Parasitology - Respiratory - Large & Small Animal Lungworm + Nasal Myiasis

Question 1

What is the lung worm that affects cattle?

Answer 1

Dictyocaulus viviparus


Question 2

Dictyocaulus viviparus is a:

1. Cestode
2. Nematode
3. Trematode
4. Protozoan

Answer 2

2. Nematode- member of Trichostrongyloidea superfamily. It’s a strongyle less than 8 cm long.

Question 3

Where is the site of infection of Dictyocaulus and how does it get there?

Answer 3

Dictyocaulus viviparus infects the trachea & bronchi of cows.

It gets there by the cow ingesting L3 infective larvae in dungpat on pasture. The larvae develop into adults & migrate via intestine → lymphatics → venous blood → **lungs ** → up respiratory tree to trachea

In trachea, adults lay embryonated eggs, which are coughed up & swallowed. Eggs hatch in alimentary tracts and pass out as larvae in faeces.

Question 4

How do the L3 larvae, passed out in faeces, get around the pasture from the dungpat?

Answer 4

Fungus Pilobolus, which “explodes”, distributing the larvae around.

Question 5

What is the condition caused by the bovine lungworm, Dictyocaulus viviparus?

Answer 5

Bovine dictyocaulosis or husk or hoose.

Reduced weight gain & milk yield.

Question 6

How does the ability of the L3 larvae of Dictyocaulus viviparus to over-winter in the hosts contribute to its epidemiology?

Answer 6

Most L3 that are excreted in faeces during the winter end up dying, but those that overwinter in the host are deposited in the spring; a relatively low number of this species appear to overwinter.

Question 7

What is the difference btween the overwintering site of Ostertagia & Dictyocaulus?

Answer 7

Ostertagia overwinter in the bovine abomasum while Dictyocaulus overwinter in the bovine lungs.

Question 8

What is the difference in carrier status of husk vs ostertagiosis?

Answer 8

With Dictyocaulus, 30% of yearlings and 5% of cows are carriers of husk & they play a much bigger role in transmission than overwintering L3. There could be several cycles of lungworm infection before an outbreak - fewer outbreaks.

With ostertagia, cows are solidly immune but all new calves are susceptible, so there’s an outbreak after just one cycle.

Dictyocaulus get around by pilobolus fungi, but ostertagia is much more motile because the worm is able to swim in a film of moisture.

Question 9

How does the fact that Dictyocaulus viviparus relies in its larval stage to be distributed by fungal Pilobolus, while Ostertagia L3 can swim on thin film of moisture?

Answer 9

Ostertagia larvae are more motile.

Question 10

Do cows acquire immunity faster against Ostertagia or Dictyocaulus?

Answer 10

Dictyocaulus

Question 11

What causes parasitic bronchitis in cattle?

Answer 11

Infection by the lungworm, Dictyocaulus viviparus. Larval migration to lungs causes eosinophilic reaction, exudate, blocking passage of air and alveolar collapse distal to blockage in the bronchioles. Adults worsen the situation by laying lots of eggs that get coughed up.

Pulmonary oedema is possible, and secondary infection.

Question 12

What is used to prevent husk?

Answer 12

Attenuated oral vaccine that contains irradiated L3: Bovilis Huskvac

Can also use ivermectin after turnout

Question 13

What are the lungworms that affect sheep & goats?

Answer 13

Dictyocaulus filaria

Muellarius & Protostrongylus spp (common but less important)

Question 14

What are the clinical signs caused by Dictyocaulus filaria in sheep and goats?

Answer 14

Chronic cough & unthriftiness in lambs & kids.

Question 15

The life cycle of Dictyocaulus filaria is similar to that of Dictyocaulus viviparus that affects cattle. It has two passes through the host system. It is direct and involves the ingestion of larvae that migrate to lungs, develop into adults that lay embryonated eggs, which are then swallowed and make their way back out with faeces. There they develop into infective larvae, which are ingested.

What are the life cycles of the other ovine lungworms, Muellarius and Protostrongylus?

Answer 15

They are indirect and involve the intermediate host of a mollusc.

L1 larvae penetrates foot of mollusc, which is eaten by the sheep or goat. Inside, larvae reaches L3 stage and enters lungs via lymphatics.

Question 16

Where are Muellerian & Protostrongylus lungworms found?

Answer 16

Muellerian are found in the alveoli & parenchyma of the lungs while Protostrongylus are found in the small bronchioles.

Question 17

Why would palpation of the ventral aspect of a cow help diagnosis of Muellerian lungworm infection?

Answer 17

Nodules containing adult worms, eggs and larvae and they are palpable just below the lung’s surface, a bit like lead shot.

Question 18

What is the lungworm that infects horses?

Answer 18

Dictyocaulus arnfieldi

Question 19

How does the life cycle of the horse lungworm differ from that of the cow & sheep/goats?

Answer 19

Unlike cow and sheep lungworm, where the eggs are coughed up, then swallowed, hatch and larvae passed in faeces, horse lungworm eggs don’t hatch in the body but are passed out as embryonated along with fresh faeces.

Question 20

What is the main source of infection for horses and other equidae?

Answer 20

Donkeys, which remain infectious for years. They contaminate pasture.

Question 21

What are the clinical signs of equine lungworm in a horse?

Answer 21

Chronic cough at rest or during exercise

Usually autumn or early winter

Question 22

What are other parasites besides Dictyocaulus arnfieldi that can cause respiratory infection?

Answer 22

Parascaris equorum, which does hepato-tracheal migration

Echinococcus granulosum, which forms hydatid cysts in intermediate hosts including horses

Question 23

What is the main porcine lungworm?

Answer 23

Metastrongylus spp - it has an indirect life cycle, in which the earthworm is the IH

Question 24

Where are metastrongylus lung worms found in the pig and how do they get there?

Answer 24

Bronchioles and smaller bronchi.

Larvae migrate via mesenteric lymph nodes from intestine to lungs.

Question 25

What is the main canine lungworm?

Answer 25

Angiostrongylus vasorum. This is also a heart worm that lives in the pulmonary arteries and right side of the heart.

Question 26

What is the intermediate host of Angiostongylus vasorum nematode that affects canids?

Answer 26

Slug

Question 27

How do Angiostrongylus vasorum larvae get to the heart and lungs from the gut?

Answer 27

They migrate via the mesenteric lymph nodes into the venous blood, to the right side of the heart, where they reach adulthood and lay eggs.

The eggs are pumped into the lungs, where they are “trapped” in the lung capillaries. There, they hatch and the larvae crawl up from the alveoli back up to the trachea, where they are swallowed and pass out with faeces.

Question 28

What is the lungworm that affects cats?

Answer 28

Aelurostrongylus abstrusus - a metastrongyloid that uses a mollusc as an intermediate host.

Larvae penetrate host, which is eaten by cat. Larvae migrate to lungs, become adults, lay eggs, which are coughed up and swallowed. They hatch and become larvae again, and are excretd by cats in faeces.

It’s pretty uncommon and is asymptomatic unless the cat is immunocompromised already.

Question 29

How can lungworm be treated in dogs and cats?

Answer 29

Angiostrongylus vasorum, which affects dogs, can be treated with moxidectin or milbemycin.

Others require high doses of benzimidazoles.

Fenbendazole can be used to treat cats with Aelurostrongylus.

Question 30

What parasite causes nasal myiasis in sheep?

Answer 30

Oestris ovis (sheep nasal bot fly)

Question 31

What is special about the way the Oestrus ovis nasal bot fly infects sheep?

Answer 31

It shoots a jet of liquid containing larvae into sheep nostrils. These crawl up and end up parasitizing the nasal passages and frontal sinus before they migrate back to the nostrils and are sneezed out to pupate on the ground.

Question 32

The sheep nasal bot can cause serious damage including neurological signs. How?

Answer 32

The larvae can erode bones in the sinuses and penetrate the brain, causing high-stepping gait and incoordination, known as “false gid”.

Question 33

What is the tongue worm? What species does it infect and what damage does it cause?

Answer 33

Linguatula serrata is the tongue worm, so-called because it looks like a tongue.

It’s a crustacean.

They are found in the nasal passages of dogs and sometimes cats. They lay eggs in the nose, and these eggs are sneezed out. Herbivores like rabbits or ruminants eat them while grazing, and the eggs hatch in the intermediate host’s intestine. As larvae, they migrate to the mesenteric lymph nodes where they encyst to become infective nymphs.

Dog eats uncooked viscera containing cysts or nymphs. While the dogs are chewing the meat, the nymphs migrate up into nasal cavity via soft palate.