Scabies is evolving evading treatments involving Permethrin


Scabies is a parasitic infestation caused by tiny mites called Sarcoptes scabiei. These mites burrow into the skin and lay eggs, causing an intense itching sensation. Scabies is highly contagious and can easily spread from person to person through close contact, such as sexual contact or sharing bedding and clothing.

The itching caused by scabies can be severe and relentless, leading to scratching and damage to the skin. This can result in skin lesions, crusting, and secondary bacterial infections. In some cases, scabies can also lead to the development of nodules or thickened skin in areas where the mites have burrowed.

Scabies can also cause psychological effects, including anxiety, depression, and social withdrawal. The constant itching and the fear of infecting others can have a significant impact on a person’s mental health and well-being.

In rare cases, scabies can also lead to more serious complications, such as impetigo (a bacterial skin infection), cellulitis (a bacterial infection of the skin and soft tissues), or sepsis (a life-threatening infection that can spread throughout the body).

To diagnose scabies, a doctor will examine the affected area of the skin and look for the characteristic burrows created by the mites. Treatment typically involves applying a topical medication, such as permethrin or ivermectin, to the affected areas of the skin. In some cases, oral medications or prescription creams may be necessary.

Overall, scabies is a highly contagious parasitic infestation that can cause significant damage to the skin, as well as psychological distress and the potential for serious complications. Early diagnosis and treatment are essential to prevent the spread of infection and minimize the negative impacts on a person’s health and well-being.

The damage caused by scabies can be more severe in certain populations, such as people with weakened immune systems or elderly individuals. In these cases, scabies can lead to a more widespread infestation and more severe symptoms.

Additionally, there are different species of scabies mites that can affect different types of animals, including dogs, cats, and other domesticated animals. These species of mites are not typically transmissible to humans, but they can cause significant skin irritation and damage to the animals they infest.

In humans, scabies is typically spread through close personal contact, such as skin-to-skin contact or sexual contact. It can also be spread through the sharing of clothing, bedding, or towels, particularly in crowded environments such as nursing homes or prisons.

The standard treatment for scabies involves applying a topical cream containing permethrin, which kills the mites and their eggs. However, recent studies have shown that scabies mites are now evolving to become resistant to permethrin, making it more difficult to treat the infection effectively.

This is a worrying development because scabies can lead to complications such as bacterial skin infections, cellulitis, and even sepsis, especially in people with weakened immune systems.

The evolution of scabies mites to evade standard treatments is not a new phenomenon. In fact, resistance to other topical creams, such as lindane and benzyl benzoate, has been documented in the past. However, the use of permethrin has been the gold standard for scabies treatment for many years, and the emergence of resistance to this medication is cause for concern.

There are several factors that have contributed to the development of permethrin-resistant scabies mites. One of the main reasons is the widespread and indiscriminate use of permethrin in many parts of the world, particularly in areas where scabies is endemic. This has created an environment in which the mites are constantly exposed to the drug, leading to the development of resistance over time.

Another factor is the use of permethrin at suboptimal doses, either due to incorrect application or dilution of the cream. This can create selective pressure on the mites, allowing those that are more resistant to the drug to survive and reproduce.

Additionally, the genetic diversity of scabies mites has also played a role in the development of resistance. Studies have shown that different populations of mites from different regions of the world have different levels of resistance to permethrin, suggesting that the genetic makeup of the mites is a factor in their ability to evolve resistance.

The evolution of permethrin-resistant scabies mites presents a significant challenge for healthcare providers, who must now find alternative treatments to combat this condition. One possible solution is the use of combination therapies that include other drugs, such as ivermectin or sulfa-based antibiotics, which have been shown to be effective against scabies in some cases.

However, these drugs also have their limitations, such as potential side effects and the development of resistance over time, and more research is needed to determine their long-term efficacy.

Another approach is to develop new drugs that target different aspects of the scabies mite’s life cycle, such as its digestive system or nervous system. This could help to overcome the mite’s ability to evolve resistance to a single drug and provide more effective and durable treatments.

Scabies is primarily caused by the human-specific species of mite called Sarcoptes scabiei var. hominis. However, there are other closely related species of scabies mites that can infest animals, such as dogs, cats, and other mammals. These different species of scabies mites have some variations in their morphology, biology, and host specificity.

  1. Sarcoptes scabiei var. hominis (human scabies mite): This species of mite is adapted to infest humans and is the most common cause of scabies in people. Female mites burrow into the skin and lay eggs, causing intense itching and skin damage. The life cycle of Sarcoptes scabiei var. hominis typically lasts 3-4 weeks, during which the mites go through several developmental stages.
  2. Sarcoptes scabiei var. canis (dog scabies mite): This species of mite is adapted to infest dogs and is a common cause of scabies in dogs. It can also infest other animals, such as foxes, coyotes, and bears. While Sarcoptes scabiei var. canis is closely related to the human scabies mite, it is not typically able to complete its life cycle on humans and will usually die off without reproducing.
  3. Sarcoptes scabiei var. felis (cat scabies mite): This species of mite is adapted to infest cats and is a common cause of scabies in felines. It can also infest other animals, such as ferrets and other small mammals. Similar to the dog scabies mite, Sarcoptes scabiei var. felis is not typically able to complete its life cycle on humans and will usually die off without reproducing.

In recent years, there have been reports of mutant scabies mites that are resistant to the standard treatments involving permethrin, which is the most commonly used medication for treating scabies. These mutant mites, also known as “super scabies” or “permethrin-resistant scabies,” are believed to have developed genetic mutations that allow them to survive exposure to permethrin, rendering the standard treatment less effective.

These mutant scabies mites pose a challenge in the management and control of scabies, as they may require alternative treatment approaches, such as higher concentrations of permethrin, other medications, or combination therapies. It underscores the importance of ongoing research and surveillance to better understand the genetics and biology of scabies mites, including any emerging resistance mechanisms, in order to develop effective strategies for their control and prevention.

Norwegian scabies is a rare skin infestation by the mite Sarcoptes scabei var hominis. This condition typically presents with widespread, crusted lesions associated with hyperkeratotic scales. The elderly, the debilitated, and patients who are immunocompromised are at risk for this more severe form of scabies. As with many dermatologic conditions, the diagnosis can be challenging. This article is intended to
provide a broad overview of this rare skin infestation to the emergency physician or primary care provider. Awareness, recognition, confirmation of diagnosis, initiation of rapid treatment and preventive measures may help to reduce widespread infestations in susceptible populations. ( )

Fig.1 Norwegian scabies in a handicapped, elderly nursing home patient.

In conclusion, the evolution of permethrin-resistant scabies mites is a serious public health concern that requires urgent attention. Healthcare providers and policymakers must work together to develop new strategies and treatments that can effectively manage this condition and prevent its spread. Failure to do so could have significant consequences for millions of people around the world who suffer from this debilitating and contagious infection.

Here are some sources for more information on scabies and scabies mites:

These sources provide information on the biology, transmission, diagnosis, treatment, and prevention of scabies, as well as the development of drug resistance in scabies mites.


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