12. Nematodes (infective larvae) Flashcards
Which nematodes are infective in their egg stages?
Trichuris trichiura
Ascaris lumbricoides
Enterobius vermicularis
which nematodes are infective in their larval stage (L3)?
Necator americanus
Ancylostoma duodenale
Strongyloides stercoralis
Trichinella spiralis
which is the new world hookworm?
Necator americanus
what is the old world hookworm
Ancylostoma duodenale
what is the most prehistoric evidence for hookworm disease?
coprolites - fossilized human feces
Where have coprolites been identified?
NA, SA and europe
where are the oldest caprolites from and how old are they?
Brazil, over 7000 y.o.
which is the second most common nematode in humans?
hookworm
what is the “Order” of hookworms
Strongylidae - large order containing important pathogens of man and domestic animals
what are the Superfamilies of Order Strongylidae?
- The Superfamily Strongyloidea (the hookworms in man)
- The Superfamily Trichostrongyloidea, intestinal nematodes important in many domesticated animals (e.g. Haemonchus brasiliensis in rodents)
- The Superfamily Metastrongyloidea (the lungworms, in domesticated animals)
what are the two hookworms capable of causing infection in humans?
Ancylostoma duodenale
Necator americanus
what determines where you will find which worms?
physical landscape: geographic features
- soil
- climate
what is required by the first two larval stages of hookworms L1 and L2 in order to undergo the first two molts, M1 and M2, to yield the L3 stage?
A. duodenale and N. americanus, the larvae require soil containing an equal mixture of sand and silt and a smaller proportion of clay
how long are hookworms
0.5 to 1.5 mm long,
A. duodenale slightly longer than N. americanus
what is found at the posterior end of the male worm? (nematodes)
a characteristic copulatory bursa, used to catch and hold the female nematode during mating
what is found near the center of the female worm, slightly anterior in NECATOR, slightly posterior in ANCYLOSTOMA
a vulva
what is the habitat of adult hookworms
attach to the wall of the small intestine, the jejunum - usually attached to the mucous layer
what is the morphology of the eggs in hookworms
- bluntly rounded,
- thin shelled,
- and are almost - indistinguishable between the different species,
whos eggs are larger, Ancylostoma or Necator?
Ancylostoma
how do the L3 larvae of hookworms usually infect humans
the eggs hatch in the soil and they usually burrow through the feet
what is the path the L3 take through the DH body
- infect man by usually burrowing through the soles of the feet
- the larvae then migrate to infect the heart and lungs before passing into the trachaea, pharynx and then the small intestine
how does an accidental host occur in hookworms and what is the hookworm’s fate?
The larvae of several species of hookworms infecting domesticated animals may penetrate human skin, causing pathology even though they do not develop the adult parasites in man
describe the life cycle of hookworms
- Eggs are passed in the stool
- Under favourable conditions; moisture, warmth, shade, larvae hatch in 1-2 days
- The released Rabditiform larvae (L1) groe in feces and/or the soil
- After 5-10 days (and 2 molts) they become filariform larvae (L3) that are infective
- These infective larvae can survive 3 to 4 weeks in favourable environment conditions
- On contact with the human host, the larvae penetrate the skin and are carries through the veins to the heart and then to the lungs
- They penetrate into the pulmonary alveoli, ascend the bronchial three to the pharynx and are swallowed
- The larvae reach the small intestine, where they reside and mature into adults
- Adult worms live in the lumen of the small intestine, , where they attach to the intestinal wall with resultant blood loss by the host
- Most adult worms are eliminated in 1 to 2 years, but longevity records can reach several years
what happens sometimes to A. duodenale larvae?
- Some A. duodenale larvae, following penetration of the host skin, can become dormant (in the intestine or muscle)