3.1.3: Coughing youngstock

Question 1

Describe the life cycle of lungworm

Answer 1

• Direct life cycle
• Relies on the presence of Pilobolus fungi to spread the larvae out of dung pat and to get eaten by cows
• Lungworm can overwinter on pasture
• L4 persist in the bronchi of grazing animals as inhibited L4
• Fomites (hooves, wellies, farm equipment) allow the larvae to travel within or between fields

Question 2

Epidemiology of lungworm

Answer 2

• Outbreaks generally seen in mid-late summer and autumn
• If coughing animals seen at pasture earlier in the year, it cannot necessarily be ruled out

Question 3

Pathology caused by lungworm

Answer 3

Question 4

Clinical signs of lungworm

Answer 4

• Mild: intermitten cough particularly when run around
• Moderate: frequent bouts of coughing at rest, tachypnoea, hyperpnoea, squeaks and crackles over the caudal lung lobes
• Severe: tachypnoea, dyspnoea, “air hunger” posture with head and neck outstretched and tongue stuck out when coughing. Sudden death may occur within 24-48hrs as airways so clogged with debris, inflammation and worms that they can’t breathe.

Question 5

Phase 1 of the host response to lungworm

Answer 5

Question 6

Phase 2 of the host response to lungworm

Answer 6

Question 7

Which of the following animals is most likely to show clinical signs due to lungworm?
a) first time grazing heifers
b) pregnant heifers
c) adult cows at grass

Answer 7

a) first time grazing heifers
They have not been exposed before to are most likely to get lungworm and have not yet got immunity to it.

Question 8

Can cattle be reinfected with lungworm even if they had it in their first grazing season?

Answer 8

Yes
* If they has low initial exposure which did not generate a long-lasting immune response e.g. just Phase 1 response which disappears after 6 months
* OR if they had a Phase 2 response but then didn’t go out to pasture for 3 years, this immunity could have waned

Phase 2 = reactivation syndrome, almost like hypersensitivity response. The immune response can end up killing the cows

Question 9

Describe how reactivation of husk can occur

Answer 9

Phase 2 immune response = reactivation syndrome, almost like hypersensitivity response. This can end up killing the cows.

Question 10

Summary of host response to lungworm including pre- and post-patent phases

Answer 10

Question 11

Diagnostic tests for lungworm in order of preference

Answer 11

• Tracheal wash/BAL OR Baermann’s test
• (Baermann’s is used most commonly)
• ELISA antibody test

Question 12

Tracheal wash / BAL to detect lungworm

Answer 12

✅ Detects adult worms in resp tract (adults are often seen first)
❌ Time consuming
❌ Expensive

Question 13

Baermann’s test to detect lungworm

Answer 13

✅ Commonly used
✅ Detects L1 in faeces - by the time we are looking at the cows, there will generally be larvae present
✅ Easy, simple and effective
✅ Non-invasive
❌ Negative result / low larvae numbers doesn’t mean you can exclude lungworm - you may just be slightyl early

Question 14

Antibody ELISA to detect lungworm

Answer 14

• Takes 4-6 weeks post-infection for antibody response (this is around the same time we will see clinical signs)
• Positive result tells us about previous exposure but not active infection
• Can do paired serology to see if rising titre
• Can do bulk milk sampling for convenience

Question 15

Answer 15

Lungworm L1 larvae

Question 16

1

Answer 16

Question 17

2

Answer 17

Question 18

3

Answer 18

Question 19

4

Answer 19

Question 20

Treatment of lungworm

Answer 20

• You must treat cattle with severe lungworm or they will die
• However, treatment may excerbate clinical signs and they may still die
• Supportive treatment: NSAIDs, not stressing/ moving cows too much
• Duration of action important in case cows get rechallenged later (unless they will be immediately housed)
• If bringing cows in: levamisole or similar
• If turning back out to grazing: ivermectin or similar duration of action
• Consider withdrawal periods and resistance; these drugs are active against gut worms so may be encouraging resistance of gut worms to the drugs.

Question 21

Control of lungworm

Answer 21

Question 22

How is delayed turnout useful for lungworm control?

Answer 22

• This gives overwintered larvae the chance to properly decline and die in hotter, drier weather
• This is not the preferred method by farmers

Question 23

How is rotational grazing useful for lungworm control?

Answer 23

• Rotational grazing not very effective for lungworms, much better for gutworms

Question 24

How is dose and move useful for control of lungworm?

Answer 24

• Can be effective
• However prophylactic treatment, and then moving straight after increases risk of resistance

Question 25

How is vaccination useful in lungworm control?

Answer 25

• Live attenuated vaccine; immunity lasts relatively long time
• Vaccine will not protect in times of really high challenge
• Vaccinated animals can still act as carriers; don’t mix vaccinated and unvaccinated calves
• If a herd has lungworm already, there is no need to vaccinate
• Do not worm the animals straight after vaccination
• Vaccine is more expensive than wormer - a barrier to its use

Question 26

Describe how you could use vaccination most effectively in control of lungworm

Answer 26

Question 27

When is lungworm larval survival poorer?

Answer 27

• Poorer in hot, dry weather
• Poorer with short sward height -> more exposed to elements

Question 28

Describe how you could use strategic treatment to control lungworm

Answer 28

• 1st time grazers = ensure coverage until at least mid-July using drugs with persistency (by this time, less fungal spores and less larvae)
• 1st treatment must be given within 3 weeks (the PPP) after turnout to eliminate the first generation of gravid female worms
• Treated cattle should be kept in the same fields throughout the grazing season; if they are moved to fields where untreated cattle have been grazed they are at risk again especially if wormers not longer active
• Treatment at housing: remove adult, larval and inhibited larvae (important in carrier animals) -> aims to get rid of residual worms and prevent carrier animals over winter)
• Targeted selective treatment does not work!
• Vaccination is the most sustainable and practical solution but it is more expensive.

Question 29

True/false: Targeted selective treatment is the best way to sustainably use anthelmintics for lungworm.

Answer 29

False
Targeted selective treatment does not work for lungworm!
If you decide to treat, you must treat the whole group otherwise some will die.