Lungworm in cattle

Question 1

Which worm is most common in cattle? And sheep?

Answer 1

• Dictyocaulus vivparus (cattle)
• Sheep (Dictyocaulus filaria/muellerius capillaris most common)

Question 2

What are risk factors for lungworm?

Answer 2

◦ Wetter/western area
◦ Late summer/Autumn
◦ High stocking densities
◦ First season grazers/naïve animals

Question 3

Lifecyle

Answer 3

• L1 passed in faeces
• Develops into infective L3 (takes <1 week in optimal conditions)
• Rain, vectors and Pilobolus fungus aid dispersion of L3 from dung.
• L3 ingested, migrate to lungs, develop into adults which produce eggs.
• Eggs hatch and L1 larvae coughed up and swallowed.
• PPP=3-4 weeks, very fecund and L1-L3 development fast = high infection levels can develop quickly.
• Carrier animals (inhibited L4) and L3 overwintering on forage are both sources of infection.

Question 4

Pathogenesis

Answer 4

• Ingested L3 become more active in the presence of bile.
• Cross small intestine into lymphatic system and mesenteric lymph nodes then to the lungs.
• Colonise alveoli then bronchioles, ending up as adults at the base of the trachea.
• Promotes inflammation, eosinophil rich mucus and parasite debris.
• Alveolar epithelialisation = cells incapable of gaseous exchange.
• Loss of ciliated epithelium = more prone to other respiratory infections.

Question 5

Different presentations of carrier animals, subclinical disease and clinical disease

Answer 5

• carrier animals
  ◦ few adverse effects for individual
• subclinical disease
  ◦ weight loss (50-100 gpb/animal)
  ◦ milk drop (3gbp/cow/day)
• clinical disease
  ◦ coughing
  ‣ may be mild and brought on by exercise through to persistent and present at rest
  ◦ dyspnoea & tachypnoea
  ‣ may have abducted elbows and outstretched neck.
  ‣ may auscultate squeaks and crackles over posterior lung lobes
  ◦ mortality
  ‣ sudden death may occur within 24-48 hours

Question 6

What are the 4 phases of clinical presentation?

Answer 6

• penetration phase
  ◦ Days 1-7 post infection
  ◦ Larvae penetrate body of host and migrate to lungs
• pre-patent phase
  ◦ Days 8-25 post infection
  ◦ Larvae develop in the lungs
  ◦ Can see clinical signs during this phase
• patent phase
  ◦ Days 26-60 post infection
  ◦ Worms mature and produce eggs
• post-patent phase
  ◦ Days 61-90 post infection
  ◦ Recovery phase once adult worms have been expelled
  ◦ Post-patent parasitic bronchitis can cause severe clinical signs/death

Question 7

How would you diagnose lungworm?

Answer 7

• Clinical signs and grazing history (risk factors)
• Detection of L1 in faeces (Baermann technique)
  ◦ If negative could cattle be in the pre or post patent phase, or could it be re-infection syndrome?
• Examination of sputum for eggs/larvae – detects patent infections slightly earlier than faecal samples.
• Bulk milk or blood ELISA (antibody)
  ◦ Sensitivity of ELISA for patent infections is low
  ◦ Seroconversion can take 4-6 weeks
  ◦ Bulk milk useful for routine monitoring of dairy herds
• Post-mortem
  ◦ Adult worms seen in bronchi and bronchioles

Question 8

How can you treat lungworm? How can you pick which one is best to use?

Answer 8

• Wormers
  ◦ Group 1 – Benzimidazoles – no persistent action
  ◦ Group 2 – Levamisole – no persistent action
  ◦ Group 3 – Macrocyclic lactones – persistent action
• When considering which wormer to use, duration of action is an important consideration if going back into a potentially ‘dirty’ field – MLs have persistent activity (4-6 weeks), neither levamisole or benzimidazoles do (last about 24hrs).

Question 9

What grazing strategies can you use to control lungworm?

Answer 9

◦ Delay turnout – keep stock in until late April/May to reduce larval levels that have overwintered
◦ Rotational grazing – Outbreaks are less predictable than parasitic gastroenteritis, so this is harder to utilise (will cover in relation to PGE)