This article describes a case of Dictyocaulus arnfieldi infestation in a horse with signs of mild pneumonia in Mashhad region. In hematological examinations leukocytosis, neutrophilia with degenerative left shift; and in parasitological examination the first stage larvae were detected in the feces. According to the authors\\\\\\\' knowledge, this is the first report of Dictyocaulus arnfieldi infestation in Iran.

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