A Lyme disease primer as the tick population rises

Although a variant was first reported in Europe in 1883, the first known outbreak of what has come to be known as Lyme disease (LD) occurred in Old Lyme, Conn., in 1975. 

LD has spread across the country to all 50 states and is now the most common tick-borne disease in the Northern hemisphere with more than 30,000 diagnosed and reported each year (a small fraction of the population that has actually been infected). 

According to the Centers for Disease Control and Prevention (CDC), probably more than 300,000 people are infected with LD and other tick-borne diseases (ehrlichiosis babesiosis, and anaplasmosis, to name two) each year. A recent Johns Hopkins study estimates the annual cost to the U.S. health care system of these diseases to be more than $1.3 billion.

Don’t blame the deer

Climate change has opened up areas formerly too harsh for ticks, with outbreaks occurring as far north as southern Canada. In the Tri-state region this year, mild days have permitted more ticks to winter over, and the cool wet spring weather has fostered the growth of tick nymphs.

LD is spread by bites from ticks infected with the Borrelia burgdorferi, bacteria acquired mostly from infected mammals, especially white footed mice and chipmunks. 

It used to be commonly thought that the explosion of the deer population was largely responsible for the spread of LD; but deer counts over the years have declined and other factors seem more responsible for the surge.

Our forests have become more fragmented because of human settlement, resulting in fewer assorted predators such as bobcats, foxes, raccoons, opossums, martens and raptor birds, hence more mice and other rodents. 

Sites with high predator diversity have fewer ticks. Although coyotes eat mice, they also eat other predators of rodents, thus reducing predator diversity. 

Most wild birds help reduce the tick population of a given area, but not dramatically, and at the same time are responsible for much of the spread of LD across the country. Poultry (chickens, turkeys, guinea fowl, etc.) eat ticks but can be otherwise troublesome as pets. 

A study by the Cary Institute of Ecosystem Studies in Millbrook found that opossum are among the most efficient foes, each killing and eating thousands of ticks every week.

Protect yourself

It takes a tick about 24 hours to infect a person after it starts biting, so a thorough search for ticks after possible exposure makes sense. 

Careful removal with fine tweezers is recommended. Early treatment with antibiotics (doxycycline, amoxicillin) during the first few weeks after infection usually works well, typically resulting in a full cure.

The usual well-known ways of trying to prevent LD, including keeping grass mowed short, wearing white clothes when outdoors, tucking pant legs into long white socks, and showering and inspecting for ticks after being outdoors are still recommended but most people are looking for easier, more effective methods for avoiding LD.

Products to try

A wide assortment of commercially available repellents and pesticides are available. Permethrin, an effective spray made from the daisy-like flower Pyrethrum cineraiifolium repels both ticks and mosquitoes and is recommended for spraying on clothing — but not on skin. 

It is also available, in different formulation, for outdoor area spraying. 

A new insecticide, Met52, kills ticks  and claims to be non-toxic to birds and bees.

For spraying on skin there are a number of repellents including DEET, picaridin and IR3535 from Merck.

Going to the source: mice

One company offers tick control cardboard tubes stuffed with cotton balls doused with permethrin. 

The idea is that mice, whose fur is laden with ticks, take the cotton balls back to their nests for bedding, where the ticks are killed by the pesticide. 

The company recommends using 24 tubes (for $75) to cover roughly an acre, twice a year. Home-made versions of this product would be easy to make. Of course they reduce tick populations but how much is not clear nor possible to test.

There have been no compelling studies to indicate whether there are any animals, including humans, with an innate immunity to LD or any of the other tick-borne diseases. 

Why there isn’t a shot (yet)

There are at least 16 different strains of Borrelia burgdorferi that cause LD. Some studies have indicated that individuals who have contracted one strain of the disease are likely to develop an immunity to that particular strain that typically lasts for at least six years. It remains to be seen whether a substantial immunity develops for the other strains.

What about vaccines? SmithKlineBeecham (now GlaxoSmithKline) developed one called LYMErix that went on the market in 1998; their tests indicated it was 78% effective. 

But it had problems, the foremost of which were lawsuits and bad publicity generated by an anti- vaccine movement (that has spread considerably over the past two decades and now is threatening the MMR vaccine used to control the current spread of measles). 

Sales of LYMErix declined from 1.5 million doses in 1999 to 10,000 in 2002 and the product was discontinued. There is, however, a new vaccine in the pipeline called VLA 15, manufactured by a company called Valneva, that may be available within the next few years.

A Lyme tick vaccine is difficult to design and manufacture. LYMErix required three doses spread over several months to work well and that had to be repeated each year. Newer formulations being tested are trying to protect against not only the 16 strains of LD but also the other tick-borne diseases afflicting much of the country.

Curiously, one can still purchase an LD vaccine for dogs, raising the question of what’s so different about vaccines for dogs and for people? What if someone took their dog’s vaccine? For further information, consult your dog’s veterinarian.

Architect and landscape designer Mac Gordon lives in Lakeville and has yet to be afflicted with Lyme disease. He consulted for this article with Dr. John S. Marr, formerly chief epidemiologist for the state of Virginia.