Adaptations to Parasitism

Question 1

What is a parasite?

Answer 1

Macroparasite: Helminths (endoparasites), arthropods (ectoparasites)
Microparasites: Protozoa, viruses, bacteria etc.

Question 2

Hookworms

Answer 2

Common human infection
Must survive environment of lungs and gut
Eggs can survive in unfavorable soil environments by undergoing cryptobiosis (forms external outer wall until conditions improve

Question 3

Malaria

Answer 3

Vector transmitted
Malaria and mosquitos are both vectors
Plasmodium gametocytes > first infected mosquito > first infected human > infected RBC > second infected mosquito > second infected human

Question 4

Mouthparts

Answer 4

Structures for penetration and attachment to host
Helminth mouthparts: hooks, suckers, teeth (grip inside on organ walls)
Needle-like mouthparts (induce immunomodulatory change)
Barbed mouthparts (i.e. ticks, saw into skin, once in barbs form a tight grip in the tissue

Question 5

Body shape and size

Answer 5

Dorso-ventrally flattened to prevent host removal
A common feature of ectoparasites (external parasites) that could be groomed off by the host
immunomodulatory activities, capable of inhibiting host defense reactions (e.g. inflammation)

Question 6

Avoiding Digestion

Answer 6

Strong impermeable cuticle (nematodes) or tegument (cestodes (tapeworms))
Several layers arranged around each other
pH of gastric acid is 1.5 to 3.5

Question 7

Helminth physiological adaptations

Answer 7

attacked by the immune system, and digestive enzymes
The helminth stimulates the host gut to secrete huge amounts of mucous that surrounds the parasite and protects it from the digestive juice of the gut
Most helminths produce antienzymes which protect them from the gastric juice and digestive enzymes of the host

Question 8

Reduced unnecessary functions

Answer 8

Reduced sense organs, nervous system, locomotion and digestive system
High fecundity – tapeworm produces proglottids (proglottid = fully functional form ready to infect)

Question 9

Antigen

Answer 9

An antigen is a substance that induces the formation of antibodies, because it is recognized by the immune system as foreign to the body

Question 10

Molecular Mimicry

Answer 10

Blood fluke
uses snail as intermediate host
possesses sugars that are similar to snail lectins
making it hard for immune system to recognise fluke as foreign

Question 11

Antigenic variation

Answer 11

bacterium or virus alters its surface proteins to evade host immunity
allows reinfection by virus

Question 12

Host finding behaviour

Answer 12

CO2, heat and movement are stimuli

ticks sit in vegetation and wait for animal to brush past

Question 13

Periodic behaviour

Answer 13

Filarial worms – live in blood and are transmitted by mosquito or flies.
Microfilariae move to peripheral blood on periodic basis
This movement corresponds to “biting hours” of vector

Question 14

Modifying host behaviour - Toxoplasma gondii

Answer 14

Rat is intermediate host
Infected rats show no fear towards scents of predators (i.e. cats)
It therefore makes it easier for cats to eat them
Parasite can then begin its reproductive cycle within the cat

Question 15

Modifying host behaviour - parasitic nematode Mymeconema neotropicum

Answer 15

infect Worker Ant Cephalotes atratus
Worker ants that are infected have altered abdomens which appear red (like a berry)
This is attractive to fruit eating birds
Birds eat the ant and spread the parasite in their droppings