Medical Parasitology Flashcards
Describe “medical parasitology”?
It is a “catch all term used for:
- worms
- single celled parasites that are NOT bacteria, viruses or fungi.
- Some bedbugs and mites (which tend to be called entomolgy).
Why is it important to use medical parasitology when considering global health issues?
What is a host?
A person or animal that is INFECTED by a PARASITE
What is a VECTOR and name some.
An AGENT of TRANSMISSION
This is how a disease is spread.
Some vectors are: mosquito’s, XXX, XXX
What is a RESERVOIR and can you name some?
A PLACE or an ANIMAL which harbours the parasite when it is NOT in a human/host.
This could be a SWAMP or a XXXX.
What does the term ZOONOSES mean and can you name some?
Zoonoses are diseases acquired from ANIMALS (directly or indirectly) and they are usually acquired from other vertebrates (animals with a backbone).
(transmission may require a non-vetebrate vector) eg XXXX
Give an overview of the range of “parasites” that a medical microbiologist in the UK may encounter in the lab.
Key points on parasites in the UK:
- Rare compared to other countries.
- Under-diagnosed in the UK.
- Becoming more of an issue due to the increase in immuno-compromised populations.
- Parasites in the UK can range from trivial to fatal.
Give an overview of the range of “parasites” that a medical microbiologist in the UK may encounter in the lab.
Trichomonas vaginalis
Trichomoniasis is the disease caused by trichomonas vaginalis, the anaerobic, flagellated protozoan parasite.
- The most common parasite in the UK.
- In women the main symptoms are purulent cervical discharge, itching and discomfort during sex
- Men are usually asymptomatic
- Epidemiological data is not available for the UK as the disease is not notifiable.
Trichomonas vaginalis life cycle and type?
The trophozoite is the active, reproductive stage of the protozoans that feeds on the host.
- It begins its life cycle in the vaginal and prostatic secretions and urine.
- It multiplies by longitudinal binary fission.
- Trophozoite then in vagina or the orifice of the urethra.
There are two stages: infective and diagnostic stage.
Toxoplasmosis
PARASITE: Toxoplasma gondii
EPIDEMIOLOGY: found worldwide
INFECTION CAUSE: Zoonotic
RESERVOIR: cats are main reservoir and spread is from accidental ingestion of cat faeces or eating undercooked contaminated meat
RISKS: It may have a role in schizophrenia
SIGNS & SXS:
- flu like illness
- in next stage, may have muscle and lymph gland pain that persists for some time.
- in severe cases (usually in the immunocompromised) the parasite can enter tissues and cause damage to the brain and other organs
- occasionally immunocompetent people can develop eye damage as a result of infection.
Toxoplasmosis in pregnancy.
What are the risks and when can this happen?
•When there are fecal oocysts from the cat during the life cycle, this can cross to the placenta. This is why pregnant women should NOT clean up cat litter.
It can result in a range of complications to the pregnancy:
●Spontaneous abortion●Stillbirth●Deafness●Seizures●Cerebral palsy●Convulsions●Jaundice●Lung inflammation●Heart inflammation●Damage to the retina
How is DX of toxoplasmosis carried out?
DX:
Antibody detection in serology (the study of blood serum) and the observation in patient samples.
Acanthamoeba
PARASITE: ancanthamoebae
EPIDEMIOLOGY: found in the environment
INFECTION SITE: the cornea (in the UK)
RESERVOIR: ? sea? water?
RISKS: Has been linked to contact lens wearing and can cause a very rare form of encephalitis (in the immunocompromised population)
SIGNS & SXS: eye infection
DX:
- observation of the parasite in corneal scrapings.
- can be observed in its amoebic form on a lawn of bacteria.
GOOD HYGIENE IS CRUCIAL for contact lens wearers.
Enterobius vermicularis
(threadworm)
PARASITE: enterobius vermicularis
EPIDEMIOLOGY: found in school age children
INFECTION SITE: terminal intestine and the female lays her eggs in the folds of the skin around the anus.
RESERVOIR: bedding, soil, kids! They can survive in bedding for 2 weeks.
SIGNS & SXS: itching, restless sleep as they hatch at night around anus.
DX:
- sellotape slide method.
- eggs have a characteristic D shape.
TX: mebendazole.
Cryptosporidium
PARASITE: cryptosporidium spp.
EPIDEMIOLOGY: increase in rural areas.
RESERVOIR: farm animals
INFECTION SITE: GI tract.
SIGNS & SXS: profuse watery diarrhoea, dehydration, weight loss, nausea and vomiting.
DX: observation of parasite in fecal samples in a wet prep or stained slide using fluorescent stain or Modified Ziehl-Neelsen.
TX: unnecessary as usually the disease is fairly mild HOWEVER it is a significant threat to immunocompromised patients. They may develop long-term infections that require TX and often never be able to fully clear the infection or suffer with recurring relapse of infection.
Life cycle of Cryptosporidiosis
Outbreaks of Crytopsporidium in the UK
Incidents increased due to petting farms over the easter holidays and swimming pools during the summer….there were also cases of a cryto bug found in the water source in Lancashire and the utilities companies were fined £300,000.
Giardiasis
PARASITE: Giardia Lamblia
EPIDEMIOLOGY: can be acquired in the UK or imported: water, lakes, streams, rivers.
RESERVOIR: farm animals
INFECTION SITE: GI tract.
SIGNS & SXS: diarrhoea, abdo cramping, wind nausea - occurs 5-25 days post infection (see life cycle).
DX: observation of cysts and/or trophozoites in fecal samples.
Immunofluorescence technique may also be used.
TX: not always necessary but METRONIZADOLE is the drug of choice in the UK if need be.
Giardia CYSTS can resist cholrination so water supplies in the UK are regularly monitored.
Avoidance advice is currently:
•Avoid swallowing recreational water•Don’t swim if you have diarrhoea•Take care changing nappies if child ill•Avoid contact with faeces during sexual activity•Wash hands thoroughly•Don’t have ice cubes in your drinks if unsure of the water source.
Giardiasis life cycle
Trophozoites and cysts…
Naegleria
PARASITE: Amoebae
EPIDEMIOLOGY: found wordwide throughout the environment, warm fresh water, lakes, streams, near industrial plants.
Usually linked to diving or swimming underwater in freshwater lakes; watersports (https://www.cdc.gov/parasites/naegleria/graphs.html)
DISEASE: PAM (primary amoebic meningoencephalitis) extremely rare but serious infection.
SIGNS & SXS: •Initial symptoms include nausea, vomiting, fever, photophobia, neck stiffness•Later signs include confusion, seizures, loss of balance, loss of control of bodily functions - brain tissue damaged••Disease progresses rapidly to coma and death :(
TX: generally unsuccessful.
Tapeworms
PARASITE: 2 species:
Taenia saginata (beef
Taenia solium (pork)
Sometimes there are occasional infections with fish or dog tapeworm.
EPIDEMIOLOGY: used to be common in the UK but now rare and often imported,
SIGNS & SXS: usually restricted to GI system – nausea, weight loss, malnutrition (pork tapeworm)
Larvae are able to migrate through the body and form CYSTS elsewhere.
DX: Observation of the eggs or adult worms can be seen in segments in the faeces.
TX: ?
