Bromethalin is a potent neurotoxic rodenticide readily available commercially, often sold in chunks or pelleted products and dyed a vivid green color. As use has become more common so have cases of toxicity in domestic and wild animals. In any mammal that ingests enough of it, it causes edema in the brain and spinal cord, which causes the characteristic neurologic signs. There is no specific treatment for bromethalin toxicosis. Treatment focuses on decontamination and supportive care.
Cats are one of the most sensitive species to it, even more so than the targeted rodent species. The usual route of exposure for a cat is eating rodenticide bait (either directly from the environment or in a consumed prey animal). So when unweaned orphan kittens come in with neurologic signs, bromethalin doesn’t usually make the differential list. A new open-access case series in JAVMA suggests it should be considered.
Of 15 kittens from 5 litters, 13 had or developed neurologic signs. Most were euthanized or died, two recovered fully, including one that had been unable to walk, and two never showed signs despite confirmed exposure. Thirteen of the kittens were estimated to be 21 days (3 weeks) or younger at presentation, seemingly too young to be ingesting bait directly. The diagnosis typically came after post-mortem examination (necropsy). The core mystery of these cases is how these kittens were exposed. While the authors were unable to definitively answer this question, they raised some interesting questions and hypotheses.
Bromethalin toxicosis might be an under-recognized problem in kittens admitted to shelters
The kittens identified in this study arrived the way shelter and rescue intakes often do, found at large in the community with a deceased, neurologic, or missing mother. Some were neurologic at time of shelter/rescue admission, while others appeared clinically normal and later developed signs.
None of the deceased kittens had green material in their GI tracts as would be expected if they had recently ingested bait. This could happen if ingestion happened several days prior to presentation, but another theory is that they may have been exposed via relay toxicosis. Relay toxicosis is secondhand poisoning. One animal eats the poison, and a second animal is poisoned by eating that animal’s body or milk. Given the ages of the affected kittens, the implication is that they may have ingested the bromethalin while nursing. Because the queens were either unavailable or not examined, we have no information to try to guess how they were exposed.
How you can make use of this information
First of all, just being aware of bromethalin as a potential cause of neurologic signs in cats of any age, and potentially maternal death may help increase the chances of survival for some of these cases.
Next, this study showed that a blood test that had not previously been used in cats could be used to detect bromethalin exposure in cats and kittens. Though it was not tested in this case series, there may even be potential to test a queen’s milk. I am unsure how widely available this test is, but it may be worth reaching out to your nearest veterinary diagnostic or toxicology laboratory to ask about a desmethylbromethalin (DMB) test if you suspect bromethalin toxicity.
Finally, look into your agency’s rodent control approaches and consider doing away with use of bromethalin. Support members of the community to do the same.
When rodents are a problem, the instinct is to reach for a different poison, but other rodenticides aren’t clearly safer for cats or wildlife, and some are worse. Second-generation anticoagulants, for instance, build up in the rodents that eat them and then poison the hawks, owls, and cats that eat those rodents. Swapping one poison for another mostly changes which animals are at risk.
An non-specific approach that works and protects cats and wildlife, is called integrated pest management. Seal the gaps that let rodents in. Remove the food and clutter that keep them around. Trap the ones already there.
One newer option is worth knowing about: rodent fertility control, a bait that curbs breeding instead of killing via 4-vinylcyclohexene diepoxide + triptolide. Its real edge is that it doesn’t kill non-target species the way a rodenticide does, and it clears the body fast rather than building up in animals higher on the food chain. Safer isn’t the same as harmless, though. It can still affect the fertility of other animals that get into it, and in females that effect can be permanent, which is why it belongs in a secured bait station and not loose in the environment. It can also be toxic to fish and insects. The effectiveness catch is real too: the strongest claims come from the companies that sell it, the effect can fade, and it works best alongside trapping and exclusion. Promising, not a magic bullet.
Any lethal strategy can reduce a population for a few weeks, but ultimately the population is likely to bounce back if nothing changes in the environment that supported the rodents in the first place. Approaches that fix the underlying conditions last longer and help keep non-target animals out of the crossfire.
Most of the kittens in this case series did not survive and some were gone before anyone suspected a toxin at all. But a couple recovered completely, including one that could not walk. Recognizing the pattern and asking about the test could mean the difference between death and survival for kittens in your care.
Beyond that, find opportunities to prevent new cases. Every poisoned kitten or wild animal started with a product someone put out for rats or mice. Rethinking how your agency and your community members handle rodents won’t help the kittens already in your care, but it is how you keep the next ones from showing up at all.
At Paws to Elevate, we keep an eye on the research so your team doesn’t have to comb through journals to stay current. If you want help turning findings like these into actional insights for shelters.
This blog post was created with the assistance of AI tools and reviewed and edited by Becky Stuntebeck. It is provided for general informational purposes and does not constitute veterinary advice.
