theme 1:parasitology

what are the three key points for defining a parasite? (where its found, what it takes, what it gives?)

-lives in/on a host, -relies on host and derives nutrients, -gives nothing in return and can harm host

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what is a host?

organism that harbours the parasite

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what classes of host harbours the adult stage parasite/where it does sexual reproduction and which class harbours the larval form/asexual stage?

-definitive, -intermediate (can have multiple intermediate hosts)

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what class of host harbours a parasite that doesnt need further development but is still viable?

-paratenic

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what is a reservoir host?

-a species infected by a parasite that acts a source of infection for other species

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whats the term for a close long term association between two different species (ie a host and a parsite)

symbiosis

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define the different forms of symbiosis: mutualism, commensalism, parasitism

-mutualism=both species benefit, -commensalism=parasite benefits, host no effect, -parasitism= parasite benefits, host harmed

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what are the 3 groups of parasites?

-protozoa, helminths, arthropods

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what are protozoa? and give the 4 subgroups and e.g.s and what diseases they cause

-micro-parasites, single celled (free living/parasitic), -flagellates (giardia lamblia=giardiasis, trichomonas vaginalis=trichomoniasis), amoeboids (entamoeba,acanthamoeba), sporozoans (plasmodium, cryptosporidium, toxoplasma), trypanosomes

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what are helminths?

-multicellular parasite

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which out of protozoa and helminths can replicate in humans?

-protozoa, helminths cant

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whats the 2 subgroups and there subgroups?

1)platyhelminths (flatworms)-cestodes,trematodes 2)nematodes (roundworms)-intestinal and tissue

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what are arthropods mainly?

ectoparasites-blood sucking/burrow into skin, transmit infection

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what are the 4 subgroups of ectoparasites?

-insects (mosquitos e.g.aedes, anopheles, culcinae), lice (pthiris pubis, pediculus humaus capitus), mites (scabies, chigger mite), arachnids (ticks)

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what do you need to know about parasites?

-distribution (where found), life cycles (how they survive), clinical manifestations (symptoms), diagnosis, treatment, control (preventative)

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outline a direct life cycle?

-1 host, infected and sheds eggs in poo, eggs mature (in environment) and are infective, then eaten by host again

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outline an indirect simple cycle?

-multiple hosts (only one directly consuming parasite), -1 intermediate host eats parasite eggs (mature), this host eaten by other host so is infected, sheds egg in poo

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outline an indirect complex cycle?

-multiple intermediate hosts and paratenic host, --> 1 hosts eats eggs (some development), eaten by another intermediate host (some more development), eaten by paratenic host (no more development), eaten by definitive host who poops out eggs

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what type of parasite causes ascariasis?

-macroparasite, intestinal nematode

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how many/who does ascariasis affect?

-1 billion worldwide, 3-8 year olds most affected

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whats the distribution/what kind of area would ascariasis be found and how is it acquired?

-tropical/poor hygiene areas, -contaminated h2o/veg has eggs, eggs ingested (1 worm=200000 eggs a day), faeco-oral route

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whats the type of life cycle of ascariasis?

-direct as 1 host (human), develop in them, human only source of infection

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what are the two clinical states of ascariasis?

-intestinal phase, -lung migration

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what symptoms in intestinal phase of ascariasis?

-malnutrition, malabsorption, migration into hepatobiliary tree and pancreas, worm burden, intestinal obstruction

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what symptoms in lung migration of ascariasis?

-get loefflers syndrome=dry cough, dyspnoea, wheeze, haemoptysis, eosinophilic pneumonitis (eosinophils accumulate in lung)

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what are the 2 ways of diagnosing ascariasis?

1)stool sample=eggs/larvae (worm in intestine), 2)blood count=raised eosinophil as of loefflers syndrome

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how to treat ascariasis?

albendazole= 1)stops worm from absorbing glucose, 2)starved, detaches, passed PR

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WHO 'action against worms' is for control of ascariasis, what does this involve?

-improving sanitation, education, targeted community deworming

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what type of parasite causes schistosomiasis? give egs of species that causes it

-macro-parasite, platyhelminth- trematode/fluke, -schistosoma.haematobium, s.mansoni, s.intercallatum, s.japonicum, s.mekongi

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whats the distribution of schistosomiasis, how many affected?

-africa, 200 million affected, called bilharzia in africa

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describe the life cycle of schistosomiasis

-snail=intermediate host become infected from poo/wee in water, human= infected by skin penetration, to liver, to bladder

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how many days is the initial incubation period of schistosomiasis?

14-84 days

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is schistosomiasis asymptomatic or symptomatic?

can be both

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what syndrome (and what symptoms does this include) accompanies acute schistosomiasis ?name the other symptoms

katayama syndrome (rash, fever, headache, myalgia, resp symptoms, eosinophilia, hepato/spenomegaly), swimmers itch

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can eggs of schistosomiasis travel?

oui, to distant sites -lungs/spine

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what can chronic schistosomiasis lead to?

bladder cancer, liver cirrhosis

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different species of schistosomiasis affect different areas, what two areas?

urinary and hepatic/intestinal

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what species causes urinary symptoms and what symptoms does this include?

s.haematobium, squamous cell CA bladder, haematuria, bladder fibrosis and dysfunction

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what species causes hepatic/intestinal symptoms and what symptoms does this include

all other species, s.mansoni, s.intercallatum, s.japonicum, s.mekongi, portal hyptertension, cirrhosis, abdo pain, hepatosplenomegaly

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To diagnose urinary schistosomiasis-> look for s.haematobium, how?

-terminal stream microscopy, serology

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To diagnose hepatic/intestinal schistosomiasis-> look for s.japonicum, s.mansoni ect, how?

-stool microscopy, rectal snip microscopy, serology

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what is the treatment for schistosomiasis? dosage and how well is it absorbed?

-praziquantel, 20mg/kgx2 4-6 hours apart, well absorbed extensive 1st pass metabolism, inactive metabolites excreted in urine

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how does treatment of s.japonicum differ to the rest of schistosomiasis?

3 doses of praziquantel instead of just 2

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give 4 ways of controlling schistosomiasis?

1) avoid snail infested waters, 2) chemical treatment to kill the intermediate snail hosts, 3)chemoprophylaxis, 4) community targeted treatment, education, sanitation

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what parasite causes hyatid disease?

-macroparasite, platyhelminth (cestode-tapeworm)- echinococcus

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whats the 3 hosts of hyatid disease?

definitive=dog, intermediate=sheep, accidental=human

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think of the intermediate host, where is hyatid disease going to be found?

-wherever sheep are farmed (all over ze world)

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how would hyatid disease present clinically?

-can be asymptomatic for years, find cysts (70% liver, 20% lung), mass effect (compress tissue due to growth of cyst), can get secondary bacterial infection

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what can happen if a cyst ruptures and what does it look like?

-hypersensitivity, waterlily appearance

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what are the two ways of diagnosing hyatid disease?

-serology, histology (careful= if ruptured cyst do not biopsy as may spread)

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how to treat hyatid disease?

albendazole and praziquantel for daughter cysts

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how to control hyatid disease? focus on each host in turn

1) definitive dog=regular deworming, 2)intermediate sheep=vaccines, 3)accidental humans=education, handwashing

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what parasite causes strongyloidiasis? how does it enter human?

-macroparasite-nematode (strongyloides), directly penetrates bare skin

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where is strongyloidiasis more present? how many affected worldwide?

-subtropical/tropical regions, temperate climates, 30-100 mill affected worldwide

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life cycle: what two actions can eggs do in strongyloidiasis? (makes this different to others)

-excreted in stools, OR autoinfection can occur (migrate from intestine to other organs)

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two parts of strongyloidiasis: strongyloides and strongyloides hyperinfection syndrome, what is this?

-when reinfected by larvae and spreads to different organs (disseminated strongyloidiasis), probs due to immunosuppression

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how to diagnose both parts of strongyloidiasis?

1)strongyloides=serology, stool culture (charcoal filtration method), 2)hyperinfection syndrome= harder (direct microscopy/serology neg), stool culture/concentration methods

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how to treat strongyloides?

-ivermectin (200 micrograms/kg for 2 days), albendazole (400mg bd for 7 days)

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how to treat hyperinfection syndrome?

-stop immunosupressive therapy, -ivermectin (200 micrograms/kg per day orally until stool/sputum is neg for 2 weeks)

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3 ways of controlling strongyloides? isnt a global public health strategy currently

1)wear shoes when walking on soil, 2)avoid sewage contact, 3)proper sewage disposal

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what parasite causes malaria? what does it use as a vector?

-microparasite (protozoa-sporozoan - plasmodium), anopheles-vector

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how many people infected each year, how many in uk, how many die

300-500 million people / year, 2000/year in uk, 1-3 million deaths/year (mostly young kids)

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what are the 4 human species of plasmodium and the one monkey one?

-p.falciparum (yikes), p.vivax, p.ovale, p.malariae, monkey=p.knowlesi

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malaria is found in tropics and subtropics, how common is it?

tropic= year round, subtropics= mostly year round

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symptoms of malaria? shakes, noggin, glucose, lungs, kidney, circulation ect

-fever/rigor, cerebral malaria (confusion, headache, coma), hypoglycaemia, renal failure (black water fever-hb straight into urine), pulmonary oedema, circulatory collapse, anaemia, bleeding, DIC

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how does the parasite cause these symptoms?

-rupture RBC, block capillaries, cause inflam reaction

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how are the erthrocytic cycles (how often to replicate in rbc) for 1) p.knowlesi 2)p.falciparum, p.ovale, p.vivax, 3)p.malariae

1)24 hours, 2) 48 hours, 3) 72 hours

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what other symptom does a returning traveller need to have to be assumed to have malaria until proven otherwise, but what else could it be

-fever, may be viral haemorrhagic fever

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3 ways of malaria diagnosis?

1) thin/thick microscopy, 2)pcr for detecting malarial DNA 3)serology=detect antigen in the blood

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initial line of treatment of p.falciparum?

-antimalarials= co-artem or atovaquone-proguanil

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what is the next line of treatment for complicated p.falciparum?

-iv artesunate, then complete full oral course when stop IV

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what complications can arise from iv artesunate and how is this checked for?

-10-15% people on iv artesunate get haemolysis, so 14 days after iv check Hb conc

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how to treat non p.falciparum malaria (p.ovale/vivax/malariae/knowlesei)?

-oral chloroquine 25 mg base/kg over 3 days, usual adult dose is 10 tablets (day 1:6, 2 for day 2/3)

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what is given if chloroquine isnt tolerated well (vomiting/cant swallow)?

-iv quinine, then once can swallow-> full course of oral chloroquine

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what does vivax and ovale need aswell and for what?

-primaquine for 14 days, treat liver to stop recurrence

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what supportive therapy exists for malaria?

-manage seizures, pulmonary oedema, acute renal failure, lactic acidosis, exchange transfusion for hyperparasitaemia

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control methods for malaria? 6 ways

1)insecticide spraying in homes, 2) larvicidal spraying on breeding pools, 3)fill in breeding pools, 4)introduce larvivorous species into mosquito breeding areas, use insecticide impregnated bed nets, chemoprophylaxis

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what is the name and type of the organism that causes trichomoniasis?

-trichomonas vaginalis (flagellated protozoan)

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how is trichomoniasis transmitted and how long is the incubation stage?

-sexually, 5-28 days

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how do symptoms differ in men and women for trichomoniasis?

-men=asymptomatic, women=smelly *** discharge, dyspareunia (painful sex), lower abdo discomfort, dysuria (painful wee), strawberry cervix (punctuate haemorrhages on cervix)

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where is trichomonas vaginalis found, how does it multiply and how is it transmitted?

-in prostatic/vaginal secretions, multiply via binary fission in these secretions, sexually transmitted via these secretions

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what 2 methods are used to identify trichomonas vaginalis from what specimen?

-pcr/direct microscopy in genital specimens

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how to treat trichomoniasis?

-metronidazole and partner simultaneously, (single dose 2g, or 200mg tds for 5-7 days)

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how to prevent people from getting trichomoniasis?

-general advice of preventing STIs, use barrier contraception

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what is giardiasis caused by and how is it transmitted?

-flagellated protozoan, faeco-oral transmission

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how would someone symptomatic with giardiasis present and how long for?

-diarrhoea, abdo pain, bloating, nausea/vomiting, 1-3 weeks

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do people with giardiasis always present with symptoms?

-no, can range from asymptomatic to severe symptoms and malabsorption, can become chronic

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summarise the 3 key points of giardiasis life cycle?

1) direct as 1 host, 2)cysts and trophozoites exit via stool, 3)only cysts survive in environment and contaminate food/h2o/hands

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how to diagnose giardiasis?

-look for cysts/trophozoites in ze poo

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what drug to treat giardiasis?

-metronidazole/tinidazole

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how to prevent giardiasis? vaccine/

-no vaccine, boil water, more about hygiene

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what parasite causes cryptosporidiosis?

-microparasite sporozoan -> cryptosporidium parvum/hominis

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where is Cryptosporidiosis found?

worldwide esp temperate/tropicals

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how is Cryptosporidiosis transmitted? what is a reservoir for it?

-faeco-oral human to human spread with animal reservoir (cattle,sheep, goats)

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how do outbreaks of Cryptosporidiosis occur?

-sporadic cases can lead to them

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does cryptosporidium have a direct or indirect life cycle and explain it?

-direct as 1 host, exits host to contaminate water/food -> ingested

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how long is the incubation period of Cryptosporidiosis?

2-10 days (~7 days)

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symptoms (self limiting): give examples, and how long will they last?

-up to 2 weeks, watery diarrhoea with no blood, bloating, cramps, fever, nausea, vomiting

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which groups of people is Cryptosporidiosis symptoms more severe in?

-very old, very young, immunocompromised (hiv, 60% become chronically infected)

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what does your risk of contraction depend on?

-way of spread and activities

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someone who is a backpacker (camper/hiker), who works in a farm and visits petting zoos and eats infected dairy products,is likely to obtain Cryptosporidiosis by what spread?

animal to human

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what increases the risk of human to human spread of Cryptosporidiosis?

-regular user of swimming pools (resistant to chlorine alot of the time), childcare workers/parents, nursing home residents/carers, healthcare workers lol, travellers

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what sample is required to diagnose Cryptosporidiosis and whats done to it?

-faece sample, acid fast staining/antigen detection by EIA (enzyme linked assay)

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how does treatment of Cryptosporidiosis differ between just symptomatic people and immunocompromsied people?

immunocompromised require many more things than just treating the symptoms

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how to treat the symptomatic Cryptosporidiosis?

-rehydration, nitazoxanide (treats diarrhoea)

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how to treat immunocompromised with Cryptosporidiosis?

-paromomycin (kill parasite), nitazoxanide, octreotide (reduce cramps), HAART for HIV

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what combination therapy would need to be used for severe cases?

paromomycin, nitazoxanide, azithromycin

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how to control Cryptosporidiosis human to human spread?

-boil/filter drinking water, hand hygiene, isolate symptomatic patients in healthcare setting, keep symptomatic kids from school

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how to control Cryptosporidiosis animal to human spread?

-pasteurise milk/dairy products, boil/filter water when camping

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why is schistosomiasis a public health risk?

-anaemia, bladder tumours, hepatic fibrosis with inc risk of oesophageal varices, renal failure, inc risk of HIV transmission, if mum infected can lead to poor birth weights/outcomes, undernutrition/inflamm mediated cachexia (suppression of appetite)

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what are the 2 reasons strongyloidiasis is a public health risk?

1)strongyloidiasis hyperinfection syndrome -> mortality rates of 90% (25 cases in uk since ww2) 2)sexual transmission in msm not in hetero, tho man to wife via larva in bronchial secretions

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theme 1:parasitology

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