JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1897187): Adult male goat.
HISTOPATHOLOGIC DESCRIPTION: Lung: Multifocally, randomly, affecting approximately 1/3 of the section bronchi, bronchiole and alveolar lumina contain nematode eggs and larvae. Within alveoli there are fewer adult nematodes. Multifocally within both small and large airways, admixed with nematodes, there is abundant mucous and low numbers of macrophages, multinucleated giant cells and fewer neutrophils; additionally, alveolar lumina contain variable amounts of fibrin, hemorrhage and necrotic debris. Adult nematodes are 50-75 um in diameter, have a thin smooth hyaline cuticle, occasional cuticular ridges, polymyarian-coelomyarian musculature, lateral cords, a pseudocoelom containing an intestine lined by few multinucleate cells and tubular reproductive organs containing ova or spermatozoa. Larvae measure 100 X 15 um and have a 1-2 um thick smooth eosinophilic cuticle and a thin posterior tip. Embryonated eggs are ovoid, measure 40 X 60 um, have an indiscernible shell, and contain multiple 8 um diameter blastomeres. Affected alveolar septa are infiltrated and thickened up to 5x normal by macrophages, fewer lymphocytes and plasma cells, occasional eosinophils, and small amounts of eosinophilic beaded or fibrillar material (fibrin) and edema. Areas of infiltration often coalesce to form more solid nodules which may contain nematodes. Multifocally there is epithelial and goblet cell hyperplasia within bronchioles and bronchi, characterized by thickening of epithelium with loss of polarity of epithelial cells. There is occasional peribronchiolar smooth muscle hypertrophy. Rarely, within the alveoli or interstitium, there is basophilic granular mineral. There is peribronchiolar lymphoid hyperplasia.
MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, interstitial, granulomatous and eosinophilic, multifocal, moderate, with nematode adults, larvae, and eggs, etiology consistent with Muellerius capillaris, breed unspecified, caprine.
ETIOLOGIC DIAGNOSIS: Pulmonary muelleriasis
CAUSE: Muellerius capillaris
- Most common lungworm of sheep, goats and chamois, found worldwide, referred to as the “nodular lungworm”
- Metastrongyle which requires a mollusk (snail or slug) intermediate host to complete larval development
- Larvae are able to survive for months in feces and for the lifetime of the intermediate host
- Adult worms are brown, hair-like, and range from 12-24 mm long; live in nodular lesions in alveoli and rarely bronchioles
- Larvae are 300 um X 15 um
- Nodules are composed of adult worms, embryonated eggs, and coiled larvae
- Worm burden accumulates over time, usually not found in animals < 6 months old
- In younger animals, there is very little inflammatory response
- In older animals (from repeated exposure), the inflammatory response is more marked, with eosinophilic aggregates surrounding larvae; not usually seen in older animals (resistant)
Indirect: Eggs are deposited by adults within nodules in lung -> L1 larvae emerge from nodules into airways and move via mucociliary escalator to pharynx-> swallowed and passed in feces -> L1 larvae penetrate the foot of the intermediate host (snail or slug) -> develop to L2, then to L3 in 2-3 weeks -> definitive host ingests intermediate host -> L3 are freed by digestion and migrate to the lungs via the lymphatic system; larvae molt into adult worms -> break out into the alveolar spaces, and induce granulomatous nodules, particularly in subpleural locations
TYPICAL CLINICAL FINDINGS:
Non-specific: cough, moderate dyspnea, and loss of condition
TYPICAL GROSS FINDINGS:
- 1-20 mm diameter (usually 2-4mm) characteristic finding is subpleural nodules in dorsal region of caudal lung lobes, but may occur anywhere in lung and regional lymph nodes; adult worms within alveoli too small to visualize grossly
- Usually, goats infected with capillaris may only have diffuse interstitial pneumonia without nodule formation
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Diffuse interstitial pneumonia; variable inflammatory response
- Nodules with masses of adult worms, embryonated eggs and coiled larvae
- Alveoli and septa contain eggs, L-1 larvae, adult nematodes and may be thickened by fibrous tissue, lymphocytes and smooth muscle hyperplasia
- Bronchioles contain adults and larvae, plugs of mucus and cellular debris
- Minimal acute inflammation, small amounts of hemorrhage
- Chronic inflammation: infiltrates of eosinophils, macrophages and giant cells surround L-1 larvae and adults
- Cellular debris mineralizes when worms die, becomes surrounded by fibrosis and persists indefinitely
- Bronchiolar epithelial and smooth muscle hyperplasia
- Muellerius capillaris: 50-75um diameter, cuticle with variably distinct ridges, polymyarian-coelomyarian musculature, accessory hypodermal chords, intestine lined by few multinucleate cells and indistinct brush border, paired reproductive tubules
- In goats, worms incite a severe diffuse interstitial pneumonia without nodular lesions
ADDITIONAL DIAGNOSTIC TESTS:
Baerman apparatus for fecal examination (larvae in fresh feces) and post‑mortem
- Interstitial pneumonia
- Grossly: CAE (lentivirus) in goats
- Mycoplasma spp.
- Parasitic pneumonia
- Cystocaulus ocreatus: Dark nodules with hair-like worms, adults and larvae located in small bronchioles and alveoli; very similar to Muellerius in life cycle and pathogenicity
- Protostrongylus rufescens: Soft, angular nodules with grossly visible worms, adults located in terminal bronchioles; often see prominent peribronchiolar lymphofollicular cuffs; common in sheep, goat, and deer; snails act as the intermediate host; european variety is called Neostrongylus linearis
- Dictyocaulus filaria: Focal atelectasis or consolidation with emphysema and catarrhal bronchitis/bronchiolitis; thread-like adult worms in bronchi; occurs in sheep, goats, and other small ruminants; direct life cycle
Lungworms of domestic species:
- Cattle: Dictyocaulus viviparous: Causes pneumonia (especially calves during first summer grazing), bronchitis, pulmonary edema, lobular atelectasis and interstitial emphysema; parasite lives in intrapulmonary bronchi
- Horses, donkeys: Dictyocaulus arnfieldi: Donkeys are the natural host; adult parasites cause obstructive bronchitis, eosinophilic bronchitis, edema, and atelectasis primarily in the dorsocaudal lung
- Pigs: Metastrongylus apri, pudendotectus, M. salmi
- Dirofilaria immitus
- Angiostrongylus vasorum
- Oslerus osleri: Pinkish gray fibrous nodules at the tracheal bifurcation and adjacent bronchi
- Eucoleus aerophilus
- Filaroides hirthi
- Andersonstrongylus milksi
- Crenosoma vulpis
- Aelurostrongylus abstrusus: Catarrhal bronchiolitis, hyperplasia of submucosal glands, granulomatous alveolitis, alveolar fibrosis, and fibromuscular hyperplasia; grossly there are multifocal subpleural granulomatous nodules throughout the lung
- Eucoleus aerophilus
- Primates: Filaroides spp.
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