Exserohilum rostratum granulomatous rhinitis in a Holstein cow and review of the literature of diseases caused in domestic ruminants by this dematiaceous fungus and its historical synonyms

Here, we describe a case of Exserohilum rostratum rhinitis in a cow and review the literature on diseases caused by Exserohilum spp. and dematiaceous fungi historically classified morphologically as Helminthosporium , Drechslera , or Bipolaris in domestic ruminants. In March 2024, an adult Holstein cow from a dairy herd in Uruguay developed bilateral nodules in the nasal mucosa, resulting in dyspnea, snoring, nasal discharge, and weight loss. Histologically, severe chronic eosinophilic granulomatous rhinitis was found, with giant cells and intra- and extracellular fungi. Exserohilum rostratum was identified by PCR and sequencing of the extended 28S rDNA region. Our literature search retrieved ~40 bovine cases in the United States, Australia, South Africa, Namibia, and Uruguay, 1 caprine case in Brazil, and no ovine cases. Clinical signs included chronic dyspnea, stertor, mucopurulent nasal discharge, epistaxis, and weight loss, generally affecting adult beef cattle. The lesions usually affected the nasal mucosa and submucosa, rarely involved the skin or regional lymph nodes, and occasionally were restricted to the skin. Bilateral, raised, 0.1–5-cm granulomatous nasal nodules resulted in restriction of airflow. The hallmark microscopic lesion is chronic eosinophilic granulomatous inflammation with giant cells and intralesional fungal structures, including ~5–30-µm, round-to-ovoid chlamydospores and short ~2–6-µm-wide septate hyphae, which may have brown-pigmented walls. Definitive fungal identification requires molecular testing, which is rarely pursued.