Parasites intro

Question 1

What is a parasite?

Answer 1

• 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

Question 2

Define the term host

Answer 2

-An organism which harbours the parasite

Question 3

Define the term symbiosis and mutualism

Answer 3

S=Living together, long term interaction between 2 different species
M= Association in which both species benefit from interaction

Question 4

Define parasitism & commensalism

Answer 4

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

Question 5

What are the different classes of hosts?

Answer 5

• 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

Question 6

What are the 2 categories parasites are classified into?

Answer 6

• Protozoa (micro-parasites)

- Helminths (macro-parasites)

Question 7

What are the different classes of Protozoa? Give examples of each

Answer 7

• Flagellates (Giardia Lamblia)
• Amoeboids (Entamoeba, Acanthamoeba)
• Sporozoans (Plasmodium, Cryptosporidium, Cyclospora, Isospora, Toxoplasma)
• Trypanosomes (Trypanosoma, Leishmania)

Question 8

What are the different classes of Helminths? What can these be subdivided into?

Answer 8

• Platyhelminths= Cestodes (tape worms), Trematodes (flukes)

- nematodes= Tissue nematodes, Intestinal nematodes

Question 9

What types of life cycles are there for a parasite? Describe them

Answer 9

• 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)

Question 10

What is Ascariasis?

Answer 10

• Macroparasite- intestinal nematode (Ascaris Lumbricoides)
• Peak prevalence 2-8yrs
• Areas of poor hygiene
• Acquired by ingestion off eggs

Question 11

What are the clinical implications of Ascariasis?

Answer 11

• Lung migration= Loefflers syndrome: dry cough, dyspnea, wheeze, haemoptsis, eosinophilic pneumonitis
• Intestinal phase= malnutrition, migration into hepatobiliary tree & pancreas, intestinal obstruction by worm

Question 12

How is Ascariasis treated or controlled?

Answer 12

Treatment= Albendazole prevents glucose absorption by worm which starves and detaches passed PR
Control= improve sanitation, education, community targeted deworming, WHO action against worms

Question 13

What is Schistosomiasis?

Answer 13

• Macroparasite (fluke Schistosoma)
• Bilharzia disease
• Causes chronic disease-bladder cancer & liver cirrhosis
• Intermediate host is snails

Question 14

What are the clinical implications of Schistosomiasis?

Answer 14

• 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

Question 15

How is Schistosomiasis treated and controlled?

Answer 15

• 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

Question 16

What is Hydatid disease?

Answer 16

• Macroparasite (Tapeworm)
• Human accidental host
• Usual host= dogs/sheep
• Caused by Echinococcus

Question 17

What are the clinical implications of Hydatid disease?

Answer 17

• Cysts 70%=liver 20%=lungs
• May remain asymptomatic for years
• Mass effect
• Secondary bacterial infection
• Cyst rupture=hypersensitivity

Question 18

How is Hydatid disease controlled?

Answer 18

• Regular worming of dogs to reduce egg production
• Hand hygiene
• Safe disposal of animal carcasses

Question 19

What is Malaria?

Answer 19

• Microparasite (Sporozoan)
• 4 species of plasmodium
• Anopheles acts as a vector

Question 20

What are the clinical implications of malaria?

Answer 20

• 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

Question 21

How is Malaria controlled?

Answer 21

• Insecticide spraying in homes
• Filling in breeding pools
• Larvicidal spraying of breeding pools
• Mosquito nets

Question 22

What is Cryptosporidiosis>

Answer 22

• Caused by Cryptosporidium parvum
• Causes diarrhoea disease
• Human to human spread with animal reservoir
• Faecal-oral spread
• Sporadic cases/ lead to outbreaks

Question 23

What are the clinical implications of Cryptosporidiosis?

Answer 23

• 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

Question 24

Who are at risk of Cryptosporidiosis>

Answer 24

• 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

Question 25

What is the treatment & control for Cryptosporidiosis?

Answer 25

-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

Question 26

What are commonly used anti-protozoal treatments?

Answer 26

- Metronidazole - Pentamidine - Anti-malarials - Nitazoxanide - Pyrimethamine

Question 27

What are commonly used anti-helminthic treatments?

Answer 27

- Albendazole - Mebendazole - Ivermectin - Praziquantel