Intro to Parasitology and Parasites of medical importance Flashcards

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1
Q

What are medically important parasites?

A

(a) Protozoa
(b) Worms (helminths):
- Nematodes (roundworms)
- Cestodes (tapeworms)
- Trematodes (flukes)

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2
Q

What is a Parasite?

A

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
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3
Q

Which parasites are unicellular and which are multicellular?

A

Unicellular→ Protozoa

Multicellular→ Helminths

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4
Q

What are the 2 main groups of medically important parasites and their common locations?

A
  • PROTOZOA (systemic / gastrointestinal)
  • HELMINTHS (worms) (systemic / gastrointestinal)
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5
Q

Gastrointestinal Parasites have two main stages?

A

Active stage

Infective stage

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6
Q

What are the properties of the active and infective stage of protozoa?

A

• Protozoa

(A)Active eg. TROPHOZOITE: causes disease / symptoms

(B)Infective eg. PROTOZAN CYST: dormant, resting stage; excreted in faeces; contaminates vegetation and water

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7
Q

What are the properties of the active and infective stage of helminths?

A

(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

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8
Q

What are the main features of a worm?

A

mouth-cutting plates

intestine

ovary

larva (3mm)

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9
Q

What is a Parasite Host?

A

•Organism eg. human that harbours a parasite (eg protozoa, worm) providing nourishment and shelter

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10
Q

What are the two types of host?Save

A

(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)

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11
Q

How does protozoa’s utilisation of a host differ from that of worms?

A

•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

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12
Q
A
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13
Q

Transmission of Gastrointestinal Parasites to Humans: Environomental contamination

A

Protozoan cysts+ Worm eggs→Environmental Contamination→

Consumption of contaminated water, fruits/ vegetation

+ Fruits / veg washed with contaminated water

+ Shellfish feeding on contaminated water

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14
Q

Transmission of Gastrointestinal Parasites to Humans: Intermediate Host Infection

A

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

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15
Q

Classify parasites of medical importace based on cellularity, reproduction and hosts

A
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16
Q

What are the general Characteristics of Protozoa?

A
  • 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

17
Q

Protozoa can be classified according to their locomotive apparatus:

How do they obtain nurition?

A
  • Amoebae
  • Flagellates
  • Ciliates
  • Apicomplexans

Obtain nutritioin through engulfing, cytostome, pinocytosis

18
Q

Example of a Medically Important Protozoan:
Giardia intestinalis

What are the gastrointestinal sympotoms associted with it?

How do humans acquire infections by it?

A

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

19
Q

What does the active and infective staeg of Giardia intestinalis look like?

A
20
Q

Describe the intestinal phase and encystation of Giardia intestinalis

A
  • 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
21
Q

How is giardiasis spread?

A
  • 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
22
Q

The Helminths (worms): Describe their basic morphology

A

NEMATODES (roundworms): round, smooth

CESTODES (tapeworms): long, flat, segmented

TREMAODES (flukes): flat, leaf-shaped

23
Q

Explain the general characteristics of NEMATODES

A
  • 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
24
Q

General Characteristics of NEMATODES: How many molts during development of adult nematodes?

A

4 molts during development of adult nematodes

25
Q
Example of a Medically Important NEMATODE
Enterobius vermicularis (pinworm):

How common is the infection?

What are some symptoms?

How is it spread?

A

Most common nematode infection in WESTERN WORLD (400 million)

Pruritus ani (itchy bottom), Insomnia, Irritability

Spread by contaminated hands and fingernails

26
Q
Example of a medically important NEMATODE:
Ascaris lumbricoides (Giant Roundworm)

How common is the infection?

How is it spread?

What symptoms are associated?

A
  • Most common nematode infection WORLDWIDE
  • 1.5 billion cases
  • Consumption of eggs on contaminated food and water
  • Gastrointestinal symptoms/weight loss/intestinal blockage
27
Q

Explain the general characteristics of CESTODES (tapeworms)

A
  • 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

28
Q

Describe the characteristics of Cyclophyllidean Cestode

A
29
Q
Example of a Medically Important CESTODE
Taenia saginata (beef tapeworm):

How many cases are there worldwide?

A
  • 50 million cases worldwide
  • Abdominal pain (scolex)/ Weight loss / Weakness/ Pruritus ani/ Pain on excreting tapeworm segments
  • Contracted by consuming undercooked contaminated beef
30
Q

Describe the general characteristics of the TREMATODES (Flukes)

A
  • 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

31
Q
Example of a Medically Important TREMATODE
Fasciola hepatica (fluke)

How is the infection spread to humans, sheep or cattle?

A
  1. Unembryonated eggs passed in feces
  2. Embryonated eggs in water
  3. Miracidium hatches in water, penetrates snail
  4. Free-swimming cercariae encyst on vegetation
  5. Metacercariae on vegetaion ingested by human, sheep or cattle
  6. Ecyst in duodenum
  7. Adults in hepatic biliary ducts
32
Q

Fasciola hepatica Infection: What are the symptoms?

A

–Fever (first symptom): 40-42°C

–GI: Abdominal pain, loss of appetite, flatulence, nausea, diarrhoea

–Hepatomegaly

–Fatty food intolerance