Parasites

Question 1

Define a parasite

Answer 1

AN organism which lives on or in another organism and benefits by deriving nutrients at the others expense

Question 2

what are the 3 major classes of parasites

Answer 2

1. Protozoa
2. Worms
3. Ectoparasites

Question 3

how are protozoa transmitted?

Answer 3

Oral-faecal route e.g contaminated food, water or person contact

Question 4

what are 4 classes of protozoa

Answer 4

amoeba - move by pseudopods
Flagellates - move by flagella
Ciliates- move by cilia
Sporozoa

Question 5

name types of amoeba

Answer 5

1. Entamoeba histolytica - carried asymptomatically to digestive tract (contaminated water with faeces that contain cysts), multiply in large intestine
2. Naegleria Fowleri - causes amoebic meningoenephalitis (brain haemorrhage and necrosis)

Question 6

what are the 3 types of amebiasis that can result? (entemoeba histolytic)

Answer 6

luminal amebiasis - least severe, asymptomatic
Invasive amebic dysentry - common, blood and mucus in stools

Invasive extra intestinal amebiasis - carried via bloodstream, most severe

Question 7

give 3 types of flagellates

Answer 7

1- trichomonas vaginalis - causes trichomoniasis (STI)

2. Giardia Lamblia - causes intestinal malabsorption - travellers diarrhoea - giardiasis.
3. Trypanosoma - causes African sleeping sickness - transmitted via humans by the tsetse fly

Question 8

What flagellates disease does not spread via blood?

Answer 8

Giardia lamblia

Question 9

name a ciliates infection

Answer 9

Blantanidium coli - contaminated food and water. Usually asymptomatic in healthy humans but can be symptoms In poor health e.g diarrhoea, weight loss.

Question 10

Name a sporozoa infection (plasmodium)

How is it spread?

Answer 10

Plasmodium malaria - cause malaria (colonise in blood of the human)
Spread via the female anopheles moaquitos.
Symptoms appear 7-18 days after infection but sometimes don’t appear for years.

Question 11

what is the most common & severe parasitic disease?

Answer 11

plasmodium malaria (sporozoa)

Question 12

what are the 2 phases of infection of p.malariae?

Answer 12

1. Exoerythrocytic phase (liver) - after transmission, it migrates to liver and proliferates asymptomatically for 8-30days, then escapes to blood to infect RBC
2. Erythrocytic phase (blood) - multiplies periodically breaking out of cells and infecting more RBC

Question 13

how are heterozygous carriers of sickle cel anaemia partially protected from malaria?

Answer 13

1. Body sends the sickled cells to the spleen for elimination and thus destroys parasite as it lives in the roc
2. The membrane of sickled cells is stretched due to shape and thus becomes porous. It leaks out nutrients e.g K+ that the parasite needs to survive, thus the parasite dies.

Question 14

what are worms (helminths)?

Answer 14

multicellular parasites that can be free living or parasitic. In their adult form they cannot multiply in humans.

Question 15

what are the 3 main helminths (worms)?

Answer 15

1. flatworms
2. thorny head worms - adult form in GI
3. roundworms - adult form in GI, blood, lymph, subcutaneous tissues

Question 16

what are life stages of worms?

Answer 16

Egg, larva, adult

• Infective stage = egg or larva
• Definitive host - harbours adult stage

Question 17

give 2 types of flatworms

Answer 17

1. Taenia solium - pork tapeworm. Usually asymptomatic, but the larval stage infects the human nervous system - neurocysticerocosis.
2. Schistomes - snail fever (schistomiasis) - urinary tract & intestine

Question 18

name a thorny head worms

Answer 18

M.moniliformis. Usually asymptomatic

Question 19

name round worms (nematodes)

Answer 19

ascaris lumbricoids - asymptomatic. BUT heavy infections can cause intestinal blockage and impair child growth.

Question 20

what are ectoparasites?

Answer 20

Ticks, fleas, lice, mites that attach or burrow into skin and remain there for a long time (weeks/months)

Question 21

what are arthropods?

Answer 21

insects, arachnoids - cause disease but also more important as vectors/transmitters for pathogens

Question 22

what is included in insecta class?

Answer 22

lice, fleas, mosquitos

Question 23

what is included in arachnida class?

Answer 23

Mites & ticks - vectors

Question 24

what are ticks?

Answer 24

Vectors for bacterial, viral and protozoan disease. They are second to mosquitos in the number of diseases they transmit e.g Lyme disease, Rocky Mountain spotted fever, tulaermia, relapsing fever.