County officials are advising bee enthusiasts to keep an eye out for signs of a disease known to be destructive to honeybee hives after one case of American Foulbrood was confirmed in October and four other unconfirmed cases were reported in the county this fall.

As a fatal bacterial disease of honeybee brood — which includes eggs, larvae and pupae — American Foulbrood can weaken and kill honey bee colonies, said Jeremy Wagner, deputy agricultural commissioner and sealer for the San Mateo County Department of Agriculture/Weights and Measures.

A spotty pattern of honeybee brood, brood cells with perforated wax coverings and darkened, brown larvae sunken to the bottom of brood cells are among the warning signs those tending to bee hives should look for in identifying the disease, said Wagner. In addition to a fishy or rotten smell, the disease can result in a sticky, mucuslike substance in brood cells, which, if stirred and pulled with a toothpick or twig, will produce a thread of 2.5 centimeters or longer, he said.

Wagner said the disease came to light when a local beekeeper in Pescadero contacted his department with a report of a home test kit that returned a positive result, so county officials took an official sample and sent it to a bee research laboratory in Maryland to be tested. Though that case was the only official determination of American Foulbrood in the county so far, Wagner’s department has received reports about the disease in El Granada, Half Moon Bay, San Mateo and Tunitas Creek. He said in each of the reported cases, the hives in question were destroyed, and the last time county officials saw a comparable number of reports of the disease was the 1990s.

“Once a colony has this disease, there’s really no cure for it,” he said. “That’s why early detection and quick response is really important for beekeepers in the area.”

Wagner said burning infected hives and hive components is the only way to prevent the spread of the disease. Because honeybees are known to take honey from neighboring hives that aren’t well-defended, the disease can easily spread if one of the hives is infected and less able to defend itself from raids, he said.

Wagner said county officials are recommending those who believe a hive may be infected to seal it to prevent it from being “robbed” by other bees and contact his department to scope next steps, which could include burning the hive and burying the ashes to ensure the disease doesn’t spread. He noted burning hives requires burn permit applications to be reviewed by the county’s Department of Agriculture/Weights and Measures, the Bay Area Air Quality Management District and a local fire department.

By wearing disposable gloves and changing them between apiaries, sterilizing tools and suits used in each apiary and using a disposable tool like a matchstick or toothpick instead of a hive tool to investigate brood cells that could be infected, beekeepers can mitigate the spread of both the American Foulbrood and other diseases and parasites, said Wagner.

Because the disease can exist in the wild at low levels and the bacterial spores can last 40 years to 50 years, it’s challenging to declare the disease eradicated, said Wagner.

“American Foulbrood is something that California beekeepers have to be aware of and be educated about,” he said. “Cleanliness and … regular hive inspections are really what we want to emphasize.”

If you think you may have detected American Foulbrood, call (650) 363-4700 to reach the San Mateo County Department of Agriculture/Weights and Measures. Visit for more information.

(650) 344-5200 ext. 106

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