L18. Eukaryotic Parasites 2 Flashcards
What is a helminth?
A parasitic worm; a fluke, tapeworm, or nematode
There are around 50-60 subtymes that commonly affect people
Describe the sexual cycle common to all helminthes
The egg hatches and develops into an adult worm with intermediate stages in between ranging from complex to very simple
Do the helminthes complete their maturity cycle in a single host?
NO
Almost all of them develop eggs OUTSIDE the host body and rely on the surrounding environment (soil, plants, other animals) for survival and transmission into new hosts.
What is the exception for the external environmental part of the helminth lifecycle?
Strongyloides is able to complete the whole life cycle in the one host
What are nematodes? Where do they mainly exist?
Roundworms that make major pathogens for humans and livestock.
It is a tubelike animal covered with a cuticle
Mostly exist free-living in soil
What are the three major pathogenic nematodes?
- Enterobius vermicularis (pinworm)
- Ascaris lumbricoides
- Strongyloides
What is enterobius vermicularis?
Who are most affected by it?
Pinworm
The most common in the clinical setting
Mainly affects children
Highly contagious
Describe the life cycle of Enterobius vermicularis
- Eggs are laid at the anus and ingested orally by contaminated fingers usually
- Eggs survive transit through the gut
- Males and females mate in the caecum
- Females travel through the colon and exit the anus and lay eggs (nocturnally usually)
- Can often crawl back in to the rectum
What are the symptoms of infection with Enteriobius vermicularis?
Many are asymptomatic
Perianal and vaginal itch (often treated empirically)
What is the detection method for Enteriobius vermicularis?
Sticky tape test across anus at night
What is the treatment for Enteriobius vermicularis
Anti-helmethics
Can reinfection occur? How is this disease controlled?
Chronic and repeated infections do occur (self-reinfection is very common)
Prevention is by improved hygeine
What is Ascaris lumbricoides?
A large intestinal ROUNDWORM that can grow to up to 40-50cm long.
Highly motile worms, especially before sexual maturity
What is the replication of Ascaris lumbricoides like?
Prolific replication
Females lay up to 200,000 eggs per day
Describe the life cycle of Ascaris lumbricoides
- Eggs are laid in the jejunum of people
- Eggs are secreted in the faeces
- The eggs reach damp soil and hatch and mature into an infective state.
- Humans ingest the very small developing worm in contaminated run off water or plant materials
- Worms survive transit into the stomach and mature in the jejunum (0.5mm by this stage)
- They are able to migrate through to the cirulation into the lungs where they are coughed back up and swallowed again. This step is important for full SEXUAL MATURITY
- Adult worms attach themselves to the wall of the jejunum where they have suckers that penetrate and take nutrients to grow
What are some symptoms of Ascaris lumbricoides?
Many are asymptomatic
Pneumonitis (due to the larval migration phase)
Intestinal obstructions
How is diagnosis made?
What is the treatment?
Eggs in the faeces, imaging of obstructions
Anti-helmithics - they paralyse the worms so they are passed in the faeces.
What is the control of the disease?
Sanitary sewage disposal
Reinfection and chronic infections can and do occur
What is Strongyloides stercoralis?
A threadworm that causes infections worldwide
How does strongyloides infect humans?
The larvae hatch in soil and do NOT require ingestion
They infect by PENETRATING THE SKIN of people
Describe the life cycle of Strongyloides stercoralis
- Infective larvae penetrate intact skin and inflammation and enter the circulatory system and are transported to the lungs
- They are coughed up and swallowed into the small bowel and mature
- Eggs are laid in the intestine and deposited into the mucosa where they hatch and migrate to the lumen
- Larvae are excreted in stool
- Can either auto infect by penetrating back into the skin of the host OR develop in free living worms and lay eggs in soil and mature and penetrate new hosts.
What is important about the Stronglyoides stercoralis infection that makes it different to other Helminthes
It is able to start and complete its whole life cycle inside one human host
What can immunosuppressed individuals suffer from with this infection?
Dissemination
and
Gram negative hyperinfection: sepsis as the worm itself is coated with gram negative bacteria
What are the symptoms of Stronglyoides stercoralis infection?
Many are asymptomatic
Pneumonitis (larval migration)
Dissemination and gram negative hyperinfection
What is disease control for Stronglyoides stercoralis?
Sewage disposal, wear shoes
Repeated and chronic infections can and do occur
What are Flukes?
Trematodes
All are parasitic (cannot live outside the human host for very long)
Have no body segmentations
What is Shistosoma mansonii infection? How is it acquired?
Causes Bilharzia disease
Acquired by bathing and working in fresh water
The larvae in water penetrate the skin
Transmitted by fresh water snails
Describe the life cycle of Shistomsoma mansonii
- Larvae penetrate the skin
- Larvae travel through the blood stream into the liver and into the portal venous system
- Migrate through into the bowel wall and lay eggs in the gut
- Eggs are passed in the species and into water supply where they hatch in the water and infect SNAILS
What are the symptoms of Shistosoma mansonii infection?
Cercarial dermatitis (swimmers itch)
Light infections are often asymptomatic
Heavy infections lead to hepatomegaly, splenomegaly, collateral circulation and portal hypertension, chronic pulmonary fibrosis
What is the worldwide distribution of Shistosoma mansonii?
Africa
Tropical South America
the Caribbean
What is the diagnosis method and treatment of the Shistosoma mansonii?
Eggs in faeces and serology
Anti-helminthic agents
What can be done in terms of disease control for Shistosoma mansonii?
Snail control (mollscasides)
Sanitary disposal of sewage
Treatment of carriers
What kind of immunity occurs with Shistosoma mansonii?
Persistent and reinfection can occur
But first presentation is with the classic inflammatory response and subsequent presentations it not seen; some form of immunity
What are tapeworms?
All are parasitic worms with segmented bodies that cause disability by consuming large amounts of host metabolic sources
What is Echinococcus granulosus?
Tapeworm,
What kind of host is the human to Echinococcus granulosus?
Humans are INTERMEDIATE HOSTS and without humans, the worms are still able to survive and replicate.
Humans do NOT produce viable eggs
Describe the life cycle of Echinococcus granulosus in the normal predator-prey scenario
- Adults in the small bowel of definitive hosts release eggs in the faeces.
- They hatch and are ingested by intermediate hosts.
- The eggs hatch and penetrate the intestinal walls
- Hyatid larval cysts form in the liver, lungs etc
- Proliferation occurs in this cyst and then mature release eggs and then ingested back again in definitive host
How do humans fit into the cycle of Echinococcus granulosus?
Humans are able to ingest the egg in faces (from contamination) and hyatid cysts enter into tissues (liver and lungs mainly)
What are the symptoms of Echinococcus granulosus?
Symptoms vary with the number, size and location of the Hyatid cysts.
Pain and discomfort
How is Echniococcus granulosus diagnosed?
Large (20-30cm) long cysts can be seen using imaging techniques
Serology
Can’t use faeces as cysts are not produced in humans
Is surgical intervention ideal in Echinococcus granluosus?
No because popping of the cysts leads to release of large amounts of proliferating protoscloleces leading to severe allergic reactions and anaphylactic shock
What is treatment for Echinococcus granuolsus?
PAIR (puncturing with needle, aspirating it and injecting anti-parasitics)
Anti-helmetics (often given before any other interventions to harden the cysts)
Surgery
What is disease control of Echinococcus granulosus
Is more veterinary orientated: prevention of infection in dogs, public education, personal hygeine, quarantine of infected livestock and vaccination of livestock
What is Taeniasis? What are the two major types?
An important cause of neurologic disease
Taenia saginata
Taenia solium
There are cestode (tapeworm) parasites, up to 10m long
What kind of hosts are humans to Taenia?
Either definitive hosts or intermediate hosts
Describe the life cycle
Zoonotic infection between predator and prey (humans often replace the predator)
- Cattle (saginata) and pigs (solium) become infected with contaimated eggs
- Hatch and penetrate the intestinal wall
- Develop in cysts in the muscle
- Humans (and predators) ingest raw or undercooked infected meat
- Attaches to the intestine and secrete eggs that leave in the stool
Which of the two types tends to cause disease (the other doesn’t tend to)
Taenia solium can invade the gut wall leading to cyst formation in many organs, some places are asymptomatic but in the brain leads to neurocystopsychosis
What is the distrubution of Taenia solium?
Africa
Latin America
Asia
How is T.solium diagonsed?
Serology
Imaging techniques
How is Taenia solium infection treated?
Anti-helminthics (but often not administered)
How is the T.solium disease controlled?
Treating carriers
Avoiding eating raw pork
Sanitary disposal of sewage
Vaccination of pigs
