Nematodes Flashcards
outline the characteristics of the phylum Nematoda
- 28,000 spp with 16,000 sp being parasitic
- step up in complexity with complete digestive system open at both ends (simple tube)
- secretes ammonia through body wall
- adapted to nearly every habitat
very successful parasite
outline the body plan of nematodes
2.5mm long but can be longer if parasitic
ornamented with ridges, rings, warts and bristles
bilaterally symmetrical body and radially symmetrical head
series of teeth on inner edge of mouth
4 nerves run length of the body which branch at the head to form a ring around pharynx = brain (more complex compared to previously studied parasites)
outline the structure of a cross section of a nematode
Tube within a tube
Thick cuticle outside with intestine as an inner tube
also has a series of long tubes running the length of the animals which are organs such as kidneys, testes, ovaries etc
outline some symptoms of soil transmitted helminths
light infections have no/few symptoms
heavy infections: abdominal pain, diarrhoea, anaemia, physical and cognitive growth retardation
outline the general nematode life cycle
separate sexes = male and female
fertilisation between sexes produces an embryonated egg (if fertilisation doesn’t occur then embryonated egg produced, non-infective)
egg hatches producing larvae which undergo many moults, getting larger at each one
larvae progress through first stage larval to fourth stage larva before they are considered mature
what are the species of soil transmitted helminths which infect humans through contaminated soils
1) Acaris lumbricoides (roundworm)
2) Trichuris trichiura ( whipworm)
3) Anclostoma dunodenale & Necator americanus (hookworms)
burrow through the skin of feet, enter the circulatory system, reach lungs, coughed into oesophagus and into digestive system
what are the names of two human hookworms which are usually discussed together as the cause of hookworm infection
1) Ancylostoma duodenale
2 )Necator americanus
found in the digestive system where they rasp using rasping plates to create an inflammatory response which they then feed on
outline the lifecycle of soil transmitted helminths
Eggs passed into the faeces of infected person
eggs deposited into the soil where they hatch releasing larvae
mature larvae penetrate skin of humans through the sole of feet
travel in circulatory system to lungs
from lungs coughed into oesophagus and into digestive tract where adults live
= common in areas where people have no shoes, children especially as dont have shoes until feet stop growing
how much of the world population is infected with soil transmitted helminths
800m- 1.1b with Ascaris
600m- 800m with whipworm
575-750m with hookworm
= warm and moist climates where sanitisation and hygiene are poor
= considered a neglected tropical disease as they inflict suffering but can be controlled
outline the lifecycle of the most common nematode worm Strongyloides stercoralis (strongyls)
1) larvae excreted in stool
2) develop into free living adult worms which produce fertlized eggs
3) eggs hatch forming larvae which developing filarial form which penetrate skin of definitive host
4) larvae migrate by various pathways to small intestine where they become adults
5) parasitic adult female in small intestine produces eggs and are either excreted or autoinfection occurs where larvae hatch and penetrate intestinal mucosa/ migrate to other organs
what species of nematode helminths use faceco-oral infection pathways
Ascaris species:
Ascaris lumbricoides: parasites to human intestine
A.summ (from pigs)
outline the Ascaris life cycle
1) Adult worms live in the lumen of the small intestine and produce 200,00 eggs per day passed out in faeces
2) unfertilized eggs are non-infective
3) fertile eggs take 18days- several months to develop into mature larvae
4) mature eggs ingested by hosts and larvae hatch out either:
- burrow through intestinal mucosa
- into the HPS, system circulation onto lungs
- mature on the lung surface for 10-14 days, then burrowing into alveoli
- climb up bronchial trees and coughed into digestive system
5) develop into diecious adults in small intestine (2-3 months)
what can Ascaris parasite species cause in humans
heavy infestations in children cause stunted growth due to malnutrition (this is rare)
- abdominal pain and intestinal obstruction
- potential perforation
migrating worms can cause blockages
nasopharyngeal expulsion= usually when just single female
outline how filarial nematode species are spread differently compared to other species
= Vector borne, not contamination
- blood feeding insects or copepod crustaceans (Dracunclus mediensis)
Adults = live in various host tissues
juveniles= wander in the circulatory system/ lymphatic system
what disease do filarial nematodes cause
Filariasis
