The ASPCA Animal Poison Control Center Sends Bio Alert to Veterinarians Regarding Spraying For West Nile Virus

American Society for the Prevention of Cruelty to Animals
Wednesday, 9 October 2002

FAQ offers answers to frequently asked questions about pesticides used for mosquito control.

To help decrease the risk of West Nile virus, many communities are taking steps to control the mosquito population through pesticide application. While the types of pesticides and method of application vary regionally, the pesticides approved for mosquito control are considered to pose low risks when used responsibly. The following provides answers to common questions about some pesticides that are being used for mosquito control in the United States.

1. How safe are the pesticides being used for mosquito control?

The Environmental Protection Agency (EPA) reviews and approves pesticides and their labeling to ensure that the pesticides used to protect public health are applied by methods that minimize the risk of human exposure and adverse health and environmental effects.

2. What types of pesticides are being used for mosquito control?

Mosquito control for West Nile virus includes adulticide and larvicides. Larvicides include biological insecticides, such as Bacillus sp, temephos, and methoprene. Although the exact pesticide and concentration used will vary regionally, approved mosquito control pesticides are generally applied at very low concentrations. It is unlikely that adverse health effects will occur as a result of this type of use, but some animals may experience adverse effects. To find out which pesticides are being used and at what application rate they are being sprayed in your community, contact your local health department.

3. Which pesticides are being used for mosquito control?

Larvacides:

Bacillus thuringiensis is a bacterial organism. B. thuringiensis strains are not considered to be serious pathogens and spray programs utilizing various varieties have not been associated with a specific illness pattern in humans or animals. The LD50 of Bacillus thuringiensisis is 5000 mg/kg.

Temephos formulations are designed to be a non-systemic organophosphate insecticide that acts by cholinesterase enzyme inhibition. The oral LD50 of technical grade temephos range from 1226 to 13,000 mg/kg in rats.

Methoprene is a compound, which mimics the action of an insect growth regulation hormone. Methoprene is a common ingredient in flea control products that are labeled for use in dogs and cats. The oral LD50 for methoprene in rats is greater than 34,600 mg/kg, and in dogs is greater than 5000 mg/kg.

Adulticides:

Naled is an adulticide used to kill adult mosquitoes. Naled is considered a non-systemic contact and stomach organophosphate insecticide. The oral LD50 of naled ranges from 91 to 430 mg/kg in rats, and 330 to 375 mg/kg in mice.

Synthetic Pyrethroids: Pyrethrins are derived from a combination of six insecticidal esters (pyrethrins, cinerins, and jasmolins) that are extracted from dried Chrysanthemum flowers. Permethrin and resmethrin are both synthetic pyrethroid insecticides.

• Permethrin: Permethrin is used in flea control products for dogs (i.e. spot-on-products that contain 45-65% concentration.) While cats are sensitive to such high concentrations of permethrin, there are some products that are labeled for use on cats that contain small concentrations of permethrin, usually less than 0.1%. Dermal LD50 in rats of over 4000 mg/kg, and in rabbits of greater 2000 mg/kg.
• Resmethrin: The oral LD50 for technical resmethrin in rats is variously reported as greater than 2500 mg/kg or 1244 mg/kg. Resmethrin is only slightly toxic through the dermal route as well. The reported dermal LD50 for technical resmethrin are: greater than 3000 mg/kg in rats, greater than 2500 mg/kg in rabbits, and greater than 5000 mg/kg in mice.

4. How can I find out what exactly is being sprayed in my area?

To find out which pesticides are being used and at what application rate they are being sprayed in your community, contact your local health department.

5. How can I educate my clients about pet safety during mosquito spraying?

The ASPCA Animal Poison Control Center and the American Veterinary Medical Association (AVMA) have issued a statement to help guide pet owners during mosquito spraying efforts. Feel free to pass this information onto your clients.

As more cases of West Nile virus-associated illness have been diagnosed in people and horses, communities have taken steps to prevent spread of the virus. Mosquito control is the most effective means of preventing spread of the West Nile virus and many communities are including spray application of pesticides in their control programs. Although approved pesticides for mosquito control pose minimal risk when used by professionals, the ASPCA Animal Poison Control Center and the American Veterinary Medical Association offer the following tips to help pet owners limit their pets' exposure to these pesticides:

Steps to Reduce Pet Exposure to Pesticides Used for Mosquito Control

• Know when pesticides will be sprayed in your community.


• Keep pets indoors during times when pesticides are being sprayed. Elderly or debilitated animals or those with preexisting health conditions, such as heart disease or asthma, may be more sensitive to airborne pesticides and chemicals.


• Close windows and turn off window-unit air conditioners when spraying is taking place in the immediate area.


• Bring pet dishes, toys, and other items inside while pesticides are being sprayed. If these items have been accidentally exposed to the spray, wash the items with soap and water and rinse well before reintroducing the items to your pets.


• Horses should be kept in their stalls or in a lean-to during spraying.


• Cover water troughs and water buckets during spraying.


• Cover fishponds during spraying, as fish can be sensitive to certain pesticides.


• If you suspect that your pet is experiencing difficulties, contact your veterinarian immediately.

West Nile viral encephalitis is a mosquito-borne infection of the brain caused by the West Nile virus. West Nile virus is spread by the bite of an infected mosquito, and can infect people and animals. Wild birds, horses, and humans are the species most often affected; however, the virus has also been identified in cats, dogs, bats, chipmunks, skunks, squirrels and domestic rabbits.

Although these latter species may become infected, they usually do not develop clinical signs of disease. Risk of contracting West Nile virus is low. In areas where mosquitoes carry the virus, less than 1% are actually infected. Even if mosquitoes are infected, less than 1% of people bitten and infected by those mosquitoes become severely ill.

Most infections in humans are relatively mild, with flu-like symptoms including fever, headache, body aches and, in some cases, skin rash and swollen lymph glands. Signs of more severe infections include high fever, neck stiffness, muscle weakness, convulsions and paralysis. Death rates associated with severe infection range from 3% to 15% and are highest among the elderly.

For more poison prevention tips, please visit the ASPCA Animal Poison Control Center's Web site at www.apcc.aspca.org. For more information about West Nile virus and ensuring your pet's good health, contact your veterinarian and visit the American Veterinary Medical Association's Web site at www.avma.org.

6. What about dogs and West Nile Virus?

Dog owners may express concern regarding the risks of their pets contracting West Nile Virus (WNV) from mosquitoes. The ASPCA Animal Poison Control Center is providing the following information regarding WNV in an effort to help educate dog owners on the risks associated with WNV and the agents that may be used to repel mosquitoes.

• World-wide here have been very few reported cases of WNV-related disease in dogs, which reflects the fact that they are not very susceptible to the virus. In the US over the past several years, only one confirmed case of WNV in a dog has been reported. The vast majority of dogs are not in any danger of contracting the disease syndromes (inflammation of the brain and/or heart) that have been associated with WNV.
• For dog owners who wish to minimize their dog's exposure to mosquitoes that can carry diseases such as heartworm disease and WNV, the following suggestions are made:
  • Keep pets indoors during times when mosquitoes are most active. These times are dawn, dusk and early evening.
  • Eliminate areas of standing water that can be breeding grounds for mosquitoes. For example, empty and re-fill outdoor water bowls daily.
  • Many pyrethrin-based flea control products for pets are also labeled to kill or repel mosquitoes and may be used on dogs. Before using these products, be sure to read and follow the label instructions carefully.
• The use of products containing DEET (N,N-diethyl-meta-toluamide) on pets is NOT recommended. Dogs (and cats) are sensitive to DEET and may develop neurologic problems such as incoordination, tremors or seizures if DEET-containing problems are applied to them.
• The use of products containing concentrated essential oils such as tea tree oil (melaleuca oil), pennyroyal oil, and d-limonine is also not recommended. Concentrates of these products can cause serious health problems in pets, such as weakness, paralysis, liver injury, and seizures. Besides, the effectiveness of these products in repelling mosquitoes is not proven.

For more information, or to contact American Society for the Prevention of Cruelty to Animals, see their website at: www.aspca.org