WHAT IS THE DIFFERENCE BETWEEN PRIMARY POISONING & SECONDARY POISONING?
Let’s start with the basics. Primary poisoning is when an animal directly ingests a rodenticide bait. Secondary poisoning occurs when an animal ingests another organism that has poison in its system. However, it’s not as straightforward as it sounds, and not every case of primary poisoning is intentional.
If a bait station is left unsecured, set up incorrectly, or installed in an easily accessible location, non-target species including pets or children could come in contact with the bait. Improper disposal of used bait can also lead to unintentional primary poisoning. This can happen if a homeowner purchases rodenticides and then stores them in a place where their dog can discover and ingest them, or if used bait is thrown in a garbage can without a secure lid.
HOW DOES RODENT POISON WORK?
A pesticide that is specifically designed to control rodents is called a rodenticide. The most commonly used rodenticides in the U.S. contain bromadiolone, brodifacoum, difethialone, or diphacinone. While there are many different variations of rodenticides, these particular ones are similar in that they are all anticoagulants, which are a type of blood thinner that prevents blood from clotting. In mammals and birds, the liver produces a particular enzyme that allows the body to recycle vitamin K, which is the main component needed to prevent humans and other animals from bleeding out. The process works the same for injuries both inside and outside the body. Anticoagulants work by targeting and disabling the enzyme that allows blood to clot.
MULTIPLE-DOSE VS. SINGLE-DOSE RODENTICIDES
There are two types of anticoagulants used in rodenticide, multiple-dose, and single-dose. These are often referred to as first-generation and second-generation rodenticides. Bromadiolone and diphacinone are multiple-dose, or first-generation baits, and require the rodent to consume several doses of rodenticide bait while feeding over several days. Brodifacoum and difethialone are considered second-generation rodenticides, which were created to control rodents that had become resistant to first-generation baits. Second-generation baits are more potent and highly toxic, because of which, a single feeding of them can result in a lethal dose for a small-bodied creature like a mouse or rat.
WHO CAN USE RODENTICIDES?
The state of Connecticut regulates the use of rodenticides through the Department of Energy and Environmental Protection (DEEP). In addition, the Environmental Protection Agency (EPA) has restrictions on rodenticides available for consumer use. In order to obtain rodenticides with the highest levels of toxicity, such as most single-dose anticoagulant baits, the purchaser must hold a valid commercial supervisory certificate. Every company that applies pesticides commercially must have a certified supervisory applicator who is either present on-site during the application or provides specific written instructions to a certified technician. Supervisors go through rigorous training and exams which test their knowledge of whether or not pesticides should be used, how and where they should be applied, which chemicals to use, and at what dosage, as well as an understanding of pesticide safety and proper handling. This wealth of knowledge is what sets a pest control professional apart from an average homeowner. While secondary poisoning is still technically possible with any rodenticide use, the danger of harming pets and non-target wildlife becomes much lower when applied by a licensed professional.
SHOULD I WORRY ABOUT MY DOG GETTING INTO BAIT?
To refresh your memory, unintentional primary poisoning happens when a non-target animal, such as a dog or cat, directly consumes rodent bait. On rare occasions, accidental primary poisoning can be fatal when bait is not handled or disposed of properly. This most often happens due to misuse of rodenticides and unnecessary outdoor bait placements. To give you an idea of how much bait it would actually take to harm a 20-pound dog, let’s go through the following scenario.
The average home of 2000 square feet would most likely require about 12-15 bait stations. Each bait station contains 1 oz of single-dose anticoagulant bait. That means at any given time, the maximum amount of bait in the entire home would be 15 oz. Now consider that these bait stations are placed by a licensed pest control professional, and they are located in the proper areas of food, warmth, and storage where mice are most likely to reside. That typically means in the mechanical room, underneath stoves, under kitchen sinks, inside attics, and in the dark corners of the garage. Now think of how frequently your pet accesses those areas, and if they do, how often are they unattended?
HOW LIKELY IS SECONDARY POISONING, REALLY?
The majority of rodenticides are made with minute amounts of the active ingredients that make them anticoagulants. To give you an idea of how small the dosage is in an average trap, the active ingredient makes up only 0.005% of the total formula in our most commonly used bait. Your dog would need to consume about 20% of its body weight in bait in order to see its fatal effects. So your 20-pound pet would need to consume approximately 64oz of rodenticides. Looking back to our average 2000 square foot home, that’s over four times the maximum amount of bait that would be present. Now you may be starting to see how unlikely it is for properly placed bait stations to cause harm to non-target animals.
WHAT SHOULD I DO IF MY DOG EATS A POISONED RODENT?
Many dog owners have had that moment of panic when they find their beloved pet with something dead in their mouth. Not only do you instantly worry about possible diseases or bacteria, but if rodenticides are present in your home you may begin to worry whether they have ingested a poisoned rodent. Well here’s the good news, unlike primary poisoning, secondary poisoning usually involves repeatedly feeding on numerous poisoned carcasses over a period of several days or even longer. The chances of your pet consuming not just one, but multiple poisoned rodents over that period of time are slim. And some more good news, even if they do manage to ingest numerous carcasses, the amount of actual poison they would have consumed is so small that it would take a very large pile of dead rodents being their only meal in order to result in death.
Mice are nibblers by nature, and on average they only consume approximately 4 grams of bait per day. That combined with the improved single-feed baits used by professionals, means that a dead mouse has such a minuscule amount of poison in its system that it is highly unlikely to affect your dog. That being said, there can be many other factors involved such as the size, age, and species of the dog. Additionally, if the dog were to consume multiple poisoned carcasses over several days, that would increase the chances of them ingesting a lethal dosage. It bears noting that this would be a rare case.
The dog would need to be particularly hungry or desperate for food to consistently seek out poisoned rodents as their primary food source. While this scenario is theoretically possible, there are many factors that would have to align which make it extremely unlikely.
HOW CAN I PREVENT SECONDARY POISONING?
While accidental secondary poisoning is rare, there are ways to help ensure it does not happen. This is done by:
Using tamper-proof bait boxes
Keeping bait boxes in enclosed areas away from non-target animals
Not leaving bait exposed or outside where children or pets can easily access it
Following these measures will help cut down the risk, but the absolute best way to prevent secondary poisoning is by preventing unwanted rodents in the first place. This starts with homeowners taking proactive steps to combat the issue. This can be achieved by doing the following:
Remove trash and food that attracts rodents to your property. This includes pet food, birdseed, waste, and compost piles.
Eliminate possible sources of water such as leaking hoses, bird baths, or depressions in the ground that frequently flood.
Do not leave open or unsecured food around the house, particularly in kitchens, pantries, and basements.
Use exclusion methods to plug holes and cracks that provide an entry point to your home.
Keep shrubs and trees trimmed back at least a foot away from the home.
Keep the perimeter of buildings free of wood and junk piles that provide shelter to small rodents.
Remove invasive English ivy—it’s known to harbor rats. Replace it with native plants that support beneficial wildlife.
DON'T BE AFRAID TO CALL IN AN EXPERT
If the above measures fail, please do not take matters into your own hands. Call an expert who is specially trained in rodenticide use to eradicate your rodent infestation safely and efficiently. If you do suspect that your pet has gotten into rodent bait, it’s always best to proceed with caution and a call to your veterinarian would be recommended. You should always keep a copy of the label for the rodenticide in question so your veterinarian can make informed decisions about potential treatments. You can also call the National Pesticide Information Center at 1-800-858-7378 to discuss a particular incident.