An outbreak of eosinophilic bronchitis in horses possibly associated with Dictyocaulus arnfieldi infection.

The research investigates an outbreak of eosinophilic bronchitis in horses, which was potentially linked to an infection of Dictyocaulus arnfieldi, a lungworm. Treatment with thiabendazole resulted in resolution of the symptoms and disappearance of eosinophils (a type of white blood cell) from the horses’ tracheal washings.

Background of the Study

• The research was conducted on eight mature horses that had been showing symptoms of a moist cough for a duration of six weeks.
• The horses were maintained on irrigated pasture and were given a diet free of hay.
• A yearling donkey, kept as a companion to the horses, was found to be passing Dictyocaulus arnfieldi larvae in its feces.

Investigation and Findings

• Upon examination, a significant presence of eosinophils was discovered in tracheal mucus samples that were obtained from the horses via transtracheal washing.
• Eosinophils are a type of white blood cell that increases in number during an infection or an allergic reaction.
• The presence of these cells indicated a possible response to a parasitic infection, in this case, suspected to be caused by Dictyocaulus arnfieldi, a species of lungworm found in horses and donkeys.

Treatment and Results

• The horses were treated with two oral doses of thiabendazole, a medication often used to treat infections caused by worms.
• The dose administered was 440 mg/kg, and it effectively led to the disappearance of the eosinophils from further transtracheal washings, suggesting the elimination of the infection.
• Also, the symptoms originally presented by the horses, including the moist cough, resolved after the treatment.
• Based on these observations, the researchers concluded that the eosinophilic bronchitis observed in these horses was likely a result of a prepatent Dictyocaulus arnfieldi infestation.