ARCHIVED - Statement on Personal Protective Measures to Prevent Arthropod Bites - Update

Canada Communicable Disease Report
Volume 31 • ACS-13
1 December 2005

An Advisory Committee Statement (ACS)
Committee to Advise on Tropical Medicine and Travel (CATMAT)^{Footnote * Footnote † Footnote ‡}

Preamble

The Committee to Advise on Tropical Medicine and Travel (CATMAT) provides the Public Health Agency of Canada (PHAC) with ongoing and timely medical, scientific, and public health advice relating to tropical infectious disease and health risks associated with international travel. PHAC acknowledges that the advice and recommendations set out in this statement are based upon the best current available scientific knowledge and medical practices, and is disseminating this document for information purposes to both travellers and the medical community caring for travellers.

Persons administering or using drugs, vaccines, or other products should also be aware of the contents of the product monograph(s) or other similarly approved standards or instructions for use. Recommendations for use and other information set out herein may differ from that set out in the product monograph(s) or other similarly approved standards or instructions for use by the licensed manufacturer(s). Manufacturers have sought approval and provided evidence as to the safety and efficacy of their products only when used in accordance with the product monographs or other similarly approved standards or instructions for use.

Introduction

There are blood feeding arthropods (insects and arachnids) that carry and transmit various pathogens, leading to diseases known as "arthropod-borne diseases" (ABDs). Usually, these pathogens complete a portion of their lifecycle within the arthropod vector before they can infect humans and are transmitted through the bite of the arthropod. Exceptions, however, include Chagas disease and louse-borne typhus, transmitted through feces defecated on the skin by the arthropod during feeding. Mosquitoes are considered to be the most important vector for ABDs (e.g. malaria and dengue), but many other types of arthropods transmit disease-causing pathogens^{(Footnote 1)}. Table 1 summarizes the information on the important arthropod vectors.

Unfortunately, there are preventive vaccines, chemoprophylactic drugs, or specific therapy for only a minority of ABDs. Even if vaccines or drugs are available, they are not totally effective, making measures to minimize insect bites an important way - and for some ABDs the only way - to reduce the risk to the traveller of acquiring ABDs . Many factors - such as the season, the time of day, and the preference for indoor or outdoor feeding - influence the feeding habits of arthropods^{(Footnote 1)} (Table 1). Although knowledge of arthropod feeding habits would allow the traveller to significantly reduce ABD risk (e.g. when to stay indoors, when to apply repellent), arthropod behaviour is unpredictable. Reducing the risk for one ABD likely decreases the risk for others, because peak seasonality for transmitting ABDs in various geographic regions overlaps.

Arthropod bite prevention is maximized by using an integrated approach that includes the following "personal protective measures":

1. avoid arthropods (e.g. stay in an insect-proof area during the period of day when arthropods bite);

2. prevent arthropod bites by using:

   1. physical barriers (e.g. clothing, bed net);

   2. chemical barriers (e.g. repellents, insecticides)

   3. Table 2 provides recommendations, as well as the evidence-based medicine (EBM) rating for each

Three Measures Used to Avoid Arthropods

1. Minimize arthropod entry into work and accommodation areas. Place screens on windows and ensure that doors are in good repair and close properly and tightly, and check that walls and roof are without holes (C III - EBM recommendations).

2. Stay in an arthropod-protected area during the time(s) of day when local arthropods are actively biting (C III - EBM recommendations).

3. Avoid travelling to certain locales during the season when transmission of ABDs is most likely (C III - EBM recommendations).

Bite Prevention at the Personal Level

If insects cannot bite, ABDs cannot be transmitted; it follows that aiming to reduce the amount of unprotected skin available to the arthropod is important.

There are both physical and chemical barriers to prevent bites:

Physical barriers

1. Clothing

   • Wear long-sleeved shirts (sleeves down, buttoned or zipped, tucked into pants) and long pants (tucked into socks or footwear) (B II - EBM recommendations).
   • Wear light-coloured clothing, which wards off some arthropods and allows people to notice and remove certain arthropods such as ticks^(2,3) (B II - EBM recommendations).

2. Mosquito net

   • Although sleeping under a mosquito net is well established as a useful barrier against arthropod bites, arthropods still bite through the mesh if the traveller's skin is against the net. Similarly, if the arthropod is smaller than the mesh size, the arthropod can pass through the netting (A I - EBM recommendations).
   • Treat (impregnate) mosquito netting with insecticide (e.g. permethrin), substantially increasing the protection afforded by the net^{(Footnote 4,Footnote 5)} (A I - EBM recommendations).

Chemical Barriers

Two types of chemical barriers reduce the risk of ABDs: repellents and insecticides. Repellents do not kill arthropods; rather, they produce an effect that causes the arthropod not to bite, whereas insecticides act primarily by killing an arthropod upon contact. These approaches are not mutually exclusive, and some chemicals have both effects, acting as a repellent and an insecticide.

A. Repellents

There are several repellent active ingredients available for use in Canada and an even larger number available in other countries (Table 3). Repellents, available for sale in most (if not all) western nations, have been reviewed for effectiveness and safety on the basis of national regulations (in Canada, by Health Canada's Pest Management Regulatory Agency [PMRA] and in the United States, by the Environmental Protection Agency [EPA]). During testing, some repellents have been more effective (e.g. longer lasting repellency) than others against certain arthropod species.

1. DEET

Generally, the repellent DEET (N,N-diethyl-3-methyl- benzamide, also known as N,N-diethyl-m-toluamide) is acknowledged as the most effective repellent and is currently available on the Canadian market^{(Footnote 6,Footnote 7)} (A I - EBM recommendations). DEET has been used as a repellent since 1954 by the U.S. military and is estimated to be applied several hundred million times yearly by North Americans alone. Scientific reviews have concluded that, when used as directed, DEET has an excellent safety record^(6-14) (A I - EBM recommendations).

The higher the DEET concentration in the repellent formulation, the longer the duration of protection; however, this relation reaches a plateau at about 30% to 35%(Footnote 6). For a given DEET concentration, DEET formulations that are "extended duration" (ED), such as polymers, are generally considered to provide longer protection times and may be associated with less DEET absorption(Footnote 6,Footnote 7,Footnote 15-Footnote 17). The ED formulations are unavailable to the general public in Canada, but they are available in the U.S.

Regulatory agencies in western nations may differ in the recommended maximum concentration and application rates of DEET, especially for children. Health Canada's PMRA allows concentrations of up to 30% in Canada for persons aged >= 12 years. Those who are younger can use up to 10% DEET; for those aged 2 to 12 years, up to three times daily; and for children aged 6 months to 2 years, no more than once daily. The PMRA disallows the use of repellents containing DEET on infants under age 6 months(Footnote 6). However, CATMAT believes that, for travel outside of Canada where ABDs are endemic or epidemic and where exposure is likely and the risk for ABDs outweighs the risk of an adverse reaction to DEET, the threshold for use of DEET should be low. In fact, CATMAT recommends that travellers use DEET concentrations of up to 35% for travel outside of Canada.

For children, alternative personal protective measures, such as insecticide-impregnated mosquito nets, should be the first line of defence, especially for infants under age 6 months. Portable mosquito nets, including self-standing nets, placed over a car seat, a crib, playpen, or stroller, provide an insect-free environment for infants. However, as a complement to the other protection methods, the judicious use of DEET should be considered for children of any age. Recent medical literature from Canada suggests that DEET does not pose a significant or substantial risk to infants and children^{(Footnote 11)}.

The reapplication intervals on the labels of DEET formulations are a general guide only, because there are many variables - for example, sweating - that affect duration of repellency. As a general rule, the reapplication interval is a function of arthropod biting activity, so if biting is noted before the interval on the label has expired, then reapplication of DEET is recommended. DEET ED formulations have useful advantages over other formulations and, overall, are preferred when ABD risk is high^{(Footnote 15-Footnote 17)} (A II - EBM recommendations).

DEET and sunscreen combination products are not generally recommended; DEET decreases the efficacy of sunscreens by 34%(Footnote 18). Further, the recommendations for application of DEET and sunscreen are opposite. Sunscreen should be used liberally and often, whereas DEET should be used sparingly and only as often as required. However, if application of both is required, the Canadian Dermatology Association recommends that the sunscreen be applied first and allowed to penetrate the skin for 20 minutes prior to applying DEET (A II - EBM recommendations).

2."Natural-based" repellents

Most repellents containing "naturally derived," or synthetic analogues of "naturally-derived," materials are not considered the preferred products for protecting against arthropod bites. Oil of citronella products, for example, can repel mosquitoes, but the protection duration is very short (generally < 1 hour and often < 30 minutes)^{(Footnote 7)}. In fact, a recent analysis by Health Canada concluded that there are insufficient data to establish that the use of citronella repellents on skin does not pose an unacceptable risk to human health^{(Footnote 19)}. Citronella-containing repellents are therefore not recommended (E II - EBM recommendations). P-menthane-3,8-diol, a synthetic analogue of a lemon eucalyptus plant extract, is registered in Canada for use as an insect repellent ("OFF! Botanicals Lotion Insect Repellent 1")^{(Footnote 20)}. However, the period of protection afforded by this product (< 2 hours) is less than that for all but very low concentration (< 5%) DEET products. Besides, it is not approved for use on children < 3 years of age. Data indicate that it is reasonably effective against mosquitoes that carry malaria^{(Footnote 21,Footnote 22)}. Repellents that contain P-menthane-3,8-diol may be considered a second-line alternative repellent where DEET use is not possible (e.g. persons who are allergic to DEET) (A II - EBM recommendations).

Soybean oil 2% "Blocker" products are equivalent to 5% to 10% DEET in efficacy, repelling mosquitoes for 1 to 4 hours and blackflies for 5 to 10 hours^{(Footnote 7,Footnote 23)}. Soybean oil has low toxicity, has no age-associated use restrictions, and is non-irritating. Consequently, it may also be considered an alternative to DEET, albeit one with a substantially shorter protection time and without a long history of use. Importantly, CATMAT is unaware of scientific studies in which soybean repellents have been tested for effectiveness against tropical malaria vectors or for many other ABD vectors. Soybean repellents therefore are considered, at best, a third-line repellent where ABDs present a significant risk (A II - EBM recommendations). Although there are "Blocker" products containing soybean oil registered and approved for use in Canada (www.biteblocker.ca), they are not widely available in retail outlets.

3 Other synthetic repellents

Bayrepel, a piperidine derivative also known as "KBR 3023" and marketed under the trade name Autan, has been used in Europe for several years^{(Footnote 24)}. It has demonstrated action against various mosquito species, including those that carry the malaria parasite, with durations of protection, compared with 15% to 50% DEET^{(Footnote 25,Footnote 26)} (A II - EBM recommendations). Toxicological analysis suggests no bioaccumulation, and rapid renal excretion with no significant toxicities was reported. Although recommended by the World Health Organization^{(Footnote 27)} and registered with the Environmental Protection Agency (U.S.) in 2002, repellents containing Bayrepel have not been registered in Canada and are not available in the U.S. (www.autan.co.uk/index.html).

B. Insecticides

1. Treated Mosquito Nets

All travellers planning itineraries to foreign destinations that are endemic or epidemic for ABDs should be strongly encouraged to use pyrethroid (e.g. permethrin, deltamethrin, lambda-cyhalothrin, cyfluthrin, alpha-cypermethrin) insecticide-impregnated mosquito nets, unless their sleeping quarters are well screened or otherwise protected from mosquitoes^{(Footnote 14)} (A I - EBM recommendations). Pyrethroids either kill arthropods directly after they land on impregnated netting or repel them. In either case, the end result is protection against arthropod bites and ABDs. Pyrethroid-impregnated nets are significantly more effective in preventing malaria than untreated nets and are safe for children and pregnant women^{(Footnote 4,Footnote 5)} (A I - EBM recommendations). Duration of efficacy of pyrethroid-impregnated nets varies from several to 12 months, depending on the product used^{(Footnote 4)} (Table 4 and Appendix 1). While pyrethroids are generally considered to be of low mammalian toxicity, care should be taken when impregnating the permethrin or an equivalent product into the net (e.g. follow the label instructions, use impervious gloves, and allow the net to dry before use) (Appendix 1). Pyrethroid treatments for bed nets are not registered by the PMRA for use by the general public. Insecticide-impregnated bed nets that are represented and sold for use in Canada require registration under the authority of the Pest Control Products Act (PCPA). However, the PMRA has an interim policy of not requiring the registration of either permethrin- or deltamethrin-impregnated bed nets if imported into Canada for sale to Canadians for use abroad.

2. Treating clothing

Treating clothing with pyrethroid will also reduce the risk of ABDs (Appendix 2). Pyrethroid clothing treatments are not registered by the PMRA for use by the general public, but several products are available in the U.S. These products usually consist of 0.5% permethin in an aerosol or pump spray. Generally, clothing that is treated with the 0.5% permethrin aerosol or pump spray is effective at preventing arthropod bites for at least 2 weeks, assuming regular laundering practices (e.g. six machine washings)^{(Footnote 28,Footnote 29)}. More recently, outdoor clothing that was pre-treated with permethrin became available in the U.S. (e.g. clothing available under the trademark "Buzz-Off Insect Shield"). This pre-treated clothing is advantageous in that it maintains protective levels of permethrin through 25 or more machine washings (i.e. frequent retreatment is not required). Combining a long-acting DEET formulation that is applied to exposed skin and the pyrethroid-impregnated clothing enhances protection against biting arthropods^{(Footnote 30,Footnote 31)} (A II - EBM recommendations).

3. Ineffective insect personal protection measures

There are additional products that are marketed as safe and "natural" and with effective measures to substantially reduce the risk of arthropod bites. However, CATMAT assesses some products as lacking in the sufficient scientific basis to recommend or as having the sufficient scientific basis to indicate the product's lack of usefulness (E II - EBM recommendations). These products include electronic (ultrasonic) devices^{(Footnote 32,Footnote 33)}, wristbands, neckbands, and ankle bands impregnated with repellents (whether for animal or human use)^{(Footnote 7,Footnote 34)}, electrocuting devices (i.e. "bug zappers")^{(Footnote 35,Footnote 36)}, odour-baited mosquito traps^{(Footnote 33,Footnote 37)}, the Citrosa plant (i.e. geranium house- plant)^{(Footnote 33,Footnote 38,Footnote 39)}, oral vitamin B1^{(Footnote 40)}, and skin moisturizers that do not contain an approved repellent active ingredient^{(Footnote 7)}.

Summary

Several personal protective measures exist to reduce the risk of acquiring ABDs. In fact, there is no single measure on which to rely that provides substantial confidence in protection; hence, CATMAT recommends and views as complementary the use of all measures.

Expiration

This document is updated every 4 years or when new information becomes available.

References

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Appendix 1 - Treating Mosquito Nets with Insecticides (Adapted from Path Canada)

Always use metric measurements: centimetre (cm), metre (m), millimetre (mm), millilitre (mL), and litre (L). Clean and dry all nets. Always wear protective gloves when soaking a net in insecticide.

1. Calculate the area of the net, in square metres.

Consider a conical net as a triangle and a rectangular net as two rectangles.

How to measure a mosquito net:

1. Conical net

   Lay the net flat to:

   • Measure the total distance around the curved base of the net (m)
   • Measure the height (m)
   • Multiply base x height = area of net

2. Rectangular net

   Hang up the net to:

   • Measure the area of the top = width x length
   • Measure the area around the sides = height x total distance around base of net
   • Add the two measurements together to obtain the total area of the net

2. Calculate the amount of water absorbed by the net, in millilitres or litres.

Using a bucket and a measuring container, measure two litres of water into the bucket. Soak the net until it is totally wet. Carefully wring out the net over the bucket. When the net has stopped dripping, measure the water remaining in the bucket.

For example: Original water in bucket (2 L) minus remaining water in bucket (1.3 L) = water absorbed by the net (0.7 L or 700 mL)

3. Calculate the amount of insecticide required.

• Obtain the highest quality product, in original packaging, specifically designed for use on mosquito netting. Avoid using products that have not undergone meticulous quality control. Avoid using substitute products.
• Check the recommended dosage of insecticide. Read the instructions on the bottle, or see Appendix 1, Table 1.
• Check the concentration of the insecticide. This follows the name of the insecticide. For example, permethrin EC 50 contains 500g of insecticide in each litre; this is also known as a 50% solution.

To calculate the amount of insecticide use the following formula:

• Dosage (mg/unit metre) x Area of Net (in square metres) to determine the amount of insecticide required in mg. (Note: there are 1,000 mg per gram, 1,000 mL/L, and 1 gm per mL.)
• Take amount of insecticide required divided by the amount in mg of insecticide per mL of product (for example, a product that contains 50% permethrin will contain 500 g permethrin/L and therefore 500 mg permethrin/mL) = amount of insecticide required in mL.

For example:

If you want a dosage of 200 mg/square metre on an 11 square metre net, using a product containing 50% permethrin w/w, calculate the amount required as follows:

• 200 mg/square metre x 11 metres squared = 2,200 mg permethrin required
• 50% permethrin = 500 mg permethrin/mL
• 2,200 mg divided by 500 mg/mL = 4.4 mL insecticide required to treat the net

If the net absorbs 0.7 L (700 mL) of water, add this amount of water to the insecticide to make a final mixture.

4. Wear protective gloves when treating nets with insecticide.

5. Measure the amount of water and insecticide needed.

Wide-mouth containers, such as an empty margarine container (1 kg = approximately 1 L), are best for measuring large amounts of water. Measure insecticide using a 250 mL empty container that can be scored inside at 50 mL intervals. For small amounts of insecticide, use a syringe.

6. Add the insecticide to the water and mix well.

Perform treatment outdoors or in a well-ventilated area. Alternatively, you can place the net in a plastic bag (ensuring that the bag contains no holes), then, add the insecticide and water solution, knead well, and remove the treated net from the bag for drying.

7. Dip the net in the solution until it is thoroughly wet.

8. Wring out the net over a bowl and hang up until it has stopped dripping.

9. Dry the net.

Wet nets can be laid out flat to dry. Avoid placing the net in direct sunlight for more than a few hours, because UV exposure may reduce the efficacy of the insecticide.

10. Wash your hands and all equipment with soap and water.

Triple rinse any containers for reuse, and punch holes in containers or equipment that will be discarded to prevent their reuse as drinking water containers.

11. Pour any waste insecticide down a pit latrine or into a pit dug into the ground, and NOT into a river or pond, because pyrethroids are highly toxic to fish and aquatic invertebrates.

Note: Prior to travelling, inquire about the availability of insecticide, and plan to purchase and apply these products at your destination. Pre-impregnated mosquito nets are available from PATH Canada on its Web site at http://www.pathcanada.org and are found in some travel and mountain equipment stores in Canada and in the U.S. These products are not currently registered by the PMRA.

For information regarding availability of insecticides in sub-Saharan Africa for application onto clothing or nets, visit the PATH Canada Web site at http://www.pathcanada.org.

Appendix 2 - How to Treat Clothing with Insecticides (Adapted from Sawyer Products)

1. Select an area that is well ventilated, but out of the wind. Avoid spraying in an enclosed area.
2. Lay the clothing flat on the ground, pin the clothes on a clothesline, or drape over porch furniture and railings or on separate clothes hangers, so each garment can be easily sprayed and allowed to thoroughly dry.
3. One treatment with permethrin spray will remain effective for 2 weeks, including weekly launderings. A treatment of 100 mL (3 ounces) of permethrin spray will cover one complete set of garments (a pair of long-legged trousers and a long-sleeved shirt). Treat jackets, windbreakers, and rain gear in the same manner. (Caution: permethrin does not adhere well to some synthetic fibres.)
4. Wear protective gloves.
5. Spray one side of the garment for approximately 60 seconds, holding the spray can or bottle upright and 15 cm to 20 cm away from the surface. Spray in a slow sweeping motion, similar to spraying paint, to evenly coat the entire surface. Turn the garment around to the other side, and repeat by spraying the second side for 60 seconds. Wet surface of clothing, but avoid completely saturating with spray.
6. Hang up garments, and allow the permethrin treatment to dry for 2 hours, or 4 hours if conditions are very humid.
7. Treat other garments and gear (do not treat underwear):
   1. Treat socks with permethrin spray. Lay socks on the ground, or pin on a clothesline, and lightly spray the upper part. Allow to dry for 2 or more hours.
   2. Treat polyurethane-coated nylon (synthetic) tent flaps and doors with permethrin spray. Erect tent outdoors, and spray all tent flaps and doors until wet. Leave standing for 2 or more hours to dry.
8. After garments have dried, pack them as you normally would for your trip. You may also want to roll up your treated clothes and store them in a plastic bag to keep them dry. Pack tents as you normally would.

Note: Prior to travelling, inquire about the availability of insecticide, and plan to purchase and apply these products at your destination. These products are not currently registered by the PMRA. For more information regarding application of insecticides onto clothing, please visit the permethrin Web site at http://www.permethrin-repellent.com.

* Members: Dr. B. Ward (Chairman); Dr. C. Beallor; M. Bodie-Collins (Executive Secretary); Dr. K. Gamble; Dr. S. Houston; Dr. Susan Kuhn; Dr. A. McCarthy; Dr. K.L. McClean; Dr. P.J. Plourde; Dr. J.R. Salzman.

Liaison Representatives: Dr. R.J. Birnbaum (CUSO); Dr. C. Greenaway (CIDS); Dr. C. Hui (CPS); Dr. R. Saginur (CPHA); Dr. P. Teitelbaum (CSIH).

Ex-Officio Representatives: Dr. R. Corrin (HC); Dr. B. Dobie (CIC); Dr. N. Gibson (DND); Dr. J. Given (HC); Dr. P. McDonald (HC); Dr. M. Parise (CDC); Dr. M. Tepper (DND).

Member Emeritus: Dr. C.W.L. Jeanes.

^† This statement was prepared by P.J. Plourde, MD, M. Tepper, MD, and S. Schofield, PhD, an entomology consultant for CATMAT. This statement was approved by CATMAT.

^‡ This statement was updated to reflect the appropriate authorship only.