Clinical and epidemiological features of simian parvovirus infection in cynomolgus macaques with severe anemia

We recently identified a simian parvovirus (SPV) in cynomolgus monkeys with severe anemia. We describe here the clinical and epidemiological findings in the original outbreak and in a second episode of anemia involving monkeys in a drug safety study at a separate facility. The major clinical findings associated with SPV infection were a severe normocytic, normochromic anemia. In the original episode the anemia was predominantly nonregenerative, whereas in the second outbreak there was an initial strong, regenerative response. In the absence of predisposing factors, SPV infection was mild or inapparent. However, the presence of concurrent acute infection with type D simian retrovirus in the original episode is believed to have been a major predisposing factor for the development of immunodeficiency and persistent SPV infection, culminating in severe anemia. It is unclear whether simian retrovirus infection played a role in the second episode, but it is possible that the drug used may have been a factor, because severely anemic monkeys were in the high drug dosage group. We conclude that SPV should be considered in the differential diagnosis of severe anemia in monkeys.