Parasites intro Flashcards
What is a parasite?
- An organism which lives in/on another organism (host) & benefits by deriving nutrients
- Doesn’t necessarily cause disease
- Parasite derives all benefits from the association & the host may either be harmed or suffer the consequences of this association
Define the term host
-An organism which harbours the parasite
Define the term symbiosis and mutualism
S=Living together, long term interaction between 2 different species
M= Association in which both species benefit from interaction
Define parasitism & commensalism
P=Association in which the parasite derives benefit & host gets nothing but suffers some injury
C=Association in which the parasite only is deriving benefit without causing injury to host
What are the different classes of hosts?
- Definitive host: Harbours the adult stage of the parasite/ parasite utilises the sexual method of reproduction, majority of human parasitic infections
- Intermediate host: Harbours larval/asexual stages of parasite, some parasites require 2 intermediate hosts
- Paratenic host: Parasite remains viable without further development
What are the 2 categories parasites are classified into?
- Protozoa (micro-parasites)
- Helminths (macro-parasites)
What are the different classes of Protozoa? Give examples of each
- Flagellates (Giardia Lamblia)
- Amoeboids (Entamoeba, Acanthamoeba)
- Sporozoans (Plasmodium, Cryptosporidium, Cyclospora, Isospora, Toxoplasma)
- Trypanosomes (Trypanosoma, Leishmania)
What are the different classes of Helminths? What can these be subdivided into?
- Platyhelminths= Cestodes (tape worms), Trematodes (flukes)
- nematodes= Tissue nematodes, Intestinal nematodes
What types of life cycles are there for a parasite? Describe them
- Direct (droppings containing eggs which become infected and eaten by an organism)
- Simple indirect (droppings containing eggs, organism eats eggs in which eggs hatch another organism eats this organism and becomes infected)
- Complex indirect (droppings containing eggs are then eaten by 2 intermediate hosts which is then eaten by end organism)
What is Ascariasis?
- Macroparasite- intestinal nematode (Ascaris Lumbricoides)
- Peak prevalence 2-8yrs
- Areas of poor hygiene
- Acquired by ingestion off eggs
What are the clinical implications of Ascariasis?
- Lung migration= Loefflers syndrome: dry cough, dyspnea, wheeze, haemoptsis, eosinophilic pneumonitis
- Intestinal phase= malnutrition, migration into hepatobiliary tree & pancreas, intestinal obstruction by worm
How is Ascariasis treated or controlled?
Treatment= Albendazole prevents glucose absorption by worm which starves and detaches passed PR Control= improve sanitation, education, community targeted deworming, WHO action against worms
What is Schistosomiasis?
- Macroparasite (fluke Schistosoma)
- Bilharzia disease
- Causes chronic disease-bladder cancer & liver cirrhosis
- Intermediate host is snails
What are the clinical implications of Schistosomiasis?
- Swimmers itch at site of parasite entry
- Katayama fever
- Chronic Schistosomiasis
- Effects of eggs in spine & lungs
- Urinary: haematuria, bladder fibrosis/dysfunction, squamous cell CA bladder
- Hepatic/intestinal: portal hypertension, liver cirrhosis
How is Schistosomiasis treated and controlled?
- Praziquantel leads to ionic permeability titanic contraction, detachment and death
- Treatment of long term complications also required
- Chemical treatment to kill snails/avoid snail infested waters
- Chemoprophylaxis
- Community targeted treatment, education, improved sanitation
What is Hydatid disease?
- Macroparasite (Tapeworm)
- Human accidental host
- Usual host= dogs/sheep
- Caused by Echinococcus
What are the clinical implications of Hydatid disease?
- Cysts 70%=liver 20%=lungs
- May remain asymptomatic for years
- Mass effect
- Secondary bacterial infection
- Cyst rupture=hypersensitivity
How is Hydatid disease controlled?
- Regular worming of dogs to reduce egg production
- Hand hygiene
- Safe disposal of animal carcasses
What is Malaria?
- Microparasite (Sporozoan)
- 4 species of plasmodium
- Anopheles acts as a vector
What are the clinical implications of malaria?
- Parasites rupture red blood cells, block capillaries & cause inflammatory reaction
- Fever & rigors
- Cerebral malaria (confusion, headache, coma)
- Renal failure (black water fever)
- Hypoglycaemia
- Pulmonary oedema
- Circulatory collapse
- Anaemia, bleeding
How is Malaria controlled?
- Insecticide spraying in homes
- Filling in breeding pools
- Larvicidal spraying of breeding pools
- Mosquito nets
What is Cryptosporidiosis>
- Caused by Cryptosporidium parvum
- Causes diarrhoea disease
- Human to human spread with animal reservoir
- Faecal-oral spread
- Sporadic cases/ lead to outbreaks
What are the clinical implications of Cryptosporidiosis?
- Incubation 2-10days
- Watery diarrhoae w/mucus (no blood)
- Bloating, cramps, fever, nausea, vomiting
- Usually self-limiting
- Severe in very young/old, immune-compromised/HIV patients
Who are at risk of Cryptosporidiosis>
- H to H: regular users of swimming pools, child care workers/parents, nursing home residents/carers, travellers, HCA
- A-H: Backpackers/campers/hikers, farm workers, visitors to farms/petting zoos, consumers of infected dairy products
What is the treatment & control for Cryptosporidiosis?
-Symptomatic: Rehydration, Nitazoxanide
-Immunocompromised: Paromomycin-kills parasite, , HAART- HIV patients, Octreotide (reduce cramps & frequency)
H to H: hand hygiene, filter/boil drinking water, isolate symptomatic patients
A to H: pasteurise milk/dairy products
What are commonly used anti-protozoal treatments?
- Metronidazole
- Pentamidine
- Anti-malarials
- Nitazoxanide
- Pyrimethamine
What are commonly used anti-helminthic treatments?
- Albendazole
- Mebendazole
- Ivermectin
- Praziquantel
