Insect-transmitted disease remains a major source of illness and death worldwide. Mosquitoes alone transmit disease to more than 700 million persons annually.1 Malaria kills 3 million persons each year, including 1 child every 30 seconds.2,3 Although insect-borne diseases currently represent a greater health problem in tropical and subtropical climates, no part of the world is immune to their risks. In the United States, arboviruses transmitted by mosquitoes continue to cause sporadic outbreaks of eastern equine encephalitis, western equine encephalitis, St. Louis encephalitis, and La Crosse encephalitis.4,5 In the fall of 1999, West Nile virus, transmitted by mosquitoes, was detected for the first time in the Western Hemisphere. In the New York City area, 62 persons infected with West Nile virus were hospitalized, and 7 persons died.6-8 The Centers for Disease Control and Prevention estimates that more than 2000 persons were infected with West Nile virus in the year 2000.9 The virus has now been detected in 27 states, and it is anticipated that it will continue to spread unabated across the United States during the next few years.9,10
Protection from arthropod bites is best achieved by avoiding infested habitats, wearing protective clothing, and using insect repellent.11,12 In many circumstances, applying repellent to the skin may be the only feasible way to protect against insect bites. Given that a single bite from an infected arthropod can result in transmission of disease, it is important to know which repellent products can be relied on to provide predictable and prolonged protection from insect bites. Commercially available insect repellents can be divided into two categories — synthetic chemicals and plant-derived essential oils. The best-known chemical insect repellent is N,N-diethyl-m-toluamide, now called N,N-diethyl-3-methylbenzamide (DEET). Many consumers, reluctant to apply DEET to their skin, deliberately seek out other repellent products. We compared the efficacy of readily available alternatives to DEET-based repellents in a controlled laboratory environment.
METHODS
Product Selection
In January 2001, we purchased a total of 16 products for testing, choosing repellents with national, rather than local, distribution (Table 1TABLE 1
Protection Times of Insect Repellents.
). Seven widely available botanical repellents were included in the study. Multiple concentrations and formulations of DEET are readily available. We chose and tested three DEET-based repellents (ranging from 4.75 to 23.8 percent DEET) that we believe represented the range of commonly purchased repellents in the United States. We also tested a controlled-release 20 percent DEET formulation to determine whether it had a longer duration of action. The only synthetic repellent containing IR3535 (ethyl butylacetylaminopropionate) that is available in the United States and three wristbands impregnated with either DEET or citronella were also tested. Finally, we tested the efficacy of a proprietary moisturizer that is commonly believed to have repellent effects.
Testing Methods
The duration of protection provided by each product was tested by means of arm-in-cage studies, in which volunteers insert their repellent-treated arms into a cage with a fixed number of unfed mosquitoes, and the elapsed time to the first bite is recorded. Testing of repellents is usually conducted either in a laboratory or at outdoor field sites.14 Conducting such studies indoors makes it possible to reduce potential confounding variables, such as wind speed, temperature, humidity, density of the mosquito population, the level of the mosquitoes' hunger, and the species of the mosquitoes, that can make it difficult to interpret comparisons among products made in outdoor-field trials. We conducted our tests with a low density of mosquitoes per cage rather than a high density (some studies use more than 250 mosquitoes per cage) because the low-density environment more accurately reflects the typical biting pressures that are encountered during most outdoor activities.
For each test, 10 disease-free, laboratory-reared Aedes aegypti female mosquitoes that were between 7 and 24 days old were placed into separate laboratory cages measuring 30 cm by 22 cm by 22 cm. A batch of 10 mosquitoes that had not been exposed to the repellent being tested was used for each arm insertion. Mosquitoes were provided with a constant supply of 5 percent sucrose solution. Cages were placed in a walk-in incubator measuring 2.2 m by 2.2 m by 2.2 m, in which the temperature was maintained at 24 to 32°C, the relative humidity at 60 to 70 percent, and the light–dark cycle at 12 hours of light followed by 12 hours of darkness.
Fifteen volunteers (5 men and 10 women) were recruited from the staff of the Medical Entomology Laboratory at the University of Florida. The study was reviewed and approved by the institutional review board of the University of Florida, and subjects gave written informed consent before participating.
As repellents were purchased, they were labeled sequentially from 1 to 16. A random-number generator was then used to determine the order in which the products would be tested on each subject. A total of 720 individual tests were conducted, with each repellent being tested three times on each subject. Most subjects only completed one test per day. The average time to completion of all three tests was 10.2 days. In the case of repellents that were identified as very short-acting in the initial test, subjects were permitted to conduct all three tests of the repellent in a single day, washing the skin with an unscented soap before each application of the repellent. Subjects did not test more than one repellent product on a single day. No information on the likely duration of action of each repellent was provided to subjects before they began their tests.
Before each test, the readiness of the mosquitoes to bite was confirmed by having subjects insert their untreated forearm into the test cage. Once subjects observed five mosquito landings on the untreated arm, they removed their arm from the cage and applied the repellent being tested from the elbow to the fingertips, following the instructions on the product's label. After the application of the repellent, subjects were instructed not to rub, touch, or wet the treated arm. Repellent-impregnated wristbands were worn on the wrist of the arm being inserted into the cage. Subjects were provided with a standardized log sheet to ensure accurate documentation of the duration of exposure and the time of the first bite. The elapsed time to the first bite was then calculated and recorded as the “complete-protection time” for that subject in that particular test.
Subjects were asked to follow the testing protocol shown in Figure 1FIGURE 1
Study Design.
. Subjects conducted their first test of each repellent by inserting the treated arm into a test cage for one full minute every five minutes. If they were not bitten within 20 minutes, then the arm was reinserted for 1 full minute every 15 minutes, until the first bite occurred. On the basis of this initial complete-protection time, the subject's next two tests of that particular repellent were conducted as follows: if the repellent had initially worked for less than 20 minutes, the subject placed his or her arm in the cage for 1 minute every 5 minutes; if the repellent had initially worked for 20 minutes to 4 hours, the subject placed his or her arm in the cage for 1 minute every 15 minutes; and if the repellent had initially worked for more than 4 hours, the subject placed his or her arm in the cage for 1 minute every hour (up to 4 hours). If a repellent was still working after 4 hours, then the subject continued to place his or her arm in the cage every 15 minutes thereafter, until the first bite occurred. If at any point during testing, subjects noted mosquitoes landing but not biting (a behavior that typically occurs when the efficacy of a repellent begins to wane), then the intervals between insertions were decreased to five minutes.
Discretionary funds from the State of Florida were used to support this study. We received no financial support from industry, including the manufacturers whose products were tested in the study. Data analysis was performed within the Florida Medical Entomology Laboratory at the University of Florida, without input from any outside sources.
Statistical Analysis
Two-way analysis of variance (involving two factors, subject and repellent) followed by Tukey's tests13 was used to compare the mean complete-protection time for the 16 tested repellents. All P values are two-sided; a P value of less than 0.05 was considered to indicate statistical significance.
RESULTS
Of the products tested, those containing DEET provided the longest-lasting protection (Table 1). The complete-protection times of DEET-based repellents correlated positively with the concentration of DEET in the repellent. The formulation containing 4.75 percent DEET provided an average of 88.4 minutes of complete protection; the formulation containing 23.8 percent DEET protected for an average of 301.5 minutes. There was a statistically significant difference in complete-protection time between each DEET-based repellent and the product with the next higher concentration of DEET (P
โรคแมลงส่งยังคง เป็นแหล่งสำคัญของการเจ็บป่วยและการตายทั่วโลก ยุงคนเดียวส่งโรคมากกว่า 700 ล้านคน annually.1 มาลาเรียฆ่า 3 ล้านคนในแต่ละปี รวมเด็กทุก seconds.2,3 30 แม้ว่าโรคแมลงโดยเชื่อว่าในขณะนี้แสดงปัญหาสุขภาพมากขึ้นในสภาพอากาศ ร้อน ส่วนหนึ่งของโลกมีภูมิคุ้มกันความเสี่ยงของพวกเขา ในสหรัฐอเมริกา arboviruses ส่ง โดยยุงยังทำให้มีการแพร่ระบาดของโรคไข้สมองอักเสบเพาะพันธุ์ตะวันออก ตะวันตกเพาะพันธุ์โรคไข้สมอง อักเสบ สมองอักเสบ St. Louis และ encephalitis.4,5 La Crosse ในฤดูใบไม้ร่วงของปี 1999 เวสต์ไนล์ไวรัส ส่ง โดยยุง พบครั้งแรกในซีกโลกตะวันตก ในนิวยอร์กซิตี้ ท่าน 62 เวสต์ไนล์ไวรัสติดที่พัก และ 7 คน died.6-8 ศูนย์ป้องกันและควบคุมโรคประเมินว่า กว่า 2000 คนติดเชื้อเวสต์ไนล์ไวรัสในปี 2000.9 ไวรัสนี้พบในอเมริกา 27 และคาดการณ์ไว้ว่า จะยังคงลุกลามรุนแรงทั่วสหรัฐอเมริกาในช่วง years.9 ไม่กี่ถัดไป , 10ป้องกันจากสัตว์ขาปล่องกัดสามารถทำได้ดี โดยหลีกเลี่ยงการรบกวนอยู่อาศัย สวมเสื้อผ้าป้องกัน และการใช้ repellent.11,12 แมลงในหลายกรณี ใช้ทาผิวอาจเป็นวิธีเป็นไปได้เฉพาะเพื่อป้องกันอันตรายจากแมลงสัตว์กัดต่อย ระบุว่ากัดเดียวจากสัตว์ขาปล้องติดไวรัสอาจทำให้ส่งของโรค จะต้องทราบว่าผลิตภัณฑ์ยาที่สามารถอาศัยในการป้องกันได้ และนานแมลงสัตว์กัดต่อย แมลงควรใช้ได้ในเชิงพาณิชย์สามารถแบ่งออกเป็นสองประเภทคือสารเคมีสังเคราะห์และโรงงานที่ได้รับน้ำมันหอมระเหยได้ สารเคมีรู้จักยุงเป็น N, N-diethyl-m-toluamide เรียกว่าตอนนี้ N, N-diethyl-3-methylbenzamide (DEET) ผู้บริโภคจำนวนมาก DEET กับผิวของพวกเขา ไม่ตั้งใจค้นหาผลิตภัณฑ์อื่น ๆ ยุง เราเปรียบเทียบประสิทธิภาพของ DEET ตามควรในสภาพแวดล้อมห้องปฏิบัติการควบคุมแทนพร้อมวิธีการเลือกผลิตภัณฑ์ในเดือน 2001 มกราคม เราซื้อทั้งหมด 16 ผลิตภัณฑ์สำหรับการทดสอบ เลือกควร มีชาติ แทนท้อง ถิ่น แจก (1TABLE ตาราง 1เวลาป้องกันแมลงควร). Seven widely available botanical repellents were included in the study. Multiple concentrations and formulations of DEET are readily available. We chose and tested three DEET-based repellents (ranging from 4.75 to 23.8 percent DEET) that we believe represented the range of commonly purchased repellents in the United States. We also tested a controlled-release 20 percent DEET formulation to determine whether it had a longer duration of action. The only synthetic repellent containing IR3535 (ethyl butylacetylaminopropionate) that is available in the United States and three wristbands impregnated with either DEET or citronella were also tested. Finally, we tested the efficacy of a proprietary moisturizer that is commonly believed to have repellent effects.Testing MethodsThe duration of protection provided by each product was tested by means of arm-in-cage studies, in which volunteers insert their repellent-treated arms into a cage with a fixed number of unfed mosquitoes, and the elapsed time to the first bite is recorded. Testing of repellents is usually conducted either in a laboratory or at outdoor field sites.14 Conducting such studies indoors makes it possible to reduce potential confounding variables, such as wind speed, temperature, humidity, density of the mosquito population, the level of the mosquitoes' hunger, and the species of the mosquitoes, that can make it difficult to interpret comparisons among products made in outdoor-field trials. We conducted our tests with a low density of mosquitoes per cage rather than a high density (some studies use more than 250 mosquitoes per cage) because the low-density environment more accurately reflects the typical biting pressures that are encountered during most outdoor activities.For each test, 10 disease-free, laboratory-reared Aedes aegypti female mosquitoes that were between 7 and 24 days old were placed into separate laboratory cages measuring 30 cm by 22 cm by 22 cm. A batch of 10 mosquitoes that had not been exposed to the repellent being tested was used for each arm insertion. Mosquitoes were provided with a constant supply of 5 percent sucrose solution. Cages were placed in a walk-in incubator measuring 2.2 m by 2.2 m by 2.2 m, in which the temperature was maintained at 24 to 32°C, the relative humidity at 60 to 70 percent, and the light–dark cycle at 12 hours of light followed by 12 hours of darkness.Fifteen volunteers (5 men and 10 women) were recruited from the staff of the Medical Entomology Laboratory at the University of Florida. The study was reviewed and approved by the institutional review board of the University of Florida, and subjects gave written informed consent before participating.As repellents were purchased, they were labeled sequentially from 1 to 16. A random-number generator was then used to determine the order in which the products would be tested on each subject. A total of 720 individual tests were conducted, with each repellent being tested three times on each subject. Most subjects only completed one test per day. The average time to completion of all three tests was 10.2 days. In the case of repellents that were identified as very short-acting in the initial test, subjects were permitted to conduct all three tests of the repellent in a single day, washing the skin with an unscented soap before each application of the repellent. Subjects did not test more than one repellent product on a single day. No information on the likely duration of action of each repellent was provided to subjects before they began their tests.Before each test, the readiness of the mosquitoes to bite was confirmed by having subjects insert their untreated forearm into the test cage. Once subjects observed five mosquito landings on the untreated arm, they removed their arm from the cage and applied the repellent being tested from the elbow to the fingertips, following the instructions on the product's label. After the application of the repellent, subjects were instructed not to rub, touch, or wet the treated arm. Repellent-impregnated wristbands were worn on the wrist of the arm being inserted into the cage. Subjects were provided with a standardized log sheet to ensure accurate documentation of the duration of exposure and the time of the first bite. The elapsed time to the first bite was then calculated and recorded as the “complete-protection time” for that subject in that particular test.
Subjects were asked to follow the testing protocol shown in Figure 1FIGURE 1
Study Design.
. Subjects conducted their first test of each repellent by inserting the treated arm into a test cage for one full minute every five minutes. If they were not bitten within 20 minutes, then the arm was reinserted for 1 full minute every 15 minutes, until the first bite occurred. On the basis of this initial complete-protection time, the subject's next two tests of that particular repellent were conducted as follows: if the repellent had initially worked for less than 20 minutes, the subject placed his or her arm in the cage for 1 minute every 5 minutes; if the repellent had initially worked for 20 minutes to 4 hours, the subject placed his or her arm in the cage for 1 minute every 15 minutes; and if the repellent had initially worked for more than 4 hours, the subject placed his or her arm in the cage for 1 minute every hour (up to 4 hours). If a repellent was still working after 4 hours, then the subject continued to place his or her arm in the cage every 15 minutes thereafter, until the first bite occurred. If at any point during testing, subjects noted mosquitoes landing but not biting (a behavior that typically occurs when the efficacy of a repellent begins to wane), then the intervals between insertions were decreased to five minutes.
Discretionary funds from the State of Florida were used to support this study. We received no financial support from industry, including the manufacturers whose products were tested in the study. Data analysis was performed within the Florida Medical Entomology Laboratory at the University of Florida, without input from any outside sources.
Statistical Analysis
Two-way analysis of variance (involving two factors, subject and repellent) followed by Tukey's tests13 was used to compare the mean complete-protection time for the 16 tested repellents. All P values are two-sided; a P value of less than 0.05 was considered to indicate statistical significance.
RESULTS
Of the products tested, those containing DEET provided the longest-lasting protection (Table 1). The complete-protection times of DEET-based repellents correlated positively with the concentration of DEET in the repellent. The formulation containing 4.75 percent DEET provided an average of 88.4 minutes of complete protection; the formulation containing 23.8 percent DEET protected for an average of 301.5 minutes. There was a statistically significant difference in complete-protection time between each DEET-based repellent and the product with the next higher concentration of DEET (P<0.001 for all comparisons). The controlled-release formulation we tested did not prolong the duration of action of DEET. The alcohol-based product containing 23.8 percent DEET protected significantly longer than the controlled-release formulation containing 20 percent DEET (P<0.001).
No non-DEET repellent fully evaluated in this study was able to provide protection that lasted more than 1.5 hours. Only the soybean-oil–based repellent was able to provide protection for a period similar to that of the lowest-concentration DEET product we tested (94.6 and 88.4 minutes, respectively).
The IR3535-based repellent prot
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