order: Rhabditida

Question 1

What class do Strongyloides species belong to?

Answer 1

Phasmidida

Question 2

What order do Strongyloides species belong to?

Answer 2

Rhabditida

Question 3

Name a Strongyloides species that infects pigs.

Answer 3

Strongyloides ransomi

Question 4

Name a Strongyloides species that infects rabbits.

Answer 4

Strongyloides papillosus

Question 5

What is the size range of Strongyloides species?

Answer 5

2-9 mm

Question 6

Where do Strongyloides species typically locate in the definitive host?

Answer 6

Small intestine

Question 7

What is a distinct morphological feature of Strongyloides species?

Answer 7

• Special shape of esophagus: long prebulbus and bulbus
• Hairy
• Free-living

Question 8

What are the two routes of infection for Strongyloides species?

Answer 8

• Tracheal route (pulmo-tracheal)
• Somatic route

Question 9

What happens during the tracheal route of Strongyloides infection?

Answer 9

Skin penetration (L3) - subcutis - lymphatic vessels - lympho-haematogenous transport to heart and lungs - pharynx - small intestine - adult females (day 6 in pigs, day 9 in ruminants)

Question 10

Lactogenic infection of piglets in the context of Strongyloides?

Answer 10

Lactogenic infection of piglets can take place until 3rd litter, as not all hypobiotic larvae are activated at once

Question 11

Describe the life cycle of Strongyloides.

Answer 11

Direct life cycle

1. L1 (rhabditiform) larva is shed in the feces of FH

Homogenic – typically happens in young animals, unfavourable conditions

• In environment some egg hatch and develop directly to infective L3 (filariform – infective stage)
• Larva re-infect host through skin or orally with pasture, food, water

Heterogenic – in favorable conditions, older, immune animals

• Larva L1 molts 4 times to free living adult worms
• They mate and female worms produce eggs
• Rhabditiform (non-infective – feeding form) hatch from the embryonated eggs, that molts 2 times to Filariform larva L3 (infective form – non-feeding)
• They can either complete development to adult males and females in the environment or infect a host through feed or skin.

2. Infection per os: larva L3 migrate directly to SI and mature there.

3. Infection per skin: The larva L3 migrate through blood to bronchi (not always), where they are coughed up and swallowed to the SI where they mature. Adult larva make egg in the intestinal mucosa.

• L1 hatch from the egg already in the intestine and autoinfection are possible. Autoinfection happens when L1 rhabditiform develop in the intestine to L3 filariform, which begin a migration from intestines to skin and then return to GIT.

OBS: Larvae produced don’t always follow the usual path to the lungs, but reach other organs, including the placenta, udders and milk. This way they can be directly transmitted to the suckling (lactogenic transmission) also transplacental is possible.

Question 12

What is the initial larval stage of Strongyloides shed in feces?

Answer 12

L1 (rhabditiform) larva

Question 13

What are the two types of cycles in Strongyloides life cycle?

Answer 13

• Homogenic
• Heterogenic

Question 14

What is the infective stage of Strongyloides?

Answer 14

L3 (filariform)

Question 15

How can L3 larvae infect a host?

Answer 15

• Through skin
• Orally with pasture, food, water

Question 16

What is autoinfection in Strongyloides?

Answer 16

When L1 rhabditiform develop in the intestine to L3 filariform and migrate from intestines to skin, then return to GIT

Question 17

What are common clinical signs in young animals infected with Strongyloides?

Answer 17

• Pulmonary symptoms
• Dermatologic symptoms
• Abdominal pain
• Distention
• Shock
• pulmonary and neurological symptoms in immunosupressed animals

Question 18

What is a common treatment for Strongyloides infections?

Answer 18

• Ivermectin
• Doramectin
• Levamisole
• Thiabendazole
• Fenbendazole

Question 19

What are some control methods for Strongyloides infections?

Answer 19

• Good hygiene
• Removal of feces
• Dry bedding
• Cleaning pens of animals

Question 20

What diagnostic methods can be used for Strongyloides?

Answer 20

• Faecal flotation
• Larvoscopic method (Baermann technique)

Question 21

Eggs of Strongyloides

Answer 21

• small
• oval, symmetrical
• 2 thin shells
• embryonated (L1)
• Light grey/transparent colour

Question 22

Strongyloides routes:

Answer 22

1. Tracheal route (pulmo-tracheal):
Skin penetration (L3) - subcutis - lymphatic vessels - lympho-haematogenous transport to heart and lungs - pharynx - small intestine - adult females (day 6 in pigs, day 9 in ruminants)

2. Somatic route:
Larvae pass in bloodstream to the lungs - blood to organs (fat, mammary gland, striated muscles) - In body tissues, parasitic larvae (L3) can remain viable in hypobiotic state for long periods - “somatic larvae” becomes activated shortly before birth and migrate to mammary gland enabling colostral and lactogenic infection. Lactogenic infection of piglets can take place until 3rd litter, since not all hypobiotic larvae are activated at once. The excretion of larvae in milk is highest at the beginning of lactation. Duration is different in different species (horse the longest, sheep and pigs the shortest).

Question 23

Strongyloides spp:

Answer 23

• Strongyloides ransomi – pig
• Strongyloides papillosus – Ru, rabbit
• Strongyloides westeri – horse, donkey
• Strongyloides stercoralis – dog, cat, man (zoonotic), monkey
• Strongyloides ratti – rats
• Strongyloides avium – birds (SI & caeca)