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Lyme Disease, Deer Ticks, and Deer Fences

deer ticks and deer fence

Will a deer fence completely protect you and your family against Lyme disease spread by deer ticks in your yard or garden? The short answer is no, but it can be a big help in keeping ticks out of the protected area. Here’s how it works:

Lyme disease cases forecast, 2022Lyme disease, a bacterial disease, often has severe consequences. The leading vector-borne disease in the United States, it causes some 450,000 new cases per year (5), mostly in the Northeast, Minnesota, and Wisconsin. The responsible bacterium, a spirochete (usually Borrelia burgdorferi, rarely Borrelia mayonii), can and often does infect the deer tick, Ixodes scapularis Say, that deer carry.  So if one keeps the deer out with a deer fence, that ends the problem. Right?

Not exactly. In fact, deer don’t get Lyme disease. They just carry the adult ticks. The ticks pick up the Lyme disease bacteria in their early (larva and nymph) stages, mostly via blood meals from the disease’s principal reservoir, the outdoor white-footed mouse. The ticks are then able (mostly as nymphs or adults) to infect people or their pets via another bite. Whether or not that happens, once they become adults the female ticks (if lucky) mate, attach to a deer, take another blood meal, get carried around, drop off, and lay thousands of eggs.

A Deer Fence by McGregorWell then, if one blocks the deer with a deer fence, won’t that help? Yes, it will. In fact, installing a deer fence is a critical first step (11). But left to itself the fence will take a while to work. That’s partly because the protected area may already contain ticks and also because a trickle of ticks may still enter the protected area – mostly on the bodies of mice, chipmunks, birds, and other small creatures to which they have attached.

This suggests that it pays to supplement the deer fence with other measures. One helpful step is to landscape in a way that encourages neither ticks nor small rodents – by removing leaf litter, brush piles, low-lying tree branches, and tall grass. Another more direct step is to spray ticks inside the fence. Various tick-killing sprays are available that use an active ingredient like cedar oil that kills ticks but is safe for both pets and people. If one erects a deer fence and then adopts such measures, one can rapidly cut the deer tick population to low levels and keep it low, thus sharply reducing the chances of infection.

For those seriously interested, here’s more:

Lyme Disease Costs: The leading vector-borne disease in the US, Lyme disease generates medical costs estimated at $3,000 per patient (1) and 0.7 to $1.3 billion a year (16). We should note that these are just health care costs, not social costs. They do not include non-medical costs and productivity costs such as time lost from work due to illness or debilitation. If one adds these social costs, the total is much higher. Indeed, one writer has gone so far as to allege all costs combined total something like $75 billion per year (17). And while it seems unlikely that the costs really are that high, they clearly are considerable.

Deer Tick Life Cycle, CDC

The Deer Tick’s Life Cycle: The deer tick (Ixodes scapularis Say), also known as the black-legged tick, goes through three life stages (larva, nymph, and adult, not counting the egg stage), which typically take 2 or 3 years to complete. Each stage seeks to attach to a passing animal or person and obtain a single blood meal. After this meal, the larvae and nymphs drop off, molt, and go on to the next (nymph or adult) stage. If a nymph succeeds in becoming an adult (male or female) it seeks to mate with another adult tick. After mating, the males die while the females try to attach to a passing animal and obtain a final blood meal—after which they drop off, lay thousands of eggs, and perish (21).

White-footed Mouse and Chipmunk

Lyme Disease Transmission: Lyme disease bacteria don’t commonly survive in tick eggs. So the eggs typically hatch into uninfected larvae. The larvae then seek low-slung “belly-to-the-ground” animals like white-footed mice, chipmunks, squirrels, or raccoons. Neither squirrels nor raccoons can carry the infection, but white-footed mice and chipmunks can. And if a larva bites an infected white-footed mouse or chipmunk, that larva is very likely to become infected with the Lyme disease bacteria. It will then drop off, molt, and emerge as an infected nymph ready to pass on the infection (2).

In areas where the disease is common (notably in the Northeast, plus Minnesota, and Wisconsin) this sequence of events typically produces high percentages of infected ticks. As of 2020, according to the Tick Research Lab of Pennsylvania, 45 percent of the adult female deer ticks examined in that state were found to carry the disease (21).

Questing Deer TickTo make matters worse, the nymphs and young adults don’t stay on the ground like the larvae. Instead, they climb up on grass, plants, or brushy growth and hold their forelegs out in what is called “questing” behavior, awaiting the passage of some taller animal to which they can attach. If the “animal” turns out to be a person or house pet, and should the nymph or young adult be infected with the Lyme disease bacteria, after being attached for a while it can pass the bacteria along (7).

Lyme disease rashesEarly Symptoms: The high cost of Lyme disease treatment is generated by its later symptoms, which can be quite severe. By comparison, the early symptoms seem rather mild. They can include fever, chills, headache, body ache, swollen lymph nodes, and the disease’s trademark — a characteristic red rash around the site of the bite. This rash (not just a small red bump that can occur after a tick is removed and does not indicate Lyme disease) typically arises 3 to 30 days after the tick bite and expands slowly, reaching up to 12 inches across. However, there are lots of variations. Sometimes there’s no rash; some rashes are far smaller than the one described; some develop a white center; and some may appear at places other than the site of the bite. The rash is not itchy or painful, though it may feel warm to the touch (10).

Later Symptoms: The later symptoms, which appear weeks or months after the responsible tick bite, can be alarming, severe, and debilitating. They include bouts of severe joint pain and swelling, especially in the knees, and a wide range of neurologic problems including meningitis, nerve damage, partial facial paralysis (Bell’s palsy), limb numbness or weakness, and impaired muscle movement. Less common problems include severe fatigue, eye inflammation, hepatitis, and heart problems (9, 10).

Medical Treatment: Because of the later symptoms, even if one ignores the chances of getting another disease spread by deer ticks (anaplasmosis, babesiosis, Powassan disease), early Lyme disease symptoms merit a quick visit to the doctor. Unfortunately, the treatment available (an oral course of the antibiotic doxycycline administered during the early phase of the disease) doesn’t always work. In fact, available data suggest that between 10 and 30 percent of those who receive the indicated course of antibiotics continue to have or develop symptoms, and that repeated antibiotic treatments are ineffective or even harmful. This means that the many people who do not seek treatment promptly, as well as those whose initial treatment fails, have no choice but to let the disease run its course. Eventually, after a period of months or occasionally years, long-term symptoms stop emerging, and most patients appear to recover. Even so, the widespread nature of Lyme disease, its potential consequences, and the lack of an assured effective treatment highlight the importance of prevention (9, 10).

Preventive Measures: Partly because of this treatment debacle, an imposing list of preventive measures has arisen. The list is long enough to be confusing, so it helps to organize it by considering particular situations and listing measures appropriate to them. The situations considered here are future situations, camping/hiking situations, and yard situations. Arranging things this way doesn’t include all preventive measures, but it includes most.

vaccineFuture Measures: One future measure fairly close to approval is a Lyme disease vaccine developed by Pfizer and Valneva that has completed its second phase trials. The vaccine is due to begin its final (third phase) trials this summer. Nothing is certain in the vaccine business (which is why trials are held), but if all goes well this product might be available fairly soon. Another product, a medicine injected once a year to prevent infection with the Lyme disease bacteria, has completed its first phase trials. For those making long-term plans to curb Lyme disease, these products offer promise. However, they don’t change the fact that at present medical measures fully effective against Lyme disease are lacking (3, 8).

Beware of Ticks Sign

Personal Measures: Well then, what about personal measures for protecting campers, hikers, and others entering tick-infested areas? Common recommendations include the following:

    • Avoid tick habitats such as fields of high grass, brushy areas, and dense woods.
    • If hiking, walk in the center of the trail.
    • Treat yourself ahead of time with an insect repellent, preferably one containing DEET.
    • Apply an insect repellent containing 0.5% permethrin to your clothes.
    • Wear a long-sleeved shirt and long trousers.
    • Tuck your shirt into your trousers and your trouser legs into your socks.
    • Wear light-colored clothes suited to showing up any ticks that get on them.
    • After being outdoors, inspect yourself carefully for ticks.
    • Get rid of any ticks found, removing any that have become attached slowly and carefully, so as not to leave any part of the tick in the bite.

Such recommendations are good for campers and hikers. However, they seem impractical for dealing with infected ticks in one’s own yard – impractical enough to drive gardeners, parents, and pet owners up a wall. So besides adopting the last two measures (and possibly others) to a practical degree, it makes sense to protect one’s yard with measures directed at sharply reducing the yard’s tick population.

deer fence and sprayer

Yard Measures: Two tools often used to rid yards of deer ticks are tick sprays and deer fences. Sprays alone tend to be unsatisfactory—because spraying is costly, has to be repeated every month or so, drenches the yard in spray, and provides no means of freeing the yard from an ongoing wholesale invasion by more ticks.

Well then, what about deer fences like those sold by my company, McGregor Fence? If a deer fence kept out all ticks, then the fence alone might be an ideal solution. However, there are two problems. First, the fence does not remove the ticks already inside the enclosure. And second, it does not prevent a trickle of ticks from entering the protected area, mostly on small animals (white-footed mice, chipmunks, squirrels, etc.).

That makes it worth supplementing the fence with an initial spray (once the fence is in place), plus occasional additional sprays at fairly long intervals – whatever seems reasonable for the site.  For this purpose, it’s best to use a spray with a safe active ingredient like cedar oil that kills ticks but is harmless to pets and people. It’s also a good idea to mow tall grass, remove brush and fallen leaves, and prune low branches in the protected area, because these places tend to harbor both ticks and small animals.

Finally, if chipmunks are present it’s worth giving these cute rodents special attention. That’s because chipmunks (unlike white-footed mice) wander about; and chipmunks (unlike squirrels and raccoons) can carry the Lyme disease bacteria. Hence, deer fences are less likely to prove an effective barrier to the disease in places with lots of chipmunks. This means that while the fence can help in such areas, it pays to place relatively higher reliance on sprays and landscaping measures, in addition to taking steps—like removing food sources and getting a cat—that will reduce the yard’s attractiveness to chipmunks.

According to Peter Aquilina, a noted deer fence expert, a newly installed deer fence, by itself, will begin producing results against the ticks in about 6 months and will achieve its full effect in about 2 years. Of course, if effectively supplemented with other measures, the fence can be expected to more rapidly reduce the tick population and keep it down (2).

The best data we have on the effect of deer fences alone comes from a 1993 study by TJ Daniels et al. of New York Medical College (11). The authors examined tick populations in five large areas surrounded by deer fences. They found that average levels of deer tick larvae inside the enclosures were almost 10 times lower than those outside, and that nymph levels inside were six times lower than those outside. The areas enclosed were large (15 to 250 acres), and the deer fences had been in place for a long time (25 years) at the time of the study, so the conditions did not match those of the average suburban yard. Even so, the findings highlight the ability of deer fences to reduce tick populations.

June 24, 2022

Jonathan Leonard, Manager
McGregor Fence Company LLC
508-888-8305, [email protected]

A Deer with Books in Its Antlers

Sources

  1. Adrion ER, et al. Health Care Costs, Utilization and Patterns of Care following Lyme Disease. PLOS One. Vol. 10, No. 2, February 2015. https://doi.org/10.1371/journal.pone.0116767
  2. Aquilina, P. Interview. June 10, 2022.
  3. Callahan, C. Lyme Disease Shot Inches Closer to Reality. Times Union: Hudson Valley News. April 14, 2022. https://www.timesunion.com/hudsonvalley/news/article/Lyme-disease-prevention-shot-17078270.php
  4. CDC. Diseases Transmitted by Ticks. March 24, 2022. https://www.cdc.gov/ticks/diseases/index.html
  5. CDC. How Many People Get Lyme Disease? January 23, 2021. https://www.cdc.gov/lyme/stats/humancases.html
  6. CDC. Lyme Disease Data Tables: Historical Data: Reported Cases of Lyme Disease by State or Locality, 2010-2019. May 5, 2021. https://www.cdc.gov/lyme/stats/tables.html
  7. CDC. Lyme Disease Transmission. January 29, 2020. https://www.cdc.gov/lyme/transmission/index.html
  8. CDC. Lyme Disease Vaccine. December 22, 2021. https://www.cdc.gov/lyme/prev/vaccine.html
  9. CDC. Post-treatment Lyme Disease Syndrome. January 10, 2022. https://www.cdc.gov/lyme/postlds/index.html
  10. CDC. Signs and Symptoms of Untreated Lyme Disease. January 15, 2021. https://www.cdc.gov/lyme/signs_symptoms/index.html
  11. Daniels TJ, Fish D, and Schwartz I. Reduced Abundance of Ixodes scapularis (Acari: Isodidae) and Lyme Disease Risk by Deer Exclusion. Journal of Medical Entomology. Vol.  30, No. 6, November 1993, pp. 1043-1049.
  12. Daniels TJ, Fish D. Effect of Deer Exclusion on the Abundance of Immature Ixodes scapularis (Acari: Isodidae) Parasitizing Small and Medium-sized Mammals. Journal of Medical Entomology. Vol. 32, No. 1, January 1995, pp. 5-11.
  13. Eisen L. Control of Ixodid Ticks and Prevention of Tick-borne Diseases in the United States: The Prospect of a New Lyme Disease Vaccine and the Continuing Problem with Tick Exposure on Residential Properties. Ticks and Tick-borne diseases. Vol. 12, No. 3. https://pubmed.ncbi.nlm.nih.gov/33549976/ May 2021, 101649.
  14. Eisen L. Barriers to Effective Tick Management and Tick-bite Prevention in the United States (Acari: Ixodidae). Journal of Medical Entomology. Vol. 58, No. 4, July 2021, pp. 1588-1600.
  15. Gandy S, et al. Experimental Evidence for Opposing Effects of High Deer Density on tick-borne Pathogen Prevalence and Hazard. Parasites and Vectors. Vol. 14, September 30, 2021.
  16. Johns Hopkins Bloomberg School of Public Health. Lyme Disease Costs Up to $1.3 Billion Per Year to Treat, Study Finds. February 5, 2015. https://publichealth.jhu.edu/2015/lyme-disease-costs-more-than-one-billion-dollars-per-year-to-treat-study-finds
  17. Johnson L. Lyme Policy Wonk: Lyme Disease Costs May Exceed $75 Billion Per Year. LymeDisease.org. July 19, 2018. https://www.lymedisease.org/lymepolicywonk-costs-75billion/
  18. Kugeler KJ, et al. Estimating the Frequency of Lyme Disease Diagnoses, United States, 2010-2018. Emerging Infectious Diseases. Vol. 27, No. 2, February 2021, pp. 616-619.
  19. Lyme Disease Association. Delayed CDC Lyme Final Case Numbers for 2019 Finally Released. May 5, 2022. https://lymediseaseassociation.org/lyme-tbd/cases-stats-maps-a-graphs/delayed-cdc-lyme-final-lyme-case-numbers-for-2019-finally-released/
  20. Stafford KC. Reduced Abundance of Ixodes scapularis (Acari: Isodidae) with Exclusion of Deer by Electric Fencing. Journal of Medical Entomology. Vol. 30, No. 6, November 1993, pp. 986-996.
  21. Tick Research Lab of Pennsylvania. The Tick Lifecycle. Lyme and Tick-borne Disease Testing and Statistics. December 1, 2020. https://www.ticklab.org/blog/2020/12/01/the-tick-lifecycle/.
  22. United States Environmental Protection Agency. Climate Change Indicators: Lyme Disease. April 2021. https://www.epa.gov/climate-indicators/climate-change-indicators-lyme-disease
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