Why Foxes Are Crucial for Keeping Down Rates of Lyme Disease

fox role lyme disease

Story at-a-glance -

  • Man-made disruptions to ecosystems that, in turn, have harmed populations of predatory animals like foxes may be driving up rates of Lyme disease
  • When the researchers tracked predators and prey (foxes and rodents) along with ticks in 20 locations, they found that areas with more foxes had fewer ticks
  • An abundance of foxes caused rodents to spend more time hiding in their burrows — and less time scurrying out and about where they became prime hosts for ticks

By Dr. Becker

Lyme disease is a tick-borne illness caused by the bacterium Borrelia burgdorferi. In humans, it often begins with a characteristic bulls-eye rash and leads to symptoms such as fatigue, fever and headache. In some cases, untreated infection can cause problems with your joints, heart and nervous system.1 In dogs, Lyme disease manifests somewhat differently, with no rash and often no symptoms at all for many months.

Months after a tick bite from an infected tick (most often a black-legged tick, aka deer tick or bear tick), a dog with Lyme disease may develop a fever, swollen lymph nodes or joints, lethargy, loss of appetite or lameness that shifts from leg to leg. Lyme disease can be serious, even leading to severe kidney disease in rare cases, but it’s important to understand that cases tend to be concentrated to about a dozen states with heavy infestations of deer ticks.

Such states are primarily located in the northeast and upper Midwest.2 Even in these areas, however, a dog may be bitten by an infected tick and not get sick. It’s common in some areas of New England, for instance, for the majority of dogs to test positive for Lyme-related antibodies in their blood, meaning they’ve had exposure to the disease. However, they have no clinical symptoms of infection and are not “sick.”

If your dog tests positive for exposure to Lyme disease, I strongly recommend discerning exposure from actual infection with a simple follow-up test called the Quantitative C6 test (QC6), which can be easily added onto the submitted sample by calling the lab. It’s the best way to find out if treatment (typically antibiotics) is necessary.

Why Foxes May Be Crucial to Keep Down Rates of Tick-Borne Diseases

Cases of Lyme disease in humans have been on a gradual rise since the 1990s.3 One reason for this, according to researchers from Wageningen University in the Netherlands, is man-made disruptions to ecosystems that, in turn, have harmed populations of predatory animals like foxes. When the researchers tracked predators and prey (foxes and rodents) along with ticks in 20 locations, they found that areas with more foxes had fewer ticks.4

It’s not simply a matter of the foxes eating the tick-infested rodents, either. The study found that an abundance of foxes caused rodents to spend more time hiding in their burrows — and less time scurrying out and about where they became prime hosts for ticks. The researchers noted:5

“Our results suggest that predators can indeed lower the number of ticks feeding on reservoir-competent hosts, which implies that changes in predator abundance may have cascading effects on tick-borne disease risk … Many prey species show decreased movement and increased refuging behavior in the presence of a predator.”

The rise of Lyme disease is often blamed on increases in deer populations, but this study and others suggest deer (which arguably do serve as common hosts to ticks) may be less important in the spread of Lyme disease than previously thought. Writing in Proceedings of the National Academy of Sciences, researchers explained:6

“[A] growing body of evidence suggests that Lyme disease risk may now be more dynamically linked to fluctuations in the abundance of small-mammal hosts that are thought to infect the majority of ticks. The continuing and rapid increase in Lyme disease over the past two decades, long after the recolonization of deer, suggests that other factors, including changes in the ecology of small-mammal hosts may be responsible for the continuing emergence of Lyme disease.”

They, too, found that increases in Lyme disease coincided with the decline of the red fox, perhaps due to increasing coyote populations. As in the featured study, they pointed out that changes in predator communities like the fox may have “cascading impacts that facilitate the emergence of zoonotic disease.”7

How Opossums Also Help Fight the Spread of Lyme Disease

Threats to fox habitats could have implications for many species, including dogs and humans, due to tick-borne disease, but they’re not the only animal that plays a role in preventing the spread of Lyme disease. Opossums also deserve mention, as they act as “ecological traps” for larval ticks, hosting perhaps more than 5,500 in a season and consuming the majority of them before they reach maturity.

Research conducted by Rick Ostfeld, Ph.D., a senior scientist at the Cary Institute of Ecosystem Studies, and colleagues revealed that more than 96 percent of ticks that attempt to feed on opossums do not survive, as the animals consume them during grooming.8 Further, of the ticks that do successfully feed on opossums, very few of them pick up the bacteria that cause Lyme disease

Their ability to help prevent the spread of tick-borne disease is yet another reason to protect, support and attempt to live in harmony with the wildlife in your area, including opossums — animals that many people regard, unfairly, as a nuisance.

Basic Steps to Prevent Lyme Disease in Dogs

It goes without saying that the best way to avoid Lyme disease is to avoid areas you know are infested with ticks. However, if you live where Lyme disease is endemic or you inadvertently wind up in a tick-infested area, check your dog for ticks carefully, ideally twice each day. Look over her entire body, including hidden crevices in the ear, under her collar, in the webs of her feet and under her tail.

Natural tick repellents, including topical diatomaceous earth, herbal sprays and collars, can be helpful as well, and while there is a Lyme disease vaccine available, I don’t typically recommend it. Instead, I recommend checking for infection at least annually, even in the absence of symptoms, using the SNAP-4Dx blood test.

If the blood test comes back positive, a QC6 should be given to confirm that your dog is, in fact, positive before starting treatment. If your dog is showing signs of Lyme disease, you should take him to your veterinarian right away.

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