Serologic Evidence of Infectious Bursal Disease Virus Exposure in Captive Whooping Cranes
American Association of Zoo Veterinarians Conference 2004
Barry K. Hartup1,4, DVM, PhD; Glenn H. Olsen2, DVM, PhD; Holly S. Sellers3, PhD; Bethan Smith4, BS; Marilyn Spalding5, DVM
1International Crane Foundation, Baraboo, WI, USA; 2USGS Patuxent Wildlife Research Center, Laurel, MD, USA; 3Poultry Diagnostic Research Center, College of Veterinary Medicine, University of Georgia, Athens, GA, USA; 4Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI, USA; 5Department of Pathobiology, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
Abstract
Between September 2001 and March 2002, unusually high morbidity and mortality was observed during releases of endangered, captive-reared whooping cranes (Grus americana) in central Florida. An ongoing epidemiologic investigation has implicated infectious bursal disease virus (IBDV) as the likely etiologic agent. The source of this virus remains unknown. A serologic survey of the two primary U.S. captive populations was undertaken to ascertain the historic exposure of the cranes to IBDV. Archived serum samples from the International Crane Foundation, Baraboo, WI and the USGS Patuxent Wildlife Research Center, Laurel, MD were screened for IBDV serotype 2 neutralizing antibodies. At ICF, samples were tested from healthy resident adults (n=32, collected annually 1998–2002) and 3–5-month-old juveniles (n=54, samples collected at pre-release quarantine exams 1997–2003). Twelve percent of adults and 7% of juveniles were seropositive in this survey (titer ≥1:32). Seropositive adults first appeared at ICF in 1998, and seroprevalence peaked at 15% in 2002. Seropositive status varied across years within three individuals with a complete serologic history. The geometric mean titer of adults increased during the study (range 1:4 in 1998, 1:11 in 2002). Seropositive juveniles first appeared at ICF in 2003, when 4 of 9 (44%) cranes had elevated titers. At Patuxent, preliminary results suggest that 4 of 32 (12%) juveniles in recent years were seropositive for IBDV. In December 2003, IBDV infection was confirmed at necropsy by PCR assay of spleen and bursa in a juvenile whooping crane that demonstrated a neutralizing antibody titer of 1:256. In addition, several Patuxent sandhill cranes (Grus canadensis) used in a West Nile virus vaccination study during 2003 developed IBDV antibody titers ≥1:64. Interpretation of these data suggests that exposure of captive whooping cranes to IBDV serotype 2 has occurred historically as early as 1998, and that exposure is more common compared to several years ago. The low titer levels observed in the vast majority of the cranes are suggestive of exposure to the virus and not believed to be associated with active infection nor the presence of a disease state, though at least one exception has been found. The risk for whooping crane recovery may lie in pathogen transfer to environments that promote disease expression such as areas used for reintroduction.