Moving between hosts

Question 1

Distinguish between horizontal and vertical transmission

Answer 1

VERTICAL - parent to offspring

HORIZONTAL - same generation, between individuals

Question 2

Vertical transmission comes in many forms:

Answer 2

• cytoplasmic
• trans ovarian
• prenatal
• adhesion to egg surface
• postnatal (lactation)
• trans placental

Question 3

a) Direct horizontal transmission requires what?

b) Indirect horizontal transmission can come in 3 forms…

Answer 3

a) - physical contact
- contaminated environment
eg. water/ food/ host to host contact

b) - vector borne
- predator prey

Question 4

What influences protozoan direct transmission?

Answer 4

• environmental contamination
• behaviour infected and uninfected hosts
• host susceptibility (eg. young mammals)

Question 5

2 types of vector

Answer 5

a) Biological vectors
- haematophagous arthropods such as mosquitoes and other biting insects

b) Mechanical vectors
- flies for transport of amoeba cysts and other parasites

Question 6

Example of a direct transmission

Answer 6

Entamoeaba Histolytica

Question 7

Plasmodium (a) is a (b)-borne parasite that attacks red blood cells. (c) arrive from host and invade liver cells, allowing them to undergo (d) and become (e) which block capillaries.

Answer 7

a) falciparum
b) vector
c) sporozoites
d) schizogeny
e) merozoites

Question 8

Sarcosystis is an example of what transmission strategy (a)? Host- specificity is shown between (b) and (c) for example.

Answer 8

a) predator prey
b) dogs
c) sheep

Question 9

How do helminths show direct cycles?

Answer 9

• egg ingestion
• penetrate host skin
• mother’s milk or passed to foetus in utero

Question 10

How do helminths show indirect cycles?

Answer 10

• arthropod vectors
• species whose larval stages are small enough to be ingested & develop within vectors
• some important human pathogens