epidemiology of helminth infections

Question 1

Answer 1

Question 2

Answer 2

Question 3

what is the general term for a parasitic worm?
a. cestode
b. helminth
c. nematode
d. trematode

Answer 3

b. helminth

Question 4

term for a parasitic worm, circular in cross section?
a. cestode
b. helminth
c. nematode
d. trematode

Answer 4

c. nematode (eg roundworms)

Question 5

term for a parasitic flatworm with a segmented body?
a. cestode
b. helminth
c. nematode
d. trematode

Answer 5

a. cestode (eg tapeworms)

Question 6

term for a parasitic flatworm with no body segmentation?
a. cestode
b. helminth
c. nematode
d. trematode

Answer 6

d. trematode (eg liver flukes)

Question 7

what is a paratenic host?

Answer 7

a host that may pick up the juvenile stages of a parasite, in which they establish and persist but do not develop

Question 8

Most helminths cannot complete their lifecycle inside the one host, unlike viruses and bacteria.

Worms can reproduce and lay lots of eggs, but typically these eggs must exit the animal and develop in the environment, or in an intermediate host, before they can infect another host.

thus, if an animal has 10 worms, what is the minimum number of larval stages it must have been infected with?
*macroparasites = worms, microparasites = bacteria/viruses

Answer 8

a bare minimum of 10 (in reality, probably a lot more)

Question 9

worm burden is down to three things:
1. how many infective stages is the animal exposed to?
2. how many of those are establishing and developing?
3. how quickly are established worms being lost?
if 2 (worms establishing and devleoping) is greater than 3 (worms being lost), what will happen to the total worm burden?

Answer 9

it will increase

Question 10

distribution… are there:
a. more larvae high up grass leaves
b. more larvae close to the ground

Answer 10

b. more larvae close to the ground

Question 11

One way to measure development in hosts is the pre-patent period (PPP). This is the time from infection of the definitive host to the commencement of egg-laying by the parasites. [Once eggs appear in the host’s faeces, infection is said to be patent]
if the host is susceptible to parasite establishment for only a short period, there can be more cycles of parasite development if the parasite has:
a. a long PPP
b. a short PPP

Answer 11

b. a short PPP

Question 12

Going back to the idea that the burden reflects the number of new parasites establishing versus the number of older parasites being lost, then parasite numbers will build more rapidly if:
a. The parasites are short-lived
b. The parasites are long-lived

Answer 12

b. The parasites are long-lived

Question 13

how does competition effect worm egg shedding?

Answer 13

more competition (higher worm burden) = adults are smaller and lay fewer eggs

Question 14

how does temperature impact helminth growth?

Answer 14

Question 15

Question - given the above comments about the harmful effects of light, the survival of parasite infectious stages in the environment will be better in:
a. a newly sown paddock with low density of only grass species
b. a paddock of old grass with a high density of plants and mixture of broadleaf plants and grasses

Answer 15

b. a paddock of old grass with a high density of plants and mixture of broadleaf plants and grasses - more shading, better moisture retention

Question 16

why are high stocking rates more likely to increase parasitism?

Answer 16

Question 17

which breed would you expect to have better resistance to nematode parasites?
a. Merino
b. Romney

Answer 17

b. Romney

Question 18

what is the difference between resilience and resistance?

Answer 18

resistant - when exposed to a high challenge they better control and eliminate the parasites, or
resilient - when exposed to a high challenge they do better, even if more worms establish

Question 19

what is faecal aversion?

Answer 19

Question 20

why is this?

Answer 20

they’re now effectively browsing instead of grazing

Question 21

aotearoa New Zealand has a ‘cool temperate climate’ with the warmest season being summer and the coldest winter. Winters are in general mild with few frosts and summer is the season with the lowest on average rainfall, otherwise rainfall is spread reasonably evenly across the other seasons.

Given the above, what would you expect in terms of the season(s) with the greatest potential for the development of free-living larval stages?

Answer 21

late spring and early autumn (warm, without it being too dry yet)

Question 22

True or false - in any mob of animals, those with the highest egg counts will always have the highest worm burdens

Answer 22

false - they clearly have some worms, but not necessarily the highest. think about competition between worms etc

Question 23

True or false - if as animals age, they become less permissive of parasite establishment, then this always indicates an acquired immune response to parasites

Answer 23

false - this would ignore the potential for age-resistance, a process that does not involve acquired immune responses and happens even without prior exposure

Question 24

Answer 24

Question 25

For parasites with an indirect lifecycle, you are more likely to see year-round transmission if the intermediate host is: a. A cold-blooded invertebrate? b. A warm-blooded vertebrate?

Answer 25

b. A warm-blooded vertebrate - invertebrates are less active and less numerous in winter, hence risk of transmission will be lower

Question 26

The best animals to cross-graze with young lambs - in terms of removing the infectious stages of ovine nematodes would be: a. ewes b. young calves c. older cattle d. older goats

Answer 26

c. older cattle