Introduction to parasites Flashcards
What is a parasite?
An organism which lives in or on another organism (its host) and benefits by deriving nutrient’s at the others expense
Do parasites always cause disease?
No
What is a parasitic disease?
When a parasite derives all benefits from the association with a host and the host may either be harmed or may suffer the consequences of this association
What is meant by symbiosis?
A long term interaction between 2 different species
What are the 3 types of symbiosis?
1) Mutualism: an association in which both species benefit from the interaction
2) Parasitism: an association in which the parasite derives benefit and the host gets nothing in return but always suffers some injury
3) Commensalism: an association in which the parasite only is deriving benefit without causing injury to the host
What are the 3 classes of host?
1) Definitive host
2) Intermediate host
3) Paratenic host
What is a 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
What is an intermediate host?
Harbours the larval or asexual stages of the parasite
Some parasites require 2 intermediate hosts in which to complete their life cycle
What is a paratenic host?
Host where the parasite remains viable without further development
What are the 2 broad categories of parasite?
1) Protozoa (micro-parasites)
2) Helminths (macro-parasites)
What are the 4 types of protozoa?
1) Flagellates
2) Amoeboids
3) Sporozoans
4) Trypanosomes
What are the 2 types of helminths and what are there 2 sub types?
1) Nematodes (round worms)
a) intestinal nematodes
b) tissue nematodes
2) Platyhelminths (flat worms)
a) cestodes (tape worms)
b) trematodes (flukes)
What are the 3 types of parasite life cycle?
1) Direct
2) Simple indirect
3) Complex indirect
What is meant by a direct life cycle?
Only one host - that is the definitive host
Eg. bird sheds parasite eggs into the environment in faeces, eggs mature in environment and become infective, infective embryonated eggs are eaten by another bird when feeding
What is meant by a simple indirect life cycle?
Has 1 intermediate host aswell as a definitive host
eg. bird shed parasite eggs into the environment in faeces, snowbug eats eggs of parasite, egg hatch in snowbug and infective larvae develop within snow bug, bird eats snowbug and becomes infected
What is meant by a complex indirect life cycle?
Has more than one intermediate host aswell as a definitive host
Ascariasis is what kind of parasite?
Macro-parasite (Helminth) - intestinal nematode (ascaris lumbricoides)
Why is ascariasis such a problem?
1 adult worm can produce 200,000 eggs per day
How is ascariasis acquired?
Ingestion of eggs
Where is ascariasis most common?
Areas of poor hygiene, most common in SE easia
What is the life cycle of ascariasis?
Has a direct life cycle
Worm in human intestine, eggs shed into the environment in faeces, eggs are then ingested, they travel in the portal circulation to the lungs where they then hatch and the worms are they swallowed and enter the intestine
Lung migration in Ascariasis causes what syndrome (with what 6 symptoms)?
Loeffler’s syndrome - dry cough, dyspnoea, wheeze, haemoptysis, eosinophilic pneumonitis
What are the 4 consequences of the intestinal phase of ascariasis?
1) Malnutrition
2) Migration - into hepatobiliary tree and pancreas
3) Intestinal obstruction
4) Worm burden
How is ascariasis diagnosed? 2
Microscopy of egg in stool
Presence if worm in stool
What is the treatment of ascariasis?
Albendazole
Prevents glucose absorption by worm
Worm starves, detaches and passes PR
What 4 controls have been put in place to reduce cases of ascariasis?
WHO ‘Action Against Worms’
Improve sanitation
Education
Community targeted deworming
Shistosomiasis is what kind of parasite?
Macroparasite (helminth) - platyhelminth - trematode/fluke
What is schistosomiasis also known as?
Bilharzia disease
Where in schistosomiasis most common?
Africa
What kind is the life cycle of schistosomiasis?
Simple indirect lifecycle with freshwater snails as the intermediate host
Describe the life cycle of schistosomiasis?
Eggs are shed in human stools or urine, the eggs hatch and the organism infects freshwater snails by penetrating snail tissue, organism matures in snail then released into water and penetrates human skin
Pass into human circulation, migrate to portal blood in liver and mature into adults which migrate to the mesenteric venules of the bowel/rectum (laying eggs that circulate to the liver and shed in stools) and venous plexus of the bladder.
What are the 4 stages of disease following schistosomiasis infection?
1) Swimmers itch (at sight of entry)
2) Katayama fever (can last a couple of weeks)
3) Chronic schistosomiasis (can persist for years)
4) Effects of eggs in distant sites: spine, lung
What are the 3 main effects of urinary schistosomiasis (S. haematobium)?
1) Haematuria
2) Bladder fibrosis and dysfunction
3) Squamous cell CA bladder
What are the 2 main effects of hepatic/intestinal schistosomiasis?
1) Portal hypertension
2) Liver cirrhosis
How is urinary schistosomiasis diagnosed? 2
1) Terminal stream microscopy
2) Serology
How is hepatic/intestinal schistosomiasis diagnosed? 3
1) Stool microscopy
2) Rectal snip microscopy
3) Serology
What is the treatment of schistosomiasis? 2
1) Praziquantel (parazinoisoquinoline derivative)
2) Treatment of long term complications
What 4 procedures are put in place to try and control schistosomiasis?
1) Chemical treatment to kill snail intermediate hosts
2) Chemoprophylaxis
3) Avoidance of snail infested waters
4) Community targeted treatment, education and improved sanitation
Hyatid disease is caused by what kind of parasite?
Macroparasite (helminth) - platyhelminth - cestode - tapeworm. Echinococcus sp.
What are the hosts in the life cycle of parasite causing hyatid disease?
Human is an accidental host
Usual hosts are sheep and dogs
Where is hyatid disease found?
All over the world wherever sheep are farmed
What is the usual lifecycle of the hyatid disease parasite (not involving humans)?
Dog has adult worm in intestines and sheds eggs in faeces
These are ingested by a sheep, they hatch and the organism penetrates the sheep intestinal wall and travels to the liver or lungs where it forms a hyatid cyst. Cyst in sheep is ingested by a dog and cycle continues
How does a human become the definitive host in hyatid disease?
If a human is in contact with a dog or dog faeces they can ingest the eggs
What are the clinical effects of hyatid disease? 4
1) Cysts form: 70% in liver, 20% in lungs
2) May remain asymptomatic for years
3) Secondary bacterial infection
4) Cyst rupture causing hypersensitivity
How is hyatid disease diagnosed? 2
1) Imaging (to show cysts)
2) Serology
What 3 processes aim to control hyatid disease?
1) regularly worm dogs to reduce egg production
2) hang hygiene
3) safe disposal of animal carcasses/ products of conception
What type of parasite causes malaria?
Plasmodium
Microparasite (protozoa) - sporozoan
What are the 4 species of plasmodium that cause malaria, which is most common?
1) P. falciparum
2) P. vivax
3) P. ovale
4) P. malariae
Roughly how many people are infected with malaria each year?
300-500 million people
How many deaths are caused by malaria each year?
1-3 million deaths per year, mainly in young children
What is different about the lifecyle of malaria?
It uses vector transmission
Anopheles mosquito acts as the vector
Where is malaria most common?
Africa
What is the plasmodium life cycle causing malaria?
Organism infected mosquito takes a blood meal from a human injecting the organism
This travels to liver cells where it replicates until the cell bursts and the organism then infects RBCs, it can continue in a cycle in which it replicates in RBCs causing them to burst and release further organisms to infect further RBCs.
It can also form gametocytes in RBCs which are ingested by another aedes mosquito when it takes a blood meal to form a new organism
What is the basic clinical effect of the malaria parasite?
It ruptures red blood cells, blocks capillaries and causes an inflammatory reaction
What are the 7 possible clinical effects of malaria?
1) Fever & Rigors
2) Cerebral malaria (confusion, headache, coma)
3) Renal failure (black water fever)
4) Hypoglycaemia
5) Pulmonary oedema
6) Circulatory collapse
7) Anaemia, bleeding, DIC
Returning traveller with a fever is diagnosed as what until proven otherwise?
Malaria
What 3 processes are carried out in the diagnosis of malaria?
1) Thick and thin microscopy
2) Serology - detection of Ag in blood
3) PCR - detection of malarial DNA
What 6 processes are carried out which aim to control malaria transmission?
1) Insecticide spraying in homes
2) Larvicidal spraying on breeding pools (for aedes mosquito)
3) Filling in of breeding pools
4) Larvivorous species introduced in to mosquito breeding areas
5) Use of insecticide impregnated bed nets
6) Chemoprophylaxis
Cryptosporidiosis is caused by what organism (and what kind)?
Cryptosporidium parvum and hominis
A micro-parasite (protozoa) - sporozoan
How is cryptosporidiosis spread?
Faecal-oral route
Human to human spread with animal reservoir (cattle, sheep, goats)
Where is cyptosporiodosis most common?
World-wide distribution (esp. temperate and tropical)
What is the life cycle of cryptosporidiosis?
Direct life cycle with no intermediate hosts
Human sheds eggs in faeces which infect water and food, human ingests eggs
What is the clinical effect of cryptosporidiosis? 3
(Incubation 2-10 days - usually 7)
Watery diarrhoea with mucus (no blood)
Bloating, cramps, fever, nausea, vomiting
Usually self limiting (lasts up to 2 weeks)
In which 3 types of people can cryptosporidiosis be severe?
1) Very young
2) Very old
3) Immuno-compromised
Which people are at risk of human to human spread of cryptosporidiosis? 5
1) Regular users of swimming pools
2) Child care workers and parents
3) Nursing home residents/carers
4) Healthcare workers
5) Travellers
Which people are at risk of animal-human spread of cryptosporidiosis? 4
1) Backpackers, campers, hikers
2) Farm workers
3) Visitors to farms/petting zoos
4) Consumers of infected dairy products
How is cryptosporidiosis diagnosed?
Faeces sample
1) Acid fast staining
2) Ag detection by EIA
How is cryptosporidiosis treated in symptomatic patients? 2
1) Rehydration
2) Nitazoxanide
How is cryptosporidiosis treated in the immune-compromised? 4
1) Paromomycin (to kill parasite)
2) Nitazoxanide (effectiveness is unclear)
3) Octreotide (reduce cramps and frequency)
4) HIV patients, HAART should be quickly initiated
How is human to human spread of cryptosporidiosis controlled? 4
1) Hand hygiene
2) Filter or boil drinking water
3) Isolate symptomatic pts in healthcare setting
4) Ensure symptomatic children are kept away from school
How is animal-human spread of cryptosporidiosis controlled? 2
1) Pasteurise milk and dairy products
2) Boil or filter drinking water if camping
Name 5 commonly used anti-protozoal treatments?
1) Metronizadole
2) Pentamidine
3) Nitazoxanide
4) Pyrimethamine
5) Anti malarials
Name 4 commonly used anti helminthic treatements?
1) Albendazole
2) Mebendazole
3) Ivermectin
4) Praziquantel
Giardia lambila is what kind of protozoa?
Flagellate
Entamoeba and acanthamoeba are what kind of protozoa?
Amoeboids
Plasmodium, Cryptosporidium, cyclospora, isospora and toxoplasma are what kind of protozoa?
Sporozoans
Trypanosoma and leishmania are what kind of protozoa?
Trypanosomes
Taenia, echinococcus and hymenolepis are what kind of platyhelminth?
Cestodes
Schistosoma, fasciola, fasciolopsis and paragonimus are what kind of platyhelminth?
Trematode
Ascaris, trichuris, necator and ancylostoma are what kind of nematode?
intestinal nematode
Wuchereria, brugia, onchocerca and loa loa are what kind of nematode?
tissue nematode
