Evaluation of the use of repellent against mosquito bite by military personnel in the Amazon Basin

Abstracts

FUNDAMENTOS: No Brasil, doenças provocadas por picadas de insetos são frequentes, o que torna extremamente importante a execução de medidas profiláticas de forma adequada, sobretudo, em áreas endêmicas como a Amazônia, que recebe um grande contingente de visitantes, a trabalho ou turismo. OBJETIVOS: Avaliar o uso dos repelentes de insetos disponíveis no mercado por militares que costumam realizar missões em ambiente de selva, na região amazônica. MÉTODOS: Foram selecionados cinquenta e um militares da região amazônica que responderam um questionário em junho/2008. RESULTADOS: 63,7% dos militares usaram produtos contendo Deet na concentração máxima de apenas 15%, que possui mínima ação de repelência; 36% relataram usar protetor solar associado, o que levou a um risco maior de intoxicação; 36,4% fizeram uso de um repelente natural em suas missões; dois militares usaram vitamina B e consideraram a sua ação de repelência ineficaz. CONCLUSÕES: Os repelentes à base de Deet utilizados pelo grupo estudado apresentam concentrações inferiores às consideradas seguras para uso em ambiente de selva. Foi frequente a associação do Deet com protetor solar, que é uma combinação potencialmente tóxica. Os repelentes naturais à base de andiroba e copaíba apresentaram o maior grau de percepção de proteção.

Deet; Mordeduras e picadas de insetos; Repelentes de insetos

INVESTIGATION

^IAssistant Professor, Master Degree in Tropical Pathology, School of Medicine. Head of the Medical Residency Program in Dermatology, Federal University of the Amazonas (UFAM), Amazonas, Brazil

^IIDermatologist, Brazilian Airforce, Amazonas, Brazil

Mailing Address

ABSTRACT

BACKGROUND: In Brazil, diseases caused by insect bites are frequent. Therefore, it is extremely important that prophylatic measures are adequately carried out, especially in endemic areas such as the Amazon which receives a great number of visitors, for both business and tourism purposes..

OBJECTIVES: To evaluate the use of insect repellents available in the market by military personnel who often go in missions in the middle of the jungle, in the Amazon region.

METHODOLOGY: Fifty - one militaries in the Amazon region were selected and they answered a questionnaire in June/2008.

RESULTS: 63,7% of the militaries used products that contained Deet in the maximun concentration of only 15% that has minimum repellent action; 36% reported to combine these products with sun protective products which increased the risk of intoxication; 36,4% used a natural repellent during their missions; two of the militaries participants used vitamin B and considered their repellent action ineffective.

CONCLUSION: The repellents that contain Deet and which were used by the group present concentrations that are lower than the concentrations considered safe for using in the jungle. It was frequent the combination of Deet with sun protective products ,which is a potentially toxic association. Natural repellents that have "andiroba" and" copaíba" as components presented a higher perception of protection from the participants.

Keywords: DEET; Insect bites and stings; Insect repellents

INTRODUCTION

Worldwide, various species of mosquitoes act as vectors in transmitting numerous diseases to around 700 million individuals annually and are responsible for the death of one in every 17 infected people.¹

Mosquitoes transmit arboviruses, which are responsible for yellow fever, dengue, hemorrhagic fever, epidemic polyarthritis and various forms of encephalitis; filariae, which cause filariasis and onchocerciasis; and the protozoan parasites that are the etiologic agents of malaria and leishmaniasis.

True mosquitoes belong to the Culicidae family and the vectors responsible for inoculation of the virus, helminths or protozoa that cause diseases in humans are found in the Culicinae and Anophelinae subfamilies. Only the females of the species are obligatorily hematophagous, since the males feed on fruit juice and flower nectar.

The factors involved in attracting mosquitoes to humans are not yet completely understood; however, mosquitoes are known to use visual, thermal and olfactory stimuli to locate their hosts.^2-4

In Brazil, diseases caused by mosquito bites are common and lead to outbreaks and epidemics in developed inner city areas where, theoretically, basic sanitation and orderly growth should facilitate vector control.⁵ The Amazon jungle, an environment infested by a multitude of insects that are vectors of endemic diseases transmitted through their bites, constitutes a region where control is impossible; therefore, primary prevention is essential.

The first reports of repellents appear in the Greek and Roman literature, published by Plinio (23-75 AD) and Dioscorides (60 AD), who recommended applying common wormwood (Artemisia absinthium) and citrus fruit to clothes for the purpose of repelling insects.⁶

Repellents are substances applied to skin, clothes or surfaces to discourage the approximation of insects. Use of these products reduces the risk of transmission of various infectious diseases, as well as the allergic reactions resulting from the bites of these arthropods. Topic chemical repellents are the most widely used products worldwide; however, they are often used inappropriately, even in endemic areas, hence often failing to guarantee adequate protection.

The ideal repellent should have the following characteristics: prolonged efficacy against a wide range of arthropods; it should not irritate the skin immediately after direct application or application onto clothing; it should not stain or bleach clothes or weaken the fabric, but should remain on clothes after repeated washing; it should have no effect on routinely used plastics; should be resistant to water and perspiration and not leave an oily residue on the skin; it should not be toxic; it should have a prolonged effect; it should be inexpensive enough to allow it to be used frequently; and it should not aggravate the environment. ^7-12

N, N-diethyl-3-methylbenzamide, also known as DEET, is the most commonly used insect repellent.¹³ It is found in concentrations of 5-100%; however, the majority of preparations contain concentrations of less than 40%. It is available as a lotion, gel, aerosol or spray and as a solution for adding to clothes during laundering. Its safety has been confirmed over the past forty years, with only minimal side effects that include urticaria, contact dermatitis and encephalopathy. ¹⁴

Picaridin [1-methyl-propyl 2-(2-hydroxyethyl)-1-piperidinecarboxylate] was recently approved for use as an insect repellent in the United States and Brazil. No significant side effects were reported in studies carried out in Europe and in Australia, and comparative studies between Picaridin and DEET have shown the two preparations to be equally effective.¹⁵

Other chemical agents include dimethyl phthalate, ethyl-hexanediol, IR35/35, bayrepel and KBR 3023.

Some botanical compounds such as eucalyptus, geranium, soja, citronella, andiroba, celery oil and garlic, have been found to have repellent properties; moreover they are inexpensive and toxicity is low. Nevertheless, up to the present moment no plant derivative has been shown to have an efficacy and duration of effect similar to those of DEET.^16-18

Pure andiroba (Carapa guianenses) oil has been reported in studies to be more effective as a repellent than using no product at all, but significantly inferior to DEET in a 50% concentration.¹⁶

Copaiba oil (Copaifera spp.) has been described as an effective repellent against phoridae or scuttle flies, which cause great damage to the rational breeding of indigenous stingless bees; however, there are no studies on its effect in humans either alone or in association with andiroba oil.¹⁹

Since the Amazon region receives many visitors, both business travellers and tourists, it would be useful to distribute information on the adequate use of insect repellents.

The objective of the present study was to evaluate the use of commercially available insect repellents by military personnel carrying out missions in the jungle environment of the Amazon basin.

MATERIAL AND METHODS

This cross-sectional study was conducted in June 2008. An intentional sample of 51 airforce personnel from the Manaus airbase squadron was selected for the study and answered a standardized questionnaire designed to obtain information with respect to the preventive methods used by these individuals against insect bites.

The questionnaire consisted of 10 objective questions related to the experience of these military personnel with respect to their use of repellents during missions, the frequency with which they used these products, any adverse events experienced and the personal evaluation of the participants with respect to the products' efficacy (Table 1).

The data thus collected were stored in a database constructed using the Epi Info software program. Variables related to the use of the repellents were submitted to descriptive and statistical analyses using Pearson's chi-square test, and arranged in tables and figures describing the findings.

RESULTS

In the group of 51 military personnel studied, 90. 2% were male and 9.8% female. Mean age was 35.2 ± 7.3 years (mean ± standard deviation) (range 21-47 years).

With respect to the number of missions carried out in a jungle environment, 52.9% of the personnel had been on more than 30 missions, 19.6% had been on a maximum of 10 missions, 15.7% had participated in 21-30 missions and 11.8% had been on 11-20 missions.

Regarding diseases transmitted by mosquitoes to these individuals during missions in the jungle environment, two (3.9%) reported having contracted malaria, two (3.9%) tegumentary leishmaniasis and two (3.9%) dengue, making a total of six participants (11.8%) who contracted vector-borne diseases while on mission.

Comparing the data of the six individuals who contracted diseases transmitted by mosquitoes with the number of missions in which they had participated, it was found that all six had participated in 30 or more missions and all had used repellents.

The third item in the questionnaire referred to the use of repellent as a preventive measure against mosquito bites and the type of repellent used by the personnel. Forty-eight of the participants (94.1%) replied that they used repellents. Of these, 62.5% used synthetic repellents with DEET as the active ingredient, while 33.3% used natural repellents, consisting of a mixture of copaiba and andiroba oil (Figure 1). Only two individuals (4.2%) used oral vitamin B.

When the participants who used repellents were asked whether they had been instructed to use a certain repellent or whether they themselves had made this choice, 43.8% replied that they themselves had chosen the repellent, while 56.3% reported that they had been recommended to use a certain type.

Regarding the individuals' perception of the level of protection offered by the repellent, 35.4% thought the protection was excellent, 31.3% thought it was good, 29.2% moderate and 4.2% believed it to be ineffective. Table 2 shows users' perception of the level of protection according to the type of repellent, indicating that the level of protection achieved with the natural repellent containing andiroba and copaiba oil was perceived as being more effective and this difference was statistically significant.

With respect to the frequency of reapplication of the product, 38.3% of the participants reapplied it twice a day, 27.7% four or more times a day and 21.3% three times a day, while 12.8% applied it only once a day. Table 3 shows that there was no statistically significant association between the number of reapplications and the type of repellent used.

Twenty-eight of the participants (60.7%) were found to have experienced some form of discomfort or side effect with the use of the repellent: excess oiliness of the skin was the most frequent complaint, mentioned by 15 individuals (53.6%), followed by a burning sensation, reported by 9 (32.1%). Other complaints were mentioned by four individuals (14.3%). Of the 15 participants who reported that their skin felt greasy, 6 (40%) had used DEET, constituting 20% of the participants who had used this product, and 9 (60%) had used the andiroba and copaiba oil repellent, constituting 56.3% of users of this product.

Regarding the vehicle used in the repellent, 54. 2% of participants reported having used a lotion, 39.6% a spray, 2.1% ointment and 4.2% oral vitamins.

The final item in the questionnaire concerned whether the airforce personnel had used sunscreen in association with the repellent and 18 (36.0%) reported that they had.

DISCUSSION

In order to be considered highly effective, repellents must have a prolonged effect of eight hours or more against all arthropods: flying mosquitoes (Aedes spp., Anopheles spp., black flies and mosquitoes), ticks, Triatoma spp., fleas and mites, among others. As a repellent, DEET has been shown to be highly effective; however, it may also cause toxic or allergic effects, particularly when used repeatedly at high concentrations. Formulae containing 50% DEET are considered to be just as effective (95%) as others containing 100% of the product for protection of more than nine hours.

Among the participants in this study sample who used repellents, 63.7% chose to use industrialized products sold in pharmacies, all of which contained DEET as their active ingredient, albeit at a maximum concentration of only 15%, which is considered too low to provide effective protection in a jungle environment. In this environment, the risk of exposure to attack from numerous arthropods makes a wide spectrum repellent indispensable, and this is only possible with concentrations of DEET above 50%.^13,14,20

At a concentration of 15%, DEET has a minimal repellent effect and the product must be consistently reapplied every two hours, which is certainly not very practical. It should also be taken into consideration that the climate in the tropics is hot and humid, increasing perspiration and reducing the time the product remains on the skin, making reapplication necessary to maintain the same level of protection.²¹ In this study sample, only 27.7% of participants reapplied the product four or more times a day.

Eighteen individuals (36%) reported using sunscreen together with repellent. This combination is another factor that alters the efficacy of the repellent. According to Ross et al., when sunscreen and repellent are used together, the systemic absorption of DEET increases 6-fold, augmenting the risk of intoxication. Therefore, the potential toxicity of this combination, which leads to an increase in the risk of side effects, should always be taken into consideration. ²² On the other hand, according to Montemarano et al., DEET has a detrimental effect on sunscreen, reducing its sun protection factor, which may result in a false sensation of protection against the ultraviolet radiation that is known to be high in the Amazon region.²³

If repellent and sunscreen are both required, the individual should opt for a product that does not contain DEET as the active ingredient. ^24,25 Picaridin has several of the characteristics of an ideal repellent and, at a concentration of 19.2%, has been shown to provide protection for up to nine hours, with efficacy of 95%; therefore, it would appear to represent a possible safe alternative to DEET.^19,20

The choice of the vehicle is another factor that may affect compliance with the use of the repellent. Creams and ointments in general leave the skin feeling greasy, while alcohol-based formulae may irritate the eyes. In a study conducted with armed forces personnel in Australia, Frances et al. reported that only 20% of the participants used the standardized 30% DEET repellent gel offered by the institution. The remaining 80% had stopped using it because the gel left an unpleasant sensation on their skin and because the repellent ruined plastic-based products. Those participants preferred to purchase a commercially available DEET-based repellent that was cosmetically more agreeable. Aerosols were the most popular form of vehicle.²⁰

In agreement with these findings, the participants in the present study also preferred less oily vehicles, 54.2% using lotion-based repellents, while 39.6% used products in aerosol form.

Natural repellents are atoxic, easily biodegradable and safer for human beings than synthetic compounds; however, they are effective for very short periods of time that vary, on average, from 5 to 15 minutes. Furthermore, they may cause allergies.²⁶ Some plant oils are used as repellents by the lay public, based on popular medicine. It should be emphasized that for these oils to be effective as repellents, the consumer should be aware of how and where they were manufactured to ensure that they have not been mixed with other substances that could alter their chemical composition, thereby losing their properties or exposing the user to a risk of intoxication.^27-29

In the present study, 36.4% of the military personnel interviewed used a natural repellent that consisted of a mixture of andiroba oil, copaiba oil and Johnson's® baby oil in equal parts. Of these users, 85.7% considered the level of protection to be excellent, leading the authors to consider a hypothesis of a possible synergistic effect of this association or, alternately, a false sense of security. Nevertheless, scientific studies are required to verify the efficacy of the combination of these oils that has been used empirically.

Two individuals in this sample reported using vitamin B and, in agreement with the literature reviewed, considered this vitamin to be ineffective as a repellent. Vitamin B1 has been widely recommended in popular medicine and publicized in the lay press. Ives et al., however, confirmed the inefficacy of this vitamin as a repellent against mosquitoes of medical interest such as Anopheles spp. and Aedes spp. Therefore, use of vitamin B as a repellent should be discouraged. ³⁰

CONCLUSION

The commercially available DEET-based repellents against insect bites that were used by the participants of the present study contained concentrations of the active ingredient that were lower than the level considered safe for use in a jungle environment.

It was common for the participants in this study to choose repellents that were available in more cosmetically agreeable vehicles such as lotions or aerosols, and to combine the use of repellents with sunscreen.

Natural andiroba and copaiba-based repellents were considered by participants to be the most effective. Studies need to be performed to analyze the level of protection offered by this combination of natural oils.

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Evaluation of the use of repellent against mosquito bite by military personnel in the Amazon Basin

Jonas Ribas^I; Ana Maria Carreño^II

Publication Dates

• Publication in this collection
  06 May 2010
• Date of issue
  Feb 2010

History

• Received
  21 May 2009
• Accepted
  27 Nov 2009