Tick Down the 'Scope

A blacklegged deer tick seen through the microscope of Cornell post-doctoral researcher Roy Faiman.

Lyme disease infection in Tompkins County and surrounding areas is on the rise. Complicating this public health issue are disputes within the medical community over specific characteristics of the disease and the best way to diagnose infection.

The blacklegged tick—also known as the deer tick—common to this area can transmit several infections, including Lyme disease. Prevention strategies range from the uncontroversial pants-tucked-into-socks approach to the hotly contested culling of deer herds. And if prevention wasn’t tricky enough, warmer winters are extending the tick season. All of this from an arachnid the size of a poppy seed at its first blood meal.

Lyme disease is spread through the bite of an infected blacklegged tick, commonly found attached to hard-to-see areas of the body such as the scalp, armpits and groin. While infected ticks can pass on the disease during the adult stage, it is in the nymph stage of tick development, during the spring and summer months, when it is small enough to be difficult to see, that human infection most often occurs. Adult ticks, active in cooler months, are larger and easier to spot, therefore frequently removed before disease transmission can occur. 

There are four stages of tick development: egg, larva, nymph, and adult; during the last three stages they must obtain a blood meal before they can molt to the next stage and before female adult ticks can develop eggs. The larva and nymph stages of blacklegged tick frequently feed on white-footed mice and the adults tend to feed on deer, though all stages can and will feed on humans. Adult male ticks remain on a deer to mate with several female ticks before falling off and a single female blacklegged tick can lay as many as 2,500 eggs.

Most ticks require three separate hosts for their three blood meals. After obtaining a blood meal the tick will drop off of its host into leaf litter where it will molt and wait for a new host to come along. Ticks do not have wings, cannot jump, and do not travel much, though according to an article written by Renée Anderson and Cornell Professor of Entomology Laura Harrington, “Tick Biology for the Homeowner,” some have been shown to travel up to 23 yards. 

Due to their limited mobility ticks rely on hosts brushing by them. For this reason many public health centers advise hikers and outdoor enthusiasts to choose well-maintained paths, free of leaf litter, and to try to keep to the center of the path avoiding brushing against the vegetation on the sides of the trail.

Lyme disease is caused by the bacterial spirochete (corkscrew shaped) Borrelia burgdorferi, named after the person to first identify the spirochete, Dr. Willy Burgdorfer, who did so in 1982. According to the Center for Disease Control’s (CDC) website, “In most cases, the tick must be attached for 36-48 hours or more before the Lyme disease bacterium can be transmitted,” although other sources suggest the window opens after the first 24 hours.

The bacterium can be transmitted earlier if the tick is removed improperly. “It takes time for ticks to insert their mouthparts and secrete a glue-like substance called attachment cement,” write Harrington and Anderson. “The cement will harden and helps to further anchor the tick firmly in place.” The secretions include an anesthetic which keeps the host from detecting the bite, making the tick that much more insidious a foe.

Adult female deer ticks (Ixodes scapularis) are about the size of sesame seed (2.7 mm or one-tenth of an inch) and males are slightly smaller. The larvae are the size of the period at the end of this sentence. In contrast, the more familiar American dog tick (Dermacentor variabilis) is nearly a quarter-inch long and can double in size when engorged with blood. (The brown dog tick (Rhipicephalus sanguineus) rarely bites people.)

To remove a tick, use thin tweezers to grasp it below the body, as close to the skin as possible, then slowly and gently pull up away from the skin, being careful not to squeeze or twist the tick. Improper tick removal that involves squeezing or pinching can result in the tick regurgitating into the bite and in this way transmitting disease before the usual infection time period has elapsed.

Symptoms of Lyme disease infection can take anywhere from three to thirty days to manifest and include the flu-like symptoms of fever, chills, nausea, stiff or painful joints, fatigue and mental “cloudiness.” Most people are familiar with the bulls-eye-shaped rash, erythema migrans (EM), as a telltale sign of Lyme infection. However, the rash develops in as few as 60 percent of those infected and the topography of the location of the bite, such as between the toes, can make the rash difficult to identify.

If left untreated Lyme disease can lead to chronic joint pain, cardiac problems, or neurological damage. The CDC recommends a two-step testing process for diagnosing Lyme disease by looking for evidence of antibodies against the infection. The first step is an enzyme immunoassay (EIA) or less frequently an indirect immunofluorescence assay (IFA), if the result is positive or indeterminate, sometimes called “equivocal,” the second step is a test called the Western blot.

If both are positive the New York State Department of Health (NYSDOH) recommends a 14-21 day course of the antibiotics doxycycline, cefuroxime axetil, or amoxicillin. According to the NYSDOH, “Serologic tests are insensitive during the first few weeks of infection. During this stage patients with an EM rash may be diagnosed clinically.” Furthermore, both steps of the two-step process recommended by the CDC are prone to false-positives, which is why they require a positive result for both tests for a positive diagnosis of Lyme disease.

Additionally, antibodies to Lyme disease persist in the body even after the infection has cleared making it impossible for the first set of tests to differentiate between previous infections and active infections. Insensitivity of the tests during the first few weeks of infection has led some doctors to prescribe antibiotics based on the presence of the rash or patient-reported symptoms following a known tick bite (in the nearly 40 percent of cases in which no rash presents).

While this approach undoubtedly alleviates the prolonged suffering of many, it presents two distinct public health concerns. The first is that clinically diagnosed cases are difficult to track because there is no positive set of tests to confirm the diagnosis. For example, in 2012 the CDC reported there were 2,044 confirmed cases of Lyme disease in New York State and 954 probable, with 22,014 confirmed nationwide and 8,817 probable. With roughly one-third of the cases identified by the CDC as probable, some suggest the actual infection rates could be much higher due to misreporting, underreporting, and people who clear the disease without seeking medical attention, which does happen.

The second public health concern associated with undiagnosed treatment of Lyme disease is the prevalent overuse of antibiotics and the concern that the misuse of antibiotics leads to the development of antibiotic resistant diseases.

This second concern becomes particularly acute when considering the controversial topic of “chronic Lyme disease,” or what the CDC calls “post-treament Lyme disease syndrome” (PTLDS). According to the CDC, “Approximately 10 to 20 percent of patients treated for Lyme disease with a recommended two- to four-week course of antibiotics will have lingering symptoms of fatigue, pain, or joint and muscle aches. In some cases, these can last for more than six months.”

The cause of PTLDS is unknown. According to one theory, the lingering symptoms are caused by residual damage to tissues and the immune system affected during the infection. On the other hand, some physicians tell their patients they are experiencing a persistent infection of Lyme disease. Proponents of the latter frequently recommend sustained antibiotic use, ranging from months to years. 

While some chronic Lyme advocates insist prolonged antibiotic use is the only source of relief, evidence suggests no more relief is gained from long-term antibiotic use than long-term placebo use. In “The chronic debate over Lyme disease,” in the journal Nature Medicine, Coco Ballantyne reports that the anti-inflammatory properties of some antibiotics may explain the relief felt by PTLDS sufferers. Ballantyne cited one study that showed the antibiotic ceftriaxone boosted cognitive function during use but ceased with the cessation of use, which may explain the regained mental focus experienced by PTLDS sufferers during long-term antibiotic use and the subsequent cognitive decline after stopping antibiotic treatment. 

Studies like these suggest the relief chronic sufferers receive from antibiotics are from the side effects of some antibiotics and do not outweigh the danger of sustained use, nor do they prove the existence of chronic infection. The most common complaints of PTLDS sufferers are joint pain, fatigue, and headaches, making chronic infection that much more difficult to prove as they are symptoms of other ailments, as well as certain lifestyle habits. 

Blacklegged ticks can also transmit the protozoan Babesia microti, which causes babesiosis (buh-BEE-zee-osus), a malaria-like illness that invades the red blood cells. The first documented case in the United States was in 1969 in Nantucket, and it has since spread throughout the Northeast and Upper Midwest. The disease has a one- to four-week incubation period after which time symptoms—ranging from mild to, in rare cases, death—include fever, muscle aches, headaches, chills, cough, loss of appetite, nausea, and profuse sweating. 

Diagnosis involves looking for the protozoan in the blood of the symptomatic; multiple blood smears may be necessary if the concentration of the protozoan is low. Anywhere from 25 to 50 percent of the infected are asymptomatic, leading to significant public health concerns. According to Dr. Douglas MacQueen, infectious disease specialist at Cayuga Medical Center, “There have been documented cases of blood transfusions transmitting babesiosis; this is a real concern because there isn’t a good test to screen for it.”

In the 2011 New York Times article, “Once rare, infection by tick bites spreads,” Laurie Tarkan reports, “Babesiosis already is the most frequently reported infection transmitted through transfusion in the United States, responsible for at least 12 deaths. In New York City, six transfusion-associated cases of babesiosis were reported in 2009. Infection by this route can be serious: One study found approximately 30 percent of people who were infected by a transfusion died.” The risk of transfusion-transmitted infection is high enough that the CDC recommends physicians make blood transfusion patients aware of the symptoms of the disease.

Babesiosis is treated with antimicrobial medications. Untreated it can lead to heart, lung or kidney failure. Co-infections of Lyme and babesiosis have been confirmed within tick populations, meaning an infected tick can transmit both diseases to its host. Those who have been diagnosed with Lyme disease but are not experiencing full symptom relief with antibiotic treatment should be tested for babesiosis; one theory suggests that PTLDS could actually be a co-infection of babesiosis.

The easiest strategies for tick-borne infection prevention require the most individual vigilance. Wear light-colored clothing to make ticks easier to spot, wear long sleeves and tuck your pants into your socks and perform daily body checks on yourself, your children and your dogs, if you have been in a location where ticks are a known problem. 

“There were an estimated 145 cases of Lyme disease in Tompkins County in 2011. We know it’s here, and we know there are a lot of cases, and the best thing to do is get people to do their best to prevent it,” said Theresa Lyczko, Director of the Health Promotion Program at the Tompkins County Department of Health. 

Lyczko advised keeping yards clear of brush and brush piles to reduce exposure to ticks. Chemical sprays of DEET, which can be applied to the skin, and Permethrin, which should only be applied to clothes, have been shown to deter ticks. 

A more controversial tick control method involves culling deer herds. The argument in favor of this method suggests that as the main host of adult ticks, decreasing deer populations will decrease tick populations. This argument often refers to a successful experiment performed on Monhegan Island in Maine in the mid-1990s in which sharpshooters were hired to shoot more than 100 deer. The experiment worked, nearly eradicating the disease on the island.

There are two problems with applying this experiment to areas such as Tompkins County. The first is that Monhegan Island had no significant populations of other large mammals on which adult ticks could attach, feed and mate. Even if deer culling were successful in our area, the presence of coyote populations alone would most likely make this an unsuccessful tactic in decreasing tick populations. 

The other problem with culling deer herds to control tick populations is the mobile nature of deer and the lack of natural geographic boundaries. Kill the deer we have and more than likely others will move in. Furthermore, as Beth Daley of the Boston Globe reported in “A minuscule foe, a massive public health challenge,” research suggests to be successful deer populations would need to be brought down to eight to ten per square mile. 

To put that number in context: the May 2013 report, “Population Analysis for White-tailed Deer in the Village of Cayuga Heights, New York,” published by researchers at Cornell University’s Department of Natural Resources, reported approximately 225 deer present in the 1.8 square mile village of Cayuga Heights, around 125 animals per square mile. To have an effect on the tick population, Cayuga Heights would need to kill over 200 deer and monitor and kill migrating deer entering the area. This would be a significant undertaking and could potentially present other public safety concerns in terms of hunters or sharpshooters operating in a populated area.

Dr. Roy Faiman of the Harrington Laboratory in Cornell’s entomology department explained, “A different study involving deer culling in a residential area in which almost half the deer population was eliminated resulted with no change in the tick population, or reduction of human disease cases. To date there is no available evidence to prove this type of measure on the U.S. mainland could result in a negative impact on Lyme transmission.”

Some municipalities are experimenting with pesticide-laced deer feeding stations, boxes that the deer must put their heads inside to access the food. The hypothesis of the experiment is the pesticide rubs off on their necks and deters ticks.

Faiman said of this prevention measure: “Results indicated a significant reduction of adult ticks as measured on a sample of treated deer. As successful as this trial was, it’s important to stress the fact that this type of treatment affects mainly the adult ticks, which are involved to a significantly lesser degree with Lyme transmission. Studies looking at tick infection rates in deer-treated areas did not detect a significant reduction in tick infection rates, nor did they find a reduction in total foraging tick numbers.”

Some researchers suggest the problem is not the deer population but the white-footed mouse (Peromyscus spp.) population, a favorite host of larva and nymph ticks, which are the most frequent cause of infection in humans because they can go undetected much longer than attached adult ticks. Mice are more likely than deer to gain access to our yards and even our homes, and the white-footed mouse population has been increasing as natural predators have decreased.

Daley identified one researcher who has developed a program of filling tiny tubes with tick-repellent cotton balls that can be placed in the yard for mice to carry back to their nests. The theory is this would keep ticks from feeding on infected mice and thus stop the spread of infection.

According to Faiman,“Although some of these methods have had small focused impacts on tick populations, we have not seen evidence of wide scale success. In order to be successful, these strategies—and any new ones—will need to be simple, inexpensive and sustainable.” 

These experiments do not seem to have made their way to the Tompkins County region, where health department efforts have focused on public education. “The best way to do anything about Lyme disease is to prevent it,” said Lyczko. “It used to be as recently as five years ago we would see only a few cases in the county, and they were people who had traveled to other places where Lyme disease was endemic. Now we do have people who are being infected in the county.”

Dr. MacQueen expressed similar sentiments: “It’s important to take monitoring very seriously, there’s been an increase this year over last year, and I expect numbers like this year will be the new normal.”

Prevention efforts may get a boost in the not-too-distant future. According to Faiman, “There was an effective vaccine on the market approximately 15 years ago, but it was discontinued. A new vaccine produced by Baxter Healthcare is in early trial stage and will not be available for at least one to five years.”

If you find and remove a tick, Cornell Cooperative Extension will identify it for $5. For more information visit www.tompkins-co.org/health, blogs.cornell.edu/Harrington, or tickencounter.org.

0
0
0
0
0

Recommended for you

(2) comments

alexander davis

The Massachusetts State Lyme Disease Commission has recommended deer removal to combat Lyme disease because deer are key to the reproductive cycle of the deer tick. The adult egg-laying deer tick requires a sizeable mammal to feed on, and over 90 % feed on deer. It cannot feed on a mouse, for instance. This is why deer removal has been the only strategy which has worked: Lyme epidemics were stopped in places like Mumford Cove CT and Great Island MA despite the presence of other mammals which can host the adult deer tick, such as coyote. These other mammals have not been able to take the place of the deer. Indeed, there has never been a Lyme epidemic in the absence of deer. Ticks from just one deer can produce up to a million tick eggs per season which are spread around our parks, neighborhoods, and yards, making them unsafe. The deer tick infects us with at least five diseases of which three (anaplasmosis, babesiosis, and Powassan viral encephalitis) can be fatal. This is a public health crisis. Deer removal should be undertaken on a large regional basis so as to prevent deer from coming in from neighboring areas. Deer should be drastically reduced in numbers and a low deer population maintained. In 1930 there were 300,000 deer in the US. Today there are 30 million.

another guy named Dave

Please, can we just remember one thing, which we all learned in kindergarten:

TICKS ARE NOT INSECTS. Count the legs. 6 legs = insect 8 legs = not insect

It's hard to take carefully written science-based articles seriously when they are glaringly incorrect in the second paragraph.