Relationships between organisms (symbionts) Flashcards
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Define parasite
an organism living in or on another living organism, obtaining from it part or all of
its organic nutrition, commonly exhibiting some degree of adaptive structural modification and potentially causing some degree of damage to its host
Define commensalism
One (usually smaller) species
benefits, the other is
unharmed
(e.g. remora fish)
Define prevalence
the proportion (%) of a population infected, e.g. 3%,
or the total number in a country or across the world
Define Incidence
The frequency of a population acquiring infection
in a unit of time, eg 3% per week, or 100,000 per annum
Define intensity
measure of the number or density of parasites per
host, e.g. ectoparasites on skin, or % of red blood cells
infected with malaria
Define mortality
the number of deaths in a given time, or
the % of deaths among all cases of infection
Define morbidity
the level of ill-health or disability
among all cases of infection, or among
the general population
Define DALYs
Disability Adjusted Life Years
A measure of overall disease burden.
Number of healthy years lost to disease,
disability or early death
What is an example of a helminth?
multicellular, Nematoda - living in intestine
What is an example of an ectoparasite?
Fleas & lice (insects), ticks (Arachnids)
What is an example of a parasitic protozoa?
Amoebic dysentery
What is polyparasitism?
When an animal hosts multiple parasites
What parasite can a dog transmit to a human?
Toxocara canis (Helminth)
Predominantly intestinal roundworm, infection by ingesting eggs from soil. Visceral larva invades liver and Ocular larva enters eye.
What parasite can a cat transmit to a human?
toxoplasma gondii (protozoan)
What parasite can a sheep / dog transmit to a human?
Echinococcus granulosus (Helminth)
What is an ectoparasite?
A parasite that lives on the outside of its host
What is an endoparasite?
A parasite that lives in the inside of its hosts
What is the life cycle of Toxocara canis?
-Eggs hatch in stomach
-Larvae migrate to lungs, liver, brain (small intestine in dogs)
-Adult females release eggs in faeces
Toxocara canis larvae can be reawakened in adult female dogs.. explain
Larvae remain arrested in tissues and reawaken during pregnancy.
Cross placenta and infect pups before birth
Also infects milk
Treated by regular anthelmintic
What is the life cycle of Echinococcus granulosus?
-(Definitive host) Adult tapeworm in small intestine releases eggs in faeces
-(Intermediate Host) Parasites encyst in tissues
-the larvae matures: Embryonated egg in faeces -> Oncosphere (embryo with hooks) hatches; penetrates intestinal wall -> Hydatid cyst in various organs
Humans can be the accidental host in which case the worm matures in brain, lung or liver. Wormers are used on dogs as there is no cure.. surgery may be necessary.
What is the life cycle of Toxoplasma gondii?
Cats are the definitive host. Toxoplasma is shed up to 2 weeks after infection by cat. Oocysts infect intermediate host of mice and then are consumed by cats. Can infect farm animals instead which are then consumed by humans.
How does toxoplasma gondii multiply?
Oocysts develop into tachyzoites to spread infection in the host.
1) Tachyzoites attach and invade, Broad cell Specificity (meaning it can infect many targets)
2) Parasitophorous Vacuole (a vacuole produced by the parasite in the host cells in which it resides and develops) - avoids fusion with lysosomes
3) Rapid multiplication - 16 daughters
What does the infection of Toxoplasma gondii look like in humans?
Oocysts are orally ingested (infections from cat litter, unwashed food or raw meat), Tachyzoites causing rapid infection, can turn into bradyzoites (dormant tissue cysts) which persist in the body, can then re-activate into tachyzoites. Tachyzoites can be passed to a foetus’ brain through congenital toxoplasmosis causing many impairments to the child.
What is a pathological consequence of a toxoplasma infection in a mouse?
Causes a cyst in the brain which changes behaviour, mice lose aversion to cats
What is the life cycle of head lice?
Nits (the eggs) take 7-10 days to hatch into nymphs. It takes 10 days for these to mature into adults which then lay 50-150 eggs.
Name the 4 species of fleas important to humans
Human flea: Pulex irritans
Cat flea: Ctenocephalides felis
dog flea: Ctenocephalides canis
The oriental/tropical rat flea: Xenopsylla cheopis
What bacterial disease is spread by the Xenopsylla cheopis?
Yersinia pestis (Black Death)
Gram -ve bacteria
Discuss Lyme disease transmitted by Ixodes ricinus ticks
Erythema, bull’s eye inflammation causing joint pains, general feeling of unwellness and muscle aches
Can cause chronic arthritis, neuropathy and fatigue.
Fully treatable with early antibiotic treatment
What is the life cycle of ticks?
Eggs are produced and hatch in spring, larva feed on birds and small mammals until next spring when they mature into nymphs and feed on bigger mammals (including humans), finally meeting full maturation in autumn.
