AD Nematoda Flashcards
What are the general characteristics of nematodes (roundworms)?
Non-segmented cylindrical worms tapering at both ends, with a body cavity
flexible cuticle
Cuticle moults periodically
Sexes are separate (diecious), male is smaller than female, internal fertilization; sperm amoeboid
Females are either
– Viviparous (produce larvae/ embryos)
– Oviparous (lay eggs) or
– Ovo-viviparous (lay eggs which hatch immediately)
Longitudinal muscle only
No blood or other circulatory system
Free-living and parasitic worms
What structure is useful in identifying nematodes?
Buccal cavity
Describe a nematode’s cuticle
Cuticle is secreted by epidermal cells and functions
to:
Resist penetration - in free-living
Resist enzymatic digestion – in parasitic
Maintain internal hydrostatic pressure
Describe nematode locomotion
Sinusoidal – not lengthening and shortening like other
worms
(i.e. whip-like undulations) because only have
longitudinal muscle
What is crytobiosis
a metabolic state entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency.
The organism lives indefinitely until environmental conditions return to being
hospitable
Anhydrobiosis is the most studied form of
cryptobiosis and occurs in extreme desiccation
e.g. promotes survival in the soils of the Antarctic Dry Valleys
What is a nematode life cycle?
4 steps/phases Eggs 4 juvenile stages Adult Egg produced
Reproduce through eggs
May be sexual or parthenogenetic (development of embryos occurs without fertilization by a male)
How do nematodes affect plants?
Because of the feeding process Puncture a cell wall Inject saliva- contain enzymes Take the cell contents And moves on within a few seconds
Describe the effects parasitic nematodes have on animals
More than 1.5 billion people, or 24% of the world’s population are infected with soil-transmitted helminth infections worldwide (World Health Organisation)
Livestock cause an estimated 6% loss farming economy
Nematodes are very common in wildlife.
They reduce population size and fecundity
What are the 4 modes of infection by nematodes?
- Ingestion of –
• Embryonated eggs contaminating food & drinks, e.g.
A.lumbricoides
• Growing embryos in an intermediate host (infected
cyclops) e.g. D.medinensis - Penetration of skin – larvae bores through the skin
e. g. A.duodenale - By blood sucking insects e.g. filarial worms
- Inhalation of infected dust containing embryonated
eggs e.g. A.lumbricoides,
Describe hookworm
Broad host range – infects humans, dogs, cats and
wildlife. Two most common in humans are
Ancylostoma duodenale and Necator americanus
Leading cause of maternal and child morbidity in the developing countries
Hookworm infections occur in an estimated 1.3 billion people worldwide
Rarely fatal, but causes anaemia
Describe ascaris eggs
Highly resistant
Infection by ingestion of eggs in contaminated food or
water. Causes morbidity rather than mortality
Very long life (at least 10-15 years)