1. Parasites Flashcards
What is a parasite?
An organism that lives in/on another organism (HOST) and benefits by deriving nutrients.
-NB. doesn’t necessarily cause disease
What is meant by symbiosis?
A close, long-term interaction between 2 different species.
What is meant by mutualism?
An association in which both species benefit from the interaction.
What is meant by commensalism?
An association where parasite only is deriving benefit without causing injury to the host.
What is meant by parasitism?
An association where the parasite derives benefit and the host gets nothing in return but always suffers some injury.
What are the 3 classes of host?
Definitive
Intermediate
Paratenic
What is a definitive host?
Harbours adult parasite/where parasite carries out sexual reproduction.
-Normally man in human parasitic infections
What is an intermediate host?
Harbours larvae/asexual stages.
-Some parasites have more than one intermediate host
What is a paratenic host?
Where parasite remains viable without further development.
What are the 2 main types of parasite?
PROTOZOA (mirco)
HELMINTHS (macro) - worms
What are the 4 main subdivisions of protozoa?
Flagellates
Amoeboids
Sporozoans
Tryponosomes
What are the 2 main subdivision of helminths?
- Platyhelminths (flatworms)
- Nematodes (round worms)
What are the 2 main subdivisions of platyhelminths (flatworms)?
- Cestodes (tape worms)
- Trematodes (flukes)
What are the 2 main subdivisions of nematodes (round worms)?
- Intestinal nematodes
- Tissue nematodes
Give an example of a cestode.
Taenia sp
Give an example of a trematode.
Schistosoma sp
Give an example of an intestinal nematode.
Ascaris lumbricoides
Give an example of a tissue nematode.
Wuchereria bancrofti
|»_space; elephantitis
Give the 3 types of life cycle of a parasite?
- Direct
- Simple indirect
- Complex indirect
What is a direct life cycle?
Parasites infect a single host (no intermediate hosts).
- eg. bird eats infective eggs»_space; mature»_space; sheds parasitic eggs
What is an indirect life cycle?
Parasite life cycle involves 2 hosts (1 intermediate).
-eg. bird sheds parasitic eggs»_space; slowbug eats them»_space; infective larvae in slowbug»_space; bird eats slowbug
What is a complex indirect life cycle?
Parasite life cycle involves more than 2 hosts.
Name 5 parasites to study in greater depth.
Ascariasis Schistosomiasis Hydatid disease Malaria Cryptosporidiosis
What type of parasite is ascariasis?
Intestinal nematode
Where is ascariasis mainly distributed?
East Asia
What type of life cycle does ascariasis have?
Direct life cycle
ingest eggs»_space; develop in faeces»_space; gut»_space; portal circulation»_space; lungs»_space; swallowed»_space;back into intestine
How is ascariasis spread?
Poor hygiene
-faecal-oral (ingest eggs)
What are the symptoms of ascariasis?
- INTESTINAL (malnutrition, worm burden)
- LUNG MIGRATION (Loefflers syndrome - dry cough, haemoptysis, wheeze)
How is ascariasis treated?
Albendazole (benzimidazole)
-prevents glucose absorption by worm
What type of parasite causes Schistosomiasis (AKA Bilharzia)?
Trematode/fluke
S. mansoni, S. intercallatum, etc.
Where is Schistosomiasis mainly distributed?
Africa
What type of life cycle does Schistosomiasis have?
Indirect life cycle
-snails are intermediate host
What are the symptoms of Schistosomiasis? (3)
- Swimmers itch
- Katayama fever
- Chronic Schistosomiasis
What are the symptoms of S haematobium (type of Schistosomiasis)? (3)
URINARY
- Haematuria
- Bladder fibrosis
- Squamous cell bladder cancer
What are the symptoms of S. mansoni/intercallatum/japonicum/mekongi (types of Schistosomiasis)?
HEPATIC/INTESTINAL
- portal hypertension
- liver cirrhosis
How is Schistosomiasis diagnosed?
URINARY -serology -terminal stream microscopy HEPATIC/INTESTINAL -serology -stool microscopy -rectal snip microscopy
How is Schistosomiasis treated?
Praziquantel (increases ionic permeability tetanic concentration»_space; detachment)
How is Schistosomiasis prevented?
- Chemicals to kills snails
- Chemoprophylaxis
- Avoid infested water
What type of parasite causes hydatid disease?
Platyhelminth-Cestode-Tapeworm
macro-parasite
What causes hydatid disease?
Echinococcus sp.
granulosus = cystic, multilocularis = alveolar
What are the normal host in hydatid disease?
Sheep & dogs
-humans are accidental hosts
What type of life cycle does hydatid disease have?
Indirect
-humans = intermediate hosts
What are the symptoms of hydatid disease?
- Cysts (70% = liver, 20% = lungs)
- 2* bacterial infection
- cyst rupture»_space; hypersensitivity
NB. may remain asymptomatic for years
How is hydatid disease diagnosed?
Imaging
Serology
How is hydatid disease prevented?
- Regularly worm dogs
- Hand hygiene
- Safe disposal of carcasses
What parasite is malaria caused by?
Protozoa-sporozoan
-Plasmodium
(micro-parasite)
What 4 species of Plasmodium cause malaria?
P. falciparum (70%)
P. vivax
P. ovale
P. malariae
What type of life cycle does malaria have?
Indirect
-anopheles(mosquito) = vectors
Where is malaria mainly distributed?
Africa (& Asia/South America)
What are the basic stages of the malaria life cycle?
Mosquito bite
» liver
» blood
» mosquito drinks blood
What is the clinical presentation of malaria?
- ruptured RBCs block capillaries»_space; inflammatory reaction
- fever & rigors
- cerebral (confusion, coma)
- renal failure
- hypoglycaemia
- anaemia
How is malaria diagnosed?
- Thick & thin microscopy
- Serology (detect antigen)
- PCR (detect malarial DNA)
What parasite is Cryptosporidiosis caused by?
Cryptosporidium parvum & hominis
-sporozoan, mirco-parasite
What are the symptoms of Cryptosporidiosis?
- diarrhoea with mucus
- bloating, cramps, nausea, fever
- usually self-limiting (>2 weeks)
How is Cryptosporidiosis spread?
Faecal-oral route
- human-human spread
- human-animal spread
Who are most at risk of Cryptosporidiosis?
HUMAN-HUMAN SPREAD: pool user, healthcare workers, parents, travellers
HUMAN-ANIMAL SPREAD: backpackers, campers, farm workers
How is Cryptosporidiosis diagnosed?
Faeces sample (acid fast staining/antigen detection by EIA)
How is Cryptosporidiosis treated?
SYMPTOMATIC - rehydration, nitazoxanide
How is Cryptosporidiosis treated in immunocompromised patients?
- Paromomycin (kill parasite)
- Nitazoxanide
- Octreotide (reduce cramps)
- HAART (HIV patients)
How is Cryptosporidiosis prevented?
Hand hygiene
Pasteurise dairy products
Boil drinking water
Name 5 commonly used anti-protozoal treatments.
Metronidazole Pentamidine Nitazoxanide Pyrimethamine Anti-malarials
Name 4 commonly used anti-helminthic treatments.
Albendazole
Mebendazole
Ivermectin
Praziquantel
