Parasites Flashcards
Parasitic organisms characteristics (2)
live on or in a host, and derive benefits or nutrients at expense of host
acquired from bites, contaminated water, contaminated environment, contaminated food
Main types of parasites (2)
1) Exoparasite
2) Endoparasite
Exoparasite
lives ON the host
causes an infestation
Examples of exoparasites (many)
scabies
public life (“crab” lice)
head lice
body louse
Endoparasite
lives IN the host
causes an infection
Global burden of parasitic diseases
incredibly high
morbidity and mortality
inadequate treatment
top death: malaria
Parasitic life cycles (2)
1) Direct
2) Indirect
Direct lifecycle
lifecycle completed in ONE host
self-limiting
eggs only viable for a short time in the environment
easier to treat
e.g. lice
Indirect lifecycle
lifecycle completed in MORE than one host
more difficult to treat
e.g. malaria, lyme disease, Toxoplasma gondii
Lyme disease lifecycle
typically a 3-host lifecycle
1st host: mouse/small rodent
2nd host: usually a rodent or rabbit
3rd host: human, dog, deer
Toxoplasma gondii lifecycle
causes the disease toxoplasmosis
humans and other mammals are DEAD END HOSTS (doesn’t get transmitted onwards)
starts out in mouse
-changes brain chemistry of mouse so that it loses fear of cats
cat: shed toxo eggs in their poop (80-90% affected)
most cat owners are infected
transmitted to humans through meat, food or water contaminated with cat feces or cat litter
not infected and then get PRIMARY infection with toxo
Main Classifications of Parasites
1) Protozoa
-single cell
2) Helminths
-multi cell
Protozoa (2)
1) Intestinal
2) Blood/tissue
T or F: All intestinal protozoa have a direct lifecycle
TRUE
Intestinal protozoa typical routes of transmission
Indirect:
-contaminated water
-food
-soil
Direct:
-zoonosis
Virulences factors produced by intestinal protozoa (2)
1) production of toxins (watery diarrhea)
2) ability to invade the GI epithelia (bloody diarrhea)
Intestinal protozoa (5)
1) Giardia lamblia
2) Entamoeba histolytica
3) Cyclospora cayetanensis
4) Dientamoeba fragilis
5) Cryptosporidium parvum
Most clinically significant intestinal protozoa
Giardia lamblia
Giardia lamblia
“Beaver Fever” - beavers are the natural hosts
associated
with contaminated H20
“rice water” stool, significant diarrhea
significant dehydration - cause of mortality in lower income countries
Entamoeba histolytica
major pathogen
associated with
poor sanitation
Cyclospora cayetanensis
Contaminated water and produce exposed to contaminated water
including raspberries, lettuce, fresh fruit and vegetables
Dientamoeba fragilis
ubiquitous and
found in children
worldwide
transmitted person
to person
Cryptosporidium parvum
major outbreaks
carried in cattle and other zoonosis
can transmit human to human or from cattle
Blood/tissue protozoa (3)
1) Trichomonas vaginalis
2) Plasmodium spp.
3) Toxoplasma gondii
Trichomonas vaginalis
common STI
increases risk of other STIs
most common complaint: vaginal discharge
other:
-urinary frequency
-dysuria
-cystitis
diagnosis: wet-prep and antigen detection
-doesn’t stain
-have to look for motion and stops moving 1 hour after collection
difficult to diagnose, no PCR yet
Plasmodium spp.
agents that lead to malaria
transmission via anopheles mosquitoes (vector)
indirect lifecycle
bite dusk to dawn so mosquito nets and other control measures work quite well
high pathogenicity
Species of Plasmodium (5)
1) Plasmodium faliciparum
2) Plasmodium malariae
3) Plasmodium knowlesi
4) Plasmodium vivax
5) Plasmodium ovale
Which species of Plasmodium is a medical emergency?
Plasmodium faliciparum
synchronize their replication/blowing up
symptoms can be timed
infect RBC and blow them up
blood count drops, oxygen drops - how they kill you, high pathogenicity
Countries/areas of the world where malaria is most common
South East Asia
-India, Malaysia, Laos, Cambodia
Africa
Plasmodium spp. lifecycle
indirect
mosquito bites human
saliva with sporozoites injected into human
blow RBCs up
sexually mature in the mosquito, asexual state in human RBCs
can stay dormant in liver and reactivate
Laboratory Diagnosis of Malaria (3)
1) Protein Detection
-PCR*
-Malaria +/-
-Faliciparum +/-
-won’t tell you species
2) Microscopy
-put on slide and look for parasites
3) Molecular detection
Toxoplasma gondii
complex life cycle with multiple hosts and environmental maturation
asymptomatic infections in immune-competent hosts
serious clinical manifestations if acute infection during pregnancy (infects the baby in utero and lead to significant morbidity to the baby including deafness, microcephaly, meningitis, encephalitis, hydrocephalus, retinitis and even death, development issues, premature abortions)
also bad if older, immunocompromised
goes into muscle tissue and brain - if you take steroids for something, can reactivate and cause issues
Helminths (3)
1) Cestodes (tapeworms)
2) Nematodes (round worms)
3) Trematodes (flukes)
Parasites are common where ________________________
human waste is accessible by intermediate animal hosts
Cestodes (3)
1) Diphyllobothrium latum
2) Tinea solium
3) Tinea saginata
Diphyllobothrium latum
mostly in fresh water fish
grows up to 40 feet in gut
fish sold in Ontario for consumption has to be FLASH FROZEN to kills eggs of parasite
complex life cycles with multiple hosts
crustaceans, fish and humans
Tinea solium
pork
multiple hosts
eggs in feces are ingested by humans they can migrate to different tissues including the eye, brain (Neurocysticercosis), muscle and bones
why you need to cook your meat
-why some cultures don’t eat pork we think
Tinea saginata
does not develop tissue phase disease
taeniasis
disease caused by:
tinea solium
-contaminated meat
tinea saginata
-contaminated meat or cattle fecal matter
Nematodes (3)
1) Ascaris lumbricoides
2) Enterobius vermacularis
3) Strongyloides stercoralaris
Ascaris lumbricoides
contaminated food / water
ingestion of eggs
one of the largest roundworms
lifecycle: goes into gut, goes into lungs and tries to go back into gut when you swallow
eggs have to mature in the environment for several days
life of the worm is between 10 months and 2 years
Enterobius vermacularis
pin worm
most common worm infection in North America*
the butt one
transmission from person to person via contaminated surfaces
often in day care centres, primary schools
leads to intense anal itching and often is passed on person to person via faecal matter (after they itch their bum)
hangs out on anal verge
-females inside of anus
-at night, travel out in the perianal area and lay eggs there
-causes itching
How to get sample for Enterobius vermacularis
“Scotch tape method”
have to get a sample early morning, get tape, go into anus, put on slide
Strongyloides stercoralaris
contact with the environment
free larval forms found in contaminated soil (can get from walking on beach)
can also get from feces
worms that are able to burrow in skin
simple cycle with only ONE host
symptoms: dermatitis, swelling, itching, larva currens
immunocompromised individuals - can develop a hyper-infective syndrome - associated with 90% mortality
What is unique about Strongyloides stercoralaris?
auto-infection
has ability to continually infect you for over 30 years
can stay dormant
most other parasites have a lifecycle and then die
Trematodes (2)
Flukes
1) Shistosoma species (blood flukes)
2) Clonorchis sinensis (chinese liver fluke)
Shistosoma species
blood flukes
risk factor: swimming in contaminated water
found in tropical to semi tropical waters
primary host: snails
burrows into skin of humans
swimmer’s itch, UTIs
complex life cycle with > 1 host
includes an environmental stage with an intermediate host
Clonorchis sinensis
chinese liver fluke
includes an environmental stage with an intermediate host
found in tropical to semi tropical waters
result of ingestion of contaminated or infected fish (sushi!)
cause liver absences and infection
Lab detection of intestinal parasites
STOOL SPECIMEN
in preservatives to maintain the parasite structure
put on slide and look at eggs
Lab detection of blood/tissue parasites
antibody detection and biopsy
PCR - more sensitive, quicker to diagnose
