New Study Compares How Quickly Popular Tick Preventives Kill Blacklegged Ticks

When it comes to preventing tick-borne diseases, speed matters.

A new study published in Parasites & Vectors compared how quickly three popular monthly oral combination parasite preventives kill the blacklegged tick (Ixodes scapularis), the primary vector for Lyme disease, anaplasmosis, babesiosis, and several other pathogens affecting both dogs and people.

The researchers found that the product containing lotilaner (Credelio Quattro™) consistently killed ticks faster than products containing sarolaner (Simparica Trio™) or afoxolaner (NexGard® PLUS) throughout the monthly dosing interval.

Why Speed of Tick Kill Matters

Ticks generally must remain attached for a period of time before transmitting many infectious organisms. Although transmission times vary depending on the pathogen, reducing the number of live attached ticks as quickly as possible may decrease the risk of infection.

For veterinarians practicing in areas where Lyme disease and other tick-borne illnesses are common, speed of kill is one factor to consider when recommending parasite prevention.

How the Study Was Performed

Researchers from Auburn University and collaborators enrolled 32 healthy dogs that were randomly assigned to one of four groups:

• Credelio Quattro™ (lotilaner)

• Simparica Trio™ (sarolaner)

• NexGard® PLUS (afoxolaner)

• Untreated controls

Dogs received one dose of their assigned product on Day 0. Investigators then challenged the dogs with 50 adult blacklegged ticks before treatment and again on Days 21 and 28 to evaluate both immediate and residual efficacy.

Live ticks were counted 4, 8, 12, 24, and 48 hours after treatment and after each subsequent infestation.

The Results

The biggest differences appeared during the earliest time points after tick attachment.

Following treatment of an existing infestation:

• Credelio Quattro was the only product to significantly reduce live tick numbers by 8 hours.

• By 24 and 48 hours, all three products significantly reduced tick counts compared with untreated dogs.

During reinfestations later in the month, differences became even more noticeable.

At Day 21, Credelio Quattro demonstrated significantly fewer live ticks as early as 4 hours, while Simparica Trio reached significant reductions at selected later time points and NexGard PLUS primarily demonstrated significant reductions beginning at 24 hours.

At Day 28, Credelio Quattro again maintained faster activity, with significant reductions beginning at 8 hours. Simparica Trio reached significance beginning at 12 hours, while NexGard PLUS again showed significant reductions beginning at 24 hours.

Perhaps most notably, researchers observed that the speed of tick kill slowed toward the end of the monthly dosing interval for both sarolaner and afoxolaner. In contrast, lotilaner maintained a consistent speed of kill from the beginning through the end of the month.

What This Means in Practice

All three products were effective at controlling blacklegged ticks within 24 to 48 hours and remain important tools for parasite prevention.

However, veterinarians practicing in regions with heavy tick pressure or high prevalence of tick-borne disease may find differences in early tick kill clinically relevant, particularly because earlier elimination of attached ticks may reduce opportunities for pathogen transmission.

As always, selecting a parasite preventive involves more than speed alone. Coverage against heartworm disease, intestinal parasites, fleas, regional parasite risks, patient lifestyle, owner compliance, product safety, and cost all play important roles in choosing the best preventive for an individual dog.

Important Considerations

This study was funded by Elanco Animal Health, the manufacturer of Credelio Quattro. Several authors are employees of Elanco or serve as paid consultants for animal health companies, including Elanco and Boehringer Ingelheim. While these relationships were fully disclosed and the study underwent peer review, they are important context when interpreting the findings.

Independent studies comparing these products under a variety of field conditions will continue to help veterinarians make evidence-based recommendations.

The study, "Comparative Speed of Kill of Induced Ixodes scapularis Infestations Following Treatment of Dogs with Endectocides Containing Either Sarolaner (Simparica Trio™), Afoxolaner (NexGard® PLUS), or Lotilaner (Credelio Quattro™)," was published July 17, 2026, in Parasites & Vectors.