JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2023

P-P15

Signalment (JPC #2019292): 9-week-old crossbred female cat

HISTORY: This cat presented with a nasal discharge, cough, and labored respiration.

HISTOPATHOLOGICAL DESCRIPTION:

Trachea: Diffusely and circumferentially, the submucosa is thickened up to 700µm by moderate numbers of macrophages, lymphocytes, plasma cells, with fewer eosinophils and neutrophils, and increased clear space (edema). Multifocally, the epithelium exhibits one of the following changes: piles up to 8-10 cell layers deep (hyperplasia); is attenuated and eroded and often lacks cilia (degeneration); is infiltrated by numerous neutrophils, lymphocytes, and plasma cells, admixed with necrotic debris and sloughed epithelial cells (necrosis); or has undergone squamous metaplasia. Within the superficial epithelium there are several cross and tangential sections of adult nematode parasites up to 80 µm in diameter with a 2 µm thick, eosinophilic cuticle; coelomyrian-polymyarian musculature; bacillary bands; and a pseudocoelom that contains an intestinal tract including a stichosome (basophilic stichocytes surrounding the esophagus) esophagus and a reproductive tract. Submucosal glands are often ectatic, lined by attenuated epithelial cells, and contain small amounts of mucin.

Lung: Multifocally affecting approximately 60% of this section, bronchial and bronchiolar epithelium is hyperplastic with cells piled up to 6 layers deep, forming papillary projections into the lumen. Bronchial and bronchiolar lumina are variably filled with an exudate composed of sloughed epithelial cells, abundant mucin, eosinophils, viable and necrotic neutrophils, macrophages, fewer lymphocytes, necrotic cellular debris, and occasional previously described adult nematodes. The inflammatory cells extend through the bronchial and bronchiolar walls and surround hyperplastic peribronchial and peribronchiolar glands. Multifocally in the adjacent pulmonary parenchyma, alveolar lumina are filled with an exudate composed of numerous neutrophils and macrophages admixed with necrotic cellular debris, colonies of 2µm coccobacilli, fibrin, hemorrhage, and edema. In these areas, the exudate often effaces alveolar septa. Less affected alveoli are filled with eosinophilic fluid (edema) and septa are thickened up to three times normal with congestion, macrophages, lymphocytes, and plasma cells. There is marked perivascular edema and mild hemorrhage with increased clear space and dilated lymphatics.

MORPHOLOGIC DIAGNOSIS

Trachea: Tracheitis, proliferative, pyogranulomatous and eosinophilic, diffuse, moderate, with squamous metaplasia, submucosal gland ectasia, and intraepithelial aphasmid nematodes, mixed breed, feline.
Lung: Bronchitis and bronchiolitis, pyogranulomatous and eosinophilic, multifocal, chronic, moderate, with respiratory and glandular epithelial hyperplasia, and intraluminal aphasmid nematodes.
Lung: Bronchopneumonia, necrosuppurative, acute, multifocal, moderate, with edema, hemorrhage, and numerous colonies of basophilic cocci.

ETIOLOGIC DIAGNOSIS:

1. Tracheal and bronchial/bronchiolar eucoliasis

2. Bacterial bronchopneumonia

CAUSE:

1. Eucoleus aerophilus (previously Capillaria aerophila)

2. Unknown bacteria (not cultured)

GENERAL DISCUSSION

Capillaria spp genera have been divided into: Eucoleus (airways), Aonchotheca (intestine), and Pearsonema (urinary bladder)
Capillaria has wide variety of hosts: Canids (dogs, foxes, coyotes, wolves), cats, birds, frogs, fish, rabbits
Eucoleus aerophilus are nematodes in Trichuridae family (stichosome esophagus), subclass Aphasmid
Aphasmids differ from phasmid nematodes because they:
- Have a row of basophilic esophageal gland cells (stichocytes) that form a stichosome and surround the esophagus - one of the most characteristic features
- Lack a tiny pair of sensory papillae (phasmids) on their caudal end (not readily identifiable histologically) and lack lateral cords
- Have bacillary bands (hypodermal bands with associated nuclei)
- Adult females have only one genital tract (most phasmids have two)
E. aerophilus parasitizes trachea and bronchi of wild canids, domestic dogs, and cats; can also infect the nasal passages of dogs

PATHOGENESIS

The body mounts an inflammatory response against developing adults in epithelium (bronchitis, bronchiolitis) > decreased mucociliary clearance > +/- secondary bacterial infection > pneumonia
Heavy infections may cause sufficient inflammation to obstruct airways

LIFE CYCLE

Life cycle is indirect - earthworms are required intermediate hosts
Host ingests earthworm containing infective larvae > infective larvae penetrate intestinal wall > larvae migrate to lungs (via blood) > develop into adult in mucosa of trachea and bronchi > eggs laid in lumen, coughed up, swallowed, passed out with feces, become infective in 5 to 7 weeks (prepatent period)

TYPICAL CLINICAL FINDINGS

Dogs and cats are usually asymptomatic
Wheezing, chronic cough, weight loss

TYPICAL GROSS FINDINGS

Adult worms (20-40mm long) embedded in mucosa of trachea and bronchi or nasal mucosa less frequently (dogs)

TYPICAL LIGHT MICROSCOPIC FINDINGS

E. aerophilus adult: Reduced polymyarian-coelomyarian musculature, two bacillary bands (hypodermal bands with associated nuclei), a stichosome esophagus (deeply basophilic esophageal gland cells [stichocytes] that surround the esophagus), a spiny sheath, and oval, embryonated, bioperculate eggs (approximately 70 µm x 35 µm) within airways
Subacute to chronic mild tracheobronchitis
Possible cause of eosinophilic bronchopneumopathy in dogs

ADDITIONAL DIAGNOSTIC TESTS

Fecal float, zinc sulfate flotation, Baerman technique, tracheal wash
Cytology: Ova are bipolar thick-walled, pigmented golden brown, 58–79 μm length, 29–40 μm width; can be found in TW/BAL in conjunction with increased eosinophils (hypersensitivity)

DIFFERENTIAL DIAGNOSIS

Common lungworms in cats: Aelurostrongylus abstrusus (P-P09, metastrongyle; most common nematode parasite in domestic cats), Troglostrongylus subcrenatus, Filaroides rostratus
Bioperculate eggs: C. feliscati, C. putorii, Trichuris spp., Pearsonema plica

COMPARATIVE PATHOLOGY

Birds: Capillaria annulata and C. contorta infect crop and esophagus in poultry
Wild canids including foxes: E. aerophilus mainly affects trachea and bronchi
Hedgehogs: Recent European study found E. aerophilus most common respiratory parasite with 82% prevalence in study animals; larynx, trachea, bronchi, and bronchioles most affected

REFERENCES

Boes KM. Respiratory Tract. In: Raskin RE, Meyer DJ, Boes KM, eds. Canine and Feline Cytology: A Color Atlas and Interpretation Guide. 4th ed. St. Louis, MO: Elsevier; 2023:225-226.
Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. Vol 2. St. Louis, MO: Elsevier; 2016:502, 585, 591.
De Terlizzi R, English K, Cowell RL, Tyler RD, Meinkoth JH. Transtracheal and Bronchoalveolar Washes. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2020:257,264.
Gardiner CH, Poynton SL. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC: Armed Forces Institute of Pathology; 1999: 40-43.
Keel MK, Terio KA, McAloose D. Canidae, Ursidae, and Ailuridae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:246.
Lehman S, Dervas E, Subira AR, Eulenberger U, Gimmel A, Grimm F, Hetzel U, Kipar A. Verminous Pneumonia in European Hedgehogs (Erinaceus europaeus). Vet Pathol. 2023;0(0):1-13.
Lopez A, Martinson SA. Respiratory System, Thoracic Cavities, Mediastinum, and Pleurae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:637.