Parasites Flashcards
Main groups of parasites
- Protozoa
- Helminths (worms)
- Arthropods (lice, ticks mites)
Protozoa
- Microscopic, one celled organisms
- Free-living or parasitic in nature
- Able to multiply in humans
- Transmission: faecal-oral route, live in intestine. Arthropod vector, live in the blood or tissue of humans
- Malaria, amoebae, flagellates
Helminths
- Nematodes, roundworms
- Cestodes, tapeworms
- Trematodes, flukes, flatworms
Malaria, species and vector
- Protozoa
- Plasmodium spp.
- Vector: Anopheles mosquito
Life cycle of malaria
- Complex
- Sporozites injected under skin by mosquito
- Travel through blood and enter liver
- Mature in liver and re-enter circulation as merozoites
- Invade red cells, multiply and lyse cells
- Sexual forms taken up by mosquito
Diagnosis, symptoms and treatment of malaria
Diagnosis: Giemsa stained blood films show infected red cells. Little rings in cells
Symptoms: Pyrexia, rigors, flu-like illness, anaemia and haemolysis
Treatment: Insecticide mosquito nets, prophylaxis
Amoebic dysentery species
- Protozoa
- Entamoeba histolytica
Life cycle of amoebic dysentery
- Trophozoite ingests red cells by throwing out pseudopodia - hot stool
- Cyst of E.histolyica: 2 nuclei and chromatoid body, typically found in formed stool
Symptoms and clinical findings of amoebic dysentery
Diarrhorea with blood/pus
Clinical findings: intestinal and extra-intestinal infections, liver abscess in late disease
Leishmaniasis species and vector
- Protozoa
- Leishmania spp.
- Vector: infection by bite from sandflies
Diagnosis and clinical findings of leishmaniasis
- Histology of biopsy material
- Clinical findings: Cutaneous or muco-cutaneous leishmaniasis, skin or mucosal ulceration
Visceral Leishmaniasis: fever, weight loss and hepato-splenomegaly
Enterobiases species and route
Helminth, roundworm
Enterobius vermicularis
Faecal-oral route
Enterobiases life cycle
Pinworms travel down to the anus at night and lay eggs
1cm, threadlike found in children
Diagnosis of enterbiases
Press adhesive tape against perianal region in the morning and ova can be seen on microscopy
Nematodes species
- Helminths
- Ascaris lumbricoides
Life cycle of nematodes
- Ingested eggs hatch in the intestine
- Larvae carries by circulation to lungs, swallowed again
- Adult worms develop in and inhabit small intestine
- Ova seen in faeces by microscopy
Have characteristic thick shell
Symptoms of nematodes
- Often asymptomatic, can get transient pulmonary symptoms
- Mass of worms may obstruct small intestine or common bile duct
Tapeworms - cestodes, species
- Flatworm
- Taenia sagniata (beef) and Taenia solium (pork)
Life cycle of cestodes
- Larvae doesn’t mature to adult form in beef or pork, needs a host
- Larval cysts are in intermediate host, meat
- Definitive host of adult tapeworm is human
- If T.solium eggs are direct consumed, you can get cystericercosis and wreck brain
Diagnosis of cestodes
Ova in stools on microscopy
Echinococcus tapeworms species, route and vector
Flatworm
Echinococcus sp.
Vector: carried by dogs, wolves and foxes
Faecal-oral route, humans ingest eggs from dog faeces
Life cycle of echinococcus
Ingest eggs
Eggs hatch and enter circulation
Hydatid cyst forms in liver
Treatment of Hydatid cyst
Need to resect whole cyst in liver otherwise you can release the fluid inside and cause anaphylaxis
Schistosomiasis species
Flukes, trematodes
S. haematobium (bladder) - haematouria, bladder ca.
S. mansoni (intestinal)
S. japonicum (intestinal) - most severe
Life cycle of Schistosomiasis
- Swimming in freshwater
- Eggs excreted in urine or faeces
- Miracidia released in fresh water
- Intermediate host, snail
- Cercaria emerge from snails
- Migrates through lungs to liver
- Mature in liver into worms (schistosomes), migrate to mesenteric or bladder venules
- Lay eggs that cause inflammation in bladder or intestinal wall
- Acute febrile episode 4-8 weeks later
Helminth infection is often accompanied by
Eosinophilia and elevated IgE
Diagnosis of parasitic infection
- Microscopy: identification of parasites in host tissue or excreta. Observing P, C and O in faeces
- Culture rarely possible
- Blood films for malaria: thick and thin films looking for ring of plasmodium
- Serology: detection of antibodies, if the parasite is located in deep tissue sites
