Head Lice Develops Resistance to Typical Medications

Key Takeaways:

• Most head lice prevalent in North America have developed a gene mutation, giving them resistance to standard over-the-counter treatments, which leads to a growing public health concern.
• The current resistance status shows over 88% of lice in the United States and Canada bear the protective TI mutation, fostering resistance against standard permethrin medications available over-the-counter.
• Due to the increasing resistance of head lice, the need for new treatments is critical. There are new drugs available on the market providing multiple mechanisms of action, offering more effective treatments.
• While new treatments are more effective, they tend to come at a higher cost as they are prescription medications, posing a challenge for the healthcare system to provide affordable, effective solutions.

A new study has raised concerns about the growing resistance of head lice prevalent in North America to standard over-the-counter treatments. It has been discovered that most head lice now possess a gene mutation rendering them resilient to these common treatments.

Head Lice Infestation – A Significant Public Health Issue

The infestation of head lice is no minor threat to public health. Researchers suggest that it accounts for around 10% of all American students’ missed school days. The main symptoms are intense itching and secondary infections, indicating exposure.

An unfortunate reality is that persistent exposure to a singular form of treatment has resulted in the survival and propagation of a subset of head lice with “knockdown resistance” in the form of the TI genetic mutation. These lice can withstand exposure to permethrin, a component found in most nonprescription head lice drugs and known as “pyrethroid” compounds.

The Rise of Resistant Insects

John Clark, a co-author of the study and professor of environmental toxicology and chemistry at the University of Massachusetts, Amherst, emphasizes that this is not contentious. However, it’s a problem that has been growing for about 20 years. New research indicates that almost all head lice are now knockdown resistant, leading to a substantial increase in resistant insects in the United States and other countries.

This discussion is featured in the March issue of the Journal of Medical Entomology.

The Seed of Resistance

In the early 1990s, over-the-counter permethrin-based medications became widespread, designed to eliminate lice by disrupting their nervous system. Despite this, decades before, the seeds of permethrin’s forthcoming inefficacy were planted. In the post-WWII period, DDT pesticide was first exposed to much of the population as a solution for body lice infestations.

According to this study, head lice inadvertently got caught up in the process, allowing a surviving population to increasingly and silently bear the protective TI mutation, decades before the release of permethrin products.

Current Resistance Status

In light of this development, the researchers endeavored to assess the constant resistance status of North American head lice. Their approach involved conducting genetic testing on lice samples, collected from 32 mostly urban locations throughout the United States and Canada.

Their findings revealed that over 88% of lice found in both countries have the specific TI mutation, which triggers nerve insensitivity and fosters resistance against standard permethrin medications available over-the-counter.

In Dire Need of New Treatments

With these growing concerns, researchers conclude that the need for fresh head lice treatments is critical. Considering that Europe and South America have ceased using these pyrethroid compounds years ago, the United States should be more inclined to find effective alternatives.

Professor Clark noted that although these compounds are not essentially harmful, using only one mode of action to treat a pest population for an extended period is not advisable. Hence, these compounds are no longer effective.

The Way Forward

Despite these challenges, there is hope. Over the past three years, new drugs have entered the market, offering various forms of compounds and mechanisms. These new alternatives, already commercially available, can provide redundant killing. Meaning, if one compound doesn’t work, another one can. Hence, there is progress to look forward to.

Dr. David Pariser, a professor of dermatology at Eastern Virginia Medical School in Norfolk, concurs about the urgency to update treatments for head lice, stating that he finds these new medications very effective based on his experience and involvement in clinical trials.

If the newer drugs are more user-friendly, however, they are also prescription medications, meaning that a higher cost is associated with them. Nonetheless, the health care system must provide effective solutions and modern mechanisms for treatment.

Additional Information

For more information about head lice, you can visit the U.S. Centers for Disease Control and Prevention.