JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
September 2021
D-P08

SIGNALMENT (JPC #1806543):  Horse

 

HISTORY:  None.

 

HISTOPATHOLOGIC DESCRIPTION:  Stomach, pars glandularis:  Focally and markedly expanding the submucosa and elevating the overlying lamina propria and mucosa is an ovoid, 3 x 1 cm, well-circumscribed “brood pouch” that contains multifocal to coalescing irregular areas of eosinophilic cellular and karyorrhectic debris (lytic necrosis) with multiple cross and tangential sections of adult spirurid nematodes admixed with few 8X20um nematode larvae and colonies of 1um bacilli.  These necrotic foci and nematodes are bounded by macrophages, lymphocytes, plasma cells, neutrophils, and eosinophils that are further bounded by a circumferential ring of plump fibroblasts and many small caliber vessels (granulation tissue). These areas are further encapsulated by abundant thick, mature collagen (fibrosis). Adult nematodes are 300um in diameter, have a smooth, 2 um thick, refractile cuticle with 2 symmetrical lateral alae, coelomyarian/polymyarian musculature, prominent lateral cords with excretory canals, an intestine lined by many uninucleate cells, a muscular esophagus with a triradiate lumen, and eosinophilic material in the pseudocoelom.  Females have a large uterus that contains multiple 4 um, oval larvae.   Multifocally within the lamina propria and submucosa, there are scattered aggregates of lymphocytes, plasma cells, and eosinophils that often surround blood vessels.  Lymphatics within the submucosa, tunica muscularis, and serosa are multifocally mildly dilated and contain similar inflammatory cells.

 

MORPHOLOGIC DIAGNOSIS:  Stomach, submucosa:  Gastritis, nodular, granulomatous and eosinophilic, with fibrosis and numerous adult spirurid nematodes (brood pouches), etiology consistent with Draschia megastoma, breed not specified, equine.

 

ETIOLOGIC DIAGNOSIS:  Gastric draschiasis

 

CAUSE:  Draschia megastoma (formerly Habronema megastoma)

 

GENERAL:

• Order Spiruridae, Suborder Spirurina, Family Spiruridae
• Includes megastoma, Habronema muscae, Habronema microstoma (H. majus), Physaloptera sp., Gnathostoma sp., Gonglyonema sp., Spirocirca lupi, Thelazia sp., Cyathospirura felineus, Dispharynx nasuta, Tetrameres americana, Drucunculus insignis and Microtetrameres sp.
• Draschia/Habronema are stomach nematodes of equids (horses, mules, zebra)
• Draschia can also infect the intestine; muscae rarely affects cecum
• Larvae of all 3 species can infect the skin (“summer sore”) and conjunctiva
• Flies act as intermediate hosts

 

LIFE CYCLE

• Seasonal occurrence corresponds with that of the fly intermediate host
• Adult worms in stomach > larvated eggs extruded through a pore in the “brood pouch” > hatch (L1) in the intestine > passed in feces and ingested by the larvae of the intermediate host- fly ( muscae and D. megastoma use the housefly [Musca domestica and other Musca sp]; H. microstoma uses the stable fly [Stomoxys calcitrans]) > develops into infective L3 in the fly larvae > fly develops to adult > L3 migrate from hemocele into the proboscis > deposited around the horse’s mouth > swallowed and mature in the stomach

 

PATHOGENESIS:

• Habronema live free in the gastric lumen and on the gastric mucosa; Draschia sp. burrows into the submucosa forming eosinophilic and granulomatous nodules
• Aberrant deposition of larvae on skin and eye may cause hypersensitivity reaction with granulomatous and eosinophilic dermatitis and conjunctivitis

 

TYPICAL CLINICAL FINDINGS:

• Usually asymptomatic; +/- mechanical obstruction; abscesses, ulcers, or perforation
• Cutaneous lesions: Pruritus; dermatitis; exuberant granulation tissue
• Ocular infections: Lacrimation, edema, and photophobia; parasitic conjunctivitis may be caused by members of the genera Thelazia, Habronema, Draschia, and Onchocerca

 

TYPICAL GROSS FINDINGS:

Stomach:

• muscae and H. microstoma (H. majus) penetrate gastric glands or lie in the lumen; large numbers of worms may cause inflammation and chronic erosive gastritis
• Draschia penetrate deeply into the glandular submucosa in the cardia near the margo plicatus, forming “brood pouches” and produce 2.5-10 cm diameter tumor-like nodules containing worms and central core of necrosis and cellular debris; hemorrhage or gastric perforation can occur

Eyes:

• Larvae attracted to moisture at the medial canthus in the conjunctival sac
• Ulcerative red-brown lesion (<2cm) progresses to granulomatous nodule +/- mineralization
• Raised, yellow, gritty plaques (“clinically pathognomonic”) on the conjunctiva

Skin:  

• Synonyms: Cutaneous habronemiasis, summer sores
• Pectoral region, distal extremities, glans penis and prepuce
• Alopecia with necrosis and a serous exudate
• Rapidly progressive, proliferative, ulcerated, red-brown masses of granulation tissue
• On cut section multiple small (1-5 mm) white, caseous, and occasionally gritty foci are scattered through the tissue
• Granulomatous and eosinophilic nodules also reported in the lungs and brain (rare)

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Parasite morphology (common to Spiruridae)
• Cuticle, lateral alae, polymyarian/coelomyarian musculature, intestine lined by uninucleate cells, extremely reduced dorsal and ventral cords, well-developed lateral cords that are often vacuolated, eosinophilic material in the pseudocoelom
• Large uteri (usually filled with classic spirurid eggs: small, oval, thick-shelled, embryonated eggs); Draschia and Thelazia produce embryos without shells
• Submucosal granulomatous and eosinophilic inflammation with a central core of necrotic and cellular debris, +/- larvae and mineralization
• Larvae may be rare or absent in many caseous foci

 

DIAGNOSIS:  Identification of larvae in feces

 

DIFFERENTIAL DIAGNOSES:

• Gastric lesions: Squamous cell carcinoma, Trichostrongylusaxei (when co-located with ruminants), Gasterophilus
• Cutaneous lesions: Pythiosis (fungal-like hyphae), botryomycosis, onchocerciasis, exuberant granulation tissue (no caseous foci), equine sarcoid, squamous cell carcinoma, nodular collagenolytic granuloma
• Common secondary infection of many cutaneous lesions, particularly penile squamous cell carcinoma
• Conjunctival lesions: Thalazia (may see nematode in eye, also a spirurid), Onchocerca sp. (filarid nematode, causes conjunctivitis, scleritis, or keratitis), squamous cell carcinoma

 

COMPARATIVE PATHOLOGY:  

Stomach worms in domestic animals:

• Horse: Draschia megastoma, Habronema mucae, Habronema majus, Trichostrongylus axei, Gastrophilus
• Swine: Spiruids Ascarops, Physocephalus spp., Simondsia spp., Gnathostoma spp., Ollulanus tricuspis, Hyostrongylus rubidus
• Cattle, sheep, goats: Haemonchus, Mecistocirrus spp., Ostergia and related spp. (Camelostroglus, Teladorsagia, Marshallagia, Trichostongylus axei),
• Dog: Habronemiasis has been reported (dog housed with ponies)- lesions on face, usually no proliferating granulation tissue; Spirocerca lupi (a spirurid nematode in the esophageal wall of dogs); Physaloptera (spirurid nematode in stomach of dogs/cats; may be in lumen or adhere to mucosa and occasionally cause ulcers)

 

REFERENCES:

1. Foster RA. Male Reproductive System. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:1217.
2. Gardiner CH, Poynton S. An Atlas of Metazoan Parasites in Animal Tissues. Washington, D.C.: Armed Forces Institute of Pathology, 1999:30-35.
3. Gelberg HB. Alimentary System and the Peritoneum, Omentum, Mesentery, and Peritoneal Cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:388.
4. Uzal FA, Platter BL, Hostetter JM. Alimentary System. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St Louis, MO: Elsevier; 2016: 54.

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