Dictyocaulus viviparus - Cattle lungworm

What are the relevant species of dictyocaulus and the species they occur in?

• Trichostrongyle lungworms

• Dictyocaulus viviparus —> cattle, dairy replacement heifer calves

• D. filaria —> sheep and goats (highly pathogenic)

• D. arnfieldi —> resp dx in horses (non patent) and donkeys (patent infection, no dx, carriers)

What lungworms occur in sheep in the UK?

• Dictyocaulus filaria (more in tropics and sub tropics)

• Muellerius capillaris

What disease is caused by dictyocaulus viviparus?

• Parasitic bronchitis = 'husk', dictyocaulosis

What is the morphology of adult dictyocaulus viviparus worms?

• 4-8cm long

• Slender, white

• Male has reduced bursa

Where in the UK are dictyocaulus vivparus most common?

Wetter west of UK

Where in the lungs are dictyocaulus viviparus found?

Trachea and bronchi

What are the general features of the life cycle of dictyocaulus?

• Direct

• Female worms ovo-viviparous —> lay larvated eggs which hatch immediately

• L1 in lungs coughed up, swallowed, passed out in faeces

What are the features of L1, L2 and L3 of dictyocaulus?

• L1 = in faeces

  • Short and stumpy

  • Refractile food granules

    

• L1-L3 develop in faecal pat on pasture

• All ensheathed —> never shed sheath from previous stage

  

• Larvae don't feed

• (L3 is infective stage)

How long does it take for L1-L3 of dictyocaulus?

Can develop to L3 in 5-7 days in optimum conditions

What are the in animal phases of dictyocaulus viviparus life cycle?

• Penetration phase

• Pre-patent phase

• Patent phase

• Post patent phase

What happens in the penetration phase of dictyocaulus viviparus life cycle?

• 0-7 days after infection

• L3 ingested, migrates

• Lympho-tracheal migration (goes via lymph and blood to reach lungs)

• Moults to L4 in LN

• L4 reaches lungs (in capillaries of alveoli supplying lungs)

What happens in the pre patent phase of dictyocaulus viviparus life cycle?

• 8-25 days post ingestion

• L4-L5 in lungs (enter alveoli)

• L5 migrate up bronchial tree

• Adults in bronchi and trachea ~3.5 weeks post ingestion

What happens in the patent phase of dictyocaulus viviparus life cycle?

• 26-55 days after infection

• Adult worm in upper respiratory tract reproduce

• Eggs and L1s produced

What happens in the post-patent phase of dictyocaulus viviparus life cycle?

• 55 days +

• Immune expulsion of adults

• Protective immunity

Which are the most pathogenic phases of the dictyocaulus life cycle?

Prepatent and patent phases

Which calves are most severely affected by dictyocaulus?

Smallest & weakest

Describe the pathology and clinical signs seen in the pre patent phase of dictyocaulus

• Intense inflammatory response

• Alveolitis, bronchiolitis, bronchitis

• Interstitial emphysema

• Pulmonary oedema

• Coughing, resp distress, tachypnoea, weight loss

Describe the pathology and clinical signs seen in the patent phase of dictyocaulus?

• Mature adults in bronchi/trachea

• Eggs and L1 swept into alveoli

• Intense inflammatory response

• Frothy, white mucus

• Emphysema, hypoxia

• Gasping, coughing, death

Describe the pathology and clinical signs seen in the post patent phase of dictyocaulus?

• Resolution of clinical signs

• In some animals, epithelialisation of lung tissue, never completely recover

What factors affect the pre parasitic stage of dictyocaulus?

• Temperature

• Moisture

• Dispersal of L3

• L3 overwinter on pasture

• L1 shed by carrier animals

How are dictyocaulus dispersed form the faecal pat?

• Pilobolus fungi in faecal pat bursts and brings L3 with them

• Can disperse quite far so hard to evaluate risk

Describe the epidemiology of dictyocaulus in the UK?

(Unpredictable)

• Usually in Aug-Sept

• Usually in dairy replacement calves

• First cycle of infection —> very few L3 picked up, no immunity, no disease

• Calves shed L1, these develop to L3, cause outbreaks of disease

• Disease can happen from turn out to Nov depending on levels of L3

• Immunity short-lived —> needs continual boosting

How many Dictyocaulus worms are needed to cause clinical disease?

800-1000

How is dictyocaulus diagnosed?

• Clinical signs

• L1 in faeces using a Baermann

• Antibody detection ELISA

How does a Baermann funnel work?

• Faecal matter suspended in filter at top, larvae are motile and will swim down and will congregate at bottom of funnel

• Run off about 10 ml at bottom and can count number of larvae

How is dictyocaulus treated?

• Rapid use of anthelmintics

• NSAIDs, antibiotics

• House most severely affected calves

Why can't you treat prophylactically for dictyocaulus?

If prophylaxis given no immunity builds so adult cattles remain naïve

How does dictyocaulus affect milk yield?

Reduction in milk yield, when overt clinical disease

What vaccine is available for dictyocaulus? What are its features?

Huskvac

• Live, attenuated vaccine

• 1000 irradiated L3 given orally

When do you give Huskvac?

• Two doses four weeks apart

• Before turnout

• Requires natural boosting to maintain immunity

What are the differences between lungworms & gut worms?