Intro to Parasites Flashcards
what is a parasite
a parasite is an** organism that lives in or on another organism** (host) and derives its nutrients at the expense of this host, very wide range of parasites globally, they can be vectors of infection or cause infection themselves, predominantly a problem of resource-poor countries
Vector
an organism which acts as an intermediate host for a parasite, the vector transmits the parasite to the next host
Classification of parsites
3 classes and examples
- protozoa e.g. malaria, amoebae, flagellates
- helminths (worms) e.g. roundworms, tapeworms, flukes
- ectoparasites e.g. lice, ticks, mites
How are parasites classified - broadly
- cellular structure
- life cycle
How are many parasites spread
by vectors
What are parasites predominantly a problem of
Resource - poor contries (equator/tropical regions)
what are protozoa
- microscopic, single-celled organisms
- can be free-living or parasitic in nature
- able to multiply in humans
how are protozoa transmitted
- protozoa that live in a human’s intestine => faecal-oral route
- protozoa that live in the blood or tissue of humans=> insect vector
Give an example of and explain protozoan infection
Malaria: mosquito-bourne disease caused by Plasmodium parasite
* patient often experiences fever, chills and flu-like illness
* Left untreated they may develop severe complications and die
How many plasmodium species are there and which is the deadliest
5 plasmodium species- P. falciparum has the highest mortality
Give some fun maleria facts :)
- causes the largest burden of death among all parasitic diseases
- present throughout the tropics and subtropics
- preventable disease
- recognition and appropriate treatment saves lives
- the complex life cycle of the parasite makes eradication very challenging
Lifecycle of maleria
- Sporozoites injected by mosquito
- Travel through blood and enter liver
- Mature in liver and re-enter circulation as merozoites
- Invade red cells, multiply and lyse cells - invade more red cells
- Sexual forms taken up by mosquito
What can show plasmodium infected red cells (parasitaemia)
Specially stained blood film
Is maleria a preventable disease
yes
What makes eradicating maleria very challenging
The complex lifecycle of the parasite
protozoal infections- amoebic dysentery
- causes bloody diarrhoea
- entamoeba histolytica invade gut wall
- microscopy: cysts in formed stool
- clinically= intestinal and extra-intestinal infections, liver abscess in late disease
- faecal-oral route of transmission for amoebae
- Causes infection in variety of body systems - can causes complications such as abscesses if left untreated
2 examples of protozoa
- Malaria (plasmodium)
- entamoeba histolytica
types of helminths
- nematodes- roundworms
- cestodes- tapeworms
- trematodes- flatworms
nematodes
enterobius vermicularis
- Cause enterobiasis (pinworm)- 1cm, threadlike, found in children
- Cause anal itch, especially at night
- Diagnosis= Press adhesive sellotape against perianal region in the morning
- Ova seen on microscopy
- faecal-oral route of transmission
Ascaris lumbricoides
neamatode
- ingested eggs hatch in the intestine - Ova seen in faeces by microscopy
- largest nematode in humans- adults 15-35 cm
- Often asymptomatic- may cause failure to thrive in children
- Mass of worms may obstruct small intestine or common bile duct
What is the route of transmission for nematodes (roundworms)
fecal-oral
Explain ascaris infection (neamatode) further
- very common globally
- Leads to developmental delay in children
- Severe complications can arise as a result of bowel obstruction
cestodes (tapeworms)
type of helminth
- Long, segmented “tapeworms”
- Larval cysts ingested (intermediate host)-Eating raw or undercooked meat
- Adult tapeworms in human (definitive host)
- Ova in stools on microscopy
- Product of poor sanitisation/hygine
3 types of cestodes
- Taenia saginata (beef)
- Taenia solium (pork)
- Echinococcus
Echinococcus
tapeworm
-Echinococcus sp. - carried by dogs, wolves, foxes
-Humans ingest eggs (dog faeces)
-Eggs hatch and enter circulation
-Hydatid cyst forms in liver- Surgical resection must involve whole cyst
What is a route of transmission for cestodes (tapeworms)
eating raw/undercooked meat
Most common tapeworms
2
Beef and pork
Pork tapeworm cycts
can form outside the gut and cause problems, especially in the brain
trematodes
- also known as “flukes” or “flatworms”
- different species cause human infection in various body sites: blood/lung/liver/pancreas/intestines
- cause schistosomiasis
Schistosomiasis
explain
**Three major species of schistosomes: S. haematobium (bladder), S. mansoni (intestinal), S. japonicum (intestinal)
Cases occur near affected fresh water - snails important in life cycle
How are trematodes (flukes) transmitted
By contact with freshwater where the snail intermediary host is present
Complications of trematode infections (schistomiasis)
Liver failure and bladder cancer if left untreasted
Summarise key points about helminths (worms)
- Heavy burden of disease, especially in resource-poor settings
- Most are transmitted by faecal-oral route but some use an intermediary host/vector
- Include: roundworms, flatworms and tapeworms
Ectoparasites
- parasites which live outside the body
- most are insects or arachnids
- many are vectors of infection
- Include: flea, tick, lice
Definitive diagnosis
identification of parasites in host tissue or faeces/urine, e.g. blood microscopy for parasites- thick and thin blood films for malaria
enteric pathogens
stool microscopy for the following- Ova, cysts and parasites
What are signs of helminth (worm) infection
- Eosinophilia
- Elevated IgE
Indirect testing (for parasites)
- Serology (immune testing)
- Rapid diagnostic tests
Diseases caused by enteric and blood-bourne parasites
- Enteric (e.g. roundworms): giardiasis, amoebiasis, cyclosporiasis, and cryptosporidiosis
- Blood-bourne: African trypanosomiasis, babesiosis, Chagas disease, leishmaniasis, malaria, and toxoplasmosis
