Repellent efficacy of four commercial DEET lotions against Amblyomma hebraeum (Acari: Ixodidae), the principal vector of Rickettsia africae in southern Africa

Encapsulation of carvacrol and thymol with yeast cell wall and its repellent activity against Amblyomma sculptum and Rhipicephalus sanguineus (Sensu Lato)

The main way to avoid contact with ticks and consequently tick-borne disease is the use of synthetic repellents. The search of new repellent compounds to increase the possibilities of use in strategies controls are necessary. The present study evaluated the repellent activity of two natural terpenes carvacrol and thymol in each one two different formulation (encapsulated and nonencapsulated with yeast cell wall) against the ticks Amblyomma sculptum and Rhipicephalus sanguineus sensu lato nymphs. Nymphs of A. sculptum and R. sanguineus s.l. of a single generation were used. The vertical filter paper repellency assay were performed with different concentration of both terpenes encapsulated and nonencapsulated in yeast cell wall. The repellent concentration 50% (RC50) were calculated to each compound formulation. Both carvacrol and thymol (encapsulated and nonencapsulated), had a repellent activity against A. sculptum and R. sanguineus s.l nymphs. Amblyomma sculptum was more sensitive to nonencapsulated carvacrol (RC50 values: 0.0032 to 0.0082 mg/cm2 after 1 and 15 min) (P < 0.05), while R. sanguineus s.l. was more sensitive to encapsulated carvacrol (RC50 values: 0.00008 to 0.0035 mg/cm2 after 1 and 15 min) (P < 0.05). Among tick species, R. sanguineus s.l. was more sensitive for most compounds than A. sculptum (P < 0.05). Although with distinct repellent activities, carvacrol and thymol encapsulated can be a promising alternative to synthetic repellents against A. sculptum and R. sanguineus s.l.

Do Commercial Insect Repellents Provide Protection against the Tick Amblyomma sculptum (Acari: Ixodidae)?

Amblyomma sculptum is a species of public health interest because it is associated with the transmission of the bacteria that causes Brazilian Spotted Fever (BSF). The use of repellents on humans is a prophylactic measure widely used to provide protection against a series of arthropod vectors, including mosquitoes and ticks. However, in Brazil, the effectiveness of commercial repellents against A. sculptum is little known. Therefore, it is necessary to carry out specific studies to evaluate the repellency of these commercial products, registered for use against mosquitoes, against the star tick. The main goal of the present work was to evaluate the effectiveness of six commercial repellents against A. sculptum. Unfed nymphs, aged between two and eight weeks, were tested against products based on DEET (OFF!® and Repelex®), Icaridin (Exposis® and SBP®), and IR3535 (Johnsons and Henlau). Three bioassays were conducted to evaluate tick behavior: (i) filter paper, (ii) fingertip, and (iii) field. All bases tested showed high repellent activity, differing significantly (p < 0.05) from the control. It was observed the formulation with DEET resulted in the best results in the filter paper bioassay. In the fingertip bioassay, the DEET base repelled a greater number of ticks compared to Icaridin. In the field bioassay, there was no significant difference between the Icaridin base and DEET, and both formulations differed from the control (p < 0.05). The six formulations tested showed significant percentages of repellency against ticks; however, for the fingertip and field bioassays, the products OFF!®, Repelex®, and Exposis® were tested as they showed better performance in the filter paper test. OFF!® showed the best percentage of repellency (100%), followed by Repelex® (96.8%), and Exposis® (93.1%), considering the two-hour period of the bioassay-field-test. Proving the effectiveness of repellents on the market against A. sculptum presented in this study is crucial, since this is the main ectoparasite of humans that can transmit Rickettsia rickettsii when infected. The effectiveness of commercial insect repellents against other tick species that parasitize humans can also be explored.

Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Management of Tick-Borne Illness in the United States

The Wilderness Medical Society convened an expert panel to develop evidence-based guidelines for the prevention and management of tick-borne illness (TBI). Recommendations are graded based on quality of supporting evidence according to criteria put forth by the American College of Chest Physicians. The guidelines include a brief review of the clinical presentation, epidemiology, prevention, and management of TBI in the United States, with a primary focus on interventions that are appropriate for resource-limited settings. Strong recommendations are provided for the use of DEET, picaridin, and permethrin; tick checks; washing and drying clothing at high temperatures; mechanical tick removal within 36 h of attachment; single-dose doxycycline for high-risk Lyme disease exposures versus "watchful waiting;" evacuation from backcountry settings for symptomatic tick exposures; and TBI education programs. Weak recommendations are provided for the use of light-colored clothing; insect repellents other than DEET, picaridin, and permethrin; and showering after exposure to tick habitat. Weak recommendations are also provided against passive methods of tick removal, including the use of systemic and local treatments. There was insufficient evidence to support the use of long-sleeved clothing and the avoidance of tick habitat such as long grasses and leaf litter. Although there was sound evidence supporting Lyme disease vaccination, a grade was not offered as the vaccine is not currently available for use in the United States.

Three molecules found in rosemary or nutmeg essential oils repel ticks (Dermacentor variabilis) more effectively than DEET in a no-human assay

BACKGROUND

Development of new personal repellents to prevent tick bites is progressing to keep up with the increasing threat of tick-borne diseases in humans. However, the market share of natural, plant-based repellents is still quite small. We tested all of the major (>1%) components found in the essential oils of rosemary (Spanish variety) and nutmeg. These were tested with Dermacentor variabilis ticks, a robust tick capable of vectoring human diseases, in a no-human horizontal Petri dish assay. For comparison, we also tested the active ingredients currently recommended by the CDC and EPA as personal repellents for use against ticks.

RESULTS

Of the 16 oil components tested, three performed significantly better than N,N-diethyl-meta-toluamide (DEET) in our assay. These compounds were myristicin and safrole found in the nutmeg oil, and terpinolene found in nutmeg oil and as a minor (<1%) constituent of rosemary oil. The current market natural product, 2-undecanone, also performed strongly in our assay.

CONCLUSIONS

Our assay focused on comparing active ingredients as potential repellents and found that many natural products can elicit a strong response from ticks. Terpinolene is the most promising active ingredient identified, owing to human health concerns regarding myristicin and safrole. Our results from examining individual terpenoids from two essential oils suggest that there remain unexploited natural compounds that could be further developed for new personal tick repellents. © 2020 Society of Chemical Industry.

Methods for Testing Repellents Against Bed Bugs (Hemiptera: Cimicidae)

Bed bug repellents should not only prevent humans from being bitten but impede an infestation of personal belongings. Only a few test proposals for evaluating the efficacy of repellents against bed bugs have been published so far. In the present study, two test systems were assessed for efficacy testing with five potential bed bug repellents (cinnamon oil, icaridin, N,N-diethyl-3-methylbenzamide (DEET), permethrin, and margosa extract). The first test setup was a harborage choice test system that consisted of a crystallizing dish with a treated and an untreated harborage. Sixty minutes and 24 h after treatment, DEET, icaridin, and cinnamon oil showed the highest repellency with a median proportion of at least 99% repelled bed bugs. The second test system was a barrier test. Bed bugs were attracted by CO2 and heat to cross filter papers treated with the potential repellents. The repellency of substances was significantly lower in comparison to the harborage choice test, except for DEET. The latter showed the highest repellency (97%) against bed bugs 24 h after application compared to controls. Results show that bed bugs are less sensitive to repellents when searching for a bloodmeal than when searching for a shelter.

Natural insensitivity and the effects of concentration on the repellency and survival of American dog ticks (Dermacentor variabilis) by DEET

N,N-Diethyl-m-toluamide (DEET) is by far the most used repellent worldwide. When applied topically to the skin, the active ingredient has been shown to provide protection from a variety of hematophagous insects, including mosquitoes and flies. DEET's effectiveness against ticks is influenced by a variety of factors (e.g., duration and concentration of application, drying time, route of exposure, tick species and developmental stage), and may differ from insects due to their unique chemosensory system that primarily involves the Haller's organ. We therefore used several approaches to investigate DEET's efficacy to repel Dermacentor variabilis at different concentrations (5, 30 or 75%), as well as explore its toxicological properties and natural variability in DEET insensitivity across populations from Manitoba, Canada. Climbing bioassays indicated that higher concentrations of DEET were more effective at repelling D. variabilis, and that ticks from some sampling localities were more sensitive to lower concentrations than others. Petri dish arena assays revealed ticks exposed to high concentrations of the repellent lose their ability to discriminate lower concentrations, perhaps due to overstimulation or habituation. Finally, our tactile assays demonstrated reduced tick survival after contact with high DEET concentrations, with mortality occurring more rapidly with increased concentration. Dermacentor variabilis from these tactile assays displayed a multitude of physiological and neurological symptoms, such as 'hot foot' and various bodily secretions. Overall, our study shows a strong association between repellency, concentration and the acaricidal effects of DEET on D. variabilis.

Considerations for Human Blood-Feeding and Arthropod Exposure in Vector Biology Research: An Essential Tool for Investigations and Disease Control

Eventually there may be a broadly acceptable, even perfected, substitute for the human host requirement for direct feeding experiments by arthropods, most notably mosquitoes. However, for now, direct and indirect feeding on human volunteers is an important, if not essential, tool in vector biology research (VBR). This article builds on the foundational publication by Achee et al. (2015) covering considerations for the use of human participants in VBR pursuits. The authors introduced methods involving human participation in VBR, while detailing human-landing collections (catches) as a prime example. Benedict et al. (2018) continued this theme with an overview of human participation and considerations for research that involves release of mosquito vectors into the environment. In this study, we discuss another important aspect of human use in VBR activities: considerations addressing studies that require an arthropod to feed on a live human host. Using mosquito studies as our principal example, in this study, we discuss the tremendous importance and value of this approach to support and allow study of a wide variety of factors and interactions related to our understanding of vector-borne diseases and their control. This includes establishment of laboratory colonies for test populations, characterization of essential nutrients that contribute to mosquito fitness, characterization of blood-feeding (biting) behavior and pathogen transmission, parameterization for modeling transmission dynamics, evaluation of human host attraction and/or agents that repel, and the effectiveness of antivector or parasite therapeutic drug studies.

Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis - United States

Tickborne rickettsial diseases continue to cause severe illness and death in otherwise healthy adults and children, despite the availability of low-cost, effective antibacterial therapy. Recognition early in the clinical course is critical because this is the period when antibacterial therapy is most effective. Early signs and symptoms of these illnesses are nonspecific or mimic other illnesses, which can make diagnosis challenging. Previously undescribed tickborne rickettsial diseases continue to be recognized, and since 2004, three additional agents have been described as causes of human disease in the United States: Rickettsia parkeri, Ehrlichia muris-like agent, and Rickettsia species 364D. This report updates the 2006 CDC recommendations on the diagnosis and management of tickborne rickettsial diseases in the United States and includes information on the practical aspects of epidemiology, clinical assessment, treatment, laboratory diagnosis, and prevention of tickborne rickettsial diseases. The CDC Rickettsial Zoonoses Branch, in consultation with external clinical and academic specialists and public health professionals, developed this report to assist health care providers and public health professionals to 1) recognize key epidemiologic features and clinical manifestations of tickborne rickettsial diseases, 2) recognize that doxycycline is the treatment of choice for suspected tickborne rickettsial diseases in adults and children, 3) understand that early empiric antibacterial therapy can prevent severe disease and death, 4) request the appropriate confirmatory diagnostic tests and understand their usefulness and limitations, and 5) report probable and confirmed cases of tickborne rickettsial diseases to public health authorities.

Tick bite protection with permethrin-treated summer-weight clothing

The number of tick bites received by individuals wearing either permethrin-treated or untreated summer clothing (T-shirt, shorts, socks, and sneakers) was compared during a controlled indoor study. Pathogen-free nymphal Ixodes scapularis Say were placed on the left shoe, right leg, and left arm of 15 (5/treatment group/d) human volunteers wearing untreated outfits or outfits treated with permethrin either commercially or using a do-at-home treatment kit. The number and location of ticks attached to subjects' skin were recorded 2.5 h postinfestation. Subjects wearing outfits treated with permethrin received 3.36 times fewer tick bites than subjects wearing untreated outfits. No statistically significant differences in number of tick bites were detected between commercial permethrin treatment (19.33%) and the do-at-home permethrin application method (24.67%). The success of permethrin-treated clothing in reducing tick bites varied depending on the specific article of clothing. Subjects wearing permethrin-treated sneakers and socks were 73.6 times less likely to have a tick bite than subjects wearing untreated footware. Subjects wearing permethrin-treated shorts and T-shirts were 4.74 and 2.17 times, respectively, less likely to receive a tick bite in areas related to those specific garments than subjects wearing untreated shorts and T-shirts. Ticks attached to subjects were classified as alive or dead before removal. On subjects wearing untreated outfits, 97.6% of attached nymphs were alive, whereas significantly fewer (22.6%) attached nymphs were alive on subjects wearing repellent-treated outfits. Results of this study demonstrate the potential of permethrin-treated summer clothing for significantly reducing tick bites and tick-borne pathogen transmission.

Health risks in travelers to South Africa: the GeoSentinel experience and implications for the 2010 FIFA World Cup

Using the GeoSentinel database, an analysis of ill patients returning from throughout sub-Saharan Africa over a 13-year period was performed. Systemic febrile illness, dermatologic, and acute diarrheal illness were the most common syndromic groupings, whereas spotted fever group rickettsiosis was the most common individual diagnosis for travelers to South Africa. In contrast to the rest of sub-Saharan Africa, only six cases of malaria were documented in South Africa travelers. Vaccine-preventable diseases, typhoid, hepatitis A, and potential rabies exposures were uncommon in South Africa travelers. Pre-travel advice for the travelers to the 2010 World Cup should be individualized according to these findings.

Tick repellent properties of three Libyan plants

Specimens of Salvadora persica Wallich (Salvadoraceae), Pistacia atlantica Desfontaines (Anacardiaceae), and Juniperus phoenicea L. (Cupressaceae) were collected at The Green Mountain in northeastern Libya. The tick-repellent effects of the essential oils from the plants were evaluated using host-seeking nymphs of Ixodes ricinus L. (Acari: Ixodidae) in the laboratory. Significant tick repellent effects were observed for the oils of all three species, but the duration of action was short. The oils were obtained by steam distillation. Volatile compounds of the essential oils were collected by solid phase microextraction and the constituents were identified by gas chromatographymass spectrometry.

African tick bite fever in elderly patients: 8 cases in French tourists returning from South Africa

BACKGROUND

African tick-bite fever, a tickborne disease caused by Rickettsia africae, is endemic in rural areas of sub-Saharan Africa and in the French West Indies. Most cases reported in the literature occurred in middle-aged, otherwise-healthy persons and corresponded to benign diseases. The course of African tick bite fever in elderly people is less well documented.

METHODS

The medical records of 8 elderly patients infected with R. africae during a trip to South Africa in 2005 are presented to summarize the epidemiologic, clinical, microbiological, treatment, and disease course characteristics.

RESULTS

Eight patients, aged 63-75 years, developed African tick bite fever symptoms after a trip to South Africa. R. africae was grown from cutaneous eschar biopsy specimens obtained from 4 patients, confirming African tick bite fever. We observed unusual findings in this elderly population. Rash was frequent (present in 87.5% of patients), vesicular (in 100% of patients with rash), and often associated with an enanthema (in 50% of patients with rash). Severe clinical manifestations occurred: lymphangitis and myocarditis in 1 patient and suspected brain involvement in 2 patients. We observed severe and long-lasting general symptoms, including fever (in 75% of patients), chills (87.5%), asthenia (50%), anorexia (50%), and weight loss (12.5%). With doxycycline therapy, the outcome was favorable in all cases, but complete recovery was slow.

CONCLUSION

Ecotourism to sub-Saharan Africa is expanding, and people of advanced age, often with underlying chronic diseases, account for an increasing proportion of travelers. African tick bite fever appears to be more symptomatic in this population. Recommendations advising personal prophylactic measures to prevent tick bites in travelers to regions of endemicity may be particularly important for elderly individuals.

From population structure to genetically-engineered vectors: New ways to control vector-borne diseases?

Epidemiological studies on vectors and the pathogens they can carry (such as Borrelia burgdorferi) are showing some correlations between infection rates and biodiversity highlighting the "dilution" effects on potential vectors. Meanwhile other studies comparing sympatric small rodent species demonstrated that rodent species transmitting more pathogens are parasitized by more ectoparasite species. Studies on population structure and size have also proven a difference on the intensity of the parasitic infection. Furthermore, preliminary results in genetic improvement in mosquitoes (genetic markers, sexing, and genetic sterilization) will also increase performance as it has already been shown in field applications in developing countries. Recent results have greatly improved the fitness of genetically-modified insects compared to wild type populations with new approaches such as the post-integration elimination of transposon sequences, stabilising any insertion in genetically-modified insects. Encouraging results using the Sterile Insect Technique highlighted some metabolism manipulation to avoid the viability of offspring from released parent insect in the wild. Recent studies on vector symbionts would also bring a new angle in vector control capabilities, while complete DNA sequencing of some arthropods could point out ways to block the deadly impact on animal and human populations. These new potential approaches will improve the levels of control or even in some cases would eradicate vector species and consequently the vector-borne diseases they can transmit. In this paper we review some of the population biology theories, biological control methods, and the genetic techniques that have been published in the last years that are recommended to control for vector-borne diseases.

Twelve-hour duration testing of cream formulations of three repellents against Amblyomma americanum

The repellent efficacies of the U.S. military repellent 33% N,N-diethyl-3-methylbenzamide (deet), 10% and 20% (1S, 2'S) 2-methylpiperidinyl-3-cyclohexene-1-carboxamide (SS220) and 10% and 20% 1-methyl-propyl-2-(hydroxyethyl)-1-piperidinecarboxylate (Bayrepel) cream formulations on human volunteers against the lone star tick Amblyomma americanum (L.) were evaluated in a simulated forest floor environment over a 12-h testing period. At 2-h intervals, volunteers, with repellent applied in a 5-cm-wide band around each ankle, stood for 5 min in plastic tubs containing leaf litter and 100 host-seeking A. americanum nymphs. Ticks were allowed to remain on a volunteer's feet and ankles for an additional 5 min after the volunteer exited the tub. All repellent formulations provided high levels of protection for the entire 12 h. No ticks crossed 5-cm-wide bands of 20% SS220 and Bayrepel during any challenge, and thus 100% protection was afforded throughout the test. These formulations showed a long-lasting efficacy hitherto unknown in tick repellents intended for use on human skin.