Studies of an outbreak of Corynebacterium equi pneumonia in foals

Five out of 6 foals between 2 and 4 months old, on a ranch in northern California, developed pneumonia within a 3 week period in June and July 1978. Corynebacterium equi was recovered from each of the 5 foals by transtracheal aspiration. Clinical signs were variable but included increased respiratory rate, fever, cough, nasal discharge, harsh airway sounds over middle sized airways and wheezing over small airways. Cyanosis was present in the most severely affected foal. Radiographic findings included diffusely increased interstitial and peribronchial densities, areas of consolidation and, in 3 cases, dense focal areas indicating abscessation. Foals were treated with several different antimicrobial agents. Most were treated with penicillin and gentamicin. Four of the 5 affected foals recovered within 2 to 3 weeks but the first foal to be affected died 2 days after first receiving veterinary attention. At postmortem examination, pulmonary changes considered typical of C equi pneumonia were found, including wet, heavy dark red lungs which failed to collapse and numerous 1 to 7 cm thin-walled abscesses throughout the parenchyma, containing inspissated exudate. C equi was cultured from the exudate. Samples of soil and dust from 9 of 20 areas inhabited by infected foals yielded C equi of the same serological group as found in the foals. Eight paddocks in which foals had not been kept were negative for C equi. The organism was recovered from cobwebs in the stalls occupied by infected foals. Aerosol infection via dust was considered to be the route of infection. Pharyngeal, vaginal and faecal cultures from the dams of 3 affected foals were negative for C equi. Early diagnosis by transtracheal aspiration and appropriate therapy are considered to be extremely important in the successful treatment of C equi pneumonia. Preventive therapy should include control of environmental dust.