ABSTRACT
An outbreak of severe parasitic pneumonia caused by Dictyocaulus viviparus was diagnosed in adult dairy cows in the municipality of Arabutã, Southern Brazil. The total morbidity in the herd was 71.9%, and the morbidity amongst adult lactating cattle was 100%. The main clinical signs observed were dyspnea, tachypnea, nasal discharge, decreased milk production, and cough. A necropsy was conducted on one animal in order to establish the diagnosis. The herd had been treated previously with levamisole; however, clinical signs persisted and became worse. After treatment with eprinomectin the severity of clinical signs decreased, and the respiratory condition subsequently disappeared. It is believed that the high morbidity presented in this outbreak is related to epidemiological factors, such as increased rainfall in 2014 and 2015, associated with low immunity of the herd. This is the first report of dictyocaulosis in adult dairy cattle in Brazil. Furthermore, it describes an outbreak presenting very high morbidity.