Exam II - Strongyloides westeri

Question 1

What is the common name for Strongyloides westeri?

Answer 1

threadworm

Question 2

What is the infective stage for Strongyloides westeri?

Answer 2

L₃

Question 3

What is/are the host(s) for Strongyloides westeri?

Answer 3

All equids

Question 4

Describe the appearance of Strongyloides westeri adults

Answer 4

slender hair-like nematode, less than 1 cm long. Long esophagus can occupy ~1/3 of body length

Question 5

Describe the appearance of the Strongyloides westeri egg

Answer 5

Thin-shelled larvated eggs 30-40 um in size in fresh feces

**Note that Strongyloides westeri eggs are laid embryonated

Question 6

List the 2 life cycle phases for Strongyloides westeri

Answer 6

Parasitic (homogonic) and Free-living (heterogonic)

Question 7

Which life cycle phase of Strongyloides westeri is parasitic?

Answer 7

homogonic

Question 8

In favorable environmental conditions, which life cycle phase of Strongyloides westeri predominates?

Answer 8

heterogonic

The free-living larvae hatch from eggs and develop in the soil directly to adult males and females. The females lay eggs, which develop into free-living L₃. These infect percutaneously and per os (from grss or through milk)

Question 9

Describe the homogonic life cycle of Strongyloides westeri

Answer 9

Eggs containing a fully developed, sheather L₁ are passes in feces. In the soil, L₁ develop to L₃.

**Infective L₃ **penetrate the host’s skin or oral mucosa to undergo migration to the heart, through the lungs and up the trachea, are swallowed and then migrate to the intestine.

There, they develop to adult females (only) and parthenogenesis takes place. PPP is 10-14 days

Question 10

What is the PPP for the homogonic life cycle of Strongyloides westeri?

Answer 10

1-2 weeks

Question 11

Which life cycle phase of Strongyloides westeri predominates in unfavorable environmental conditions?

Answer 11

homogonic

Question 12

How soon after infection is Strongyloides westeri larvae present in the milk of a mare?

Answer 12

by the 4^th day

Question 13

What is/are the site(s) of infection for Strongyloides westeri?

Answer 13

Adults in small intestine. Larvae in somatic tissues

Question 14

Describe any pathogenesis associated with Strongyloides westeri

Answer 14

Erythematous reaction (redness) where larvae penetrate the skin

Question 15

What are some clinical signs associated with Strongyloides westeri larvae

Answer 15

Larvae cause urticaria. “Frenzy” has also been described

Question 16

What are some clinical signs associated with Strongyloides westeri adults

Answer 16

diarrhea. Primarily observed in young horses. Can occur in older horses, but less common

Question 17

At what age might you expect to see Strongyloides westeri in horses?

Answer 17

Expect to see in horses less than 5 months old

Question 18

Which life cycle stage is revealed with fecal flotation of Strongyloides westeri?

Answer 18

L₁ in egg

Question 19

If you think you see a Strongyloides westeri in fecal flotation, but the horse is older than 5 months, what should you suspect instead?

Answer 19

Any suspect egg seen in older animals is likely a strongyle egg

Question 20

Which diagnostic method(s) would you use to diagnose Strongyloides westeri?

Answer 20

Fecal flotation, Baermann technique