4 - An introduction to parasites

Question 1

Commensalism definition

Answer 1

An association in which the parasite only is deriving benefit without causing injury to the host

Question 2

Definitive host definition

Answer 2

Harbours the adult stage of the parasite or where the parasite utilises the sexual method of reproduction (majority of human parasite infections)

Question 3

Intermediate host definition

Answer 3

Harbours the larval or asexual stages of the parasite

Question 4

Paratenic host definition

Answer 4

Host where the parasite remains viable without further development

Question 5

Classification of parasites

Answer 5

Protozoa (microparasites)

Helminths (marco-parasites)

Question 6

Classification of protozoa

Answer 6

Flagellates
Amoeboids
Sporozans
Trypanosomes

Question 7

Classification of helminths

Answer 7

Platyhelminths (flatworms)

Nematodes (round worms)

Question 8

How to approach parasitic stages

Answer 8

Distribution
Life cycles
Clinical manifestations
Diagnosis
Treatment 
Control

Question 9

Ascariasis background

Answer 9

Macroparasite - intestinal
More than 1 billion people worldwide
Peak in 3-8 yo
Areas of poor hygiene
Ingest eggs

Question 10

Clinical presentation of ascariasis

Answer 10

Lung migration
Loefflers syndrome - dry cough, dyspnea, wheeze, haemotypsis, eosinophilic pneumonitis
Intestinal phase: Malnutrition, migration (heptobiliary tree + pancreas), intestinal obstruction, worm burden

Question 11

Diagnosis of ascariasis

Answer 11

Via observing egg or worm

Question 12

Ascariasis treatment/control

Answer 12

Treatment: albendazole - prevents glucose absorption by worm and is therefore starved

Control: WHO ‘Action against worms’
Improve sanitation
Education
Community targeted deworming

Question 13

Schistosomiasis background

Answer 13

Macro-parasite (helminth)
Bilharzia disease
Caused by fluke, Schistosoma
Causes chronic disease resulting in bladder cancer and liver cirrhosis
Snails are intermediate host

Question 14

Schistosomiasis clinical presentation

Answer 14

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

Question 15

Schistosomiasis diagnosis

Answer 15

Urinary - terminal stream, microscopy, serology

Hepatic/intestinal - school microscopy, rectal snip microscopy, serology

Question 16

Schistosomiasis treatment

Answer 16

Praziquantel (parazinoisoquinoline derivative)
One course of 40-60mg/kg with food 3 doses 8-hourly
Mechanism unknown
Well-absorbed, extensive 1st pass metabolism

Question 17

Schistosomiasis - control

Answer 17

Chemical treatment to kill snail intermediate hosts
Chemoprophylaxis
Avoidance of snail infested waters
Community targeted treatment, education and improved sanitation

Question 18

Mydatid disease background

Answer 18

Macro-parasite (tapeworm)
Human is accidental host
Usual hosts are sheeps or dogs
Found all over world

Question 19

Hyatid disease clinical presentation

Answer 19

Cysts: 70% liver, 20% lung
May remain asymptomatic for years
Mass effect 
Secondary bacterial infection
Cyst rupture - hypersensitivity

Question 20

Hyatid disease - diagnosis

Answer 20

Imaging
Serology

Control - regularly worm dogs to reduce egg production, hand hygiene, safe disposal of animal carcasses/products of conception

Question 21

Malaria background

Answer 21

Microparasite - protozoa
4 species of plasmodium
Anopheles as a vector

Question 22

Malaria clinical presentation

Answer 22

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)

Question 23

Malaria - diagnosis

Answer 23

Thick and thin microscopy
Serology - detection of antigen in blood
PCR - detection of malarial DNA

Question 24

Control of malaria

Answer 24

Insecticide spraying in homes
Larvicidal spraying on breeding pools
Filling in of breeding pools

Question 25

Malaria control

Answer 25

Larvivorous species introduced to mosquito breeding areas
Use of insecticide impregnated bed nets
Chemoprophylaxis
Vaccine?

Question 26

Cryptosporidiosis background

Answer 26

Causes diarrhoeal disease 
Human to human spread with animal reservoir
Faecal-oral spread
World-wide distribution 
Sporadic cases or lead to outbreaks

Question 27

Cryptosporidiosis clinical presentation

Answer 27

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

Question 28

Who is at risk of cryptosporidiosis?

Answer 28

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

Question 29

Cryptosporidiosis diagnosis

Answer 29

Faeces sample - acid fast staining

Question 30

Cryptosporidiosis treatment

Answer 30

Symptomatic - rehydration, nitazoxanide

For immunocompromised: paromomycin, nitazoxanide, octreocide, HIV patients, HAART

Question 31

Cryptosporidiosis control

Answer 31

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

Question 32

Commonly used treatments

Answer 32

Antiprotozoal: metronidazole, pentamidine, nitazoxanide, pyrimethamine, antimalarials: treatment, prophylaxis
Antihelminthic: albendazole, mebendazole, ivermectin, praziquantel