Could Reducing Deer Populations Reduce Lyme Disease?

white tailed deer

White-tailed deer (Odocoileus virginianus) are a primary host of adult blacklegged ticks (Ixodes scapularis), which carry and transmit Lyme disease. Research suggests that reducing deer populations can reduce tick populations accordingly. (Photo credit: Rebekah D. Wallace, University of Georgia, Bugwood.org)

By Josh Lancette

Lyme disease has been a growing problem in the United States, with the number of cases increasing throughout the past few decades.

Josh Lancette

Josh Lancette

The disease primarily is spread through a bacterium vectored by the tick Ixodes scapularis, also known as the blacklegged tick (or the deer tick, in some regions). The increasing spread of Lyme disease could be due to a variety of factors, such as suburbanization, reforestation or forest fragmentation, and changes to human behavior, just to name a few.

Because of the diversity of reasons for the spread of Lyme disease, controlling and reducing the number of occurrences of the disease takes a multitude of approaches. One popular approach is to reduce the population numbers of ticks that vector the disease.

In a new article published in the open-access Journal of Integrated Pest Management, Sam Telford, Ph.D., from the Department of Infectious Disease and Global Health at the Tufts University Cummings School of Veterinary Medicine, argues that reducing deer populations is a key component of managing tick populations.

First, a Little Background

To understand Telford’s argument, it’s helpful to know about the life cycle of I. scapularis ticks.

First, a female mates and feeds in the fall, then overwinters. In the spring, the female lays a batch of eggs, which could contain as many as 2,000 eggs. In the summer, the larvae emerge from eggs and seek hosts to feed on. After feeding, the larvae molt into nymphs during the fall or early the following spring, when they feed as nymphs.  If they feed, they will molt into adults during the summer and seek hosts that fall.

Larvae and nymphs both feed on small to medium animals, such as mice, chipmunks, shrews, or birds. These animals, especially mice, are where the ticks pick up the bacterium that causes Lyme disease. The adults feed only on larger animals, with white-tailed deer being one of their favorite hosts. Unlike the small mammals, deer do not infect ticks with the bacterium that causes Lyme disease.

blacklegged tick with eggs

An adult female blacklegged tick (Ixodes scapularis), once fed, will lay a clutch of up to 2,000 eggs. (Photo credit: James Gathany, CDC Public Health Image Library)

How Reducing Deer Populations Could Help

If ticks don’t get Lyme disease from deer, why would reducing deer populations help curb Lyme disease transmission?

Telford argues that it goes back to the tick life cycle. If an adult female tick can’t feed, she isn’t able to reproduce. That means a reduction in the number of larval- and nymphal-stage ticks. Lyme disease is primarily spread to humans through nymphal-stage ticks, so having less of those ticks around could lead to less human infections.

“One might suggest reducing the density of mice, chipmunks, or certain birds to reduce the chance that larvae and nymphs will feed on them and develop further (and also become infected), but killing one fed adult female deer tick is equivalent to killing 2,000 larvae or several hundred nymphs,” writes Telford. “It might be argued that without subadult development, there would be no adult ticks, but the successful feeding of a single female tick would compensate for great subadult tick mortality.”

It Sounds Good in Theory, but Does it Actually Work?

While the method requires further study, there is some evidence that reducing deer populations reduces human incidence of Lyme disease. For example, one study found that reducing deer populations in a community led to a 76 percent reduction in tick abundance and 80 percent reduction in resident-reported cases of Lyme disease. In another study, removing deer from an island resulted in less ticks found per hectare.

However, people critical (or unconvinced) of the method would say that the evidence isn’t clear that deer reduction was the cause of Lyme disease reduction in humans. For example, it could have been because of better education, changes in human behavior, or something else. Furthermore, some of the places where deer reduction did appear to reduce tick populations were islands or peninsulas, which could have led to different outcomes than studies on a mainland location would have found.

Deer Reduction as a Tool, Not a Silver Bullet

In the article, Telford is clear that he isn’t suggesting deer reduction is the best or only option to reduce incidence of Lyme disease in humans. On the contrary, he mentions that it might not be appropriate in some cases where other measures to reduce the disease could be more effective due to monetary cost, ethical reasons, specific ecology, or other reasons.  In either case (using deer reduction or not), short-term methods (repellents, insecticide applications to leaf litter, permethrin treated clothing) to reduce the risk of the disease must also be used. However, he does argue that deer reduction shouldn’t be ruled out as an option simply because the evidence for a reduction in Lyme disease is not as strong as that for reducing ticks.

“It is wrong to conclude that deer reduction does not reduce risk based on the published acarological studies, a less than complete surrogate for human exposure studies,” writes Telford. “Indeed, such a conclusion is based on absence of evidence, not evidence of absence of an effect, and harms future attempts to use deer reduction as part of an integrated tick management system.”

Journal of Integrated Pest ManagementRead More

Deer Reduction Is a Cornerstone of Integrated Deer Tick Management

Journal of Integrated Pest Management

 

Josh Lancette is manager of publications at the Entomological Society of America.

Comments

  1. Reblogged this on Project ENGAGE.

  2. I’m no expert, but in pest control you were always taught to start to eliminate the problem first, and then work up from there into other techniques for elimination

  3. Interestingly, current research out of CT has found that unless deer populations are reduced to a threshold of about 10/km2 that tick risk for human bites is actually higher. Fewer deer = ticks seeking other hosts that include people. In addition, ticks tend to be generalists so ticks may swap over to other species.

  4. Reducing deer populations is absurd – deal with the problem. People do not use repellents such as permethrin, they do not do a tick check and they in general refuse to take the time to learn about ticks. You can hand it to them and most do nothing with it. In the absence of deer do you really think the ticks will not find an alternative host during the adult mating stage? Ticks are well adapted and fully equipped to deal with such an adversity.

    • Another viewpoint – “when you have the enemy consolidated in one location – hit them with everything you have”. There was research years ago user the “cattle rubbers” and using a rub of either permethrin or deltamethrin. Why not expand the tests to deer feeding stations and misting a low grade .25% solution? When I give hunter training I strongly suggest they carry a can (besides using it themselves) of .5% permethrin and spray those rabbits and other game they take, don’t allow those ticks to get away. I emphasize that they have a chance to significantly reduce ticks in their hunting area if they all make an effort.

      • Spot on! There are some cattle/horse feed blocks that contain garlic this is at least something that may help. The problem is most state DNR ban any form of attractant for deer to unsuccessful control CWD… Yes for a herd animal. One thing to mention is the fleas on rabbits, bartonella (cat scratch fever) is extremely easy to contract and rabbits are major carriers. Bartonella is not fun, very painful and debilitating and hard to get rid of.

  5. Instead of reducing one species, consider increasing another. https://thistle25.wordpress.com/2014/03/07/fighting-lyme-disease-behold-the-lowly-possum/

    • Absolutely correct, have you seen any (most) states report, promote or suggest opossums for ticks? None yet, like Wisconsin

  6. This is absolutely idiotic and based on terrible science, mice are the incubators if mice are controlled to some extent the nymphs will not survive. Killing off deer is a way for state DNR agencies to decimate deer herds…this way of thinking is what causes problems for a correct resolution. Ticks DO NOT only feed on deer…. How many animals are their? How about birds? Search for bird migrations and ticks, this should be the real concern. Ticks will adapt to any given situation. Mr Gadd’s reply is a well thought, intelligent and accurate response.
    I’m an avid outdoorsman, hunter (until Lyme disease destroyed me) and I’ve worked in the hunting industry for 20 years. I gaurentee I’ve spent more time watching/caring for deer than these desk jockeys and clean coats who write these articles and the people who produce this bogus research/science.

  7. Denise S. says:

    If there are no deer, won’t the ticks just feed on cows or horses, etc?

    • There were some studies on reduction of deer population I believe they were conducted in Connecticut and they found that the instances of human interaction with the ticks increased. They are certainly not the only host for mature ticks during mating season so the ticks will find Alternatives I’m certain.

  8. Christopher Sloane says:

    They tried deer feeding stations here in the Northeast but stopped. Once some of the hunters found out where these stations were they started to hunt there. It was, leading cattle to the slaughter house.
    There have been some great products over the years that have been successful at eliminating ticks on mice and other small animals. Dammix, cotton balls infused with pesticide. Tick Management System, a smaller version of feeding station designed for small rodents. The later cleared one square acre of ticks over a two year period when used. Once they found Grey Squirrels were able to chew through the station it became an issue.
    IPM people, killing deer is not the answer!

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