Parasitology Flashcards
Where are Protozoa found?
Digestive system
Blood
Water
Soil
What is a Protozoa?
Eukaryotic, essentially single called animals
What are the limitations to where parasitic protozoans can live?
Need a vector or host
Don’t necessarily need a host but parasitic is adapted to host
Example of a flagellate (mastigophora)
Giardia duodenalis
Example of amoeba (sarcodina)
Entamoeba histolitica
Example of ciliate (ciliophora)
Paramecium spp.
Example of sporozoan (apicomplexa)
Plasmodium spp.
Appearance of giardia duodenalis cyst
Nuclei
Remains of flagella
7 micro meters
(Trophozoite)
Appearance of entamoeba histolytica cyst
1-4 nuclei
Faecal smear with iodine stain
12 micro meters
Faecal debris around it
Appearance of paramecium
Elongated
Cilia
Appearance of plasmodium falciparum
Trophozoites in blood slides stained with giemsa stain
Pink nucleus, blue cytoplasm
RBC infected
Faecal oral transmission
Which parasitic Protozoa are transmitted through this route?
E. Histolytica
C. Parvum
I. Belli
G. Duodenalis
How many species of giardia are there?
6- but a different number of strains in each species
Found in cattle, sheep, beavers, guinea pigs, chinchillas and other mammals
Also present in humans
Each species have a restricted host range, duodenalis is only found in humans
What does recent work with giardia reveal?
There may be movement of parasite strains between different animal hosts (e.g. G.duodenalis in other animals)
What is the life cycle of giardia?
Cyst in ingested in contaminated food or water
Travels through alimentary canal yo small intestine - here they open out (excyst) into the flagellate form
In small intestine - it attaches to gut wall using suction
Absorb nutrients from host gut contents
Start to multiply and detach from gut wall to move around inside the intestine
Patient has very loose bowel movements, greyish fatty faeces
As flagellates pass through the large intestine it closes up into the resistant cyst form- passed in the faeces and can persist in water or on food for several weeks
Faeces may contain flagellates that do not survive long outside body or infect another host
What does the faeces of a patient having giardia duodenalis have?
Greyish, H2S smell
What does the flagellate form of giardia look like
Nuclei
Flagella for movement in intestine
Sucking disk
Approx 10 micro meters
What are duodenalis cysts resistant to?
Storage at 4-6 degrees Celsius and chlorine
What are the 3 types of laboratory identification for duodenalis?
Concentration method (formal ether) Wet preparation (iodine) Fixed faecal smear (trichrome stain)
Give 5 examples of parasitic Protozoa transmitted in blood (usually via invertebrate vector)
T.brucei T. Cruzi Babesia spp. Theileria spp. Plasmodium spp.
How many species of plasmodium are there?
120 species
Found in mammals (humans, primates, bats) birds and reptiles
What 5 species of plasmodium spp. Cause disease in humans?
Falciparum Vivas Malariae Ovale Knowlsei
Statistics for malaria
200-300 million people every year
2012- 207 mil cases 627 000 deaths
Most cases 90% Africa
Mostly children under 5 years die
Transmission of malaria
Insect vectors- Mosquitos, sandlfies, biting midges
Plasmodium spp. Which Infects humans and are all transmitted by mosquitoes of Anopheles species (malaria)
422 anopheles species, 70 are known malaria vectors
Why can’t all anopheles spp. Transmit malaria?
The parasite might not develop inside the mosquito
It’s behaviour, biting preferences etc. Preclude the mosquito becoming infected
Characteristic of malaria vector?
It is female anopheles
7 mm
Take blood meal only 3 times in life
Proboscis- it injects anticoagulant into the blood to suck blood more effectively
Explain the lifecycle of plasmodium spp.
Infection is transmitted through bite by anopheles
Mosquito carries sporozoites in saliva so injected she insect takes a blood meal
The sporozoites enter the blood stream and quickly migrate to the liver where they use surface proteins to attach to hepatocytes (CSP)
They multiply exponentially to produce many schizonts (collection of merozoites- nucleus surrounded by cytoplasm)
Eventually hepatocyte bursts releasing the merozoites into the blood stream
P.vivax and P. Malariae - some sporozoites take a dormant form in the liver and reactivate months or a year later
Has specific surface proteins (MSPs) which allow attachment to glycoproteins on RBC membrane
Each merozoites develops into the ring form Trophozoite
Inside the RBC plasmodium grows
As it is a eukaryote it produces its own proteins
Parasite proteins expressed on the surface of RBC called knobs
The trophozoites feed on Hb grow and divide to form schizonts which contain more merozoites
The break down product of this metabolism is called - haeomozoin (malaria pigment)
Burst out of the RBC and infects new RBC
The plasmodium parasites hide in the liver cells and RBC so immune system won’t detect
Infect RBC move around systemic circulation
Can get stuck in small blood vessels due to knobs e.g. In the brain
Reduction of nutrients in host blood (maybe) - Trophozoites develop into gametocytes instead of more merozoites
Gametocytes is taken up when host is bitten (take up male and female gamete- continue cycle)
The gametes fuse in mosquito gut to form zygote - ookinete - invade mosquito gut wall where it forms oocyte
Grows - form sporozoites
Oocyte bursts - sporozoites released into Mosquitos body and enter salivary gland
What is the basis of the RTS S vaccine for malaria
Circumsporozoite protein
Why the the malaria parasite not killed by the immune system?
At different life cycle stages the parasite expresses different cell surface antigens
By the time the host had made a suitable antibody the parasite has moved on to the next stage
One parasite can produce vast numbers of progeny so immune system cannot respond adequately
Where does the asexual and sexual reproduction stages of plasmodium spp. Occur?
Asexual- human host
Sexual- mosquito host
Laboratory identification of plasmodium
Blood giemsa stain
Thick - release parasites
Think - stay in the cell, can find out what species it is
What does MSP protein do in merozoites?
Merozoites surface proteins enable attachment of glycoproteins on red blood cell membrane
What are helminths?
Worms Large compared to Protozoa and prokaryotes Relatively complex Life cycle - changes in morphology Sexual reproduction - production of eggs
Where are helminths found?
GI tract muscle of secondary host, soil, water, skin, eyes
What are the limitations on where parasitic helminths can live?
Ph, temperature (they have enzymes), need a host as part of life cycle
What are the classification of helminths?
Roundworms - Ancylostoma duodenalis, Necator americanus (Nematoda)
Tapeworms - beef tapeworm - Taenia saginata (Cestoda)
Flukes - liver fluke (fasciola hepatica) - common infection in sheep (Trematoda)
What is the old world and new world hookworm?
Ancylostoma duodenale ‘Old World’ hookworm, Although now found throughout the world including N and S America and Caribbean
Necator americanus ‘New World ‘ hookworm, Accounts for 95% hookworm infections in US, but also found in Africa and South East Asia
How is hook worm acquired?
Infection acquired when larval worm in contaminated soil burrows through skin (usually base of foot)
Eventually leads to severe and chronic anaemia
Life cycle of hook worm
Infective larvae found in contaminated soil
Penetrate host’s skin , enter small blood vessels and thus main circulation
Larvae travel to the heart, through the cardiac blood supply to the lungs
Coughed up and swallowed
Enter intestinal tract and migrate to small intestine
In small intestine, grow in size and develop into mature adult worms
Adult female worms up to 15mm long and males about 10mm
Attach to gut wall using their sharp ‘teeth’ and suck membrane and blood from the host’s blood vessels
Produces an anticoagulant to reduce clotting of host’s blood
At least half of the blood taken in passes through the worm’s digestive tract but is not metabolised and passes out again undigested
So worm has to continually feed and continually migrate to fresh sites on the host’s intestinal wall
Adult worms can live for 10 years inside their hosts if undetected
Cause severe anaemia, due to the blood ingested by the worm and bleeding at ‘old’ sucking sites
Usually each host is infected with more than one worm
If male and female present, they mate
Female produces fertile eggs, each containing a ‘rhabditiform’ larva
Eggs fall into intestine and thus are excreted with faeces
As long as egg reaches, damp warm soil surface, it starts to hatch
Goes through an series of developmental stages to form a filariform larva
Process takes 7-10 days
Filariform larva wait for suitable host to arrive
Can survive for several months, but often die after a few weeks from dessication and exposure to sunlight
What does a hookworm egg in faeces look like?
Thin outer shell, larval worm
Treatment for hookworm
Easily preventable disease
Wear shoes!
Can treat with anthelminthic drugs (mebendazole, albendazole) , iron tablets etc
Not everybody has same ‘worm burden’, but if re-infected, tend to acquire a similar number of adult worms
Plenty of studies have shown this, but not really explained why!
Laboratory identification of helminth
Concentration method ( e.g. formol-ether) Wet preparation- no stain needed
