Scabies: a parasite of the past now frequent again

What is the cause of scabies?

Mites are tiny parasites that are invisible to the naked eye. They have adapted over millennia to live on both animals and plants, including plant derivatives. On human skin, the Sarcoptes scabiei mite can be found and, although it is not known at which point it began to live in unison with humans, the fact remains that its existence is inextricably linked to humans. In other words, Sarcopts scabiei survives only on humans and not on other animals.

Who can be affected by scabies?

In the 1700s, for example, it was practically the norm to have scabies or lice at some point or another. Today, the thought of living with such parasites is automatically associated with poor hygiene and/or destitution. While these parasites can affect anyone, regardless of their social status, they are spread more easily within unhygienic, close living quarters, or through having many sexual partners.

How is scabies transmitted?

Scabies is transmitted through interhuman contact, either directly (intimacy) or indirectly (bed sheets or shared clothing). For example, there are many recorded cases of individuals becoming infected with scabies following stays in luxury hotels in popular tourist destinations. Similarly, patients with scabies who attend an outpatient clinic can easily spread the parasite before hospital staff have even realized there is an infestation and, therefore, before they can perform a deep-clean of the area.

What are the symptoms of scabies?

Itching is the main symptom of scabies and usually appears nocturnally two weeks after infection. At first, the abdomen, buttocks and genitals will become itchy, before this itching spreads up the body. The head is the only area that will not become itchy. If scabies is not diagnosed and treated promptly, the itching may become so unbearable that it is difficult to sleep.

Diagnosing scabies

A dermatologic examination is usually sufficient to make a diagnosis of scabies. In cases where there is any doubt, the dermatologist will perform a microscopic search for mites. Here, the dermatologist will take a scalpel razor blade to remove flakes of skin in areas that have been colonized by scabies, before analyzing them under a microscope.

How to treat scabies

There are various commercially available anti-parasitic products that can be used to treat scabies. The most commonly used compounds are:

• Ivermectin
• Permethrin
• Benzyl benzoate

Ivermectin is an antiparasitic drug that is used extensively in veterinary medicine. As a scabies treatment, it can be used either orally or topically as a cream. Despite having considerable acaricidal properties, ivermectin is not a widely used scabies treatment because the topical product is not registered for this specific parasite (but for acne rosacea), while the oral option has a fairly high level of toxicity. Permethrin, a synthetic derivative of pyrethrum, can be used as a topical cream at a concentration of 5%. However, over the past few years, there have been increasing numbers of reports of the scabies mite becoming resistant to permethrin. Moreover, individuals who are prescribed permethrin are still parasitized even after treatment, meaning they are still infectious to others. Finally, as permethrin cream often causes considerable skin irritation, it can be difficult to determine if this is a reaction to the cream, or the presence of resistant scabies mites. During treatment, the skin will not tolerate new treatments in the immediate future, meaning that dermatologists are particularly cautious to prescribe permethrin. Benzyl benzoate is a derivative rich in acaricidal properties and can be found in the bark of some legumes and within peru balsam. It is available as an oil, has a notable odor and, while it is often added to creams, it is better for a pharmacist to prepare the solution on the spot. The prescription is as follows and the solution should be stored in a 100ml bottle: R/ Benzyl benzoate 30g Edible seed oil 70g

Label: external use only

Apply the solution to the whole body every evening, avoiding the head and scalp. Repeat over four consecutive evenings. Seven days after the final application, make one additional evening application. A 100ml bottle provides around five applications, meaning that around 20ml should be used per application. In the morning, wash the body with a mild detergent. For children under ten years of age, apply benzyl benzoate for two consecutive days instead of four. The amount to be applied should be proportionate to the age of the child. For example, the bare minimum application should be enough to cover the entire body and, for children up to two years of age, should include the feet and hands, areas in which the mite often nests. No other precautions are necessary and the scabies will soon resolve itself.
The parasite will survive for only one or two days outside of a human host. After the fourth day of treatment, change bedsheets, towels and bathrobes. There is no need to boil, wash clothing or linens, nor is there a need to disinfect the home.

Conclusion

Scabies is a relatively common infestation today. Recognizing scabies early and treating it with an effective remedy benefits both the patient and the community beyond.