More than one in three Norwegian dogs shows signs of tick-borne disease

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Ph.D. student Hanne Kloster at the University of Agder (UiA) is behind the first Norwegian study to look at three tick-borne diseases in dogs simultaneously, covering the whole country. The paper is published in the journal Acta Veterinaria Scandinavica.

"It's a very high figure, and it says something about just how vulnerable our dogs actually are. At the same time, it gives us an indication of how great the risk of infection is for humans," she says, speaking of the study results.

Kloster has herself worked for several years as an assistant at a veterinary clinic, and believes that many dog owners do not know enough about ticks and tick-borne diseases. Together with colleagues, she analyzed blood samples from 433 dogs in 15 counties, collected between 2016 and 2023. The blood samples were taken during routine veterinary visits, i.e., without any suspicion of tick-borne infection. This helps to make the study representative.

Thirty-eight percent of the dogs had antibodies against one or more of the microbes the researchers were looking for: Lyme disease, tick-borne encephalitis (TBE) and anaplasmosis.

"This doesn't mean that all these dogs have been ill, but that they have been bitten by ticks carrying these microbes," says Kloster.

Just like a previous study on horses, this study on dogs can also tell us something about the risk to humans.

"Dogs go where we go, but they are even more exposed to ticks than we are. They are closer to the ground, they have fur that ticks can easily hide in, and they move through tall grass and scrub. When we see a high incidence of infection in dogs in an area, there is good reason to believe that humans are also at risk," says Kloster.

The study showed a clear link between borreliosis in dogs and recorded cases in humans. But it also demonstrates how infection in dogs can detect viruses in circulation before they potentially manifest in humans.

In Western Norway, 11% of dogs had antibodies against the TBE virus, which can cause severe encephalitis. Yet not a single case of TBE in humans has ever been recorded in the region.

"It is a paradox we do not yet have an answer to. It could be down to several different factors; perhaps there are variants of the virus that cause asymptomatic infection," says Kloster.

In Northern Norway, the tick has traditionally been less widespread, but the study nevertheless found antibodies in one in ten dogs.

"This may suggest that exposure is also increasing in the north, but the sample size is small, and we must be cautious in our interpretation," says Kloster.

She points out that ticks are constantly spreading to more areas, and that a warmer climate is likely to be a factor. Migratory birds and animals that have been traveling may also bring new tick species and new bacteria into the country.

"In Denmark, there are many more tick-borne diseases than in Norway, and it's only a short boat ride for us here in Agder," says Kloster.

She expects that we will see new tick-borne diseases in Norway in the years ahead, as well as an increase in those we already have.

The vast majority of dogs that had antibodies in their blood did not fall ill. Many have only experienced temporary symptoms that can resemble a cold, or no symptoms at all.

It is nevertheless important to book an appointment with the vet if you have a dog that is behaving strangely after having a tick.

"Some animals do become seriously ill. TBE is particularly dangerous. We have seen cases where dogs have developed meningitis," says Kloster.

She believes the most important thing dog owners can do is to use tick repellents that are proven and prescription-only. She warns against relying on natural tick repellents, as these often have no proven effect, and—in the worst case—can cause the dog to have severe allergic reactions.

It is also important to check your dog regularly.

"That applies to us too, by the way. Feel free to use tick spray before your walk, and check yourself after walks in the woods and countryside."

Tips for you and your dog

• Check yourself and your dog thoroughly after a walk, or after sunbathing on the lawn.
• Dogs can wear tick collars or use other tick repellents in consultation with a vet.
• Never use tick repellents intended for dogs on cats. This can be dangerous for the cat.
• People can use mosquito or insect repellent, particularly on the lower body.
• Change your clothes after your walk, and comb your hair with a lice comb.
• If you have your dog on a lead, try to stick to the path and avoid walking through tall grass or bushes.
• The sooner you remove the tick, the better. If you or your dog has picked up a tick, pull it straight out with tweezers or your fingernails. It is not dangerous if a small part of the tick remains attached.

More information

Hanne Kloster et al, Antibodies against tick-borne pathogens in domestic dogs in Norway: Borrelia burgdorferi sensu lato, tick-borne encephalitis virus, and Anaplasma phagocytophilum, Acta Veterinaria Scandinavica (2026). DOI: 10.1186/s13028-026-00863-8

Key concepts

disease vectorszoonotic diseasescarnivoresOdd-toed Ungulates

Provided by University of Agder