Many form ‘dormant, resistant’ stages: CYSTS (consumed by host
Protozoa can be classified according to their locomotive apparatus:
How do they obtain nurition?
- Amoebae
- Flagellates
- Ciliates
- Apicomplexans
Obtain nutritioin through engulfing, cytostome, pinocytosis
Example of a Medically Important Protozoan:
Giardia intestinalis
What are the gastrointestinal sympotoms associted with it?
How do humans acquire infections by it?
Abdominal pain, bloating , diarrhoea, loss of appetite, weight loss
Humans acquire infection through consumption of contaminated water or food, or be fecal-oral route or by hands or fomites
What does the active and infective staeg of Giardia intestinalis look like?
Describe the intestinal phase and encystation of Giardia intestinalis
- Ensystation occurs in the small intestine
- Two trophozoites are released from each cycts
- The trophozoites multiply by longitudinal binary fission
- They remain in the lumen of the proximal small bowel where they can be free or attached to the mucosa by ventral sucking disk
- Encystation occurs as the parasites transmit towards the colon
- Cysts are resistant forms and are responsible for transmission
How is giardiasis spread?
- Contaminated water (domestic supplies, wilderness)
- Swallowing recreational water contaminated with Giardia cysts
- Eating uncooked / unwashed food contaminated with Giardia cysts
- Swallowing Giardia cysts picked up from surfaces: bathroom fixtures, changing tables, or toys contaminated with faeces from an infected person
The Helminths (worms): Describe their basic morphology
NEMATODES (roundworms): round, smooth
CESTODES (tapeworms): long, flat, segmented
TREMAODES (flukes): flat, leaf-shaped
Explain the general characteristics of NEMATODES
- Eukaryotic / Multicellular (cuticle, lips, mouth, oesophagus, intestine, pseudocoel, anus, reproductive organs)
- Dioecious (male and female)
- Produce eggs (resistant, infective stage)
- 2 mm to 3 feet (eg. pinworm / guinea worm)
- Nematodes undergo 4 molts and 4 larval stages to reach adult stage
General Characteristics of NEMATODES: How many molts during development of adult nematodes?
4 molts during development of adult nematodes
