PARA 410 Lecture Notes - Lecture 5: Ascaris Lumbricoides, Gastrointestinal Tract, Ascariasis
12 Jun 2018
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Ascaris lumbricoides – January 19
Macroparasite transmission Dynamics Using Ascaris lumbricoides (roundworm) as an Example
• Bolus of worms expelled after drug treatment
• Live in gut of human
Disease - Ascariasis
• Intestinal discomfort/blockage
• Distended abdomen
• Decreased food intake, nutrient loss, malabsorption
• Worms can migrate into bile duct, out the nose
• Large numbers of larvae penetrating lungs can cause edema and block air passages
• Larvae = highly immunogenic
o Intense allergic response
Disability Adjusted Life Years (DALYs)
• Measure of overall disease burden, expressed as the number of years lost due to ill-health,
disability or early death
• Incorporates both years of life lost from premature death (YLL) and years of life lived with
disability (YLD) into a composite estimate
• Morbidity refers to disease; Mortality refers to death
Ascaris Geographical Distribution
• Temperate and sub-tropical zones but greatest prevalence in tropical regions
Ascaris
• Top right image: adult
• Top left: fertilized and unfertilized
• Bottom left: Inside egg = has larval stage
• Bottom right: Once ingested by host: larvae exits egg and can cause infection in the host
Life Cycle
• Molts like a snake into larval stage 2
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• Adult worms live in the lumen of the small intestine
• A female may produce up to 240 000 eggs per day, which are excreted with the feces
• Fertile eggs embryonate and become infective after 18 days to several weeks depending on the
environmental conditions
o Optimum: moist, warm, shaded soil
• After infective eggs are swallowed, the larvae hatch, invade the intestinal mucosa and are carried
to the lungs via the portal and systematic circulation
• The larvae mature further in the lungs (10-14 days), penetrate the alveolar walls, ascend the
bronchial tree to the throat and are swallowed
• The larvae develop into adult worms in the small intestine
• Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the
adult female
• Adult worms can live 1 to 2 years
Reproduction - Transmission
• One egg = one adult worm !!
• Each female worm releases eggs directly into the environment. Eggs don't multiple in the host.
• The only way for the number of worms to increase within a host is if the host ingests more eggs
• Eggs can be laid whether they are fertilized or not
Some Factors Influencing Ascaris Transmission
• Poor living conditions
o Crowding
o Poverty
o Latrines (physical locations of defecation) or flush toilets
• Behaviours (bad ones for ingestion/transmission)
o Lack of hand washing
o Open defecation = go not in toilet or latrine
▪ Eggs are already in environment = available for transmission
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Macroparasite transmission dynamics using ascaris lumbricoides (roundworm) as an example: bolus of worms expelled after drug treatment. Intestinal discomfort/blockage: distended abdomen, decreased food intake, nutrient loss, malabsorption, worms can migrate into bile duct, out the nose. Large numbers of larvae penetrating lungs can cause edema and block air passages. Disability adjusted life years (dalys: measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death. Incorporates both years of life lost from premature death (yll) and years of life lived with disability (yld) into a composite estimate: morbidity refers to disease; mortality refers to death. Ascaris geographical distribution: temperate and sub-tropical zones but greatest prevalence in tropical regions. Ascaris: top right image: adult, top left: fertilized and unfertilized, bottom left: inside egg = has larval stage, bottom right: once ingested by host: larvae exits egg and can cause infection in the host.
