Flashcards in Introduction to parasites Deck (40)
What is a definitive host?
Either habours sexual stage of parasite or adult stage. Majority of human parasitic infections.
What is an intermediate host?
- Harbours the larval or asexual stages of the parasite
- Some parasites require two intermediate hosts in which to complete their life cycle
What is a parantetic host?
Host where the parasite remains viable without further development.
What is a direct lifecycle?
Only one host (definitive).
What is a simple indirect lifecycle?
One definitive host and one intermediate host.
What is a complex indirect lifecycle?
More than one intermediate host.
What is Ascaris?
What is the route of infection for Ascaris?
Faeco-oral - ingestion of eggs from contaminated water.
What kind of lifecycle does Ascaris have?
Direct - Human sheds eggs in faeces
What is the lung phase of Ascaris?
Loefflers syndrome - dry cough, dyspnea, wheeze, haemoptysis, eosinophilic pneumonitis
Larvae migrate from intestines to alveolae where they are then coughed up and swallowed.
What is the intestinal phase of Ascaris?
Migration – into hepatobiliary tree and pancreas
What is the treatment/control of Ascaris?
- Prevents glucose absorption by worm
- Worm starves-detaches-passed PR
- WHO “Action Against Worms”
- Improve sanitation
- Community targeted deworming
What is the intermediate host of Schistosomiasis?
What is the clinical progression of schistosomiasis?
- Swimmers itch
- Katayama fever
- Chronic Schistosomiasis
What is Katamaya fever?
What are the signs/symptoms of chronic schistosomiasis?
- Bladder fibrosis and dysfunction
- Squamous cell CA bladder
- Portal hypertension
How is schistosomiasis diagnosed?
- Terminal Stream Microscopy
- Stool Microscopy
- Rectal Snip Microscopy
What is the treatment of schistosomiasis?
- Praziquantel (parazinoisoquinoline derivative)
40-60 mg/kg with food 3 doses 8-hourly
- Mechanism unknown- increased ionic permeability tetanic contraction, detachment, death
- Well absorbed, extensive 1st pass metabolism, inactive metabolites excreted in urine
Treatment of long term complications
How can schistosomiasis be controlled?
- Chemical treatment to kill snail intermediate hosts
- Avoidance of snail infested waters
- Community targeted treatment, education and improved sanitation
What kind of disease is caused by Echinococcus?
E. multilocularis - alveolar
E. granulosus - cystic
What are the usual hosts of Echinococcus?
Sheep and dogs
Humans are accidental hosts
What kind of lifecycle does Echinococcus have?
Simple indirect. Sheep is definitive host, dog is intermediate.
What are the clinical features of hydatid disease?
- Cysts: 70% liver, 20% lungs
- May remain asymptomatic for years
- Mass effect
- Secondary bacterial infection
- Cyst rupture- hypersensitivity
How may hydatid disease be controlled?
- Regularly worm dogs to reduce egg production
- Hand hygiene
- Safe disposal of animal carcasses/products of conception
What are the four species of malaria and which causes the most infections?
P. falciparum - 70% of infections
Which insect acts as a vector for malaria?
What kind of lifecycle does malaria have?
Simple indirect. Anopheles definitive host, human intermediate host.
What are the clinical features of malaria and what is their cause?
- Fever & Rigors (alt. days with falciparum malaria, every 48hrs or 72hrs with benign malaria)
- Cerebral malaria (confusion, headache, coma)
- Renal failure (black water fever)
- Pulmonary oedema
- Circulatory collapse
- Anaemia, Bleeding and DIC
Red blood cells bursting and releasing parasites.
Cyclical fever result of parasite lifecycle (not usually present in falciparum infection).
How is malaria diagnosed?
- Thick and thin microscopy
- Serology - detection of Ag in blood
- PCR - detection of malarial DNA
How might malaria be controlled?
- Insecticide spraying at homes
- Larvicidal spraying on breeding pools
- Filling in of breeding pools
- Introduction of lavivorous species
What kind of parasite is cryptosporidium?
What mode of spread does cryptosporidium use?
What kind of lifecycle does cryptosporidium have?
Direct - human host
What are the clinical features of cryptosporidium
- Incubation 2-10 days (usually 7 days)
- Watery diarrhoea with mucus (no blood)
- Bloating, cramps, fever, nausea, vomiting
- Usually self-limiting (last up to 2 weeks)
- Can be severe in:
- very young
- very old
- immuno-compromised (60% HIV patients infected go on to chronic infection- can loose up to 25 litres fluid/day)
Which animals may act as a reservoir for cryptosporidium?
Cattle, sheep, goats
What is a vector?
An organism that does not cause disease itself but which spreads infection by conveying pathogens from one host to another.
What is a reservoir?
Any person, animal, plant, soil or substance in which an infectious agent normally lives and multiplies. The reservoir typically harbors the infectious agent without injury to itself and serves as a source from which other individuals can be infected.
What kind of parasite is Acariasis?
What kind of parasite is schistosomiasis?