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MICR2209 > 25 - Helminth Parasites > Flashcards

25 - Helminth Parasites Flashcards

1
Q

Helminth parasite

A
  • Complex, multicellular
  • Extracellular
  • Large genomes, very immunogenic
  • Can survive for decades
  • Drugs are toxic
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2
Q

Categories of helminths

A
  • Nematodes round worms
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3
Q

Types of Platyhelminths flat worms

A
  • Cestodes
  • Trematodes
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4
Q

Caenorhabditis elegans

A
  • Most important nematodes for medicine
  • Transparent, emit blue/green fluorescence when they die
  • Subject of three Nobel Prizes
  • Only worm in space
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5
Q

Nematodes (Nematoda)

A
  • Second largest phylum in animal kingdom
  • Half are parasitic
  • Cylindrical, male & female, have teeth
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6
Q

Gastrointestinal nematodes

A
  • Commonest worm infections
  • No intermediate host, not zoonotic
  • Eggs or larvae infect humans
  • Ingested larvae burrow into skin
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7
Q

Trichinella spiralis

A

Only intracellular helminth

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8
Q

Toxocara canis

A

Worm often targets the eye

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9
Q

Cestodes (tapeworms)

A
  • Haemaphrodite (each worm has male and female reproductive organs)
  • Body composed of segments or proglottids
  • Adults attach to gut by scolex
  • Live for decades
  • Intestinal infections mainly asymptomatic, tissue stages cause pathology
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10
Q

Intestinal tapeworms

A

Exists as worms in intestine

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11
Q

Tissue tapeworms

A

Form cysts in the tissues

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12
Q

Trematodes (flukes)

A
  • Haemaphrodite
  • Complex life cycles (primary vertebrate host, intermediate invertebrate host)
  • Obligate parasites
  • Live for decades
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13
Q

Blood Flukes (Schistosomes)

A

Pathology caused by eggs

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14
Q

Tissue (liver) flukes

A

Live in organs (liver, lung)

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15
Q

Why are there so few drugs and why no recent drug development?

A
  1. Helminths are eukaryotes (similar metabolic pathways to humans, drugs are toxic)
  2. More prevalent in the tropics, countries that
    have limited resources (drug companies cannot make a profit)
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16
Q

Ascaris

A
  • Found worldwide
  • Largest nematode parasites
  • Adults live in upper part of small intestine
  • Pathology caused by large amounts of worms
17
Q

Ascaris lumbricoides (Ascariasis) pathology

A
  • 85% asymptomatic
  • Worms cause intestinal obstruction
  • Can move around the body inadvertently blocking narrow organs like the bile duct
  • Can cause sensitising phenomena
  • Malnutrition especially in children
  • Migrate away from gut to avoid drugs
18
Q

Trichuris trichura

A
  • Whipworm
  • Human pathogen
  • Adult worms are 3-5 cms
  • Eggs very distinctive,
    barrel shaped with mucus plugs
19
Q

Trichuris trichura life cycle

A

Eggs hatch in intestine, larvae then migrate to the villus crypts for protection, later migrating to large intestine where they attach and mature in ~ 3 months,
living for about 1 year.

20
Q

Trichuris trichura transmission

A
  • Eggs are shed in human feces, become mature through embryonation and infective to humans
  • Disease contracted from contaminated food or water
21
Q

Trichuris pathology

A
  • Most infections are asymptomatic
  • Cause some anemia and eosinophilia
  • In heavier infections the cecal mucosa is damaged, can also cause appendicitis
  • Lead to nutritional deficiencies and stunted growth
22
Q

Filariasis

A
  • Caused by Wuchereria bancrofti and Brugia malayi
  • Vectors are various genera of mosquitoes
  • Adult worms block the lymphatics and
    cause immune reaction
23
Q

Lymphatic filariasis transmission

A

Mosquitoes that transmit the infective filarial worm larvae from one human to another

24
Q

Lymphatic filiariasis clinical features

A
  • Asymptomatic with microfilaraemia
  • Acute: inflammation of lymph nodes, mild fever
  • Chronic: filarial fever, lymphadenitis, Swelling of
    peripheral limbs, Eosinophilia
25
Q

Filariasis treatment

A
  • No treatment for chronic filiariasis
  • Acute infection can be treated with doxycycline (does not target the worm but an obligate bacterial symbiont)
26
Q

Echinococcus tissue tapeworm (Hydatid disease)

A
  • Tissue dwelling tapeworms
  • Adult tapeworms in dog intestines
  • Humans are dead end hosts
  • Larvae hatch in gut, migrate around the
    body into tissues and organs and create large slow growing cysts
  • The cysts contain the daughter parasites which turn into adults worms when eaten by dogs.
27
Q

Echinococcus tissue tapeworm (Hydatid disease) treatment

A

Requires surgery and aggressive treatment with albendazole

28
Q

Schistosomiasis (Bilharzia)

A
  • Adult worms are mesenteric (intestinal) or vesicular (bladder)
  • Contracted by bathing or washing in water contaminated with motile form of the parasite that burrow into the skin.

MICR2209 (26 decks)

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