Respiratory Parasitic Infections - Pathology
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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
- 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
- Penetration phase (week 1)
- 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
- 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
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