Ovine progressive pneumonia and caprine arthritis encephalitis together are referred to as small ruminant lentiviruses (SRLVs). Along with caseous lymphadenitis (CL), SRLV are 2 of the so-called "iceberg diseases" of sheep and goats. In the case of SRLV, healthy tissue can be replaced with unproductive lymphoid tissue causing loss of milk, poor growth in lambs, swollen and painful joints, and shortened productive lives of infected animals. Understanding the characteristics of the SRLVs and the bacteria that causes CL and how to use the serologic tests available will help with prevention and eradication efforts.