Avian Flu In California Mountain Lions

HPAI H5N1 better known as the Eurasian Avian Flu, was first reported in California in July, 2022. The disease is mostly impacting birds but can be transferred to carnivorous animals when the infected bird is ingested. To date, this virus has been found in 45 of the 58 counties in California. In December, 2022 and January, 2023, the virus was detected in two dead mountain lions in Mono County.

These detections were unique because the cats were both part of a CDFW population study and wearing GPS collars. Even more unique is these two mountain lions were related (mother/daughter). With both cats wearing GPS collars, CDFW received a mortality notification and were able to recover the remains quickly. Both cats underwent a necropsy to determine the cause of death. They determined that the cause of death was swelling of the brain (encephalitis). They also noted that the cats had lesions in the lungs which caused a buildup in fluid. They are performing more testing to rule out the possibility of co-infections, but these two findings are associated with the Avian Flu.  

Although detections in carnivorous mammals aren’t widespread, CDFW is worried that the detections were so far away from the Butte County detection in a bobcat (January 2023). Mono County also had not had any detection in wild birds yet either. CDFW does not expect this virus to have a population level impact on California mountain lions, bobcats or other carnivorous mammals.

CDFW considers this a low-risk zoonotic pathogen, which means that it poses low risk of jumping from non-human animals to humans. Even with the low transmission risk to humans, the Center for Disease Control still recommends that you take protective measures if you encounter dead birds or mammals. If you run across a dead carnivorous mammal or bird and it doesn’t have obvious signs of the cause of death (I.e., shot, or hit by a car), call CDFW and report the finding. Do not handle the specimen if you can avoid it.  

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