4 - An introduction to parasites Flashcards
Commensalism definition
An association in which the parasite only is deriving benefit without causing injury to the host
Definitive host definition
Harbours the adult stage of the parasite or where the parasite utilises the sexual method of reproduction (majority of human parasite infections)
Intermediate host definition
Harbours the larval or asexual stages of the parasite
Paratenic host definition
Host where the parasite remains viable without further development
Classification of parasites
Protozoa (microparasites)
Helminths (marco-parasites)
Classification of protozoa
Flagellates
Amoeboids
Sporozans
Trypanosomes
Classification of helminths
Platyhelminths (flatworms)
Nematodes (round worms)
How to approach parasitic stages
Distribution Life cycles Clinical manifestations Diagnosis Treatment Control
Ascariasis background
Macroparasite - intestinal More than 1 billion people worldwide Peak in 3-8 yo Areas of poor hygiene Ingest eggs
Clinical presentation of ascariasis
Lung migration
Loefflers syndrome - dry cough, dyspnea, wheeze, haemotypsis, eosinophilic pneumonitis
Intestinal phase: Malnutrition, migration (heptobiliary tree + pancreas), intestinal obstruction, worm burden
Diagnosis of ascariasis
Via observing egg or worm
Ascariasis treatment/control
Treatment: albendazole - prevents glucose absorption by worm and is therefore starved
Control: WHO ‘Action against worms’
Improve sanitation
Education
Community targeted deworming
Schistosomiasis background
Macro-parasite (helminth) Bilharzia disease Caused by fluke, Schistosoma Causes chronic disease resulting in bladder cancer and liver cirrhosis Snails are intermediate host
Schistosomiasis clinical presentation
Swimmers itch
Katayama fever
Chronic schistosomiasis
Effect of eggs at distant sites e.g. spine, lung
Urinary - haematuria, bladder fibrosis and dysfunction, squaemous cell cancer bladder
Hepatic/intestinal - portal hypertension, cirrhosis
Schistosomiasis diagnosis
Urinary - terminal stream, microscopy, serology
Hepatic/intestinal - school microscopy, rectal snip microscopy, serology
Schistosomiasis treatment
Praziquantel (parazinoisoquinoline derivative)
One course of 40-60mg/kg with food 3 doses 8-hourly
Mechanism unknown
Well-absorbed, extensive 1st pass metabolism
Schistosomiasis - control
Chemical treatment to kill snail intermediate hosts
Chemoprophylaxis
Avoidance of snail infested waters
Community targeted treatment, education and improved sanitation
Mydatid disease background
Macro-parasite (tapeworm)
Human is accidental host
Usual hosts are sheeps or dogs
Found all over world
Hyatid disease clinical presentation
Cysts: 70% liver, 20% lung May remain asymptomatic for years Mass effect Secondary bacterial infection Cyst rupture - hypersensitivity
Hyatid disease - diagnosis
Imaging
Serology
Control - regularly worm dogs to reduce egg production, hand hygiene, safe disposal of animal carcasses/products of conception
Malaria background
Microparasite - protozoa
4 species of plasmodium
Anopheles as a vector
Malaria clinical presentation
Parasites rupture RBCs, block capillaries and cause inflammatory reaction Fever and rigors Cerebral malaria Renal failure Hypoglycaemia Pulmonary oedema Circulatory collapse Anaemia, bleeding and DIC (disseminated intravascular coagulation)
Malaria - diagnosis
Thick and thin microscopy
Serology - detection of antigen in blood
PCR - detection of malarial DNA
Control of malaria
Insecticide spraying in homes
Larvicidal spraying on breeding pools
Filling in of breeding pools
Malaria control
Larvivorous species introduced to mosquito breeding areas
Use of insecticide impregnated bed nets
Chemoprophylaxis
Vaccine?
Cryptosporidiosis background
Causes diarrhoeal disease Human to human spread with animal reservoir Faecal-oral spread World-wide distribution Sporadic cases or lead to outbreaks
Cryptosporidiosis clinical presentation
Incubation 2-10days
Watery diarrhoea with mucus (no blood)
Bloating, cramps, fever, nausea, vomiting
Usually self-limiting (2 weeks)
Can be severe in very young/old/immunosuppressed
Who is at risk of cryptosporidiosis?
Human-human spread: swimming pool users, childcare, nursing home, healthcare, travellers
Animal-human: backpackers, campers, hikers, farm workers, visitors to farms/petting zoos, consumers of infected diary products
Cryptosporidiosis diagnosis
Faeces sample - acid fast staining
Cryptosporidiosis treatment
Symptomatic - rehydration, nitazoxanide
For immunocompromised: paromomycin, nitazoxanide, octreocide, HIV patients, HAART
Cryptosporidiosis control
Human-human:
Hand hygiene, filter or boil drinking water, isolate symptomatic patients, ensure symptomatic children are kept away
Animal-human: pasteurise milk and dairy. Boil or filter drinking water
Commonly used treatments
Antiprotozoal: metronidazole, pentamidine, nitazoxanide, pyrimethamine, antimalarials: treatment, prophylaxis
Antihelminthic: albendazole, mebendazole, ivermectin, praziquantel
