Earth Matters: Of mice, men and ticks

Earth Matters: Of mice, men and ticks
Dr Hildur Palsdottir

By Dr. Hildur Palsdottir

If you enjoy the outdoors and live on Long Island, chances are you´ve encountered ticks and you probably know about the diseases derived from tick bites, the most notorious being Lyme Disease. The life cycle of ticks includes metamorphosis from eggs to six-legged larva, molting into eight-legged nymphs that mature into adults. At every stage, they rely on host blood for nourishment.

Interestingly, every larva is born innocent. Diseases like Lyme are not transmitted from adult ticks to larva. Instead, the nymphs get infected through small mammal hosts (mice, shrew, chipmunks) and pass that infection on to large vertebrates like us.

Fossils of ticks engorged with dinosaur blood reveal they have been around for at least a hundred million years and the bacterial pathogen Borrelia burgdorferi that causes Lyme Disease has been around for long before humans arrived to Long Island. So why did Lyme recently become a problem? Again, human-caused changes to the environment are to blame.

It wasn’t an epidemiologist but rather an ecologist who connected the dots to reveal the real causes for Lyme. Dr. Rick Ostfeld at the Cary Institute of Ecosystem Studies in Millbrook, N.Y., realized that white-footed mice are critical agents in Lyme Disease transmission and humans have facilitated the spread by eradicating their predators.

Furthermore, human-caused climate change has resulted in favorable conditions for ticks to multiply in numbers. According to Ostfeld, Lyme is the fastest-growing zoonotic disease in North America with Lyme doubling in reported incidences from 2002 (240,000) to 2017 (420,000).

Ostfeld leads an impressive research project, the Tick Project, that includes large-scale community treatments in Western Dutchess County with the aim to reduce the tick load and therefore Lyme infections using a naturally occurring fungus that kills ticks and bait boxes with Frontline.

Lyme was diluted among a wide variety of hosts (reservoirs) in biodiverse woodlands and wasn’t a public health threat until humans moved into areas previously assigned to wildlife. Habitat fragmentation increases the number of competent hosts like mice, and warming climate increases the number of ticks who need wet, humid and warm weather to reproduce.

It may not be much comfort to reflect on this if you’re suffering from this debilitating and often tragic disease, but it’s important to understand the real causes for Lyme in order to prevent this growing epidemic from becoming worse.

We must address our natural defenses. We must do what we can to curb climate change and restore healthy ecosystem function by recreating habitats with predators that reduce critter numbers. The larger the nature preserve, the more likely it is to foster biodiversity.

Deer aren’t great at transmitting Lyme to ticks, with only 10 percent likelihood of transmitting the pathogen in contrast to mice who have host competence of 90 percent.

Adult ticks date and mate on deer bodies, that’s how deer come into play. One deer can support as many as 2 million fertilized tick eggs. In a behavior referred to as “questing” ticks are attracted to your breath and body warmth.

In the case of Lyme, humans are the end station, we are the incompetent reservoir host, dead-end hosts. Once in us, the disease doesn’t spread further. We are the random host for these opportunistic parasites that aren’t very picky and feed on whatever blood they encounter, including vertebrates, birds and reptiles.

To summarize, mice and shrews make the ticks sick and ticks make us sick and we don’t pass this disease on to make anybody else sick – but we are the ones to blame for the spread because we disturbed the existing balance in the ecosystem by reducing biodiversity that kept this infection in check. Habitat destruction and warming climate are to blame for the spread of Lyme, and we are to blame for both. Here´s what we can do to restore balance.

First, support tick and Lyme research.

Second, prevent the disease by taking all the necessary precautions. The best way to prevent getting Lyme disease includes regular tick checks.

Third, curb climate change with your energy choices and conserve nature by dedicating large areas of land to wildlife sanctuaries and in that way support biodiversity and bring back our natural defenses. Ecological restoration of wildlife habitats dilutes the disease reservoirs with hosts less likely to pass on the infection. Support tick eaters like opossums, fowl, and quail and bring balance back to the ecosystem by recreating livable spaces for predators like owls, hawks, foxes, raccoons, and bobcats, who eat small mammals.

Human development and habitat destruction with associated loss of biodiversity upset the existing balance in the ecosystem. By eradicating keystone species and apex predators, the story of mice and men unfolded. And the story continues. It’s not too late to restore balance. Let’s do what we can!

This is a classic tale where overdevelopment and human range expansion without regard for the sanctity of wilderness and the composition of natural inhabitants has endangered our own well-being.

Humans now inhabit all corners of the world in our attempt to conquer the wilderness. Hundreds of years of aggressively insisting on domination of life and colonization of cultures who were better equipped to live in wild places have by the utter disregard for non-human life increased the risk of transmission of diseases that were previously carefully contained within animal reservoirs in areas out of reach for humans. It’s about time that we do what we can to restore balance and reclaim wilderness.

Catskills Mountainkeeper warn that this year is especially bad in terms of tick infestation. Warm winters together with record-high acorn yields a couple of years ago have resulted in an expected “tick time bomb” for this summer. Dress accordingly and tuck your pants into your socks. In this case, prevention is the best medicine. Wear whites so you can spot the ticks easily. Wear a hat, long pants, long-sleeved shirts, and closed-toe shoes. Avoid walking in overgrown areas and stick to the center of trails when hiking or walking in wooded areas.

Prepare vinegar and water mix (1:1) augmented with Rose Geranium oil and lavender essential oil and lather yourself and your dog in it. CDC recommends the use of insect repellent that has at least 20 percebt DEET, picaridin, or IR3535. Treat your clothes and gear with a product that contains 0.5% permethrin.

Always inspect yourself, your pets, and your loved ones for ticks after spending time outdoors. Get in the habit of taking off your outdoor clothes at the door and give them a good 10-minute spin in the dryer.

Excellent resources with experts discussing transmission, prevalence and prevention titled Ticked off: Everything you need to know about ticks is available in the video library at the Catskill Mountainkeeper website

Tips for how to avoid ticks:

How to id a tick:

Submitting a tick for testing:

Infographics and posters about ticks and tick safety from Cornell:

Dr. Hildur Palsdottir
Sol Center
[email protected]

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