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Canada Communicable Disease Report
Volume 31 ACS-4
15 May 2005
An Advisory Committee Statement (ACS)
Committee to Advise on Tropical Medicine and Travel (CATMAT)*
Statement on Personal Protective Measures
to Prevent
Arthropod Bites
PDF Version
20 Pages - 299 KB
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(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(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.
|
Table 2. Evidence-based medicine (EBM)
recommendations |
Recommendation |
EBM Rating |
Measures for all travellers
who are at risk of exposure to arthropod-borne infections
- Minimize entry of arthropods into work and accommodation areas,
including placing screens on windows, and check to ensure that
doors are in good repair and close properly and tightly and that
the walls and the roof are "without holes".
- Stay in an arthropod-protected area during the time(s) of day
when local arthropods are actively biting.
- Avoid travelling to a locale during the season that is most
strongly (or only) associated with transmission of arthropod-borne
infections.
|
C III |
Physical barriers for all travellers
who are at risk of exposure to arthropod-borne infections
- Wear long-sleeved shirts (sleeves down, buttoned or zipped,
tucked into pants) and long pants (tucked into socks or footwear)
to inhibit or prevent arthropod bites.
- Dress in light-coloured clothing, which may ward off some arthropods
and allow people to notice and remove certain arthropods, such
as ticks(2,3).
- Sleep under a mosquito net that is intact (without tears or
large holes), tucked in under a mattress. Note that arthropods
may still bite through the mesh (if the traveller's skin is against
the net), or if the arthropod is smaller than the mesh size, it
can pass through the netting.
|
B II |
All travellers at risk of exposure to serious
arthropod-borne infections should appropriately use insect repellent
containing DEET(6,7)-the preferred insect repellent, unless
contraindicated (e.g. allergic reaction). |
A I |
For children, there are alternative personal
protective measures:
- Use insecticide-impregnated mosquito nets as the first line
of defense, especially for infants aged < 6 months.
- Utilize portable mosquito nets, including the self-standing
type, placed over a car seat, a crib, playpen, or stroller, providing
an insect-protected environment for infants.
- Consider the judicious use of DEET for children of any age as
a complement to the other methods of protection(11).
|
A II |
Extended duration (ED) DEET formulations have useful
advantages over other formulations and, overall, are preferred(15-17).
Where ED formulations are unavailable, products that contain up to
35% DEET are preferred. |
B I |
DEET and sunscreen combination products are not generally
recommended(18); however, if DEET and sunscreen application
are both required, apply the sunscreen first, allowing skin penetration
for 20 minutes, followed by DEET application (Canadian Dermatology
Association). |
A II |
Avoid using repellents containing citronella oil(7,19). |
E II |
Consider P-menthane-3,8-diol (lemon eucalyptus
oil) as a second-line alternative repellent, where DEET use is not
possible (e.g. persons allergic to DEET)(20). |
A II |
Consider soybean oil 2% "Blocker" repellents as a
third-line repellent, where arthropod-borne infections present a significant
risk(7,23). |
A II |
Bayrepel (KBR 3023, Autan), available in Europe(24),
recommended by the World Health Organization(27) and registered
with the Environmental Protection Agency (U.S.), may be as effective
as 15% to 50% DEET(25,26). Repellents containing Bayrepel
are not registered for use in Canada. |
A II |
For all travellers who are at risk of exposure
to arthropod-borne infections:
- Sleep under insecticide (pyrethroid)-impregnated mosquito nets
(in areas where insects cannot be excluded from sleeping area)(4,5,14).
- Consider wearing insecticide (permethrin)-impregnated clothing(28,29).
|
A I
AII
|
Ineffective insect personal protection measures that
are not recommended:
- Electronic (ultrasonic) devices(32,33)
- Wristbands, neckbands, and ankle bands impregnated with repellents(7,34)
- Electrocuting devices ("bug zappers")(35,36)
- Odour-baited mosquito traps(33,37)
- Citrosa plant (geranium houseplant)(33,38,39)
- Orally administered vitamin B1(40)
- Skin moisturizers that do not contain an approved repellent
active ingredient(7)
|
E II |
All travellers should take, as directed, all prophylactic
medications recommended for the prevention of arthropod-borne illnesses
(such as malaria), regardless of personal protection methods used. |
A I |
|
|
|
Three Measures Used to Avoid Arthropods
- 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).
- Stay in an arthropod-protected area during the time(s) of day when
local arthropods are actively biting (C III - EBM recommendations).
- 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
- 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).
- 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(4,5) (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.
- 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.
- 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(6,7) (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%(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(6,7,15-17). 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(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(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(15-17) (A II - EBM recommendations).
DEET and sunscreen combination products are not generally recommended;
DEET decreases the efficacy of sunscreens by 34%(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).
|
|
|
- "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)(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(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")(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(21,22). 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(7,23). 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.
- 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(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(25,26) (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(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).
- Insecticides
- 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(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(4,5) (A
I - EBM recommendations). Duration of efficacy of pyrethroid-impregnated
nets varies from several to 12 months, depending on the product
used(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.
- 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)(28,29). 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(30,31) (A
II - EBM recommendations).
- 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(32,33),
wristbands, neckbands, and ankle bands impregnated with repellents
(whether for animal or human use)(7,34), electrocuting
devices (i.e. "bug zappers")(35,36), odour-baited mosquito
traps(33,37), the Citrosa plant (i.e. geranium house- plant)(33,38,39),
oral vitamin B1(40), and skin moisturizers that do not
contain an approved repellent active ingredient(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.
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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.
- 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:
- 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
- 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
- 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)
- 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.
Table 1. Doses of commonly used insecticides
in mg per square metre of material (polyester) |
Compound and formulation |
Dose (mg of active ingredient/ square metre) |
Permethrin EC |
200-500 |
Deltamethrin SC |
15-25 |
Deltamethrin tablet |
1 tablet per net |
Lambda-cyhalothrin CS |
10-15 |
Cyfluthrin EW |
30-50 |
Alpha-cypermethrin SC |
20 |
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.
-
Wear protective gloves when treating nets with insecticide.
-
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.
- 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.
-
Dip the net in the solution until it is thoroughly wet.
-
Wring out the net over a bowl and hang up until it has stopped
dripping.
- 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.
- 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.
- 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)
-
Select an area that is well ventilated, but out of the wind. Avoid
spraying in an enclosed area.
-
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.
-
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.)
-
Wear protective gloves.
-
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.
-
Hang up garments, and allow the permethrin treatment to dry for 2
hours, or 4 hours if conditions are very humid.
- Treat other garments and gear (do not treat underwear):
- 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.
- 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.
- 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.
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