Parasites

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  • Created by: hadar
  • Created on: 31-01-18 11:44
What is a parasite?
An organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other's expense.
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Define host
An organisms which harbours the parasite
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Define symbiosis
Living together; close, long term interaction between two different species
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Define mutualism
An association in which both species benefit from the interaction
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Define parasitism
An association in which the parasite derives benefit and the host gets nothing in return but always suffers some injury
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Define commensalism
An association in which the parasite only is deriving benefit without causing injury to the host
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What are the classes of host? (3)
1) definitive host 2) intermediate host 3) paramedic host
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Define definitive host
Either harbours the adult stage of the parasite or where the parasite utilizes the sexual method of reproduction In the majority of human parasitic infections, man is the definitive host
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Define intermediate host
Harbours the larval or asexual stages of the parasite Some parasites require two intermediate hosts in which to complete their life cycle
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Define paratenic host
Host where the parasite remains viable without further development
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What is a direct life cycle?
One which has a definitive host- only one gets infected
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What is an indirect lifecycle?
One which has a definitive and intermediate host- not direct infection
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What is a complicit lifecycle?
One which has 2 intermediate hosts- the second becomes infected by eating the first
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Describe ascariasis
macroparasite intestinal nematode (ascaris lumbricoides) acquired by ingestion of eggs
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Describe the life cycle of ascariasis
Direct lifestyle-no intermediate host only definitive host -Fertilized eggs embryonate in the environment-Human comes into contact-swallow-GI tract-larvae intestinal mucosa  into lungs  alveolar wall bronchial tree- swallowed again
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Describe the clinical manifestation of ascariasis
Lung Migration: Loefflers syndrome- dry cough, dyspnoea, wheeze, haemoptysis, eosinophilic pneumonitis Intestinal Phase: Malnutrition Malabsorption Migration – into hepatobiliary tree and pancreas Intestinal obstruction Worm burden
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What is the treatment of ascariasis?
Albendazole Prevents glucose absorption by worm Worm starves-detaches-passed PR
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How do you control ascariasis?
WHO “Action Against Worms” Improve sanitation Education Community targeted deworming
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Describe schistosomiasis
Macro-parasite (Helminth- Platyhelminth- Trematode/Fluke) Also known as Bilharzia disease- Causes chronic disease resulting in bladder cancer and liver cirrhosis Snails as intermediate host
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What is schistosoma cause by? (5)
1)S. haematobium 2)S. mansoni 3)S. intercallatum 4)S. japonicum 5)S. mekongi
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What is the life cycle of schistosomiasis?
Indirect lifecycle-- indirect host is human
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What are the clinical symptoms of schistosomiasis?
Swimmers itch Katayama fever Chronic Schistosomiasis (can persist for years) Effects of eggs in distant sites: spine, lung
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What are the clinical symptoms of urinary S.haematobium?
Haematuria Bladder fibrosis and dysfunction Squamous cell CA bladder
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What are the clinical symptoms of Hepatic/Intestinal (S. mansoni; S. intercallatum, S. japonicum; S. mekongi)?
Portal Hypertension Liver cirrhosis Abdo pain Hepatosplenomegaly
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How do you diagnose schistosomiasis?
Urinary-->Terminal Stream Microscopy Serology Hepatic/Intestinal -->Stool Microscopy Rectal Snip Microscopy Serology
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What types of schistosomiasis are seen diagnostically?
1) S. haematobium in urine. 2)S. mansoni in stool. 3)S. japonicum in stool.
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What is the treatment for schistosomiasis?
Praziquantel 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 urine
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How is schistosomiasis controlled?
Chemical treatment to kill snail intermediate hosts Chemoprophylaxis Avoidance of snail infested waters Community targeted treatment, education and improved sanitation
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Describe hydatid disease
Macro-parasite (Platyhelminth- Cestode-Tapeworm) Human is accidental host caused by echinococcus sp.
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What is the life cycle of hydatid disease?
indirect lifecycle- definitive host= dog
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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 From trauma
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How is hydatid disease diagnosed?
Imaging and Serology
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How is hydatid disease controlled?
Regularly worm dogs to reduce egg production Hand hygiene Safe disposal of animal carcasses/products of conception
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Describe malaria
Micro-parasite (protozoa- sporozoan)
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What are the 4 species of plasmodium?
1)P. falciparum 2) P.vivax 3)P.ovale 4) P.malariae
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What are the clinical features of malaria?
Fever & Rigors (alt. days with falciparum malaria, every 48hrs or 72hrs with benign malaria) Cerebral malaria (confusion, headache, coma) Renal failure (black water fever) Hypoglycaemia Pulmonary oedema Circulatory collapse Anaemia, Bleeding and DIC
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How is malaria diagnosed?
Thick and Thin Microscopy Serology- detection of antigen in blood PCR- detection of malarial DNA
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What is the treatment for malaria? (antimalarial)
Antimalarials Non falciparum malaria: chloroquine + primaquine (prevents relapse) Falciparum malaria Uncomplicated (oral regime): quinine + doxycycline, co-artem (artemether/lumefantrine), atovaquone - proguanil Complicated: IV quinine, artesunate
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What is the treatment for malaria? (supportive)
Supportive therapy Management of seizures, pulmonary oedema, acute renal failure and lactic acidosis Exchange transfusion may be helpful in hyperparasitaemia
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How is malaria controlled?
Insecticide spraying in homes Larvicidal spraying on breeding pools Filling in of breeding pools Larvivorous species introduced in to mosquito breeding areas Use of insecticide impregnated bed nets Chemoprophylaxis
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Describe cryptosporidiosis
Caused by Cryptosporidium parvum and hominis (micro-parasite, sporozoan) Causes diarrhoeal disease Human to human spread with animal reservoir (cattle, sheep, goats) Faecal-oral spread
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What is the life cycle of cryptosporidiosis?
Direct
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What is the clinical manifestation of cryptosporidiosis?
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)
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How is cryptosporidiosis diagnosed?
Feaces sample--> acid fast staining/ antigen detection by EIA
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How is cryptosporidiosis treated in symptomatic?
Rehydration etc. Nitazoxanide
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How is cryptosporidiosis treated in immunocompromised?
Paromomycin (to kill parasite) Nitazoxanide (effectiveness is unclear) Octreotide (reduce cramps and frequency) HIV patients, HAART should be quickly initiated
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How is cryptosporidiosis controlled?
Human-Human: Hand hygiene Filter or boil drinking water Isolate symptomatic patients in healthcare setting Ensure symptomatic children are kept away from school Animal-Human: Pasteurise milk and dairy products Boil/ filter drinking water if camping
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Describe trichomoniasis
Caused by Trichomonas vaginalis Flagellated protozoan Sexually transmitted Incubation 5-28 days
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What are the signs and symptoms of trichomoniasis?
Men = asymptomatic Women = smelly vaginal discharge, dyspareunia, dysuria and lower abdominal discomfort, punctuate haemorrhages on cervix (“strawberry cervix”).
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How id trichomoniasis diagnosed?
Identification of organism in genital specimens
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How id trichomoniasis treated?
Metronidazole single dose of 2g or in divided doses for 7 days Treat partner simultaneously
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How id trichomoniasis prevented?
General advice about prevention of STIs Use of barrier contraceptive methods if sexually activate
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Describe giardiasis
Flagellated protozoan Faecal oral transmission Spectrum of disease: asymptomatic carriage to severe diarrhoea and malabsorption. Can cause chronic disease
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What are the symptoms of giardiasis?
usually last 1-3 weeks Diarrhoea Abdominal pain Bloating Nausea and vomiting
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How is giardiasis diagnosed?
Identification of cysts or trophozoites in faeces
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How is giardiasis treated?
Metronidazole/tinidazole
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How is giardiasis prevented?
No vaccine available Hygiene measures Boling water
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Card 2

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Define host

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An organisms which harbours the parasite

Card 3

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Define symbiosis

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Card 4

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Define mutualism

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Card 5

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Define parasitism

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