Controlling Rodents & Protecting People

Like other pests, rodents can cause health problems for the public and for rodent control professionals working to protect the public. Illness and even death can occur when people are exposed to one of the several dozen viral, bacterial and protozoan infections rodents are known to carry.

Some of these germs are contained in rodent feces, urine, saliva, shed hairs and carcasses. Sometimes particles of these infected materials become airborne and are inhaled, resulting in an infection such as Hantavirus. Other times infected particles are ingested with contaminated food, causing a case of Salmonella enteritis, a type of food poisoning. Infections such as rat bite fever may be the result of a bite.

Disease organisms are also picked up on rodents’ feet and fur as they move about in their territory and then deposited someplace else such as a food item or a food contact surface. Salmonella and E. coli infections can be spread this way. Finally, rodents are hosts to a variety of parasites just as are fleas, ticks, mites and mosquitoes. The parasite bites a rodent and then bites a human and infects them. Plague (via a flea), West Nile virus (via a mosquito) and Lyme disease (via a tick) are examples of this infection route.

IMPORTANT RODENT BEHAVIORS. To control rodents, it is necessary to understand important species-specific behaviors.

Norway rats live in burrows in the earth, as well as voids in walls, ceilings and equipment. They avoid anything new placed in their territory, so they often eject block-type rodenticides placed in their burrow. Treat burrows with loose pellets or meal products which to a rat resemble seeds, a natural food source.
Roof rats prefer high places, such as trees and attics. Controlling them requires ladders and a creative approach to anchoring traps and bait stations in nesting areas and along travel routes.

House mice rarely venture far from their nest, so you must take the control material to them. They nest in hidden places such as in walls and under slabs. Mice naturally hoard seeds and may translocate pellets, so use them carefully.

CHOOSING A RODENTICIDE AI. Rodent control professionals need a variety of materials and tactics to eliminate rodent populations quickly, cost effectively and with minimal risk. One option — anticoagulant rodenticides — are a good choice for several reasons:

• A variety of forms and flavors make it easy to find a rodenticide to fit almost any situation.
• Rodents have a keen sense of taste. Active ingredients taste bad. Anticoagulants work at concentrations much lower than those of acute toxicants — 25 or 50 ppm vs. 100, 750 or 2,000 ppm. Less bad taste means more rodents eat a lethal dose.
• The delayed effect of an anticoagulant eliminates bait shyness and allows time to treat non-target animals that may be accidentally exposed. The antidote for all anticoagulants is Vitamin K1.
• After feeding on the bait, a rodent loses blood, runs out of energy and dies.

CHOOSING A FORMULATION. How a rodenticide is presented makes a big difference in how it’s accepted by the rodent population. Consider these formulations:

• Mini blocks have a hole in the middle that lets you secure them in tamper-resistant bait stations. You also can lower them on wire into nesting voids. This technique puts the bait in the right place, simplifies recovery to check for signs of feeding and makes it possible to remove uneaten material.
• Paraffin bars contain extra wax, making them excellent for wet environments, such as in sewers. Use wire secured to the manhole ladder or other anchoring points to suspend the bait on a ledge above the normal water level.
• Pellet and meal place packs protect the rodenticide from contaminants and moisture, and minimize applicator exposure. They also tolerate heat better than wax-based blocks.
• Bulk pellets resemble seeds so they are well suited for burrow-baiting Norway rats. Paraffinized pellets withstand moisture in burrows. Place them deep into the burrow. Take care not to cave the burrow in, or the rat will likely kick out the pellets when it re-opens the burrow.
• Meal baits are usually the most palatable, and a good choice for situations with a lot of competing food, as well as for burrow baiting (to further reduce the small risk of pellets being kicked out).
• Liquid rodenticides may be accepted if there is a shortage of free water available.
• Tracking powders are Restricted-Use Pesticides labeled primarily for indoor use. Use extra caution to comply with the label.

PROTECTING YOURSELF. Pest management professionals need to wash their hands vigorously with soap and water after handling traps and bait stations, as well as any other items possibly contaminated by pests. Hand sanitizers also have been proven to be effective as long as they contain at least 60 percent alcohol.

Wear appropriate respiratory protection when working in environments that may be infested with deer mice, especially dusty environments. Use a disinfectant to wet down nesting materials, droppings and carcasses before disturbing them. Refer to the Centers for Disease Control and Prevention (www.cdc.gov) for more information about protective measures.

Be cautious about where you place your hands. Bait stations can harbor resting rodents, poisonous spiders and snakes or stinging insects. A dark void could conceal a drug syringe and needle.

Work carefully. Rodent control is often performed in dark and potentially dangerous places. Avoid slips, trips, falls, bumped heads, cuts and punctures by using caution and the appropriate Personal Protective Equipment.

Finally, always read and heed the entire rodenticide label and MSDS before using any product.

Every treatment situation is unique, so carefully select the materials best suited for the job. Your knowledge of rodent behavior and rodenticide options will help you make informed choices. Combined with your persistence and commitment to protecting public health, your chosen approach will surely be the right solution.

The author is technical support manager, Liphatech. He can be reached at tbruesch@giemedia.com.

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Liphatech’s Approach to Managing Risks

All rodent control methods involve risk, including rodenticides. Snap traps can break fingers and glue traps can draw criticism from animal rights activists.

When using rodenticides at food facilities and other audited accounts, the main risk is product contamination. This can occur in various ways. Rodents, especially mice, tend to pick up rodenticide and move it — a drawback to using pellets. Air currents can blow crumbs from in or around a station.

Vibration can cause particles, or entire bait placements, to fall from high places. Vandals or disgruntled employees could deliberately contaminate a product or surface.

Some of these risks can be managed by using rodenticides that guard against crumbs; highly durable block formulations. Liphatech’s BlueMax Mini Blocks, with the active ingredient difethialone, is an example. This anticoagulant rodenticide is formulated with finely milled food grade ingredients and paraffin to provide optimal protection against bait crumbs, which could be scattered.

Moldy and rancid rodenticide is not attractive to rodents. This may result in control failures and subsequent public health issues. A mold-resistant rodenticide such as BlueMax Mini Blocks with advanced preservatives will remain effective even in humid or moist environments, according to Liphatech. — Ted Bruesch