More Acorns = More Mice = More Lyme Disease

The white-footed mouse has been found to be a competent reservoir for the Lyme disease-causing spirochete, Borrelia burgdorferi – Wikipedia image

MedicalResearch.com Interview
Richard S. Ostfeld, PhD

Distinguished Senior Scientist
Cary Institute of Ecosystem Studies
Millbrook, NY 12545, USA

MedicalResearch.com: What is the background for this study? What are the main findings?

Response: Lyme disease and other tick-borne infections occur in large portions of the eastern and Midwestern United States and adjacent Canada, and the geographic range is expanding rapidly, engulfing new communities every year.  Despite the observed increases in incidence rates and geographic range at the national level, considerable variation occurs across space and time, with persistent hot spots, colder spots, bad years, and not-as-bad years.  We undertook this long-term study (19 years) to ask what causes some places and years to be particularly risky and others not as risky, in terms of human exposure to tick-borne disease.  Because diagnosis and treatment of Lyme disease are problematic and highly controversial, and because no vaccines or effective tick-control methods are currently available, we hoped that understanding the causes of high risk would facilitate prevention of human exposure.

We found that, in the oak-dominated forests that pervade the Lyme-disease-endemic zone, acorn production in the autumn is a strong leading indicator of Lyme disease risk two summers later.  Acorn production is associated with marked population increases of white-footed mice and eastern chipmunks, which use abundant acorns as a key over-winter food source, leading to population growth the following year.  Dense summer populations of mice and chipmunks provide the local population of blacklegged ticks with abundant sources of blood-meal hosts.  These small rodents are more permissive of successful tick feeding (other hosts kill many ticks by grooming them as they attempt to feed), and they are also the primary natural reservoirs of infection with the microbial agents causing Lyme disease, anaplasmosis, and babesiosis.  Larval ticks emerging when rodents are highly abundant are highly likely to survive and acquire infection, molting the next year into infected nymph-stage ticks.  Bites from nymph-stage ticks are responsible for the great majority of tick-borne disease cases.  The one-year lag from acorns to rodent populations plus the one year lag from larval ticks biting rodents to nymphal ticks biting people together are responsible for the total two-year lag.

By using motion-sensitive cameras set in over 100 sites over two years, we were also able to ask whether the local community of mammal predators can affect human risk of exposure.  We found that sites with a diverse assemblage of predators, especially foxes, bobcats, and opossums, were associated with reduced tick infection prevalence with the agents of Lyme disease, anaplasmosis, and babesiosis.  When these predators were absent, which sometimes occurred when coyotes displaced them, infection prevalence was significantly higher.  Infection prevalence was also lower in sites within extensive, unbroken forest, and higher in sites with small forest remnants.  Taken together, we determined that an understanding of the food webs within which ticks and pathogens dwell can strongly facilitate the ability to predict when and where risk will be high.  Acorns exert what ecologists call a “bottom-up” effect, whereas the predators enforce “top-down” control.  We found that the ticks were remarkably resilient to most weather-related factors.  However, when winter-spring weather was particularly warm and dry, tick abundance the following summer was reduced.  Cold winters did not kill off the ticks. 

MedicalResearch.com: What should readers take away from your report?

Response: The ecology of tick-borne disease is incredibly complex, but still we can find big signals amongst the noise and predict risk with a good degree of confidence.  Predicting times and places of enhanced risk is particularly important given the frustrations within the public health community and the public at large over the slow pace of progress in improving diagnostic capabilities and treatments.  We are still relying fundamentally on individual efforts to prevent exposure using various self-protections, such as repellents, tick-checks, protective clothing and the like.  Targeting these efforts to times and places where risk is particularly high should help protect public health. 

MedicalResearch.com: What recommendations do you have for future research as a result of this work?

Response: Long-term monitoring of tick populations is crucial for evaluating the importance of ecological variables, like wildlife abundance and weather, in determining risk of human exposure.  In addition, the longer we monitor these variables the more likely we are to see extreme events, which might play outsized roles.  Intensive monitoring like this is also crucial for detecting invasions by other species of tick that are important to public health. For instance, we expect lone star ticks to invade our area from the south, with unpredictable consequences for blacklegged ticks and human health.  We are also concerned about potential invasions by non-native ticks, like the long-horned tick that was recently detected in several eastern and Midwestern states to our south. 

No disclosures 

Citation:

Richard S. Ostfeld, Taal Levi, Felicia Keesing, Kelly Oggenfuss, Charles D. Canham. Tick-borne disease risk in a forest food web. Ecology, 2018; 99 (7): 1562 DOI: 1002/ecy.2386

 

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CDC Study Finds Lyme Disease Remains a Public Health Challenge

MedicalResearch.com Interview with:

This 2007 photograph depicts the pathognomonic erythematous rash in the pattern of a “bull’s-eye”, which manifested at the site of a tick bite on this Maryland woman’s posterior right upper arm, who’d subsequently contracted Lyme disease. Lyme disease patients who are diagnosed early, and receive proper antibiotic treatment, usually recover rapidly and completely. A key component of early diagnosis is recognition of the characteristic Lyme disease rash called erythema migrans. This rash often manifests itself in a “bull's-eye” appearance, and is observed in about 80% of Lyme disease patients. Lyme disease is caused by the bacterium Borrelia burgdorferi, and is transmitted to humans by the bite of infected blacklegged ticks. Typical symptoms include fever, headache, fatigue, and as illustrated here, the characteristic skin rash called erythema migrans. If left untreated, infection can spread to joints, the heart, and the nervous system. Note that there are a number of PHIL images related to this disease and its vectors.

This 2007 photograph depicts the pathognomonic erythematous rash in the pattern of a “bull’s-eye”, which manifested at the site of a tick bite on this Maryland woman’s posterior right upper arm, who’d subsequently contracted Lyme disease.
Lyme disease patients who are diagnosed early, and receive proper antibiotic treatment, usually recover rapidly and completely. A key component of early diagnosis is recognition of the characteristic Lyme disease rash called erythema migrans. This rash often manifests itself in a “bull’s-eye” appearance, and is observed in about 80% of Lyme disease patients.
Lyme disease is caused by the bacterium Borrelia burgdorferi, and is transmitted to humans by the bite of infected blacklegged ticks. Typical symptoms include fever, headache, fatigue, and as illustrated here, the characteristic skin rash called erythema migrans. If left untreated, infection can spread to joints, the heart, and the nervous system. From CDC image library

Kiersten Kugeler, PhD
Division of Vector-Borne Diseases
CDC

MedicalResearch.com: What is the background for this study? What are the main findings?

Response: Lyme disease has been a nationally notifiable disease in the United States since 1991. Each year, possible cases of Lyme disease are investigated and tallied by state and local public health officials according to criteria set by the surveillance case definition. States voluntarily share human case data with CDC, which summarizes the data to provide a national perspective on disease trends.

This report summarizes national Lyme disease data reported during 2008-2015. Lyme disease continues to be the most commonly reported vector-borne disease in the United States with more than 275,000 cases of Lyme disease reported to CDC during the study period. Although most cases continue to be reported from states with high incidence in the Northeast, mid-Atlantic, and upper Midwest regions, case counts in most of these states have remained stable or decreased during this time. In contrast, case counts have increased in states that neighbor those with high incidence. The trend of stable to decreasing case counts in many states with high incidence may be due to multiple factors, including the possibility that occurrence of the disease has stabilized in these areas or that some state health agencies have changed their reporting practices to lower the resource burden associated with Lyme disease surveillance. Lyme disease surveillance is not meant to document every case, but rather to indicate disease trends over time, define high-risk groups, and describe the geographic distribution of the condition.

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Lyme Disease Ticks Common in Eastern US National Parks

MedicalResearch.com Interview with:
Tammi L. Johnson PhD, Microbiologist

Division of Vector-Borne Diseases
CDC

MedicalResearch.com: What is the background for this study?

Response: Lyme disease is caused by the bacterium Borrelia burgdorferi and is transmitted to humans through the bite of infected blacklegged ticks, also called deer ticks. Lyme disease is the most commonly reported vectorborne illness in the United States, with approximately 300,000 humans becoming infected each year.

While Lyme disease infections are highly concentrated in the northeast and upper Midwest, the number of counties in which the blacklegged tick has become “established” has more than doubled in the past two decades. Established populations of these ticks are found in 35 states.

Knowing that Lyme disease is increasing both in numbers of infections and in geographic range in the United States, we did this study to determine if people are at risk of encountering infected ticks while recreating in eastern national parks. This is the first large-scale survey in multiple national parks, and though suspected, it had not been confirmed that ticks in many of these parks were infected.

So the purpose of the study was to survey national park units across six Northeastern and Mid-Atlantic States and the District of Columbia, ranging from Maine in the north to Virginia in the south and characterize the risk of human exposure to ticks-borne bacteria.

Researchers from the Centers for Disease Control and Prevention and the National Park Service evaluated frequently used trails in Acadia National Park, Catoctin Mountain Park, Fire Island National Seashore, Gettysburg National Military Park, Manassas National Battlefield Park, Monocacy National Battlefield, Prince William Forest Park, Rock Creek Park, and Shenandoah National Park.

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Modified Microscopy for Lyme Disease Found Unreliable

MedicalResearch.com Interview with:

Audun Aase, PhD Department Director, Infectious Disease Immunology Norwegian Institute of Public Health Oslo, Norway

Dr. Audun Aase

Audun Aase, PhD
Department Director, Infectious Disease Immunology
Norwegian Institute of Public Health
Oslo, Norway

MedicalResearch.com: What is the background for this study?

Response: Controversies related to Lyme disease and tick transmitted diseases have gained much attention in the public media in Norway, both regarding treatment regimens and diagnostics. People with long-lasting disease may relate their symptoms to previous tick bite and/or suboptimal-treated Lyme disease and have adopted the diagnosis chronic Lyme disease. As many of these patients lack objective proof of Lyme disease, they look for alternative test to signify their suspicion.

A modified microscopy method for detection of the Borrelia burgdorferi s.l. (the causative agent of Lyme disease) in human blood was published in 2013. The authors behind the method examined blood from suspected chronic Lyme disease patients, and the results showed presence of Borrelia spirochetes in most of the specimens. Using the same method, they also claimed to detect the Babesia parasites in many of the samples. The method gained much publicity and the patients advocated strongly for this method as most other laboratory tests had failed to prove their diagnosis.
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microRNAs in Joint Fluid As Biomarker For Antibiotic Refractory Lyme Arthritis

MedicalResearch.com Interview with:
Robert B. Lochhead PhD
Clinical Fellow in Medicine 
Division of Rheumatology, Allergy & Immunology
Massachusetts General Hospital
Harvard Medical School, Boston, MA

Medical Research: What is the background for this study? What are the main findings?

Dr. Lochhead: Lyme arthritis (LA), caused by the tick-borne spirochete Borrelia burgdorferi, usually resolves appropriately with antibiotic treatment, called antibiotic-responsive Lyme arthritis. However, in some patients, arthritis persists for months or years after spirochetal killing with oral and IV antibiotic therapy, called antibiotic-refractory Lyme arthritis. Synovial lesions in these patients show marked synovial proliferation, inflammation, and vascularization, accompanied by autoimmune T and B cell responses. MicroRNAs (miRNAs) regulate many biological processes including inflammation, immune responses, and cell proliferation, and are effective biomarkers that may reveal molecular mechanisms of disease. Our objective here was to identify extracellular miRNAs (ex-miRNAs) in synovial fluid (SF) that distinguish regulated (responsive) from dysregulated (refractory) immune responses in Lyme arthritis, thereby providing insights into underlying biological processes and potential diagnostic biomarkers to distinguish between  these disease courses.

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Three Cases of Cancer Misdiagnosed as Chronic Lyme Disease

MedicalResearch.com Interview with:
Christina Nelson, MD, MPH, FAAP

Medical Epidemiologist
Centers for Disease Control and Prevention
Division of Vector-Borne Diseases | Bacterial Diseases Branch
Fort Collins, CO

Medical Research: What is the background for this study?

Dr. Nelson: Evidence-based guidelines for the diagnosis and treatment of Lyme disease have been provided by the Infectious Diseases Society of America for many years. These comprehensive guidelines have been vetted by external review panels as the best option for patient care. In endemic areas, patients with the typical rash (erythema migrans) can be diagnosed with Lyme disease clinically. Otherwise, the guidelines recommend that diagnosis be based on a history of possible exposure, compatible clinical features, and positive two-tier serologic testing.

Some patients who have been treated for Lyme disease may develop post-treatment Lyme disease syndrome (PTLDS) – fatigue, arthralgias, or other symptoms that persist after completing antibiotic treatment. Although the exact cause of post-treatment Lyme disease syndrome is unknown, it is thought to be due to an altered immune response or residual damage to tissues during the acute infection. A diagnosis of exclusion, PTLDS should only be diagnosed after the patient has been thoroughly evaluated and other potential causes of symptoms ruled out.

On the other hand, “chronic Lyme disease” is a loosely defined diagnosis that has been used to describe a variety of ailments. A small cadre of providers use unconventional methods to diagnose patients with chronic Lyme disease, and sometimes there is no objective evidence that the patient ever had Lyme disease. Multiple factors contribute to this phenomenon, including misconceptions about serologic testing, use of unvalidated diagnostic tests, and clinical diagnosis of Lyme disease based on nonspecific symptoms alone.

We know that patients have been – and continue to be – harmed by treatments for chronic Lyme disease. Patients have suffered from emboli, severe allergic reactions to antibiotics, neutropenia, and infections such as Clostridium difficile. This is terrible and should never happen. However, there is another important danger related to these alternative practices. Some patients who have been diagnosed and treated for chronic Lyme disease later discover that another condition is the root of their physical problem. We wanted to highlight some of these cases in order to help educate providers and patients about this issue.

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Lyme Disease A Year Round Threat in Northern California

Daniel Salkeld, PhD Lecturer & Research Associate Stanford Woods Institute for the Environment Professor Colorado State UniversityMedicalResearch.com Interview with:
Daniel Salkeld, PhD
Lecturer & Research Associate
Stanford Woods Institute for the Environment Professor
Colorado State University


Medical Research: What are the main findings of the study that were just published in Ticks and Tick-borne Diseases?

Dr. Salkeld: The primary findings of this new study show that western black-legged ticks, which can transmit Lyme disease, are active throughout the year in Northwest California, making the threat of Lyme disease year-round phenomenon.

More specifically, my colleagues from California Department of Public Health Vector-borne Disease Section and University of California, Berkeley and I found that the activity of Western Black-legged ticks (Ixodes pacificus), which are the ticks most commonly known to carry Lyme disease (caused by Borrelia burgdorferi) in Northwest California, is largely predictable and year-round. In general, tick larvae (newly hatched immature ticks) are active April to June, and sometimes activity extends into October, while adult ticks are active from October to May. Nymphal ticks (the tick stage following larvae and preceding adults) are active from January to October but peak from April-June. This is important because nymphs are responsible for most Lyme disease infections.
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