Respiratory Parasitic Infections - Pathology

()Map CARDIORESPIRATORY SYSTEM (Map) RESPIRATORY SYSTEM INFLAMMATION

In Dogs

Filaroides osleri

• = Oslerus osleri
• Colonise the trachea of dogs
• Larva and adults accumulate in submucosal nodules of up to 1cm diameter at the tracheal bifurcation.
• Minimal inflammatory host reaction to the nematodes when they are alive - the size of the nodule is related to the number and size of the nematodes within it.
• When the parasites die, an intense foreign body reaction develops
• Tracheal nodules can cause coughing, usually in young dogs <18 months old.
• Severe infestation can cause significant occlusion of the airway.
• Uncommon, but sometimes seen in coughing greyhounds

Linguatula serrata

• Synonym: tongue worm
• In nasal passages of dogs, sometimes cats
• May reach the sinuses
• Heavy infections may cause sneezing, coughing, nasal discharge

Angiostrongylus vasorum

• Adult worms live in the pulmonary arteries and right side of the heart dogs and foxes
• Cause a proliferative endoarteritis
• More severe damage is caused however by eggs lodging in arterioles and capillaries
• In severe infection, this can result in pneumonia and pulmonary oedema as an acute syndrome
• Circulatory impedance can result in congestive cardiac failure
• Particularly a problem if dogs eats snails
• Gross:
  • Patchy white appearance with haemorrhagic areas within
• Microscopically:
  • Golden pigment within macrophages (haemosiderin)
  • Inflammation and scarring of alveolar walls -> enlargement of remaining air spaces
• Worms secrete anticoagulant -> haemorrhage in other parts of body
• May present as neurological cases due to the haemorrhage
• May cause pulmonary thromboembolism

Dirofilaria immitis

• Establish in heart and pulmonary arteries
• Larvae migrate through connective tissue
• Immature adults move to caudal distal pulmonary arteries causing diffuse eosinophilic reaction in lung parenchyma, then migrate back to right ventricle
• May cause pulmonary thromboembolism

Capillaria aerophila

• In nasal passages, sinuses, trachea and bronchi of cats and dogs
• Some dogs cough but often no symptoms
• Mild catharral inflammation
• In heavy infestation may cause obstruction of the lumen of airways and may develop into secondary bronchopneumonia

Toxoplasmosis

• Caused by Toxoplasma gondii
• Cats are definitive hosts but other species may become intermediate hosts if they ingest the oocysts
• Usually induces antibody response but remains silent clinically
• Often show clinical signs when immunosuppressed
• Involves many different tissues
• Multifocal necrotising interstitial pneumonia
• Proliferation of type II pneumocytes
• Macrophage and neutrophil infiltration

Crenosoma vulpis

• Mainly parasite of foxes but dogs may become infected from snails and slugs
• Adults in small bronchi and bronchioles
• Grossly:
  • Greyish lesions and consolidation in dorsal aspect of caudal lung lobes
• Histologically:
  • Catharral, eosinophilic bronchitis ans bronchiolitis

In Cats

• Useful websites:
  • Cat and dog respiratory parasites (part 1) - Nasal Mucosa and Sinuses, and Respiratory Parenchyma
  • Cat and dog respiratory parasites (part 2) - Trachea and Bronchi, and Pulmonary Vessels

Linguatula serrata

• As in dogs above

Aelurostrongylus abstrussus

• Live in lung parenchyma and small bronchioles
• Grossly:
  • Firm yellow nodules scattered throughout parenchyma, more frequently at periphery
• Microscopically:
  • Eggs and larvae in the alveolar spaces cause a foreign body type reaction (surrounded by mononuclear cells and giant cells)
  • Submucosal gland hypertrophy and smooth muscle hypertrophy in airway and vessel walls
• Associated clinical signs are mild although heavy infestations may -> chronic coughing
• The airway eosinophilia which may be detected can be confused with a diagnosis of asthma

Dirofilaria immitis

• As in dogs above
• Not very infective in cats but one dead adult causes acute pulmonary crisis - thromboembolism

Capillaria aerophila

• As in dogs above

In Horses

Parascaris equorum

• Causes transient nasal discharge when migrating through lungs
  • Foals and weanlings

Dictyocaulus arnfieldi

• 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

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