Successful treatment of megaesophagus with sildenafil in juvenile Pacific harbor seals (Phoca vitulina richardii) undergoing rehabilitation

Objective: To describe the outcome of megaesophagus in harbor seal pups undergoing rehabilitation from January 2021 to December 2023.

Methods: 5 harbor seal (Phoca vitulina richardii) pups, 2 males and 3 females, were included in the study. All 5 cases had no clinical signs associated with megaesophagus on initial presentation to the rehabilitation facility. Case 1 presented with regurgitation, diarrhea, bloating, and poor gain of body mass starting 24 days into rehabilitation. Case 2 presented with regurgitation and bloating on day 12. Case 3 presented with hyporexia, bloating, poor gain of body mass, and regurgitation between days 55 and 60. Case 4 presented with lethargy, diarrhea, and regurgitation starting on day 12 of rehabilitation. Case 5 presented with difficulty gavage feeding 14 days into rehabilitation and regurgitation starting day 28. Radiographs in all 3 cases revealed dilation of the esophagus and gas distention of the stomach and intestines, consistent with megaesophagus. Cases 1, 2, and 3 were treated with 1 mg/kg sildenafil by mouth every 12 hours for 14 days at the time of diagnosis.

Results: Cases 1 and 2 showed improvement in radiographic lesions and resolution of clinical signs after treatment and were released after 1 and 3 months of posttreatment monitoring respectively. None of the clinical signs returned after medications were discontinued. Postrelease survival was monitored in case 2 via a satellite-linked transmitter for 39 days. Case 3 was euthanized due to worsening lethargy, difficulty tube feeding, and continued loss of body mass after 6 days of treatment. Case 4 was euthanized at the time of diagnosis of megaesophagus on radiographs due to dull mentation and declining clinical status, and case 5 died a few hours after diagnosis of megaesophagus on radiographs before sildenafil treatment could be initiated.

Conclusions: Sildenafil successfully managed megaesophagus in 2 of 3 P vitulina richardii juveniles. This case series highlights that sildenafil may be a potential treatment option for megaesophagus in P vitulina richardii pups undergoing rehabilitation.

Clinical relevance: Based on the results of these cases, it is hypothesized that megaesophagus in rehabilitated harbor seals is not always a congenital defect but possibly an iatrogenic condition.