Theme 1: Lecture 5- Parasites Flashcards
What is a parasite?
- an organism which lives in or on another organism (its host) and benefits by deriving nutrients at other expense
- does not necessarily cause disease
What is a host?
an organism which harbours the parasite
What does symbiosis mean?
living together; close, long term interaction between two species
What is mutualism?
an association in which both species benefit from the interaction
What is parasitism?
an association in which the parasite derives benefit and the host gets nothing in return but always suffers some injury e.g ticks feed on animal blood and can also pass on infections to hosts such as lyme disease
What is commensalism?
an association in which the parasite only is deriving benefit without causing injury to the host
What are the 4 classes of hosts?
- definitive host
- reservoir host
- intermediate host
- paratenic host
What is a definitive host?
- where the parasite reaches its mature form and is capable of reproduction
- either harbours adult stage of parasite or where parasite sexually reproduces
What is a reservoir host?
an animal or species infected by a parasite which serves as a source of infection for humans or other species
What is an intermediate host?
- harbours the larval or asexual stages of parasite
- often acts as a vector of parasite to reach its definitive host
- host harbours parasite that grows but not to the point of reaching sexual maturity
- some parasites require two intermediate hosts to complete their life cycle
What is a paramedic host?
host where the parasite remains viable without further development
What are the three main types of parasites and their subdivisions?
- phylum protozoa
- flagellates
- ameoboids
- sporozoans
- trypanosomes - Platyhelminthes and phylum nemathelminthes
- flat worms (flukes and tapeworms)
- round works (nematodes) - phylum arthropoda
- ectoparasites (lice & mites)
- blood sucking arthropods
How are protozoa sub-classified?
- flagellates —> giardia lambda, trichomonas vaginalis
- amoeboids —> entamoeba sp
- sporozoans —> plasmodium sp, cryptosporidium sp, toxoplasma sp
- trypanosomes —> trypanosome sp, leishmania sp
What are helminths?
- large multicellular organisms
- macroparasites
- ‘worms’
- adults generally visible by eye
- adults cannot multiply in humans
What are protozoa?
- micro- parasites
- single celled organisms
- can be free-living or parasitic in nature and multiply in humans
How are helminths divided?
- platyhelminths
- cestodes (tape worms) e.g taenia sp.
- trematodes e.g schistosoma sp. - nemates
- intestinal nematodes
- ascarias sp.
- tissue nematodes
What is a platyhelminths?
flat worm
What is a nematode?
round worm
What are ectoparasites?
- broadly include blood sucking arthropods and those that burrow into skin
- arthropods are important transmitters of infections
How are ectoparasites divided?
- insects
- lice
- mites - scabies sp.
- arachnids (ticks)
What are the two types of lice parasites?
- pediculus humaus capitus (head lice)
- pthiris pubic (pubic lice)
What are the 3 types of life cycle of a parasite?
- direct
- simple indirect
- complex indirect
What is the difference between direct and simple indirect lifestyles?
direct- the simple parasite lives their lifespan and reproduces within one host
indirect - the complex parasite lives in many hosts
What is ascariasis and what is it caused by?
- macroparasite: intestinal nematode
- caused by ascaris lumbricoides, species of roundworm
- acquired by ingestion of eggs
- more than 1 billion people affected worldwide
What are the clinical effects of ascariasis?
- lung migration (loefflers syndrome)- dry cough dyspnoea, wheeze, haemoptysis, eosinophilic pneumonitis
- intestinal phase - malnutrition, malabsorption, migration, intestinal obstruction, worm burden
How do we treat ascariasis?
albendazole
How does albendazole treat ascariasis?
prevents glucose absorption by worm
worm starves, detaches, passed out
What is schistomiasis?
- macro-parasite (helminth–> platyhelminth—> trematode/fluke)
- a.k.a “bilharzia”
- snails are intermediate host
- causes chronic disease resulting in bladder cancer and liver cirrhosis
What are some examples of schistosomas (flukes)?
- S. haematobium
- S.mansoni
- S. intercallatum
- S.japonicum
- S.mekongi
What are the possible symptoms of schistosomiasis?
- often asymptoatic
- symptomatic acute infection / katayama syndrome
- rash, fever, headache, myalgia and respiratory syndrome
- often with eosinophilia and hepato/splenomegaly
- swimmers itch
- katayama fever (rash, eosinophilia)
- chronić schistosomiasis (can persist for years)
What systemic effects/ further risks to schistosomiasis cause?
- undernutrition due to suppression of appetite and inflammation - mediated cachexia
- anaemia
- hepatic fibrosis and oesophageal varices
- renal failure
- bladder tumours
- increased risk of transmission of HIV
- poor birth outcomes in material infection
What is a serodiscordant couple?
one is HIV+ and one is not
How long is the infective incubation period for schistosomiasis?
14-84 days
What are the two main locations that schistosomiasis will effect?
- urinary system
- hepatic/intestinal
What is the treatment of schistosomiasis?
praziquantel
What is chemoprophylaxis?
using drugs to prevent disease, causes resistance
Where does S. haematobium cause schistosomiasis?
- urinary
- haematuria
- bladder fibrosis and dysfunction
- squamous cell CA bladder
Which types of schistosomiasis cause hepatic/intestinal disease?
- S.mansoni
- S. intercallatum
- S. japonicum
- S. Mekongi
What is hydatid disease?
- macroparasite (platyhelminth–> cestode/tapeworm—> echinococcus sp)
- usual host are sheets and dogs, humans are accdiental
- caused by echinococcus sp
What are the clinical effects of hydatid disease?
- cysts: 70% in liver, 20% in lungs
- may remain asymptomatic for years
- cyst rupture: hypersensitivity
- secondary bacterial infection
What is the treatment for Hyatid disease?
albendazole and praziquantel
What is malaria?
- micro-parasite
- protozoa —> sporozoan—> plasmodium sp
What are the 4 human species of plasmodium?
- P.falciparum
- P.vivax
- P. ovale
- P. malariae
+ P. knowlesi (monkey species)
What are the clinical effects of malaria?
- parasites rupture red cells, block capillaries, cause inflammation reaction
- fevers and rigors
- confusion —> headache—> coma
- renal failure (black water fever)
- hypoglycaemia
- pulmonary oedema
- circulatory collapse
- anaemia, bleeding and DIC
If a returning traveller has a fever, what condition is assumed until prove otherwise?
malaria
What is the erythrocytic cycle of plasmodium?
- 24 hrs: P.knowlesi
- 48 hrs: P.falciparum, P.vivax, P.ovale
- 72 hrs: P.malariae
What are the treatments of malaria?
- antimalarials
- oral chloroquine
- proguanil, primaquine
- supportive therapy - management of seizures pulmonary oedema, acute renal failure and lactic acidosis
What is the most dangerous type of malaria?
falciparum malaria - caused by plasmodium falciparum
What are the vectors of malaria?
anopheles - a genus of mosquitos
What is cryptospordiosis caused by?
- cryptosporidium parvum and hominis
- micro-parasite, sporozoan
How does cryptospordiosis spread and what is its main symptom?
- human to human spread with animal reservoir (cattle, sheep, goats)
- faecal-oral spread
- causes diarrhoeal disease
What is the incubation period in cryptospordiosis?
2-10 days
What are the effects of cryptosporidiosis?
- watery diarrhoea with mucus (no blood)
- bloating, cramps, fever, nausea, vomiting
- usually self limiting (resolves on its own)
- can be severe in very young, old and immunocompromised
How do we treat cryptosporidiosis?
- symptmatic: rehydration, nitazoxanide
- paramomycin (kills parasite)
What causes trichomoniasis?
trichomonas vaginalis
What is trichomonas?
flagellated protozoan
How is trichomoniasis transmitted?
sexually
What is the incubation period of trichomonas?
5-28 days
What symptoms do men and women display if infected with trichomoniasis?
men - asymptomatic
women - smelly vaginal discharge, dysuria and lower abdominal discomfort, punctuate haemorrhages on cervix “strawberry cervix”
How does trichomonas vaginalis multiply?
binary fission
How do we treat trichomonas?
- metronidazole
- treat partner simultaenously
What is auto infection and which parasite can cause it to occur?
- eggs can hatch in GI tract and reinfect
- can occur with strongyloidiasis
What is strongyloidiasis hyper infection?
rare but fatal disease escalated from strongyloidiasis, usually seen in immunocompromised patients
What drug is used to treat strongyloidiasis?
- thiabendazole
- invermectin (hyper infection)
- albendazole
What is giardiasis and how is it transmitted?
- flagellated protozoan
- faecal oral transmission
What are the symptoms of giardiasis?
severe diarrhoea, malabsorption, abdominal pain, bloating, nausea, vomiting
How do we diagnose giardiasis?
identification of cysts or trophozoites in faeces
What is the treatment for giardiasis?
metronidazole/ tinidazole
How do we prevent giardiasis?
no vaccine available, hygiene measures, boiling water
