Outbreak of fatal illness among captive macaques in the Philippines caused by an ebola-related filovirus

Following the detection of an Ebola-like virus in cynomolgus macaques recently imported into the United States from The Philippines, studies were initiated to document transmission at export facilities located in the latter country. At one export facility, 52.8% of 161 monkeys that died over a 2.5- month period were shown to be infected with this virus using an enzyme-linked immunosorbent assay to detect antigen in liver homogenates. A case fatality rate of 82.4% was documented for the infected monkeys. The initial anti-viral antibody prevalence among the captive macaques at this facility was 25.9% (indirect fluorescent antibody titer ≥ 1:16). Followup documented infection of 24.4% of initially seronegative animals and 8.7% of initially seropositive monkeys. Being held in a gang cage versus a single cage was found to be a significant risk factor for subsequent virus infection, and the presence of IFA antibody was shown to predict protection. This study documents unequivocally for the first time the presence of an Ebola-related filovirus in Asia.