111 - Eukaryotic Parasites 2 Flashcards
Three major types of worms
1) Roundworms
2) Tapeworms
3) Flukes
Similarities between all helminths
1
2
3
1) No lungs (extegument across which gasses exchange)
2) Sexual reproduction
3) Complex life-cycles, involving more than one host
Examples of human roundworms
1
2
3
1) Pinworms
2) Ascaris
3) Strongyloides
Examples of human tapeworms
1
2
1) Echinococcus
2) Taenia
Example of a human fluke
Schistosoma
Nematodes
1
2
3
1) Roundworms
2) Tube-like animal, covered with a cuticle
3) Most are free-living
Most clinically-important Nematode
Pinworm (enterobius vermicularis)
Features of pinworm infection 1 2 3 4
1) Most children infected at some time; highly contagious
2) 1cm long female crawls out of anus at night to release eggs
3) Fingers, sheets contaminated
4) Pre-patent period 4-6 weeks
Ringworm life-cycle 1 2 3 4 5
1) Embryonated eggs ingested
2) Larvae hatch in small intestine
3) Mate in caecum
4) Leave body through anus at night, lay eggs around anus
5) Transferred by scratching eggs
Symptoms of pinworm
Many asymptomatic infections.
Perianal/vaginal itch
Diagnosis of pinworm
Detection of eggs.
No serology, as never enters blood.
Treatment for pinworm
Antihelminth medication
Ascaris lumbricoides
Large intestinal roundworm
Number of eggs laid by Ascaris
200, 000 eggs per day (laid by female)
Size of Ascaris lumbricoides
Can be 30cm long
Ascaris lumbricoides life-cycle 1 2 3 4 5 6 7
1) Maturation in jejunum
2) Eggs passed in faeces, mature in damp soil over a few weeks
3) Eggs get into water, contaminate plant material.
4) Are ingested, infect jejunum
5) After maturation in jejunum are about 1/2mm long. Enter hepatic circulation, break through alveolar walls into alveolar space.
6) Migrate up the trachea, get swallowed again.
7) Attach to wall of jejunum, stay there for the rest of their lives
Distribution of Ascaris lumbricoides
Worldwide, but mostly in tropics (soil is too cold in many places, EG Melbourne)
Symptoms of Ascaris infection 1 2 3 4 5
1) Mainly asymptomatic.
2) Pneumonitis (from larval migration).
3) Intestinal obstruction (pancreatitis, cholangitis).
4) Because of repeated coinfections with different stages of 5) Ascaris lifecycle, have all symptoms at the same time (EG: asthma from larval migration irritating lungs)
Diagnosis of Ascaris
Eggs in faeces.
Imaging of large worms causing obstructions (EG ultrasound)
Number of Strongyloides infections worldwide
100 million
How do Strongyloides stercoralis infect host?
Penetrate skin of host.
Strongyloides stercoralis features of infection
1
2
3
1) Gram- co-infection (thought to be covered in G- bacteria, introduces these into the blood stream). Septicaemia.
2) Can come about if someone is immunosuppressed (EG: glucocorticoids prescribed)
3) Autoinfection. Entire life-cycle can occur within a human.
Strongyloides sterocoralis life-cycle 1 2 3 3 4 5 6 7 8 9
1) Rhabditiform larvae excreted in stool
2) Develop into free-living adult worms
3) Eggs produced by female worms
4) Rhabditiform larvae hatch from eggs.
5) Infective filariform larvae can penetrate intact skin of host
6) Filariform enters bloodstream, transported to lungs, enter alveolar spaces.
7) Carried into the trachea, are swallowed.
8) Female lays eggs
9) Autoinfection.
Example of a fluke
Schistosoma
Where do Schistosoma mansonii live?
In intestinal veins of humans, in freshwater snails
How do Schistosoma mansonii larvae enter human host?
Through intact skin
Schistosoma lifecycle 1 2 3 4 5
1) Penetrate skin
2) Go through blood to liver, into portal system
3) Penetrate bowel wall
4) Lay eggs in mesenteric venules of bowel, rectum, eggs are passed in stools
5) Infect freshwater snails
Distribution of Schistosoma mansonii
Africa, tropical South America, Caribbean
Symptoms of Schistosomisasis 1 2 3 a, b, c, d 4
1) Cercarial dermatitis
2) Light infections often itch
3) In heavy infections:
a) Hepatomegaly
b) Splenomegaly
c) Collateral circulation, portal hypertension
d) Pulmonary fibrosis
4) Can be asymptomatic
Diagnosis of Scistosoma mansonii
Characteristic eggs in faeces, serology
Treatments for Schistosoma mansonii
Antihelminthics
Disease control of Schistosoma monsonii
Eradicating freshwater snails
Immunity to Schistosoma
Persistent infections and reinfections are common, concomitant immunity can be demonstrated in animal hosts, immune evasion by immunological masking
Features of tapeworms 1 2 3 4 5
1) All parasitic
2) Segmented body
3) Surface tegument
4) No gut
5) Organs in parenchyma
Cause of hydatid cyst disease
Echinococcus granulosus
Normal cycle of Echinococcus infection
1
2
3
1) Definitive hosts are dogs
2) Intermediate hosts are sheep
3) Humans can be accidentally infected, but can’t pass viable eggs
Pathology of Echinococcus granulosus infection in humans
1
2
1) Hydatid cysts form in tissues, principally in lungs, liver, but can occur in any body site.
2) Liver cysts are the most common, can persist for years
Diagnostic tests for echinococcus infection
Imaging, serology
Treatment for hydatid infections
Surgery, PAIR (percutaneous drainage of hydatid cysts - Puncture, Aspiration, Injection, Reaspiration), antihelminthics
Disease control of Echinococcus
Livestock vaccination
Taeniasis hosts
1)
2)
1) Zoonotic infection.
2) Humans can be both intermediate and definitive host
Size of Taenia tapeworms
Can be up to 10m long
Helminth that can cause neurological problems
Taenia solium cysts form in brain
Taenia solium distribution
Africa, Latin America, Asia
Symptoms/pathology of Taenia solium
Cysts (cysticerci) in subcutaneous and neural tissues
Diagnosis of Taenia solium
Serology, imaging techniques
Dosease control of Taenia solium
Treatment of carriers, avoidance of eating raw pork, sanitary disposal of sewage, personal hygiene, vaccination in pigs
Immunity against Taenia solium
Concomitant immunity, vaccination induces protection against egg infection
