Respiratory Parasitic Infections - Pathology

Found in smaller bronchi
Cause of chronic cough
Donkeys are a reservoir mostly without any clinical signs
Gross pathology:
- Raised areas of over-inflated pulmonary tissue surrounding small bronchus, containing worms and mucopurulent exudate
- Hyperplastic bronchial epithelium
- Coiled worms in small bronchi
- Peribronchial cuffing
- In caudal lung lobes
Histologically
- Central coiled parasites and associated chronic catharral bronchitis
- Goblet cell hyperplasia
- Lymphoid cell infiltration
In horses, the worms usually fail to achieve sexual maturity

Papilloma like lesions in larynx, skin and sclera
Thick walled parasitic cysts, covered by hyperplastic epithelium, may be ulcerated

In Cattle

Dictyocaulus viviparus (Image sourced from Bristol Biomed Image Archive with permission)

Parasitic bronchitis (Image sourced from Bristol Biomed Image Archive with permission)

Found in trachea and large bronchi
Causes parasitic bronchitis, synonyms: bovine dictyocauliosis, husk, hoose
Primary infection:
- Penetration phase (week 1)
  - Larvae migrate to lungs, no clinical signs
- Prepatent phase (weeks 1-3)
  - Development and migration of larvae -> bronchiolitis -> eosinophilic exudate -> air passage blocked -> alveolar collapse (distal to blockage) -> clinical signs (tachypnoea, coughing)
- Patent phase (weeks 4-8)
  - Egg-producing mature worms
  - Bronchitis - due to mature worms
  - Parasitic pneumonia - due to aspiration of eggs and larvae -> cellular infiltration of neutrophils, macrophages, giant cells
- Postpatent phase (weeks 8-12)
  - Majority of worms are expelled
  - In 25% of cases clinical signs may reappear as a result of alveolar epithelialisation
  - May be together with interstitial emphysema and pulmonary oedema, or secondary bacterial infection
Reinfection syndrome:
- Immune cattle show clinical signs only if exposed to large numbers
- Pathogenesis - large numbers of larvae reach bronchioles where they are killed by immune response
- Pathology - parasite granulomata (grey-green, 5mm diameter, macrophages, giant cells, eosinophils) and eosinophilic plugs in bronchioles

Above from RVC Parasitology study guide (2005-2006)

Two other types of lesion in lung tissue due to this worm have been reported:
- Nodules (2-4mm in diameter) with greenish centres in the reinfection of an immune animal - the host mounting a successful defence and preventing larval migration
- Pulmonary oedema and emphysema - thought to be a hypersensitivity response to a massive invasion of larvae in previously- sensitised animals - the gross and microscopic appearance is similar to that of fog fever

Echinococcus cysts (Image sourced from Bristol Biomed Image Archive with permission)

The intermediate stage of Echinococcus granulosus can be found in the lungs of many species, most commonly in lungs of cattle and sheep
They range in size up to 5-10 cm diameter and although of little clinical significance, are important as a zoonosis (can be upto football size in man) and because of carcass condemnation

As in cattle (above)

Adult worms block small bronchioles resulting in accumulation of eggs, larvae and cellular debri distal to the blockage
Lesions resemble Dictyocaulus filaria but are fewer in numbers, lobular and at periphery of caudal lobes, they are very similar to Muellerius capillaris lesions

Common in sheep and goats
Rarely any clinical significance
Grossly:
- Multifocal interstitial pneumonia grossly evident as firm "lead-shot" nodules throughout the parenchyma, often with enveloping granulomatous response
- Early stages are reddish in colour, turning later to greyish green, may calcify
- Mostly in dorsal region of caudal lung lobes
Histologically:
- Damaged alveolar septa with mild fibrous thickening and lymphocytic infiltrate
- In more developed host resistance, foci of eosinophils around larvae, hyperplastic epithelium, macrophages, giant cells
- May be some calcification

Found in bronchioles and smaller bronchi
Grossly:
- Small grey nodules, especially along ventral border of caudal lobes
- Adult worms in bronchi and bronchioles
Histologically:
- Catarrhal and eosinophilic bronchitis and bronchiolitis
- Possibly atelectasis
Rarely becomes extensive
May transmit swine influenza

May cause parasitic pneumonia during a part of its migration
Larvae may be infected with Swine influenza
May cause severe pneumonia in calves housed where infected pigs were housed previously
Cause diffuse interstitial pneumonia with haemorrhage, atelectasis, interlobular oedema and emphysema