This case represents what clinical impression indicates is the most common form of pleuropneumonia seen in equine practice. These cases present with fever of unknown origin (FUO) with few if any signs referable to the respiratory system. Several texts and the literature were reviewed and this form of pleuropneumonia is rarely discussed. In general, the more severe form of pleuropneumonia with extensive purulence and exudation, lung infarction, etc is the focus of most literature discussion.
Signalment and history
A 10-year-old Hanovarian mare presented with a 3 week history of sporadic malaise. It was noted that the depression would invariably occur late in the afternoon. Most often, the following morning, the horse appeared bright, alert and responsive. This did not occur daily, but the owner felt it had occurred at least every other day. The horse was in light use, and continued to jump 1 meter fences. She was transported from Ohio to California 40 days prior to presentation. Other than the chief complaint the horse had shown no other clinical signs.
The horse was first seen in the morning and physical examination revealed no abnormalities. Based on the history alone, a thoracic ultrasound was completed (Figure 1).
Figure 1. Ultrasonographic images captured from the thorax of a horse. There is evidence of mild low volume pleural effusion.
As was expected, the sample was purulent with a >250,000 white blood cells per microliter (Figure 2). The cells were fairly non-reactive. The culture was negative for aerobic and anaerobic bacteria. A serum chemistry profile, fibrinogen concentration and complete blood count were performed simply for screening purposes. The results were predictable and included a slight neutrophilic leukocytosis (12,600 total cell/ul with 8200 neutrophils/ul) with no band neutrophils evident. The horse had a normal fibrinogen (150 mg/dl). All other parameters were within normal limits with no concerning tendencies.
Figure 2. Thoracic fluid from a horse with fever of unknown origin.
Treatment and outcome
The horse was kept for treatment and observation. She was administered Naxcel™ (ceftiofur sodium) at a rate of 1 mg/pound (2.2 mg/kg), q12h, intravenously via percutaneous injection for 10 days. Temperature was evaluated in the morning and afternoon. As often occurs with pyrexia in horses, the fever was evident in the afternoon, but not the morning evaluation. The horse would vary in the afternoon between 102.1 F (38.9 C) and 103 F (39.4 C) with a tendency to decline, but not to resolve, over the course of the 10 day drug regimen. The pyrexia occurred intermittently over the next 8 days and resolved on day 8 after antimicrobial treatment was ceased (18 days from the start of antimicrobial therapy). A recheck ultrasonographic evaluation was performed (Figure 3) on day 28 and indicated extensive resolution of the purulent fluid. The horse went on to do well with no other episodes of pyrexia.
Figure 3. A recheck ultrasonographic image collected from the same horse as Figure 1. Note the near resolution of the pleural pathology. Some small amount of fluid still persists.