First Cases of Bird Flu Reported in SLO County

Throughout February and March, San Mateo County experienced a small outbreak of the H5N1 virus, also known as bird flu, in their local sea lion population. However, in late March, a confirmed case was reported in SLO County, when a dead sea lion tested positive for the virus. 

This is the first recorded case of bird flu in a mammal in SLO County, according to KSBY. The sea lion was reportedly found on the Morro Strand State Beach. The SLO County Public Health Officials state that the public risk of catching the virus is low, as it primarily circulates among marine mammals and wildlife; however, the risk is not zero. They encourage the public to stay away from wildlife, especially individuals who appear sick or deceased. 

In San Mateo County, the virus has reportedly killed at least two animals, and “the spread to two other species concerns scientists studying the outbreak, but the slow progression suggests that the outbreak is not spreading,” according to the SLO Tribune. 

Bird flu symptoms in humans include coughs, eye redness, headaches, fatigue, and, in severe cases, seizures and pneumonia. The last human case, however, was recorded in November of 2025. In sea lions specifically, observed symptoms include tremors and seizures. 

The Marine Mammal Center (MMC) typically responds to any calls regarding sick, injured, or deceased wildlife. However, with the high level of transmissibility that this disease holds, the MMC will not be physically responding to any calls regarding deceased or sick sea lions for the time being, according to the SLO Tribune. 

“The Marine Mammal Center is taking reports of stranded [sea lions], but because they don’t want to risk bringing this contagious virus back to their hospital, they will not send responders to evaluate or rescue the seal,” said Christine Heinrichs with the Tribune. 

This outbreak has not been nearly as bad as outbreaks in other areas, however. In South America, there have been hundreds of outbreaks in the last few years, primarily taking place in 2023 to 2024. Ecuador, in particular, was heavily affected by the disease. Across 35 separate outbreaks, over 1.2 million cases were recorded in poultry, with 924,000 deaths across that. 

Bird flu has been more prevalent in the last few years, with cases arising across the California coasts. Despite how it has become more widespread, most research scientists and marine mammal care volunteers have seen it start to be brought down a notch, as the number of deaths along specifically the CA Coast has decreased since the first reported case.

Sources: CDPH, SLO Tribune, KSBY, Science Direct