An Everyday Health blog by New Jersey-based husband and wife team Brad and Robynn Mann notes that more time spent outdoors during the warmer months means more potential encounters with insects that can be disease vectors, notably mosquitos and ticks. Mr. Mann, who is diagnosed with Multiple Sclerosis (MS), Narcolepsy w/Cataplexy, and REM Sleep Behavior Disorder (RBD) among other afflictions can speak from experience that persons already living with a neurological disease like multiple sclerosis (MS) must be knowledgeable and vigilant in protecting themselves against further challenges from insect-borne illness
Lyme Disease And MS
The Centers for Disease Control and Prevention (CDC) has singled out the bacterial infection known as Lyme Disease (LD) as currently the most common and fastest growing vector-borne, infectious disease in America, According to Texas A&M University’s Lyme Lab, LD is a zoonotic, tick-borne illness caused by the spirochetal bacterium Borrelia burgdorferi, with a total of 22,572 human cases of Lyme disease reported to the CDC in 2010.
The Manns note that typically, deer ticks spread LD in the Northeast and Midwest, while Western blacklegged ticks transmit the illness along the Northern Pacific coast. However, ticks have been migrating south and westward. A recent study conducted by an international research team from seven U.S. and Mexican universities and institutions has confirmed that risk for Lyme Disease is significant in the state of Texas and northern parts of Mexico. Since 2002, the CDC has reported 783 confirmed cases of Lyme disease in Texas, for example, and the Texas Lyme Disease Association (TXLDA) contends that numbers infected are likely dramatically higher because there is no reliable test to diagnose the disease, and many sufferers are never aware they are infected.
Lyme borreliosis is an important public health issue, particularly in endemic areas where it contributes to significant rates of morbidity. Lyme disease occurs as a multi-systemic disorder leading to carditis (10% of untreated adults), arthritis (60% of the cases) and other neurological symptoms. Moreover, there are few therapeutic solutions for Lyme disease patients and there are no effective vaccines available on the market.
Because diagnosis and treatment of Lyme disease are still evolving, TXLDA emphasizes that prevention is critical, and recommends when engaging in outdoor activities to wear light-colored clothing so that crawling ticks can be seen. Inspect yourself, your children, and your pets frequently for ticks, and remove any attached ticks promptly using proper removal procedures; avoid areas with high grass. When hiking, stay on the trails; don’t sit on stone walls; and wear shoes and socks, not sandals. According to the Lyme Disease Association “Ticks are most likely to be in woods, where woods meet lawn, where lawn meets fields, tall brush/grass, under leaves, under ground cover (low growing vegetation), near stone walls or wood piles, shady areas, around bird feeders, and in outside pet areas.” The organization ] suggests tucking pant legs into boots or socks so that ticks do not have access to skin and may more easily be seen; and recommends using insect repellents with DEET or Permethrin (cream 5%) in high-risk areas as well as tick and flea preventatives on pets.
Characteristic Lyme disease symptoms can include a round and red expanding “bull’s-eye” rash at the tick bite site, and flu-like symptoms at onset. When LD is left untreated, neurological symptoms may develop, including tingling, fatigue, pain, weakness, and cognitive issues. The Manns note that it may be difficult to distinguish LD symptoms from an MS exacerbation, but appropriate treatments are radically different.
West Nile Virus And MS
Mosquitos are carriers of West Nile virus in North America. While the vast majority of persons who become infected with West Nile have no symptoms or very mild symptoms, in some cases an infection can cause swelling of the brain or spinal cord, resulting in an array of neurological symptoms, including headaches, fatigue, pain in the eyes, rash or nausea. In severe cases, debilitating effects can linger for months or years. In the United States, arboviruses transmitted by mosquitoes also cause sporadic outbreaks of eastern equine encephalitis, western equine encephalitis, St. Louis encephalitis, and La Crosse encephalitis.
Obviously, avoidance of bites from potential Lyme Disease and West Nile (et al.) carriers is a wise precaution for anyone, but especially crucial for people with MS, for whom living with chronic neurological illness is challenging enough without additional health burdens. Its pretty much boilerplate to recommend using insect repellents when venturing outside, but these chemicals can bring with them their own classes of health risks and hazards.
DEET And Human Health
For example, the repellent known as “DEET” (N,N-diethyl-3-methylbenzamide) has been the gold standard of insect repellents for many years. A 2002 study published in the New England Journal of Medicine titled “Comparative Efficacy of Insect Repellents against Mosquito Bites” tested 16 different insect repellents, including three containing DEET, and reports that of the products tested, the DEET-containing ones provided the longest-lasting protection, and that only products containing DEET offer long-lasting protection after a single application. The investigators concluded that when in areas with prevalent mosquito-borne disease that could be transmitted through a single bite, use of non-DEET repellents would seem to be ill-advised.
As to questions regarding the safety of DEET, the NEJM report coauthors contend that this repellent had been subjected to more scientific and toxicologic scrutiny than any other repellent substance, and demonstrated a remarkable safety profile after 40 years of use and nearly 8 billion human applications, with fewer than 50 cases of serious toxic effect documented in the medical literature from 1960 to 2002, three quarters of which were resolved without sequelae. They also note that as part of the 1998 Reregistration Eligibility Decision on DEET, the Environmental Protection Agency reviewed accumulated data on DEET toxicity and concluded that “normal use of DEET does not present a health concern to the general U.S. population,” commenting that when applied with common sense, DEET-based repellents can be expected to provide a safe as well as a long-lasting repellent effect when it is crucial to be protected against arthropod bites that might transmit disease.
However, that report was published a dozen years ago, and in Health Canada’s Pesticide Incident Reporting Program more current 2012 Report on Pesticide Incidents, the agency reports that potential health risks have been identified for the pesticides N-diethyl-m-toluamide (DEET), metofluthrin, and chloropicrin, with major effects were noted in 32 individuals in the U.S. and two in Canada, in four instances involving death.
The report notes that DEET consistently appeared as one of most frequently reported active ingredients in human incidents from 2007 to 2011, with children implicated in a high proportion of these incidents, and that a review of all human incidents reported to the PMRA involving the active ingredient DEET was initiated in 2012.
Somewhat encouraging was that human incidents involving DEET were largely minor in severity, with the products reported in these incidents domestic class insect repellent sprays containing 15% or 25% DEET. There was a fairly high degree of association between the symptoms reported and exposure to a DEET insect repellent due to prevalence of direct exposure to the product, either via the skin or eye, resulting in irritation shortly after exposure as well as the occurrence of mild respiratory or general reactions (for example, headache or nausea) soon after product application.
The report also notes that most exposures were very short in duration (less than 15 minutes) and resulted in symptoms, within 24 hours of exposure, which resolved within one week, and that overall, the assessment of human incident reports involving DEET did not identify any significant health effects, although they recommend advising parents that children not be allowed to apply or handle DEET insect repellents.
However, several new mosquito-fighting options have entered the market.
One that shows particular promise is Icaridin, a new repellent that is the active ingredient in proprietary products like All-Family Insect Repellent Spray, Avon Skin-So-Soft SSS Bug Guard Plus Icaridin Insect Repellent I, Avon Skin-So-Soft SSS Bug Guard Plus Icaridin Insect Repellent II, OFF! Active Insect Repellent Clean Feel, OFF! Deep Woods Pump Spray Insect Repellent Clean Feel and OFF! Family Care Clean Feel Insect Repellent Towelettes. Icaridin entered the U.S. market in 2005 (as “picaridin”) and was approved by Health Canada in 2012.
Icaridin is applied to human skin, with mode of action not fully understood, although one hypothesis is that the chemical affects arthropod olfactory neurons, resulting in their inability to detect host attractants. An alternative explanation is that as the repellent evaporates from the skin into the air it forms a layer of scent that camouflages attractants (eg: carbon dioxide and lactate) emitted by the human host, rendering the insect unsable find the host.
Health Canada notes that exposure to icaridin will occur through the application of insect repellent products containing this active ingredient to human skin, but is unlikely to affect your health when used according to label directions.
Studies of animals given repeated doses of Icaridin have noted effects on the liver and kidney, but the chemical did not cause cancer in animals or damage genetic material, and here was no indication that Icaridin caused damage to the nervous system or immune system or had any effect on the ability to reproduce, and that the risk assessment protects against the effects of Icaridin by ensuring that the level of human exposure is well below the lowest dose at which any effects occurred in animal tests.
Health Canada concludes that sufficient efficacy data were provided to support use of All-Family Insect Repellent Spray (containing 20% icaridin) for seven hours of protection from mosquitoes and eight hours of protection from ticks, as well as eight hours of protection from blackflies was conditionally supported. Avon Skin-So-Soft SSS Bug Guard Plus Icaridin Insect Repellent I and Avon Skin-So-Soft SSS Bug Guard Plus Icaridin Insect Repellent II (containing 10% icaridin) provided five hours of protection from mosquitoes, with use of these products to provide seven hours of protection from ticks conditionally supported. OFF! Active Insect Repellent Clean Feel (containing 10% icaridin) gave five hours of protection from mosquitoes, while OFF! Deep Woods Pump Spray Insect Repellent Clean Feel and OFF! Family Care Clean Feel Insect Repellent Towelettes (containing 20% icaridin) provided seven hours of protection from mosquitoes and eight hours of protection from ticks.
Oil Of Lemon Eucalyptus
Health Canada has granted full registration for sale of p-menthane-3,8-diol and related oil of lemon eucalyptus compounds sold under the trade name Citriodiol, as well as the personal insect repellents Citrepel Insect Repellent 30 and Natrapel Insect Repellent, containing the technical grade active ingredient p-menthane-3,8-diol and related oil of lemon eucalyptus compounds, for use to repel mosquitoes.
Citriodiol is used to formulate skin-applied personal insect repellents, although its action in repelling mosquitoes is not known. Laboratory studies p-menthane-3,8-diol and related oil of lemon eucalyptus compounds has been seen to repel mosquitoes as they approach the zone near the treated skin, rather than acting as a masking agent so that they do not find the host. The agency reports that while potential exposure to p-menthane-3,8-diol and related oil of lemon eucalyptus compounds may occur when handling and applying the end-use products they are unlikely to affect human health when used according to label directions.
Specifically, In laboratory animals, p-menthane-3,8-diol and related oil of lemon eucalyptus compounds, were demonstrated to have low acute toxicity via oral and dermal routes of exposure, and be only slightly acutely toxic via inhalation exposure. The chemical was also a slight skin irritant, a moderate eye irritant, but not a skin sensitizer. Consequently, the hazard signal words, ‘WARNING – EYE IRRITANT’ and ‘CAUTION POISON’ are required on the label.
Citrepel Insect Repellent 30 and Natrapel Insect Repellent are skin-applied insect repellents that repel mosquitoes for 4 to 6 hours following application, and Health Canada affirms that these products provide additional choice for mosquito repellent users.
Metofluthrin (Clip-on Mosquito Repellent)
The product, OFF! Clip-on Mosquito Repellent containing the active ingredient metofluthrin, was registered for use by Health Canada as a personal insect repellent in October of 2011.
The agency notes that when using this product, the chemical metofluthrin is vaporized into air surrounding the user in order to repel mosquitoes, and within the first year of registration, the Pesticide Incident Reporting Program received six human incident reports associated with the product. Affected individuals presented with wide range of symptoms, including dizziness, swelling, nausea, lethargy, muscular weakness, pruritus, irregular heart rate, or loss of consciousness.
The ill effects reported were considered to be either possibly or probably related to pesticide exposure, resulting in the product currently holding a registration in Canada conditional upon submission of additional data on product exposure. Although only a few incidents were reported, this is a new product and the authority will continue to monitor incidents reported in the following year.
Additionally Consumer Reports testing of OFF! Clip-ons found that that in contrast to a promised 11 hours protection, about two hours was more typical.
Mosquito Lamps And Lanterns
A class of devices that heat pads containing the insecticide allethrin with butane heaters or candles are claimed to provide up to 15 feet of odorless bug protection, but potential effectiveness is presumably highly dependent on local wind velocity. Allethrin is a chemical also used in mosquito coils (see below), and there have been several incidents reported in Canada and the U.S. involving breathing problems and skin irritations from people using mosquito lanterns.
Citronella Candles And Citronella Incense
A 1996 study published in the Journal of the American Mosquito Control Association evaluated efficacy of 3% citronella candles and 5% citronella incense for protection against Aedes mosquitoes. under field conditions. On average, participant subjects received 6.2 +/- 0.4, 8.2 +/- 0.5, 8.2 +/- 0.4, and 10.8 +/- 0.5 bites/ 5 min at positions with citronella candles, citronella incense, plain candles, and no candles, respectively. The researchers concluded that although significantly fewer bites were received by subjects at positions with citronella candles and incense than at nontreated locations, the overall reduction in bites provided by the citronella candles and incense was only 42.3 and 24.2%, respectively.
Essential Oil Candles
A 2008 study published in the Journal of the American Mosquito Control Association investigated the ability of essential oil candles to repel biting insects in high and low biting pressure environments, measuring the effect of geraniol, linalool, and citronella candle (5%) vapors outdoors, where such products are commonly used. At a distance of 1.0 m, citronella candles reduced the number of female mosquitoes caught in Centers for Disease Control and Prevention traps by 35.4% and sand flies by 15.4%, linalool candles reduced female mosquitoes by 64.9% and sand flies by 48.5%, while geraniol candles reduced female mosquitoes by 81.5% and sand flies by 69.8%. However, by increasing the distance to 2 m and 3 m, repellency effectiveness dropped significantly. The second goal was to compare the degree of personal protection provided by the best performing candle, geraniol, under conditions of high and low biting pressure. The introduction of geraniol candles to protect volunteers in a high biting pressure environment reduced the mosquito pressure by an average of 56% and the sand fly pressure by 62% over a distance of 1.0 m. In the low biting pressure environment, geraniol reduced the mosquito pressure by an average of 62%.
However, a September 2010 paper published in the journal Air Quality, Atmosphere & Health (Volume 3, Issue 3, pp 131-137) investigating organic aerosol formation in citronella candle plumes found that because these essential oils are unsaturated, they have a unique potential to form secondary organic aerosol (SOA) via reaction with ozone, which is also commonly elevated on summer evenings when the candles are often in use. In repeated experiments, the researchers observed rapid and substantial SOA formation after ozone addition, concluding that this process must be considered when assessing the risks and benefits of using citronella candle to repel insects.
A 2003 paper entitled “Mosquito coil emissions and health implications” published in Environmental Health Perspectives notes that burning mosquito coils indoors generates smoke that can control mosquitoes effectively, a practice currently used in numerous households in Asia, Africa, and South America, and also sometimes in North America as well. However, the researchers say the smoke may contain pollutants of health concern.
The scientists report that they identified a large suite of volatile organic compounds, including carcinogens and suspected carcinogens in the coil smoke, and in examining the size distribution of particulate matter contained in the coil smoke they found that the particles were ultrafine and fine, suggesting that exposure to the smoke of mosquito coils similar to the tested ones can pose significant acute and chronic health risks. For example, burning one mosquito coil would release the same amount of PM(2.5) mass as burning 75-137 cigarettes. The emission of formaldehyde from burning one coil can be as high as that released from burning 51 cigarettes.
Insect Repellent “Solutions” That Don’t Work
A 2006 study published in the Journal of the American Mosquito Control Association notes that a plant recently introduced into North America as the citrosa, Pelargonium citrosum (‘Van Leenii’), has been marketed as a biological repellent against mosquitoes. The researchers observe that Citrosa is claimed to repel mosquitoes within a 10 ft.2 (0.93 m2) area due to a continuous fragrant release of citronella oil. However, when the effectiveness of the citrosa as a repellent against field populations of spring Aedes spp. mosquitoes was evaluated and compared with a 75% deet (N,N-diethyl-3-methylbenzamide) formulation, Deet provided > 90% reduction in mosquitoes biting subjects for up to 8 hours post-treatment, while there was no significant difference between citrosa-treated and nontreated subjects.
Electric “Bug Zappers”
A Biodiversity report entitled
Density and Diversity of Nontarget Insects Killed by Suburban Electric Insect Traps reports that a survey of insects electrocuted during routine use of electric insect traps purported to use ultraviolet light to lure flying insects toward an electrified metal grid, where they are supposedly destroyed by the thousands on warm summer nights. Homeowners buy these traps in hope of ridding their surroundings of annoying biting insects, and continuous snaps, crackles, and pops emanating from an active zapper seem to confirm their effectiveness.
However, the researchers report that scientific investigation revealed only 31 biting flies zapped; a minute proportion (0.22%) of total insects counted in the immediate vicinity. In contrast, species from 12 orders and more than 104 nontarget insect families, including 1,368 predators and parasites (13,5%) and 6,670 nonbiting aquatic insects (48.4%) were destroyed. The coauthors conclude that the heavy loll on nontarget insects and the near absence of biting flies in catches suggests that electric insect traps are worthless for biting insect reduction — and probably are counterproductive — to homeowners and other consumers.
Garlic And/Or Vitamin B12 As Anti Insect Bite Strategies
A report entitled “A double-blinded, placebo-controlled trial of garlic as a mosquito repellant: a preliminary study” published in Medical and Veterinary Entomology (Volume 19, Issue 1, pages 84–89, March 2005 DOI: 10.1111/j.0269-283X.2005.00544.x) investigated the hypothesis that ingestion of garlic provides protection against mosquito bites. Subjects were asked to consume either garlic (one visit) or a placebo (the other visit), and were then exposed to laboratory-reared Aedes aegypti (Linnaeus) (Diptera: Culicidae) mosquitoes. The numbers of mosquitoes that did not feed on the subjects, the number of mosquito bites, the weights of the mosquitoes after feeding and the amounts of blood ingested were determined. The data derived provide no evidence of significant systemic mosquito repellence, although the scientists note that a limitation of the study is that more prolonged ingestion of garlic may be needed to accomplish repellence.
The Centers for Disease Control and Prevention
Health Canada’s Pest Management Regulatory Agency (PMRA)
Texas A&M University Lyme Lab
Texas Lyme Disease Association
Journal of the American Mosquito Control Association
Parasites and Vectors
New England Journal of Medicine
Environmental Health Perspectives
Air Quality, Atmosphere & Health
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