Respiratory Parasitic Infections - Pathology

()Map CARDIORESPIRATORY SYSTEM (Map) RESPIRATORY SYSTEM INFLAMMATION

In Cats

Linguatula serrata

• As in dogs above

Capillaria aerophila

• As in dogs above

In Horses

Besnoitia bennetti

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

In Cattle

Dictyocaulus viviparus

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)

• Preferentially in dorsocaudaland ventrocaudal regions

• Histologically
  • Bronchial epithelium may show hyperplasia due to the chronic irritation
  • Cross-sections of the parasites
  • Exudate contains many eosinophils
  • Foci of necrosis in the rest of the lung tissue due to aspiration of eggs and larvae fromhese adults
  • In mild infestations, the adults are normally expelled in two months - self cure
• Repeated infestation and secondary bacterial infection are common

• 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

Hydatid cysts

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

Syngamus laryngeus

• In larynx of cattle in Asia and South America

In Sheep

Hydatid cysts

As in cattle (above)

Oestrus ovis

• Larvae in the nasal cavity of sheep and goats = Nasal bots
• Causes reaction in sinuses

Media:Oestrus ovis.mp4

Protostrongylus spp.

• 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

Muellerius capillaris

• 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

Dictyocaulus filaria

• Most susceptible when first exposed to contaminated pasture
• Animals < 1 year old
• Pathogenesis and pathology similar to Dictyocaulus viviparus in cattle
• Bronchitis

In Pigs

Metastrongylus spp.

• 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

Ascaris suum

• 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