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Prevention of arthropod-related disease.

Arthropods of medical importance include vespids, ticks, mosquitoes, mites, flies, and fleas. They spread illness as disease vectors, are associated with lethal allergic reactions, and produce potentially deadly toxins. Strategies for prevention of illness include avoidance, vector reduction programs, chemoprophylaxis, and repellents. Strategies must be tailored to regional risks.

Anaphylaxis↗

Anopheles gambiae (Diptera: Culicidae) oviposition in response to agarose media and cultured bacterial volatiles.

Anopheles gambiae s.s. Giles accepted a range of agarose gels, varying from 0.5 to 8% (wt:vol), for oviposition; laid more eggs on 0.5% agarose gels than on moist filter paper or on drier agarose; and laid equal numbers of eggs on 0.5% agarose gels and distilled water. Larvae hatched on agarose gel substrates and crawled onto the surface of moist agarose gels, but they tended only to burst the egg cap and remain within the egg case on drier gels. A mixture of cultured bacteria, originating from a natural larval habitat of An. gambaiae s.s. in western Kenya, was classified by 16S rDNA sequence analysis, and then this mixture or individual colonies from it was used as odor sources in ovipositional experiments with agarose substrates. Of 61 sequences from a mixed clone sequence library, most (78%) were Pseudomonas strains, whereas the remainder were Stenotrophomonas, Enterobacter, Pantoea, Klebsiella, Acinetobacter, Aeromonas, and Bacillus. Oviposition was significantly reduced when mixtures of bacterial colonies of these strains, or a lawn of colonies of a field isolate of S. maltophilia, was presented. Oviposition was neither reduced nor enhanced when field isolates of Pseudomonas putida or Pseudomonas alcaligenes colonies were presented. These results suggest that gravid An. gambiae females are sensitive to bacterial-derived odors emanating from cultured bacteria from natural larval habitats and that some bacterial odors may be repellent.

Animals↗

Response of Culicoides sonorensis (Diptera: Ceratopogonidae) to 1-octen-3-ol and three plant-derived repellent formulations in the field.

The potential attractant 1-octen-3-ol and 3 potential repellents were assayed for activity for Culicoides sonorensis, the primary vector of bluetongue virus in North America. Collections using octenol were low, but numbers in suction traps were greater in the high-octenol treatment (11.5 mg/h) than in the low-octenol treatment (1.2 mg/h) or unbaited control for both sexes. Collections using high octenol, CO2 (approximately 1,000 ml/min), or both showed octenol alone to be significantly less attractive than either of the CO2 treatments and that octenol did not act synergistically with this level of CO2. A plant-derived (Meliaceae) extract with 4.5% of active ingredient (AI) (Ag1000), heptanone solvent, Lice free (2% AI from plant extracts in water), Mosi-guard with 50% Eucalyptus maculata var. citriodora Hook extract, and N,N-diethyl-m-toluamide (deet) were applied to polyester-cotton coarse mesh nets and deployed in conjunction with suction light traps plus CO2. Collections in the trap with deet were 66% lower (P < 0.05) than the heptanone and 56% (P > 0.05) less than the untreated (negative) control. Relative to deet, collections in the traps with the lice repellent, Ag1000, and Mosi-guard were reduced by 15, 34, and 39%, respectively (P > 0.05). The method has promise for field screening of potential repellents before on-animal testing.

Animals↗

Laboratory evaluation of two commercial repellants against Leptotrombidium fletcheri (Acari: Trombiculidae).

Two commercial repellants were evaluated in the laboratory against Leptotrombidium fletcheri chiggers. The active ingredient in one was DEET and in the other was citrus oil. Excito-toxicity effect was studied and it was determined by the time ("escape time") chiggers took to move off filter papers treated with the repellants. All chiggers exposed on filter papers treated with DEET died and did not move off the treated papers. None of the chiggers that were placed on papers treated with citrus oil were killed. Escape times on papers treated with a 2-sec spray of citrus oil were longer than those for the 4- and 8-sec sprays. The weights of citrus oil deposited increased with increasing spray times. Electron microscopy showed that the repellants had no effect on the texture of the filter papers. It was concluded that the spray containing DEET was more effective; however, both repellants should be further evaluated under field conditions for protection against chigger bites.

Animals↗

Topical mosquito repellents XIII: Cyclic analogs of lactic acid.

Numerous cyclic analogs of lactic acid were synthesized to ascertain whether they might act as agonists of antagonists of lactic acid, a known attractant for mosquitoes. These compounds were evaluated with an in vitro blood-feeding test system and an in vivo cloth test. Two of the compounds in the blood-feeding test system showed biphasic results, acting as attractants at low concentrations and as repellents at higher concentrations. Several compounds (III, V, VII, and X) repelled Aedes aegypti mosquitoes in the blood-feeding test system. However, in the in vivo cloth test system, only III repelled the mosquitoes significantly.

Aedes↗

Tick repellents II: N-substituted azacyclopentanones and azacyclopentenones.

Several N-substituted azacyclopentanones and azacyclopentenones were synthesized and evaluated as repellents for the brown dog tick Rhipicephalus sanguineus. Several of these compounds were more effective in our test system than were the standard repellents, N,N-diethyl-m-toluamide and butopyranoxyl.

Animals↗

An olfactometer for discriminating between attraction, inhibition, and repellency in mosquitoes (Diptera: Culicidae).

We constructed an olfactometer that differentiates and quantifies attraction, inhibition, and repellency to mosquitoes. Using this device, 22 formulations of various chemicals on gauze pads and 8 dilutions of DEET on skin were tested. Four novel formulations were discovered acting as true repellents, whereas DEET did not act as a true repellent but as an inhibitor.

Aedes↗

Chemical odorant of colonial seabird repels mosquitoes.

The crested auklet, Aethia cristatella, emits a class of aldehydes shown to be potent invertebrate repellents when used by heteropterans against their predators. Our aim was to determine the efficacy of these aldehydes against mosquitoes in the laboratory. Synthetic analogues of the auklet odorant were strongly repellent to mosquitoes in controlled laboratory trials. Furthermore, the efficacy was similar to previous reports for commercial mosquito repellents. These results, in combination with a previously published study, show that constituents of the aldehyde odorant are broad spectrum in efficacy against ectoparasitic arthropods of birds. Our report is the first empirical evidence for an endogenous mosquito repellent in birds.

Aedes↗

Absolute configuration of a new mosquito repellent, (+)-eucamalol and the repellent activity of its epimer.

(+)-Eucamalol (1) and (-)-1-epi-eucamalol (2) were synthesized from (S)-(-)-perillaldehyde to determine the absolute configuration of 1, the structure of natural (+)-eucamalol being determined to be (1R,6R)-(+)-3-formyl-6-isopropyl-2-cyclohexen-1-ol. (+)-Eucamolol (1) and its 1-epimer (2) exhibited significant repellent activity against Aedes albopictus, and inhibited its feeding as well as DEET.

Aedes↗

Repellency of IR3535, KBR3023, para-menthane-3,8-diol, and deet to black salt marsh mosquitoes (Diptera: Culicidae) in the Everglades National Park.

IR3535, KBR3023, para-Menthane-3,8-diol (PMD), and deet were evaluated in controlled studies with human subjects (n = 5) for repellency to black salt marsh mosquitoes (Ochlerotatus taeniorhynchus Wiedemann), in the Everglades National Park, FL. In tests of 6-h duration, with an average mosquito biting pressure on exposed forearm skin of 19.5 (+/- 13.7) bites per minute, the mean percent repellencies (SE) for IR3535, KBR3023, PDM, and deet was 88.6 (3.2), 97.5 (1.7), 89.2 (2.9), and 94.8 (2.5), respectively. Mean complete protection times (SE) for IR3535, KBR3023, PMD), mean deet were 3.0 (1.0), 5.4 (0.6), 3.8 (1.4), and 5.6 (0.5) h, respectively. Untreated (ethanol) controls provided 0% repellency. When mosquito biting rates on the untreated forearm skin of repellent-treated subjects were compared with biting rates on the forearm skin of control subjects, the former were 23%-40% lower early in tests and as much as 22% higher late in tests. These differences cast doubt on the technical merit of test designs comprising evaluation of more than one repellent at a time on the same human subject while underscoring the importance of untreated subjects as negative controls in field repellent bioassays.

Activity Cycles↗

Reduction of mosquito (Diptera: Culicidae) attacks on a human subject by combination of wind and vapor-phase DEET repellent.

In a Central Michigan wetland setting, air drawn through a DEET-impregnated screen using an electric fan and projected toward a human subject significantly reduced mosquito orientation by 74%, landing by 75%, and probing by 70%, relative to no applied wind or DEET. The DEET vapor effect was significant as revealed by a statistically significant wind/DEET interaction. The wind speed at the downwind human subject was 0.6 m/s and the DEET vapor concentration was estimated at 2 microg/liter air. We suggest a combination of directed wind and volatile repellent might be developed as a mosquito deterrent strategy for the backyard setting.

Animals↗

Prevention of Lyme disease.

Lyme disease and the use of tick repellents and physical protective measures to prevent the disease are discussed. Lyme disease is a multiple-organ-system, immune-mediated inflammatory disorder transmitted by the bites of ixodid ticks infected with Borrelia burgdorferi. An individual is at greatest risk for infection when a tick has been attached to the skin for more than 24 hours. Lyme disease occurs in three stages and may affect the skin, nervous system, cardiac system, and joints. Antimicrobials used in management consist primarily of penicillins, cephalosporins, tetracyclines, and erythromycin. Tick repellents are divided into those applied to the skin and those applied to clothing. Skin repellents include N,N-diethyl-meta-toluamide (DEET), 2-ethyl-1,3-hexanediol, and dimethyl phthalate. Permethrin is by far the most effective clothing repellent. DEET plus a permethrin-containing clothing repellent offers the best overall protection. The adverse effects of repellents are minimal, but cases of hypersensitivity have been reported, especially in children. Physical measures to prevent tick bites include avoiding tick-infested areas, wearing light-colored clothing for easy identification of crawling ticks, regularly checking the body and pets for ticks, wearing protective garments and closed-toed shoes, and removing attached ticks promptly by using tweezers or forceps to apply a steady upward pull. A vaccine for the active immunization of humans against Lyme disease remains to be developed. Although antimicrobial therapy is available for persons with Lyme disease, the best approach for those who may be exposed to infected ticks is to apply topical skin or clothing repellents and to practice common-sense measures of physical protection.

Animals↗