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
Example of a Medically Important NEMATODE Enterobius vermicularis (pinworm):
How common is the infection?
What are some symptoms?
How is it spread?
Most common nematode infection in WESTERN WORLD (400 million)
Pruritus ani (itchy bottom), Insomnia, Irritability
Spread by contaminated hands and fingernails
Example of a medically important NEMATODE: Ascaris lumbricoides (Giant Roundworm)
How common is the infection?
How is it spread?
What symptoms are associated?
- Most common nematode infection WORLDWIDE
- 1.5 billion cases
- Consumption of eggs on contaminated food and water
- Gastrointestinal symptoms/weight loss/intestinal blockage
Explain the general characteristics of CESTODES (tapeworms)
- Cyclophyllidean Cestode –most important tapeworm of humans and domesticated animals
- Characteristics of Cyclophyllidean Cestodes
(a) 5mm - 30 feet in length
(b) SCOLEX: 4 suckers, two rings of hooks
(c) TEGUMENT: no mouth / digestive system
(d) SEGMENTED (proglottids)
(e) HERMAPHRODITIC: produce 1000s eggs
(f) EGGS consumed by intermediate host; immature tapeworm develop in
INTERMEDIATE HOST organs / muscle
Describe the characteristics of Cyclophyllidean Cestode
Example of a Medically Important CESTODE Taenia saginata (beef tapeworm):
How many cases are there worldwide?
- 50 million cases worldwide
- Abdominal pain (scolex)/ Weight loss / Weakness/ Pruritus ani/ Pain on excreting tapeworm segments
- Contracted by consuming undercooked contaminated beef
Describe the general characteristics of the TREMATODES (Flukes)
- Two subclasses: Aspidogastrea (parasites of mollusks) and Dignea (parasites of mollusks and vertebrates)
- Flat, oval / leaf shaped worms
- Usually small (few cm in length)
- Tegument / Primitive intestine
- Hermaphroditic
- Complicated life cycles usually involving one or more intermediate hosts and various stages of sexual and asexual development:
(a) adult trematode / egg (sexual)
(b) miracidium
(c) cercariae
(d) metacercariae
Example of a Medically Important TREMATODE Fasciola hepatica (fluke)
How is the infection spread to humans, sheep or cattle?
- Unembryonated eggs passed in feces
- Embryonated eggs in water
- Miracidium hatches in water, penetrates snail
- Free-swimming cercariae encyst on vegetation
- Metacercariae on vegetaion ingested by human, sheep or cattle
- Ecyst in duodenum
- Adults in hepatic biliary ducts
Fasciola hepatica Infection: What are the symptoms?
–Fever (first symptom): 40-42°C
–GI: Abdominal pain, loss of appetite, flatulence, nausea, diarrhoea
–Hepatomegaly
–Fatty food intolerance
