An Inyo county black bear found dead during our fall ungulate captures was likely poisoned by the pesticide carbofuran. The adult black bear was spotted by our helicopter crew lying dead across irrigation piping on a top of a knoll in the John Muir Wilderness. The situation was very odd so the helicopter crew collected to carcass and flew it into base camp for a post mortem examination by the Department wildlife veterinarian. While examining the dead bear some of the biologists noted that flies which contacted the bear’s saliva or diarrhea quickly died. In light of this finding, and the likely association with what appeared to be an illegal marijuana grow, we decided to shuttle the bear carcass straight to the California Animal Health and Food Safety (CAHFS) laboratory for a full post mortem examination including necropsy and toxicological testing.
The initial necropsy findings were unremarkable. Toxicological testing detected carbofuran in stomach contents. No other carbamate or organophosphate pesticides were detected. In addition to the toxicology findings, microscopic examinations of tissues showed non-suppurative inflammation in the brain. Inflammation of this sort is typically caused by a virus, but rabies and canine distemper viruses were not detected. A cause for the encephalitis has not yet been determined and we are screening tissues for a possible gammaherpes virus that has been identified in other bears with similar brain inflammation. The significance of this finding in this bear is unknown, but was unlikely to be a contributing factor in the bear’s death. The detection of carbofuran and no other pesticides in conjunction with a decreased brain cholinesterase activity, a hallmark of organophosphate or carbamate pesticide intoxication, strongly supports carbofuran intoxication as the cause of death.
Carbofuran causes death by extreme over stimulation of the nervous system, which often ultimately leads to respiratory failure. The extreme toxicity of this material is illustrated by the fact that about approximately 64 rats or 12,000 sparrows would be killed by a single aspirin-sized tablet of the technical material. Carbofuran is one of the most toxic carbamate pesticides ever produced, and as such all legal uses of carbofuran have been banned in the United States since 2009. That’s not to say that carbofuran itself is banned in the U.S., but that there are no legal uses of carbofuran in the U.S., so for all intents and purposes it has been banned. Prior to its discontinued use in the U.S., it was responsible for losses of thousands of birds, mammals, and fish. In recent years, there have been numerous cases of illegally imported carbofuran being found on trespass marijuana grows in California and regular reports of associated wildlife losses. Some of these losses appear intentional. Carbofuran is still sold in other parts of the world, including some countries in Africa, Asia, and Latin America.
Prepared by Brandon Munk and Stella McMillin