The Wildlife Conservation Society maintains one of the largest captive flocks of thick-billed parrots (Rhynchopsitta pachyrhyncha). Since initial diagnosis in 2005, sarcocystosis has led to 51.7% of mortalities in birds over 30 days of age. In all cases tested by PCR, Sarcocystis falcatula is consistently identified, and disease predominantly impacts younger animals (median age 5.62 yr; age range 0.19–26.09 yr). Administration of antiparasitic medications prior to development of respiratory signs prolonged life in infected birds, but disease was uniformly fatal until utilization of a three-drug combination (pyrimethamine, trimethoprim-sulfamethoxazole, and ponazuril). This protocol requires in excess of 6 mo of therapy to achieve clinical resolution, resulting in ongoing efforts to develop alternate treatments. Plasma creatine kinase activity appears to be the most useful minimally invasive test to diagnose infection, as well as a means to monitor response to therapy. PCR for apicomplexan organisms on antemortem whole blood, blood smears, or blood cards helps confirm suspected cases, but may be misleading when assessing response to therapy or resolution of clinical disease. Historically, preventive measures focused on excluding Virginia opossums (Didelphis virginiana), the definitive host for Sarcocystis falcatula, from the parrot areas and removal of opossums from zoo grounds. Despite these management efforts, birds continued to develop sarcocystosis resulting in additional steps, including modifying food stations to exclude potential arthropod paratenic hosts. Additionally, prophylaxis trials with diclazuril were implemented. Given treatment and antemortem diagnostic challenges, preventing exposure to Sarcocystis spp. and their hosts is essential for continuing ex situ conservation of thick-billed parrots.
The authors thank the animal care staff, veterinary, pathology, and histology technicians at the Queens Zoo and the Bronx Zoo Wildlife Health Center for their care and treatment of these animals.