Nematodes- infective larvae Flashcards
What are the similarities between Ancylostoma duodenale and Necator americanus?
similar life cycle, infect host by penetrating skin (not orally!)
What are the differences between Ancylostoma duodenale and Necator?
A. duodenale can also be transmitted orally and trans-mammary. N. americanus requires a trans-pulmonary stage
Where are hookworms found?
North and South America (earliest in Brazil) and Europe +
What are the three divisions of the order Strongylida?
Strongyloidea (man hookworms), Trichostrongyloidea (intestinal hookworms in domestic animals), Metasrongyloidea (lungworms in domesticated animals)
What are the two hookworm species to cause disease in man and where are they found?
Ancylostoma duodenale Mediterranean, Southeast Asia, Southern America (scattered) Necator americanus Africa, Asia, Europe, predominantly in the Americas and Australia. South & Southwestern US
What happens if a larva infects humans?
they can penetrate the skin and cause a localized pathology, but they cannot complete their life cycle
Which human hookworm species is larger?
Ancylostoma duodenale is a bit bigger, usually around 0.5-1.5mm
What are the characteristics of the eggs?
bluntly rounded, thin shelled, almost indistinguishable between different species, Ancylostoma eggs slightly larger than Necator eggs will not bother to differentiate the species because it is not efficient
What feature does the male have to aid with copulation?
copulatory bursa at the anterior end
What distinguishing feature do the female worms have?
a vulva near the centre of the body
What are the two more common species of hookworms where humans are not the definitive host?
A. braziliense and A. caninum. Cause cutaneous larval migrans, when the larva penetrates the skin and migrates through the body
Describe adult hookworm pathology
attach to intestinal wall via bucal capsules and suck blood. heavy infections can leads to chronic iron deficiency anaemia
Describe larvae hookworm pathology
Ground itch: allergic rxn at site of penetration common in N americanus infection cough and pneumonitis: may result when larva get into lungs and travel up the trachea
What is the most common way humans become infected?
walking barefoot in an infected area
Can you become auto-infected from hookworm?
no
Describe the path the larva takes after skin penetration
carried in the veins to the heart, then to the lungs, where they penetrate pulmonary alveoli. They ascend up the bronchial tree to the pharynx, and are swallowed. They reach the small intestine and mature into adults. Larva can become dormant after penetrating the skin
How can hookworm infection be diagnosed?
microscopic examination of eggs in the stool. to know the genus, the eggs need to be cultured. the two human species can be distinguished microscopically but this is not often done
How can hookworm infection be treated?
benzimidazoles: albendazole and mebendazole
How do benzimidazoles work?
binds beta-tubulin, so that microtubules cannot be synthesized. affects glucose and other nutrient uptake, leading to immobilization and death
When is albendazole effective?
in the intestinal stage and when the larva is migrating under the skin
Where are Strongyloides stercoralis (threadworm) found?
tropical and subtropical areas, but also some cases in temperate Southern United States
What is the niche of Strongyloides stercoralis?
mucosa of small intestine or free-living
Which sex of threadworm is larger?
the female
Describe the threadworm eggs
ellipsoid in shape, thin wall containing a larva
What drug is used to treat Strongyloides stercoralis infection?
ivermectin interferes with nervous system and muscle function (enhancing inhibitory neurotransmission). Drug binds and activates glutamate-gated chloride channels
