Take a bite out of infestations

That creepy, crawly sensation. The itch. The sores. Bugs not only invade your patients’ space and their skin, they can be challenging to identify and treat. Raegan D. Hunt, MD, PhD, will give facts and exterminate rumors surrounding mite infestations and arthropod bite reactions during Friday’s session “Infestation Situations: Updates on Bothersome Bugs (U017).”

Raegan D. Hunt, MD, PhD.

What just bit me?

Dr. Hunt will discuss the diagnosis and management of skin disease by mites and insects, including head lice, scabies, and flying insects. In spotlighting clinical findings that occur in particular patient populations, Dr. Hunt will review bedside microscopy as well as emerging treatment resistance trends and recently approved therapies.

“While it is typically not possible to diagnose the type of insect responsible for a specific bite based solely on the appearance of the lesions, there may be clues from the history and the arrangement and distribution of the bites,” Dr. Hunt said. “For example, fleas do not have wings, but they can jump about 8 inches. If someone has numerous erythematous itchy papules on lower legs only, especially near the ankles, and has a pet cat or dog, then fleas are the likely cause.”

They see you when you’re sleeping

Another example, she said, is bed bugs. Bed bug bites tend to manifest as linear or triangular arrays of edematous pink papules, she said.

“This is known as the ‘breakfast, lunch, and dinner’ sign. It is presumed that this pattern results from the bed bug’s feeding being interrupted by movement of the patient, and as such, the bug moves on to a new, nearby feeding site. Most often, bed bugs bite on skin exposed at night during sleep.”

As anyone knows, biting bugs can be found both indoors and outdoors. Flying insects, which bite or sting, are more commonly found outside, while bed bugs are an indoor menace and remain well hidden. Some insects travel indoors on pets, such as fleas, she said.

Where the wild things are

Unfortunately, certain patient populations are more prone to severe infestations, according to Dr. Hunt. For example, people who are immunocompromised, elderly, or disabled may be more susceptible to crusted scabies, an itchy infestation in which numerous mites (Sarcoptes scabieivar. hominis) burrow into the skin. Scabies spreads by skin-to-skin contact and can spread easily in crowded conditions, nursing homes, and daycare settings.

“This population may develop crusted scabies, a more severe version of scabies characterized by infestation with many more mites than in a typical scabies infestation (up to 2 million per patient),” Dr. Hunt said. “Crusted scabies is much more contagious, due to the high density of mites. In cases of crusted scabies, scabies may be transmitted with brief skin-to-skin contact or may even be transmitted indirectly via skin shed onto furniture or clothing which contains many mites.”

Netting the best treatment

Treatment varies by infestation or bite, of course. For scabies, the gold standard treatment remains permethrin 5% cream overnight, repeating at 1 week, she said. Based on available evidence, a recent Cochrane review showed that oral ivermectin, which is off label in the U.S. for the indication of scabies but used in many other countries, was not superior to topical permethrin 5% cream.

For outdoor biting insects, the best protection remains a DEET insect repellant, she said. The American Academy of Pediatrics (AAP) and the CDC recommend DEET 20%-30% to exposed skin areas as directed per packaging for individuals older than two months of age.

In the U.S. in recent years, lice have become highly resistant to pyrethroids, Dr. Hunt said.

“This means that in many cases the over-the-counter lice treatments no longer work. There are several available FDA-approved medications that effectively treat pyrethroid-resistant head lice,” she said. “Laborious nit-picking is also an option, if done thoroughly.”

Dermatologists should be on the watch for papular urticaria, an insect bite hypersensitivity reaction that is common in young children, she said. This condition tends to recur seasonally for a few years and new insect bites appear to induce delayed type hypersensitivity at old sites. Dr. Hunt recommends daily, non-sedating antihistamines and applying insect repellants and topical steroids to itchy bites to help manage this condition.

In general, Dr. Hunt said good observation and detective work can provide clues as to the insect in question and it may be possible to eradicate the source of the bites.