Divergent Simian Arteriviruses Cause Simian Hemorrhagic Fever of Differing Severities in Macaques

Simian hemorrhagic fever (SHF) is a highly lethal disease in captive macaques. Three distinct arteriviruses are known etiological agents of past SHF epizootics, but only one, simian hemorrhagic fever virus (SHFV), has been isolated in cell culture. The natural reservoir(s) of the three viruses have yet to be identified, but African nonhuman primates are suspected. Eleven additional divergent simian arteriviruses have been detected recently in diverse and apparently healthy African cercopithecid monkeys. Here, we report the successful isolation in MARC-145 cell culture of one of these viruses, Kibale red colobus virus 1 (KRCV-1), from serum of a naturally infected red colobus (Procolobus [Piliocolobus] rufomitratus tephrosceles) sampled in Kibale National Park, Uganda. Intramuscular (i.m.) injection of KRCV-1 into four cynomolgus macaques (Macaca fascicularis) resulted in a self-limiting nonlethal disease characterized by depressive behavioral changes, disturbance in coagulation parameters, and liver enzyme elevations. In contrast, i.m. injection of SHFV resulted in typical lethal SHF characterized by mild fever, lethargy, lymphoid depletion, lymphoid and hepatocellular necrosis, low platelet counts, increased liver enzyme concentrations, coagulation abnormalities, and increasing viral loads. As hypothesized based on the genetic and presumed antigenic distance between KRCV-1 and SHFV, all four macaques that had survived KRCV-1 injection died of SHF after subsequent SHFV injection, indicating a lack of protective heterotypic immunity. Our data indicate that SHF is a disease of macaques that in all likelihood can be caused by a number of distinct simian arteriviruses, although with different severity depending on the specific arterivirus involved. Consequently, we recommend that current screening procedures for SHFV in primate-holding facilities be modified to detect all known simian arteriviruses.