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Basics ⬇

Outline

BASICS

Overview!!navigator!!

The development of an inflammatory response in the airways and lung parenchyma due to an infection with the lungworm Dictyocaulus arnfieldi.

Signalment!!navigator!!

  • Donkeys and mules are most likely to harbor patent lungworm infections
  • There is no breed or sex predilection
  • All ages can be affected, but the prepatent period for D. arnfieldi is 6 weeks; therefore, disease is less likely in very young foals

Signs!!navigator!!

  • Chronic, nonprogressive cough that is unresponsive to antibiotic or anti-inflammatory therapy. More than 1 horse can be affected at the same time
  • An elevated respiratory rate, and bilateral nasal discharge possible
  • Audible wheezes and crackles may be evident during thoracic auscultation
  • Donkeys and mules do not typically exhibit clinical signs of infection

Causes and Risk Factors!!navigator!!

  • Ingestion of infective larvae of D. arnfieldi from contaminated pasture
  • Horses kept on green or irrigated pastures that concurrently or previously contained donkeys or mules
  • Infections usually occur during warm, wet weather in temperate climates

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Equine asthma, tumor or polyp in the airway, tracheobronchial foreign body, chronic bacterial pneumonia, pulmonary abscess, postviral airway hyperreactivity. In an individual horse, signs are often indistinguishable from those associated with severe equine asthma (heaves).

CBC/Biochemistry/Urinalysis!!navigator!!

  • CBC—peripheral eosinophilia is variable but if present is strongly suggestive of a parasitic infection
  • Routine biochemistry and urinalysis are unremarkable

Other Laboratory Tests!!navigator!!

  • The definitive diagnosis is established with the identification of larvae in a TTA or identification of larvae recovered from feces using the modified Baermann technique
  • Horses will commonly be negative for larvae using the modified Baermann technique but co-pastured donkeys should be tested and will likely be positive
  • The larvae in TTA fluid can be concentrated using centrifugation to improve the likelihood of discovery
  • Cytologic examination of the TTA will reveal a mixed inflammatory response with eosinophilia

Imaging!!navigator!!

Thoracic radiography can be useful to rule out chronic bacterial pneumonia or pulmonary abscesses.

Other Diagnostic Procedures!!navigator!!

Endoscopy may reveal an increase in mucus production in the airways. Rarely, an adult worm may be seen.

Treatment ⬆ ⬇

TREATMENT

Lungworm infection in the horse can be successfully treated with anthelmintic therapy and removal of horses from the contaminated pasture.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Ivermectin (0.20 mg/kg PO) and moxidectin (0.40 mg/kg PO) have been confirmed to be highly effective against the mature and larval forms of D. arnfieldi. Moxidectin is highly lipophilic and persists in the tissues longer than ivermectin
  • Eprinomectin (0.50 mg/kg) used as a pour-on is reported to be highly effective in treating D. arnfieldi in donkeys

Contraindications/Possible Interactions!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • If donkeys are treated, then repeating the modified Baermann technique on feces will allow the efficacy of therapy to be monitored
  • Horses can be monitored for the resolution of clinical signs

Prevention/Avoidance!!navigator!!

Do not pasture horses with donkeys that are not on a helminth control program.

Expected Course and Prognosis!!navigator!!

Lungworm infection in the horse has an excellent prognosis for full recovery post treatment. Resolution of clinical signs should be seen in 7–10 days after treatment.

Miscellaneous ⬆ ⬇

MISCELLANEOUS

Abbreviations

TTA = transtracheal aspirate

Suggested Reading ⬆ ⬇

Boyle AG, Houston R. Parasitic pneumonitis and treatment in horses. Clin Tech Equine Pract 2006;5:225–232

Veneziano V, Di Loria A, Masucci R, et al. Efficacy of eprinomectin pour-on against Dictyocaulus arnfieldi infection in donkeys (Equus asinus). Vet J 2011;190:414–415.

Author(s) ⬆

Author: Johanna L. Watson

Consulting Editors: Mathilde Leclère and Daniel Jean