Volume 20, No. 5 August 2000 Insecticides and Repellents Used In this issue... for Mosquito Control With Emphasis on Preventing the Insecticides and Repellants Used 17 for Mosquito Control With Spread of West Nile Virus Emphasis on Preventing the Spread of West Nile Virus A Guide For Healthcare Providers A Guide for Healthcare Providers measures are not effective, and the risk of human These guidelines were developed to assist health exposure to WNV is considered high or rapidly care providers in answering questions relating to growing, the application of insecticides, either by mosquito control measures and preventing the ground or air, may be done to reduce the potential spread of West Nile virus (WNV). Information threat to people. concerning the insecticide product that may be MOSQUITO CONTROL PRODUCTS used, the likelihood of human exposure to the The product most likely to be used in Connecticut insecticide, signs and symptoms of overt for controlling adult mosquitoes is Scourge. insecticide poisoning, and steps to follow if a Scourge contains resmethrin (18%) and piperonyl person presents to your office with possible butoxide (54%), with the balance petroleum insecticide poisoning are included. distillate and inert ingredients. Resmethrin, is a Although we do not anticipate pesticide-related synthetic pyrethroid insecticide similar chemically poisonings associated with use of insecticide to natural insecticides that are derived from spraying to control the adult mosquito population, chrysanthemum flowers (pyrethrins). The the Connecticut Department of Public Health pyrethroids are neurotoxins. Selective toxicity of (DPH) is requesting that suspect cases be pyrethroids in insects (compared to mammals) reported to the Division of Environmental can be explained by higher intrinsic sensitivity of Epidemiology and Occupational Health by the insect sodium channel isoforms, by temperature dependent effects of pyrethroids calling 860-509-7742. o o (greater at 20 than 37 C), and by higher rates of BACKGROUND metabolic degradation in mammals (1-4). WNV is transmitted to humans through the bite of an infected mosquito. In 1999, WNV was Piperonyl butoxide also has some intrinsic responsible for 62 cases of severe illness, including insecticidal activity and provides synergistic 7 deaths, in New York City and surrounding activity when applied with pyrethrins. It does this counties. WNV was isolated in mosquitoes and in by inhibiting mixed function oxidase enzymes that 72 crows, 1 hawk, and a crane that died in Fairfield degrade pyrethrins and are responsible for and New Haven counties during September and increased resistance in target insects. Piperonyl October, 1999. Although persons living in these butoxide is found in many different topical areas were at risk of becoming infected, and 78 pyrethroid preparations used by humans (gels, symptomatic persons were tested, there were no liquids, and shampoos) for treatment of lice. confirmed human cases of WNV. In addition to using insecticides to kill active adult mosquitoes, it may be necessary to recommend During the fall of 1999, insecticides were sprayed in the use of insect repellents during outdoor several towns in Fairfield and New Haven counties activities in areas where there is a higher risk of to reduce populations of adult mosquitoes. This exposure to infected mosquitoes. A recent review year, a comprehensive plan to reduce mosquito found that although more than 20,000 compounds populations has been developed. If these have been studied as insect repellents, little is 17 Connecticut Epidemiologist known about how they act on their target insects, Workers involved in the mixing and application of and other insect species may react differently to the these products have the greatest risk of same repellent. Moreover, of all the tested exposure. These personnel, however, are repellents, DEET (N, N-diethyl-3-methylbenzamide, specifically trained to use these pesticides safely, previously called N,N-diethyl-m-toluamide)- to be aware of the signs and symptoms of containing products are the most effective and best- overexposure, and to seek medical attention studied agents for reducing the risk of bites from promptly for possible toxicity. essentially all species of mosquitoes. DEET is available in concentrations of 5-100% in multiple TOXIC EFFECTS OF PYRETHROIDS/ formulations including solutions, lotions, creams, PIPERONYL BUTOXIDE INSECTICIDES gels, aerosol and pump sprays, and impregnated Resmethrin (and other pyrethrin compounds) towelettes. Under most conditions, a high may be absorbed by respiratory, gastrointestinal concentration of DEET is not recommended, and or transcutaneous routes. They DO NOT cause products with 10-35% DEET will provide some cholinesterase inhibition. Resmethrin is only protection for at least 1-2 hours. slightly toxic to humans after acute inhalation or dermal absorption, and slightly toxic to practically EXPOSURE POTENTIAL TO INSECTICIDES non-toxic by ingestion (5). The low toxicity of Generally, there is no need to relocate during resmethrin may be attributable to limited spraying. The following common-sense steps absorption and rapid biodegradation by recommended by the EPA will reduce possible mammalian liver enzymes. In addition, pyrethrins exposure to pesticides during spraying.. have low efficacy on neural activity at mammalian · Look for notices about sprayng in the body temperatures, and generally effect newspapers and stay tuned to radio and TV for mammalian nerve sodium channels less than announcements. those of lower animals. In humans, most · Whenever possible, remain indoors with pyrethroid metabolites are promptly excreted, at windows closed and window-unit air least in part, by the kidney. Chronic toxicity conditioners turned off when spraying is taking testing of resmethrin in animals has documented place. hepatomegaly and hepatotoxicity, thyromegaly · Do not let children play near or behind truck- and thyroid cysts after treatment with high doses mounted applicators when they are in use. (25-250 mg/kg, p.o., QD) for months to years. · People who suffer from chemical sensitivities or These dosage levels are many-fold higher than feel spraying may aggravate a preexisting those expected in the human population following health condition, may consult their physician or repeated use of Scourge for mosquito control. the DEP's Pesticide Division (see next section) and take additional measures to avoid exposure Clinically, the signs and symptoms of resmethrin or its possible consequences to them. toxicity in humans following extremely high exposures by any route include incoordination, The Mosquito Management Program recommends twitching, loss of bladder control, and seizures. the following additional common-sense steps to Erythema and irritation (numbness, tingling, minimize the low-level potential for irritive effects burning or itching) may occur at sites of dermal from Scourge and toxicity to fish. exposure (5). · Avoid direct contact with surfaces that are still Piperonyl butoxide has limited dermal absorption wet from pesticide spraying. Do not allow on contact. The risk of acute toxicity is very low children to play in areas that are still wet until for the concentrations of piperonyl butoxide in they have dried. (approximately 1 hour.) Scourge that would be encountered by the public. · If you have to remain outdoors, avoid eye Large absorbed doses of piperonyl butoxide contact with the spray. If you get pesticide could, in theory, enhance the toxicity of some spray in your eyes, immediately rinse them with insecticides. Exposure to high concentrations of water. piperonyl butoxide may cause significant health · Cover ornamental fish ponds to avoid direct effects, including skin irritation, respiratory exposure. symptoms (wheezing, coughing, shortness of breath or burning sensations of the oropharynx or 18 Connecticut Epidemiologist chest), vomiting, diarrhea, anorexia, and mild Discretion should be exercised when central nervous system depression. It is recommending DEET for persons who have recommended that a victim of significant exposure acne, psoriasis, an atopic predisposition, or other to piperonyl butoxide be transported immediately to chronic skin conditions. People with particular a hospital for monitoring and stabilization, even if concerns about potential toxicity from DEET asymptomatic when first seen (6). should limit application of the repellent to their clothes. One should be cautious with this TOXIC EFFECTS OF DEET approach as DEET-repellents may damage some DEET is generally well tolerated when applied to synthetic fabrics (rayon and spandex), plastics the skin, although tingling, mild irritation, and (watch crystals and eyeglass frames), leather, sometimes desquamation have occurred following and painted or varnished surfaces. DEET repeated applications. DEET has caused contact products generally do not damage nylon or dermatitis and, in some cases, exacerbation of pre- natural fiber (cotton or wool) products (7). existing skin diseases. Toxic encephalopathic reactions have occurred in rare instances following SENSITIVE POPULATIONS dermal application, mainly in children, where Although most people should not experience extensive applications of products containing high symptoms given the low level of exposure, some concentrations of DEET were used (contrary to individuals may be particularly sensitive to these label instructions). Manifestations of toxic agents. Such individuals could experience short- encephalopathy