Development and validation of a fecal PCR assay for Notoedres cati and application to notoedric mange cases in bobcats (Lynx rufus) in Northern California, USA

Abstract

Notoedric mange in felids is a devastating disease caused by a hypersensitivity reaction to the mite Notoedres cati. The burrowing of the mite causes intense pruritis resulting in self-mutilation, secondary bacterial infection, and often death of affected felids if left untreated. Our understanding of how notoedric mange is maintained in felid populations, and the true geographic extent of infestations, has been hampered because wild felids are elusive and, thus, traditional diagnostic methods are difficult to implement. To create a noninvasive diagnostic test, we developed and validated a novel PCR assay to detect N. cati DNA in fecal samples of bobcats (Lynx rufus) and used this assay to investigate a recent outbreak of mange in northern California, United States. Although the fecal PCR assay was 100% specific and could detect as few as 1.9 mites/200 μg of feces, it had a moderate sensitivity of 52.6%, potentially due to intermittent shedding of mites in feces or fecal PCR inhibitors. In a field investigation, 12% (95% confidence interval [CI]: 0.06, 0.23) of fecal samples (n=65) collected from Rancho San Antonia County Park and Open Space Preserve in Santa Clara County, California were PCR-positive for N. cati. When this estimate was adjusted for test sensitivity, the corrected proportion for fecal samples containing N. cati was 23% (95% CI: 0.14, 0.36), suggesting widespread mange in this area. This novel PCR assay will be an important tool to assess the distribution and spread of notoedric mange in bobcats and could be validated to test other wild felids such as mountain lions (Puma concolor). The assay could also be used to detect notoedric mange in domestic cats (Felis catus), particularly feral cats, which may also suffer from mange and could represent an important contributor to mange in periurban bobcat populations.