The Dangers of Anticoagulant Poisons

Many people choose to use poisons or rodenticides, such as warfarin, as a solution to rodent pests. Warfarin, used in human medicine as a blood thinner, is an anticoagulant, which means it prevents the formation of blood clots. Anticoagulants block an enzyme that activates vitamin K; without vitamin K, normal coagulation or clotting pathways based on factors from the liver cannot function once those existing factors are depleted. Therefore, vitamin K is an antidote to the effects of anticoagulant rodenticide. Rodents that eat enough poisoned bait die from massive hemorrhage in 3 to 5 days. This unfortunately can happen to any animal that directly ingests anticoagulant bait (primary exposure) or any animal that eats another animal (or carcass) that contains the rodenticide toxin (secondary exposure).

A turkey vulture (Cathartes aura) presented to the Janet L. Swanson Wildlife Health Center (WHC) last year with presumed rodenticide toxicity from a poisoned meal. Turkey vultures are commonly found on rooftops sunning or in the sky soaring up high circling over a carcass, as they are scavengers. Physically, they have bald, featherless red heads and black bodies with a wide wingspan. More information about this species and other birds can be found at the Cornell University Lab of Ornithology.

This patient was found lethargic and unable to fly, and when evaluated at the WHC had pale pink gums, blood in the feces, and bruising across much of its body. A blood sample was taken to see how many red blood cells the creature had, and it came back low, indicating anemia. In addition, when the blood sample was taken, the vulture had difficulty clotting at the venipuncture site. Based on these findings, the vulture was hypothesized to have anticoagulant rodenticide toxicity. There is no definitive way to diagnose rodenticide toxicity in birds while they are alive. Other clinical signs that may point towards this diagnosis include bleeding (external or internal without adequate clot formation) and/or loss of appetite. Blood clotting times can be evaluated in domestic animals but may be prolonged for various reasons besides anticoagulant toxicity, and are not available in birds at this time. Post-mortem (after death) laboratory tests of the liver may reveal high toxic rodenticide values and sometimes the poison is found in the stomach contents.

During evaluation of the vulture, a lead test was also performed, and blood lead levels were normal (For more information on lead toxicity in wildlife, see “The Price of Freedom: How our choice to use lead is killing the bald eagle”).

Fluids to increase blood volume and bolster hydration were part of this vulture’s supportive care. Vitamin K was administered to treat the presumptive anticoagulant rodenticide toxicity. Over the course of its treatment, the turkey vulture’s bruising resolved, its gums became a healthy pink, and its anemia was corrected as evident from another red blood cell count a few days later. Throughout its time at the WHC, the turkey vulture retained its wild nature, using the species’ characteristic projectile vomiting as a defense mechanism whenever it was restrained for treatment. Getting rid of a recent meal decreases their weight so they can fly away and is repulsive to the predator trying to catch them, giving them more time to escape. In total, the turkey vulture was at the WHC for 10 days before being transferred to a rehabilitator for continued treatment, physical conditioning, and eventual release.

In a recent study (Kelly 2014), rodenticide toxicity was reported to be highly likely in turkey vultures as a primary or contributing cause of death, due to their scavenged carrion diet. It is unknown what the true impact of anticoagulant rodenticides is on wildlife, as some of the animals in that study were found to have rodenticides in their bodies and yet did not show signs of poisoning. Chronic anticoagulant rodenticide exposure may predispose birds to adverse growth rates, alterations in their physiology, and suppressed immunity. Monitoring of wildlife rodenticide concentrations, such as through deceased hospital and rehabilitation animals, may be useful in understanding and addressing this issue in wildlife. Alternatives to the use of anticoagulant and other types of rodenticides for rodent control include using Havahart® or other live traps, consulting pest control professionals, and maybe adopting a cat.

Though this review focused on turkey vultures, any species of bird or mammal is susceptible to anticoagulant rodenticide toxicity. In many studies and surveys, rodenticide residues were found in well over 50% of necropsied raptors and other birds, which encouraged the founding of such organizations as Raptors are the Solution (RATS, which aims to educate about raptors’ ecological role and the dangers of rodenticides). From the Pet Poison Helpline, rodenticide toxicity is second on their top ten pet poisons list for dogs and tenth for cats. Frighteningly, thousands of children ingest toxic amounts of rodenticides yearly, and frantic parents make calls to the Centers for Disease Control and Prevention (CDC). Fortunately, there are safety precautions: second generation anticoagulant rodenticides (even more dangerous than warfarin, which is of the first generation) were prevented from registration for use in products geared for consumers in residential communities of the U.S. starting in 2011. Be sure to keep rodenticides away from your children, pets, and wildlife.

Further information about anticoagulant and other types of rodenticides that animals may be exposed to can be found here.


Lauren Jacobs is a third year Cornell veterinary student and student wildlife technician from Poughquag, NY. She received her Bachelor of Science Degree in Animal Science from Cornell University College of Agriculture and Life Sciences in 2015, with minors in Biology and Music. Lauren is interested in mixed animal private practice and plans to continue to work with wildlife and enjoy music after graduation.

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