Habronemiasis (Summer Sores)

Question 1

What are the 3 major etiologies of Habronemiasis? What does this result in?

Answer 1

1. Habronema muscae
2. Habronema majus
3. Draschia megastoma
   (NEMATODES)

cutaneous ulcerative granulomas

Question 2

What acts as the intermediate host to Habronemiasis?

Answer 2

flies

• Stomoxys calcitrans (stable fly)
• Musca domestica (house fly)

Question 3

What are the 5 major stages in the life cycle of the nematodes that cause Habronemiasis?

Answer 3

1. adult nematodes inhabit the stomach (H. muscae, H. majus, D. megastoma)
2. eggs and larvae pass within the feces
3. fly maggots serve as the IH and ingest the larvae found in the feces –> Stomoxys calcitrans, Musca domestica
4. nematode larvae develop within the fly to the infective stage (L3)
5. flies are attracted to moist areas, such as wounds and mucocutaneous junctions, and deposit the larvae which migrate locally within the skin

Question 4

What clinical signs are indicative of Habronemiasis?

Answer 4

ulcerative granulomas with necrotic and calcified foci most commonly see at the medial canthus, nostrils, vulvae, teats, commisure of lips, and wounds (flies attracted to moist areas!) –> can develop intense pruritus and hypersensitivity reactions to the nematode larvae

• called summer sores because flies are most active in the summer

Question 5

What is a unique presentation with a specific species of nematode causing summer sores?

Answer 5

Draschia megastoma –> large masses and abscesses in the stomach, which can lead to perforations

• GI symptoms not usually common!

Question 6

What is a common sequelae to Habronemiasis when larvae are deposited near the nostrils?

Answer 6

pulmonary habronemiasis - nodular granulomas with central necrosis present in the interstitial and peribronchial areas of the lung

Question 7

What are some differentials for Habronemiasis in the horse?

Answer 7

• infectious granulomas
• eosinophilic granulomas
• neoplasia - SCC, sarcoids
• exuberant granulation tissue

Question 8

How can Habronemiasis be diagnosed?

Answer 8

• deep scrapings or smears from lesions may reveal nematode larvae and an eosinophilic infiltrate
• biopsy

(flies are attracted to wounds, so sarcoids and eosinophilic granulomas are commonly seen, too!)

Question 9

What treatments can be pursued for cases of Habronemiasis?

Answer 9

• topical ivermectin +/- glucocorticoids
• surgical excision or cryotherapy for larger masses
• systemic glucocorticoids or antihistamines to manage inflammatory-associated tissue proliferation and pruritus

(for most horses, the lesions resolve by the end of summer)

Question 10

How can Habronemiasis be prevented?

Answer 10

• regular deworming to eliminate nematodes in the stomach –> Ivermectin. Moxidectin
• fly control –> remove manure, environmental sprays, clean bedding