Introduction to Parasites Flashcards
What is a parasite?
An organism that lives in another and gets its food at the expense of the host
What parasitic disease causes the most deaths globally?
Malaria
What are the 3 classification of parasites?
- Protozoa
- Helminths
- Arthropods
What are protozoa?
- Microscopic, unicellular organisms
- Can be free-living or parasitic in nature
How are protozoa transmitted?
- Protozoa that live in human’s intestines= fecal-oral route
- Protozoa that live in blood/tissue=arthropod route
What kind of infection is malaria?
Protozoan
Describe malaria.
- Mosquito-borne disease caused by a parasite
- Patient often experiences fever, chills and flu like symptoms
- Left untreated they may develop sever complications and die
What is the name of the parasite involved in malaria?
Plasmodium spp
P. falciparum has the highest mortality rate
How is malaria diagnosed/
-Giesma stained blood fil shows infected red cells
-Thick and thin blood films
Variety of rapid diagnostic testing
Describe the life cycle of plasmodium spp.
- Sporozoites are injected under the skin
- They travel through th blood and enter the liver
- They mature in the liver and re-enter circulation as merozoites
- They invade RBC, multiply and lyse cells
- Sexual form is then taken up by mosquito
How can the spread of malaria be controlled?
- Insecticide treated mosquito nets
- Prophylaxis
- Malaria vaccine currently being researched
What kind of infection is amoebic dysentery?
Protozoal
What causes amoebic dysentery?
Entamoeba histolytica
What are the clinical signs of amoebic dysentery?
- Diarrhoea with blood/pus
- Intestinal and extra intestinal infections
- Liver abscess in late disease
What would be found on microscopy of amoebic dysentery?
Cysts in formed stool
What do trophozoites do in amoebic dysentery?
Ingest red cells by throwing out pseudopodia
What are nematodes?
Roundworms
What are cestodes?
Tapeworms
What are trematodes?
Flatworms
How is enterobiasis diagnosed?
Nematode
- Press adhesive sellotape against perianal region in the morning
- Ova seen on microscopy
Describe Ascaris lumbricoides.
- Nematode
- Ingested eggs hatch in the intestine
- Larvae carried by circulation to lungs
- Swallowed again
- Adult worms develop in and inhabit small intestine
- Ova seen in faeces by microscopy
What symptoms are usually seen with Ascrais lumbricoides?
- Often asymptomatic
- Transient pulmonary symptoms in Loefler’s syndrome
- Mass of worms may obstruct small intestine or common bile duct
What are 2 examples of cestodes?
- Taenia saginata (beef)
- Taenia solium (pork)
What are the hosts in the Taenia spp?
- Larval cysts ingested in meat (intermediate host)
- Adult tapeworm in human (definitive host)
How is the taenia spp diagnosed?
- Tissue cysts in humans infected with T solium- cysticercosis
- Ova in stools on microscopy
What is Echinococcus sp carried by?
Trematode
Dogs, wolves and foxes
Describe the life cycle of Ecjinococcus.
- Humans ingest eggs (dog faeces)
- Eggs hatch and enter circulation
- Hydatid cysts forms in liver
- Surgical resection must involve whole cyst
What is serology?
Detection of antibodies
What diagnostic principles apply to parasitology?
- Culturing is rarely possible
- Blood films (thick/thin) for malaria
- Serology
- Identification of parasites in host tossue or excreta
- Microscopy ate P,C and O in faeces
What is helminth infection often accompanied by?
- Eosinophilia
- Elevate IgE
What can Schistosoma haematobium cause?
- Haematuria
- Bladder cancer
What are the 3 major species of Schistosomes?
- S. haematobium (bladder)
- S. mansoni (intestinal)
- S. japonicum (intestinal)
Describe infection of schistosomiasis.
-Eggs excreted in urine or faeces
-Miracidia released in fresh water
-Penetrate body of snail (intermediate host)
-Cercaria emerge from snails after 4-6 weeks
Penetrate human skin
-Migrate through lungs to liver
-Mature in liver into worms that migrate to mesenteric or bladder venules
-Lay eggs that cause inflammation in bladder or intestinal wall
Katayma fever- acute febrile episode
What kind of parasite causes schistosomiasis?
Trematode
