Parasites

Question 1

What are parasites?

Answer 1

A parasite is an organism that lives on or in a host organism and derives its nutrients at the expense of the host- they can be vectors of infection or can cause infection themselves.

Question 2

Where are parasites a most prevalent issue?

Answer 2

Third world countries which are poorly resourced.

Question 3

What is a vector?

Answer 3

A vector is an organism which acts as an intermediate host for a parasite. The vector transmits the parasite to its next host.

Question 4

What are the classifications of parasites?

Answer 4

Protozoa- malaria, amoebae, flagellates
Helminths (worms)- roundworms, tapeworms, flukes
Ectoparasites- lice, ticks, mites

Question 5

What are protozoa?

Answer 5

Microscopic, single-celled organisms
Can be free-living or parasitic in nature
Able to multiply in humans

Question 6

Describe malaria.

Answer 6

Malaria is a mosquito-borne parasitic infection caused by Plasmodium species. It causes the largest burden of death among all parasitic diseases, and presents throughout the tropics and subtropics. It is a preventable disease- recognition and appropriate treatment saves lives.
The complex life cycle of the parasite makes eradication very challenging. Prevented by awareness of risk, bite prevention, chemoprophylaxis, diagnosis.

Question 7

What are helminths?

Answer 7

Nematodes (roundworms)
Cestodes (tapeworms)
Trematodes (flatworms)

Question 8

Describe nematodes (roundworms).

Answer 8

 Nematodes (roundworms):
 Faecal-oral route of transmission
 In UK, pinworm very common in childhood
 Ascaris infection very common globally
 Can lead to developmental delay in children
 Severe complications can arise as a result of bowel obstruction

Question 9

Describe cestodes (tapeworms)

Answer 9

 Cestodes (tapeworms):
 Eating raw/undercooked meat is route of transmission
 Beef and pork tapeworms commonest
 Pork tapeworm cysts can form outside of the gut and cause problems, especially in brain

Question 10

Describe trematodes (flatworms).

Answer 10

 Commonest type globally is schistosomiasis
 This is transmitted by contact with freshwater where the snail intermediary host is present
 “Swimmer’s itch” common sign- can lead to complications such as liver failure and bladder cancer if left untreated

Question 11

What is a definitive diagnosis within parasitology?

Answer 11

Identification of parasites in the host tissue or urine/faeces

Question 12

Name some direct tests for parasites.

Answer 12

Blood microscopy for parasites- thick/thin blood films for malaria
Stool microscopy for ova, cysts and parasites
Worm infection usually accompanied by eosinophilia and elevated IgE levels.

Question 13

Name some indirect tests for parasites.

Answer 13

Serology (immune) / rapid diagnostic testing