July 25, 2024

Lyme disease may cause as many as 476,000 illnesses each year—but what if something as simple as taking a pill could prevent it?

A California-based company is developing a drug designed to do just that. Tarsus Pharmaceuticals is still testing the pill, but if approved by the Food and Drug Administration, it would be the first medication to prevent Lyme disease and other tick-borne illnesses in humans.

“We have medication for dogs to prevent tick bites, but we do not have [anything] for humans, except for some repellents,” Luis Marcos, MD, an infectious disease physician at Stony Brook Medicine in New York, told Health.

The drug has the potential to “drastically” reduce the number of Lyme disease cases, Barbara Bawer, MD, a primary care physician at The Ohio State University Wexner Medical Center, told Health. “It is really exciting, especially because some [complications of Lyme disease] can be deadly, or you can have lifelong problems.” 

Here, experts explain how the medication works, when it might be available, and steps you can take in the meantime to reduce your risk of contracting Lyme disease.

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Lyme disease is typically caused by the bacterium Borrelia burgdorferi, which spreads via the bite of an infected black-legged tick (or deer tick). The ticks live primarily in the Midwest, mid-Atlantic, and Northeast but can be found across the U.S. Rising temperatures and shifting rainfall patterns have boosted deer tick populations and, in turn, Lyme disease infections, according to the Centers for Disease Control and Prevention. 

In the disease’s initial stage, symptoms may include a low-grade fever and characteristic “bullseye” rash, known medically as erythema migrans. If left untreated, Lyme disease can affect the brain, heart, and nervous system. 

Tarsus’s pill, called TP-05, may address the growing Lyme disease problem by including an anti-parasitic called lotilaner. Tarsus also uses lotilaner in an ophthalmic solution that treats a disease of the eyelids caused by mites. The compound is also found in flea and tick medications for dogs.

“The pill has a very unique mechanism,” Bobby Azamian, MD, PhD, CEO of Tarsus, told Health. “You would take a tablet the day before or hours before going somewhere [you] could be exposed to Lyme,” he said. “Our drug targets the tick [and] kills the tick,” should you get bitten.

Because a tick must be attached for at least 24 hours before it can transmit Lyme disease, swiftly killing the tick would help prevent the disease.

The drug could be effective for as long as a month.

Tarsus has conducted two small studies to investigate the drug, a phase 1b trial and the more recent phase 2a trial.

For the phase 2a, sterile, non-pathogenic nymphal ticks were placed on human volunteers at two different times. One day after the first tick placement, researchers randomly assigned volunteers to receive either a placebo or a low or high dose of TP-05.

On average, 97% of ticks on people given the higher dose died, while 92% of those given the lower dose died. Five percent of those on people given the placebo died.

Thirty days later, scientists again placed ticks on the volunteers; the following day, 89% of ticks found on those given a high dose and 91% on those given a low dose had died. In contrast, only 9% of those placed on volunteers given a placebo had died.

Tarsus said the medication was “generally well tolerated.”

The results of the trials have not been published, and “a lot more data” is needed to understand the medication’s potential benefits and downsides, Bawer said.

Specifically, showing that the pill works for people taking medications for other health conditions are necessary, she said.

Azamian said the company has not yet started the phase 2b or phase 2c trials. It’s “too early to say” when the medication may be available.

Additionally, the company doesn’t yet know the medication’s cost or exactly how health insurance policies would factor into coverage. If the pill is too expensive, it might not help as many people as it could, experts pointed out.

“I think we’ll be able to say more by the end of this year,” Azamian said.

Tarsus’s medication isn’t the only preventative option in the works. The pharmaceutical companies Pfizer and Valneva have manufactured a new vaccine that’s still being tested in human clinical trials.

The vaccines would work by targeting the outer surface protein A (OspA) of Borrelia bacteria.

Whether someone should opt for the pill or vaccine if they both become available would “depend on how effective each one is, side effects, long-term protection, etc.,” Marcos said. 

Another option, a human monoclonal antibody, has also been developed. The single seasonal shot produced by the University of Massachusetts Medical School’s MassBiologics would work by killing the bacteria in a tick’s gut before it can be transmitted to humans. The treatment is still being tested.

Until a pill or vaccine becomes available, the best prevention is to try to avoid encountering ticks when you go outside. Some strategies include:

  • Being on the alert for ticks in grassy, bushy, or wooded areas
  • Using EPA-approved bug spray and treating clothing with products containing permethrin, an antiparasitic agent, before venturing out
  • Staying in the middle of the trail when hiking
  • Wearing long-sleeved tops and long pants, if possible, and tucking your shirt into your pants and pants into your socks

When you return from hiking or camping trips, you should thoroughly examine yourself, your pets, and your outdoor gear for ticks.

Though TP-05 or other new prevention strategies may change the Lyme disease prevention landscape, it’s important to continue practicing traditional protection methods in the meantime. “We need to make sure we decrease the number [of new cases] every year,” Marcos said.

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