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 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