What's eating you?

July 1, 2006

National report - To itch is human and to successfully treat - divine.

National report - To itch is human and to successfully treat - divine.

Arthropods and humans have always coexisted, the latter seemingly receiving the shorter end of the stick.

Dirk M. Elston, M.D., of the Geisinger Medical Center in Danville, Pa., discusses which infestations cause humans to itch and what can be done about them.

Treatment of bites ranges from topical antipruritic products like Sarna lotion (Stielfel) or Rhuli gel (containing camphor and menthol) to topical, systemic and intralesional corticosteroids, the latter being useful for the treatment of persistent delayed-type hypersensitivity reactions.

Classic protection

Classic protection against bites include avoidance and protective clothing.

Years of research offers a slew of chemical repellents including diethyl-toluamide (DEET), dimethyl phthalate, dimethyl carbate, ethyl hexanediol, butopyronoxyl (indalone), benzyl benzoate and permethrin (Permanone, Repel). Each of these products has varying levels of efficacy and safety. Toxic encephalopathy, especially in infants and children, anaphylactic reactions and even deaths have occurred with the use of DEET.

"DEET dermatitis is an irritant dermatitis of the face, neck and flexures. In my experience, it is associated with formulations containing a high percentage of DEET. A new long acting DEET cream has been developed for the military, containing only 30 percent DEET. Dermatitis is much less of a problem with this product," Dr. Elston explains.

Dr. Elston says that flying insects and crawling arthropods can be addressed with long-acting DEET cream/lotion (Military formulation, Amway Hour Guard), as well as treating the clothes with permethrin. He suggests that for children and adults with sensitive skin, a product with 10 percent to 30 percent or less DEET is appropriate.

Fleas, lice

When combating flea infestation, treating the environment seems more effective than using repellents.

Dr. Elston says that permethrin/ methoprene products and boric acid as well as organophosphate and carbamate insecticides can be very helpful. Newer agents include oral lufenuron for dogs and cats, injectable long-acting lufenuron for cats and topical fipronil.

The pubic (Phthirus pubis), head (Pediculus humanus capitis), and body (Pediculus humanus corporis) louse are common human ectoparasites, and classrooms remain the major focus for the spread of the infestation. Their eggs can be found on hairs, scalp and clothing fibers. Body lice are known to transmit typhus, trench fever and relapsing fever.

Dr. Elston says that the treatment of body lice centers on treatment of the infected clothing. Laundering and ironing may be adequate, but is not always possible for those living under less-than-sanitary conditions. He therefore suggests treatment of clothing with DDT, permethrin or fumigants. He says that permethrin-treated clothing has been shown to offer protection against body louse infestation, even after 20 wash cycles.

Mechanical removal

As Arthropods ' resistance to commonly used agents becomes widespread, it is important to note that mechanical removal of lice can be an important adjunctive "chemical-free" form of treatment.

Many schools have adopted a "no nit" policy, requiring mechanical removal of all nits before a child may return to school, using nit combs and other methods. No nit policies exclude many children from school.

"Permethrin (NIX, Heritage) has proved to be an effective agent for the treatment of head and pubic lice," Dr. Elston says. "Because resistance is developing, some communities use different agents on a rotating basis to slow the development of resistance. It has been suggested that pyrethrins and piperonyl butoxide (RID, Bayer, A-200, Hogil) and malathion may be more effective against nits than lindane. Newer agents that hold promise are those that kill lice via asphyxiation."