A Pill That Kills Ticks Is a Promising New Weapon Against Lyme Disease

If you have a dog or cat, chances are you’ve given your pet a flavored chewable tablet for tick prevention at some point. What if you could take a similar pill to protect yourself from getting Lyme disease?

Tarsus Pharmaceuticals is developing such a pill for humans—minus the tasty flavoring—that could provide protection against the tick-borne disease for several weeks at a time. In February, the Irvine, California–based biotech company announced results from a small, early-stage trial showing that 24 hours after taking the drug, it can kill ticks on people, with the effects lasting for up to 30 days.

“What we envision is something that would protect you before the tick would even bite you,” says Bobby Azamian, CEO of Tarsus.

Lyme disease is a fast-growing problem in the United States, where approximately 476,000 people are diagnosed and treated for it each year, according to the most recent data from the Centers for Disease Control and Prevention. That number is likely an overestimate, because many patients are treated after a tick bite even if an infection isn’t confirmed, but it underscores the burden of Lyme disease on the health care system—which researchers at the CDC and Yale University put at nearly $1 billion per year.

The disease is caused by the bacteria Borrelia burgdorferi, which gets passed to humans through the bite of an infected tick. In most cases, a tick has to be attached for around 36 to 48 hours before the bacteria can be transmitted. Symptoms include fever, headache, fatigue, and a characteristic skin rash that looks like a bullseye.

Without a vaccine for Lyme disease on the market, current prevention includes using insect repellents such as DEET and permethrin and wearing closed shoes, long pants, and long sleeves when in a tick-infested area.

“We’ve seen increasing rates of tick-borne diseases over the years, despite being told to do tick checks, use DEET, and impregnate your clothes with permethrin,” says Paul Auwaerter, a professor of medicine at the Johns Hopkins University School of Medicine who studies Lyme disease.

A more effective treatment strategy would be welcome, Auwaerter says, especially because Lyme disease can sometimes cause serious health issues. Antibiotics are usually effective when taken early, although about 5 to 10 percent of patients can have lingering symptoms for weeks or months. If left untreated, the infection can spread to the joints and cause arthritis. It can also become established in the heart and nervous system, causing persistent fatigue, numbness, or weakness.

The experimental pill that Tarsus Pharmaceuticals is testing is a formulation of lotilaner, a drug that paralyzes and kills parasites by interfering with the way that signals are passed between their nerve cells. Lotilaner is already approved as a veterinary medicine under the brand name Credelio to control fleas and ticks in dogs and cats.

“Our animals have better options than we do for tick prevention,” says Linden Hu, a professor of immunology at Tufts Medical School who led the Tarsus trial. “There are quite a few drugs and vaccines available for dogs and cats, but there’s nothing for us.”