CP5 - Introduction to Parasites Flashcards
what is a parasite?
an organism which lives in or on another organism and benefits by deriving nutrients at the other’s expense. it does not necessarily cause disease
what is a host?
an organism which harbours the parasite
what is symbiosis?
close, long-term interaction between 2 different species
what is mutualism?
an association in which both species benefit from the interaction
what is parasitism?
an association in which the parasite derived benefit and the host gets nothing in return but always suffers some injury
what is commensalism?
an association in which the parasite is only deriving benefit without causing injury to the host
what are the 3 classes of hosts?
- definitive host
- intermediate host
- paratenic host
what is a definitive host?
a host that harbours either
- the adult stage of the parasite
- the parasite in the duration of its sexual reproduction
what is an intermediate host?
a host that harbours larval or asexual stages of the parasite. some require 2 intermediate hosts
what is a paratenic host?
where the parasite remains alive without any further development
what are the 2 broad classes of parasites?
protozoa (micro parasites) and helminths (macro parasites)
what are the types of protozoa?
- flagellates - guardia lambía
- amoeboids - entamoeba ep
- sporozoans
- trypanosomes
what are the types of helminths?
platyhelminths (flat worms) 1. cestodes (tape worms) 2. trematodes (flukes) nematodes (roundworms) 1. intestinal nematodes 2. tissue nematodes
what are the 3 types of life cycles of parasites?
- direct - only 1 definitive host
- simple indirect - 2 different hosts, 1 intermediate and 1 definitive
- complex indirect
which parasite causes ascariasis?
ascaris lumbricoides, an intestinal nematode
what is the distribution of ascaris lumbricoides?
areas of poor hygiene
3-8 year olds
contaminated soil, water or food
Central Asia and Africa
what is the lifecycle of ascaris lumbricoides?
direct.
ingested by humans, causes infection and reproduces
eggs passed in faeces
eggs ingested by humans
what is the clinical manifestation of ascaris lumbricoides?
intestinal phase 1. malnutrition 2. intestinal obstruction 3. worm burden 4. migration to hepato-biliary tree and pancreas lung migration causes loeffler's syndrome dry cough dyspnoea wheeze haemoptysis eosinic pneumonitis
how is ascariasis diagnosed?
stool sample sent for testing, can either see eggs or the worm itself in the stool
what is the treatment for ascariasis
albendazole, a type of benzimidazole, which prevents the worm from absorbing glucose. the worm starves, detaches and is passed PR
how can the spread of ascariasis be controlled?
improve sanitation, education and community targeted deworming
what organism causes schistosomiasis?
the genus schistosoma, a macro parasite (fluke)
where can schistosoma be found?
fresh water places
South America, Asia
which parts of the body do schistosoma affect?
some affect the liver, some affect the bladder, some affect both
what is the life cycle of schistosoma?
simple indirect cycle
snails are intermediate hosts
eggs hatch in water and larvae enter snails, mature and leave
enter humans, mature into adults in liver, paired worms migrate to bladder
eggs are passed out
what is the clinical manifestation of schistosomiasis?
swimmer’s itch
katayama fever
chronic schistosomiasis - eggs can affect the spine and lung
when the bladder is affected: haematuria, fibrosis and dysfunction, cancer
when liver is affected: hypertension, cirrhosis
eggs cause more problems than worms do
how is schistosomiasis diagnosed?
urine sample - terminal stream
microscopy and serology to look for eggs
hepatic/intestinal - stool microscopy, renal snip microscopy, serology
how is schistosomiasis treated?
praziquantel 40-60mg/kg with food every 8 hours
increases ionic permeability, titanic contraction
detachment and death
well absorbed and excreted in urine
this can be more complicated therefore important to treat long term complications
how can schistosomiasis be controlled?
chemical treatment to kill intermediate host snails chemoprophylaxis avoid snail infected waters education improved sanitation
what is the distribution of echinococcus (tapeworm)?
all over the world where sheep are present
what is the life cycle of echinococcus?
humans are accidental hosts. sheep and dogs are real hosts
egg penetrates sheep via ingestion of faeces (intermediate) causes cysts in organs
dogs (definitive) ingest infected organs, maturation, adult in small intestine. eggs passed in faeces. eggs can be accidentally ingested by humans, effective at the sub larval stage only
what are the clinical manifestations of echinococcus?
70% liver cysts, 20% lungs, may be asymptomatic for years.
can lead to a secondary bacterial infection
cyst rupture causes hypersensitivity
how is echinococcus infection diagnosed?
imaging
serology
how can the spread of echinococcus be controlled?
worm eggs to reduce egg production
hand hygiene
safe disposal of animal carcasses/conception products
which organism causes malaria?
plasmodium genus (sporozoan)
what is the distribution of plasmodium?
south america
africa
asia
what does echinococcus cause?
hydatid disease
what type of a lifecycle does plasmodium have?
complex indirect (ref to slide) vector is anopheles mosquito
what is the clinical manifestation of malaria?
parasites rupture RBCs, block capillaries and cause inflammatory reactions
fevers and riggers
cerebral malaria - confusion, headache, coma
renal failure - black water fever
hypoglycaemia
pulmonary oedema
circulatory collapse
anaemia, bleeding, disseminated intravascular coagulation (DIC)
how is malaria diagnosed?
thick and thin microscopy
serology to detect antigen in blood
PCR to detect malarial DNA
how can malaria be controlled?
spray insecticide in homes larvicidal spraying on breeding pools filling in of breeding pools introduction of larvivorous species insecticide impregnated bed nets chemoprophylaxis
which organism causes cryptosporidiosis?
cryptosporidium parvum and hominis (sporozoan)
what is the distribution of cryptosporidium parvum?
worldwide, especially in tropical and temperate zones
what is the life cycle of cryptosporidium parvum?
faecal-oral spread, human to human spread with cattle reservoir, eggs in faeces (in water)
people bathe in/drink contaminated water and are infected
what is the clinical manifestation of cryptosporidiosis?
watery diarrhoea with mucous (no blood) bloating cramps fever nausea and vomiting usually self-limiting but can be very severe in very young or old and immunocompromised patients (eg. HIV)
how is cryptosporidiosis diagnosed?
faeces sample - acid fast staining
antigen detection by EIA
how is cryptosporidiosis treated?
incubation 2-10 days
for symptomatic patients - rehydration (nitrazoxanide)
for immunocompromised, additionally give paromomycin to kill parasite and octreotide to reduce cramps and frequency; initiate HAART for HIV patients
how can the spread of cryptosporidiosis be controlled?
hand hygiene filter or boil drinking water isolate symptomatic patients pasteurise dairy products boil or filter drinking water
what should be suspected if a patient presents with a history of recent travel and fever?
malaria until proven otherwise
what are the common anti-protozoal treatments?
- metronidazole
- pentamidine
- nitrazoxanide
- pyrimethamine
- antimalarials for treatment and prophylaxis
what are the common anti-helminthic treatments?
- albendazole
- mebendazole
- Ivermectin
- Praziquantel
