Parasites Flashcards
Define a parasite
AN organism which lives on or in another organism and benefits by deriving nutrients at the others expense
what are the 3 major classes of parasites
- Protozoa
- Worms
- Ectoparasites
how are protozoa transmitted?
Oral-faecal route e.g contaminated food, water or person contact
what are 4 classes of protozoa
amoeba - move by pseudopods
Flagellates - move by flagella
Ciliates- move by cilia
Sporozoa
name types of amoeba
- Entamoeba histolytica - carried asymptomatically to digestive tract (contaminated water with faeces that contain cysts), multiply in large intestine
- Naegleria Fowleri - causes amoebic meningoenephalitis (brain haemorrhage and necrosis)
what are the 3 types of amebiasis that can result? (entemoeba histolytic)
luminal amebiasis - least severe, asymptomatic
Invasive amebic dysentry - common, blood and mucus in stools
Invasive extra intestinal amebiasis - carried via bloodstream, most severe
give 3 types of flagellates
1- trichomonas vaginalis - causes trichomoniasis (STI)
- Giardia Lamblia - causes intestinal malabsorption - travellers diarrhoea - giardiasis.
- Trypanosoma - causes African sleeping sickness - transmitted via humans by the tsetse fly
What flagellates disease does not spread via blood?
Giardia lamblia
name a ciliates infection
Blantanidium coli - contaminated food and water. Usually asymptomatic in healthy humans but can be symptoms In poor health e.g diarrhoea, weight loss.
Name a sporozoa infection (plasmodium)
How is it spread?
Plasmodium malaria - cause malaria (colonise in blood of the human)
Spread via the female anopheles moaquitos.
Symptoms appear 7-18 days after infection but sometimes don’t appear for years.
what is the most common & severe parasitic disease?
plasmodium malaria (sporozoa)
what are the 2 phases of infection of p.malariae?
- Exoerythrocytic phase (liver) - after transmission, it migrates to liver and proliferates asymptomatically for 8-30days, then escapes to blood to infect RBC
- Erythrocytic phase (blood) - multiplies periodically breaking out of cells and infecting more RBC
how are heterozygous carriers of sickle cel anaemia partially protected from malaria?
- Body sends the sickled cells to the spleen for elimination and thus destroys parasite as it lives in the roc
- The membrane of sickled cells is stretched due to shape and thus becomes porous. It leaks out nutrients e.g K+ that the parasite needs to survive, thus the parasite dies.
what are worms (helminths)?
multicellular parasites that can be free living or parasitic. In their adult form they cannot multiply in humans.
what are the 3 main helminths (worms)?
- flatworms
- thorny head worms - adult form in GI
- roundworms - adult form in GI, blood, lymph, subcutaneous tissues
what are life stages of worms?
Egg, larva, adult
- Infective stage = egg or larva
- Definitive host - harbours adult stage
give 2 types of flatworms
- Taenia solium - pork tapeworm. Usually asymptomatic, but the larval stage infects the human nervous system - neurocysticerocosis.
- Schistomes - snail fever (schistomiasis) - urinary tract & intestine
name a thorny head worms
M.moniliformis. Usually asymptomatic
name round worms (nematodes)
ascaris lumbricoids - asymptomatic. BUT heavy infections can cause intestinal blockage and impair child growth.
what are ectoparasites?
Ticks, fleas, lice, mites that attach or burrow into skin and remain there for a long time (weeks/months)
what are arthropods?
insects, arachnoids - cause disease but also more important as vectors/transmitters for pathogens
what is included in insecta class?
lice, fleas, mosquitos
what is included in arachnida class?
Mites & ticks - vectors
what are ticks?
Vectors for bacterial, viral and protozoan disease. They are second to mosquitos in the number of diseases they transmit e.g Lyme disease, Rocky Mountain spotted fever, tulaermia, relapsing fever.
