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Therapeutics in Dermatology
A reference textbook in dermatology

Arthropod stings and bites

5 June 2012, by DOMPMARTIN A.

Arthropods are invertebrate animals whose bodies are divided into segments covered with a cuticle or outer skeleton. Depending on their mouthparts, they can be divided into the chelicerates which include arachnids (spiders, scorpions, mites, ticks and harvest mites) and the mandibulates or antennates which includes both winged and other insects and millipedes. A distinction is generally made between bites, in which mouthparts are used to inoculate venom, and stings, for which a specific apparatus or "stinger" generally situated in the posterior part of the animal is used.

1 - GENERAL

Arthropods can transmit cytotoxic or allergenic substances and cause a local or locoregional infection through their sting or bite but, most importantly, some of them are active or passive carriers of disease. 

1.1 - PREVENTION

Some stings can be prevented by simple precautionary measures: 

– never walk barefoot in the grass;

– avoid handling flowers and food outdoors;

– wear clothing that covers the arms and legs.

In areas where malaria, dengue fever and chikungunya (Bulletin Epidémiologique Hebdomadaire BEH 24/2007) are endemic, more stringent measures are required, with the combined use of insect repellents on the skin, residual insecticides on clothing and mosquito nets and mosquito coils:

– at night-time, children’s beds should be protected by mosquito nets impregnated with residual insecticides (deltamethrin, permethrin). Electric insecticide vaporizers (but beware of power cuts) and smoke coils will also provide a measure of protection;

– air conditioning makes mosquitoes less aggressive but does not prevent them from biting;

– repellants (or insectifuges), applied regularly to the skin (but only to exposed areas, paying particular attention to the feet and ankles and avoiding the mucous membranes and open cuts) will keep arthropods away. Which one to use depends on the active ingredient, the concentration, duration of action and the age of the subject. The product used must also be appropriate for the country in which it is being used: for example, a less concentrated product will be required by someone spending a few hours in the garden in France than someone on a trekking expedition in a malaria-infested zone.

Repellents and insecticides are covered by European "biocide" legislation. France’s national health authority, the HAS, does not recommend them for children aged less than 30 months. (BEH 24/2007).

The most effective are:

– diethyltoluamide (DEET), which is effective against tropical mosquitoes at a concentration of 50 percent and but works at lower concentrations in France. The 50 percent concentration is used for both adults and children > 12 years old; lower concentrations, i.e. 20 to 35 percent, can be used for children aged between 30 months and 12 years old, unless there is a history of convulsions. On average, these products protect the wearer for 5 hours. It may damage plastics, varnish, watch faces and glasses lenses;

– a 25 percent concentration of hydroxylethyl-isobutil piperidine carboxylate (KBR 3023) provides effective protection against tropical mosquitoes for an average of 5 hours. It is also suitable for children > 30 months old.

– ethyl -butyl-acetyl-amino-propionate (IR 3535) provides an average of 2 hours of protection at concentrations of 20 to 35 percent. It is can be used for children aged 30 months and over. It is the only repellent authorised by the HAS for pregnant women;

– the menthol derivative p-menthane diol (Citriodiol), is the most effective of the natural repellents and works at concentrations of 30 and 40 percent for an average 4 hours. It can also be used in children aged 30 months old.

Repellants are not as effective against sandflies (phleobotominae) and stink bugs and are ineffective against hymenoptera.

Residual pyrethroids are recommended for impregnation of materials: deltamethrin or permethrin for mosquito nets and tents and permethrin for clothing. Permethrin is effective against mosquitoes from concentrations of 150 mg/m2 and against harvest mites and ticks at a concentration of 300 mg/m2. In addition to their knock-down effects, the pyrethroids also have insectifuge potential. An industrial process has been developed for long-term impregnation (4 to 5 years) of mosquito nets. Clothes are either sprayed or soaked; the effects only wear off after several washes.

1.2 - CURATIVE TREATMENT

Bites and stings can cause an itchy spot, an infected wound, blisters or necrosis. The treatment is the same as for any cut: checks must be made to ensure that the patient is up to date in his/her tetanus vaccinations, the area should be disinfected with an antiseptic (chlorhexidine, hexamidine or iodinated polyvidone), dead tissue should be removed, blisters should be pierced and disinfected, taking care to preserve the skin covering and the sting, if there is one, should be removed. These wounds are quick to become infected, particularly in tropical countries, and should be cared for promptly to prevent hypodermitis or erisypelas for which antibiotics are required; the antibiotics most commonly given for these conditions are pristinamycin (3 g/day) or amoxicillin (3 g/day). When the animal is a Rickettsiosis or Borreliosis carrier, specific antibiotics are prescribed (see section on cutaneous Borreliosis and Rickettsiosis).

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