Lyme disease: You can't blame the deer

Date: July 21, 2016

Source: University of Oslo, Faculty of Mathematics and Natural Sciences

The last decades the disease Lyme borreliosis that is spread by ticks has been increasing, but this increase cannot be explained by the increasing deer population only.

Results from the research project TickDeer, recently published in Nature Communications, shows that the percentage of ticks with Borrelia is decreasing in areas with a high deer population (deer, red deer and moose). However, the total number of ticks is higher.

This means that the risk of catching Borrelia is not decreasing as much as one could hope for despite the "clean host," and all in all a high density of deer give a netto increase in borreliosis.

Since 1991 Norway has registered all incidents with borreliosis in a so-called MSIS-statistics for reportable diseases.

At the same time data on the wild deer population over all of Norway has been recorded. This is why Norway has a unique set of data material for comparing the relation between the disease progression over time, says professor Atle Mysterud, who led the project.

In addition the researchers at the TickDeer-project, which represent a cooperation between the Department of Biosciences (University of Oslo), Norwegian Veterinary Institute, and NIBIO, looked at how the number of deer affects the number of ticks, and in particular ticks with Borrelia. The results show that borreliosis has increased more than the density of deer would suggest.

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Ticks that vector Lyme disease move west into North Dakota

Date:

September 11, 2014

Source:

Entomological Society of America

Summary:

Ixodes scapularis, also known as the blacklegged tick or deer tick -- is moving westward, and for the first time has been found to be established in North Dakota.

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Reducing deer populations may reduce risk of Lyme disease

Date:

July 1, 2014

Source:

Entomological Society of America

Summary:

Reduced deer populations can lead to a reduction in Lyme disease cases, researchers in Connecticut have found that after a 13-year study was conducted. White-tailed deer serve as the primary host for the adult blacklegged tick (Ixodes scapularis) -- the vector for Lyme disease. The study found that the number of resident-reported cases of Lyme disease per 100 households was strongly correlated to deer density in the community.

Continued

Amber discovery indicates Lyme disease is older than human race

Date:

May 29, 2014

Source:

Oregon State University

Summary:

Lyme disease is a stealthy, often misdiagnosed disease that was only recognized about 40 years ago, but new discoveries of ticks fossilized in amber show that the bacteria which cause it may have been lurking around for 15 million years -- long before any humans walked on Earth. The findings were made by researchers who studied 15-20 million-year-old amber from the Dominican Republic that offer the oldest fossil evidence ever found of Borrelia, a type of spirochete-like bacteria that to this day causes Lyme disease.

Continued

Essential Factor for Lyme Disease Transmission Identified

Dec. 19, 2013 — Borrelia burgdorferi, the bacterium that causes Lyme disease, hitchhikes in ticks for dissemination to mammalian hosts--including humans. An article in the 19 December issue of PLOS Pathogens identifies HrpA, an RNA helicase, as a crucial player in the transmission from ticks to mammals.

George Chaconas, from the University of Calgary, Canada, and a member of the university's Snyder Institute for Chronic Diseases, and colleagues had previously identified HrpA as a modulator of B. burgdorferi protein expression. For this study, Chaconas' group joined forces with Justin Radolf and Melissa Caimano from the University of Connecticut Health Center, USA, to analyze the molecular function of the HrpA protein and further explore its role in the bacterium's complicated life cycle, in particular for transmission of the pathogen.

Continued

Wild Mice Have Natural Protection Against Lyme Borreliosis

Apr. 4, 2013 — Like humans, mice can become infected with Borrelia. However, not all mice that come into contact with these bacteria contract the dreaded Lyme disease: Animals with a particular gene variant are immune to the bacteria, as scientists from the universities of Zurich and Lund demonstrate. Wild mice are the primary hosts for Borrelia, which are transmitted by ticks.

Springtime spells tick-time. Lyme borreliosis is the most common tick-borne disease in Switzerland: around 10,000 people a year become infected with the pathogen. The actual hosts for Borrelia, however, are wild mice. Like in humans, the pathogen is also transmitted by ticks in mice. Interestingly, not all mice are equally susceptible to the bacterium and individual animals are immune to the pathogen. Scientists from the universities of Zurich and Lund headed by evolutionary biologist Barbara Tschirren reveal that the difference in vulnerability among the animals is genetic in origin.

Protective gene variant

Tschirren and colleagues examined wild mice for signs of a Borreliainfection in a large-scale field study. Borrelia afzelii -- the scientific name for the bacteria -- feed on mouse blood. The researchers discovered that mice with a particular variant of the antigen receptor TLR2 were around three times less susceptible toBorrelia. "The immune system of mice with this receptor variant recognizes the pathogen better and can trigger an immune response more quickly to destroy the Borreliain time," says Tschirren. Infected mice exhibit similar symptoms to humans -- especially joint complaints. Consequently, in the wild infected mice probably do not survive for very long and weakened animals soon fall victim to foxes and birds of prey. 

Continued:  http://www.sciencedaily.com/releases/2013/04/130404072925.htm

NSF, NIH Award Grants To Study Spread Of Diseases

September 29, 2012

The National Science Foundation (NSF), the National Institutes of Health (NIH), and other US and UK agencies are joining forces to determine whether or not human-induced changes to the environment have played a role in the spread of West Nile virus, Lyme disease and other ailments.

The NSF, the NIH’s Ecology and Evolution of Infectious Diseases (EEID) program, the USDA’s National Institute of Food and Agriculture (NIFA) and the UK’s Biotechnology and Biological Sciences Research Council (BBSRC) are among the organizations studying the possible ecological and biological mechanisms that could be at least partially responsible for the increased number of cases of infectious diseases spreading in both people and animals.

“Threats to human health, food security and ecosystem services are growing, in part due to increases in the spread of diseases,” Sam Scheiner, the NSF’s EEID program director, said in a statement Thursday. “These research projects will provide a new understanding of the causes of that spread and help us control these growing and myriad threats.”

“The interdisciplinary collaborations fostered by the EEID program promote a deeper understanding of how infectious diseases emerge and spread,” added Irene Eckstrand of the NIH’s National Institute of General Medical Sciences. “This knowledge is enormously helpful in developing effective strategies for suppressing the transmission of infectious agents in animal populations and reducing the burden of disease in humans.”

Twelve grants worth a combined $12.7 million have been awarded, and the projects that are being funded will allow scientists to investigate how habitat destruction, invasive species, pollution and other large-scale environmental factors might have contributed to the prevalence of disease-causing viruses, bacterium and parasites in both people and in various animal species, the NSF said in their September 27 statement.

redOrbit (http://s.tt/1oGd6)

Continued:  http://www.redorbit.com/news/science/1112703271/infectious-disease-spread-grants-092912/

Precautions for Tick-Borne Disease Extend 'Beyond Lyme'

ScienceDaily (Sep. 7, 2012) — This year's mild winter and early spring were a bonanza for tick populations in the eastern United States. Reports of tick-borne disease rose fast.

While Lyme disease is the most common tick-borne disease in the Northeast and Upper Midwest, new research results emphasize that it is not the greatest cause for concern in most Southeastern states.

The findings are published today in a paper in the journal Zoonoses and Public Health.

The majority of human-biting ticks in the North--members of the blacklegged tick species--cause Lyme disease, but these same ticks do not commonly bite humans south of mid-Virginia.

Biologist Graham Hickling of the University of Tennessee, co-author of the paper, says many patients in Southeastern states, who become sick from a tick-bite, assume they have Lyme disease, but the odds of that being the case are low.

"Ticks in the eastern U.S. collectively carry more than a dozen agents that can cause human disease," says Hickling.

Continued: http://www.sciencedaily.com/releases/2012/09/120907142341.htm

Lyme disease warning after herbicide banned

SCOTS outdoors enthusiasts are being warned to be extra vigilant against tick bites after a herbicide ban raised concerns that the insects' population is likely to soar.

The number of cases of Lyme disease – a potentially debilitating condition transmitted by ticks – has already risen from 28 in 2001 to 308 in 2010, but an EU ban on the herbicide Asulam has left nature watchers fearful that the increase in infections could accelerate.

Asulam is used to control the spread of bracken which provides a perfect habitat for ticks. It was withdrawn from sale at the end of 2011 and its use will be prohibited from December this year.

Lyme disease is transmitted via the bite of an infected tick and can lead to complications, including damage to the nervous system and heart.

Tick-borne disease charity BADA-UK has now expressed fears that the Asulam ban will lead to a rise in cases of the disease.

The charity's patron, survival expert Ray Mears said: "The spread of bracken as a result of the Asulam ban will lead to increased tick numbers making it all the more important that the public takes precautions against tick bites when out and about in rural areas."

Wendy Fox, chairwoman of BADA-UK, was left disabled as a result of Lyme disease. She said: "Increased interest in outdoor pursuits, combined with an increasing tick population is resulting in a year-on-year rise in cases of tick-borne disease."

The charity is backing a Scots research firm which is seeking hillwalkers to help them assess whether there would be a market for a device which removes ticks. Roslin-based Xeroshield is looking to develop the gadget.

http://www.heraldscotland.com/news/health/lyme-disease-warning-after-herbicide-banned.17116952

Lyme Disease Surge Predicted for Northeastern US: Due to Acorns and Mice, Not Mild Winter

ScienceDaily (Mar. 16, 2012) — The northeastern U.S. should prepare for a surge in Lyme disease this spring. And we can blame fluctuations in acorns and mouse populations, not the mild winter. So reports Dr. Richard S. Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, NY. 

What do acorns have to do with illness? Acorn crops vary from year-to-year, with boom-and-bust cycles influencing the winter survival and breeding success of white-footed mice. These small mammals pack a one-two punch: they are preferred hosts for black-legged ticks and they are very effective at transmitting Borrelia burgdorferi, the bacterium that causes Lyme disease.

"We had a boom in acorns, followed by a boom in mice. And now, on the heels of one of the smallest acorn crops we've ever seen, the mouse population is crashing," Ostfeld explains. Adding, "This spring, there will be a lot of Borrelia burgdorferi-infected black-legged ticks in our forests looking for a blood meal. And instead of finding a white-footed mouse, they are going to find other mammals -- like us."

Read on:  http://www.sciencedaily.com/releases/2012/03/120316094452.htm

Predicting the Spread of Ticks Across Canada

ScienceDaily (Mar. 5, 2012) — Researchers are watching as ticks that carry Lyme disease colonize Canada, but their research aims to predict the communities most likely to be hit by this sickness.

"Our findings will help community groups and government agencies to alert the Canadians who may be at risk of picking up Lyme disease -- those of us who like to visit the outdoors in spring and summer, when nymphal ticks are active but difficult to spot because of their size," said lead author Patrick Leighton of the University of Montreal's Faculty of Veterinary Medicine. Nymphal ticks are ticks that have not yet reached full maturity. "Identifying where the ticks are setting up home helps pinpoint where Lyme disease risk will occur before people start getting the disease."

Changes in temperature are one of the most important factors that have contributed to the spreading of tick populations across Canada since 1990. As average temperatures continue to increase over the coming decades, the area where ticks may live and reproduce will continue to reach further north. Lyme-transmitting ticks were virtually unknown in Canada in 1990, but today they may be found in areas where 18% of the country's population lives. This figure will rise to 80% in eastern Canada by 2020, according to the researchers' findings.

Read on:  http://www.sciencedaily.com/releases/2012/03/120305223610.htm

Impact of the experimental removal of lizards on Lyme disease risk. (Via HerpDigest)

Impact of the experimental removal of lizards on Lyme disease risk.
A Swei, RS Ostfeld, RS Lane, and CJ Briggs
Proc R Soc B, February 16, 2011; .
Department of Integrative Biology, University of California, , 3060 Valley Life Sciences Building, Berkeley, CA 94720-3140, USA.

The distribution of vector meals in the host community is an important element of understanding and predicting vector-borne disease risk. Lizards (such as the western fence lizard; Sceloporus occidentalis) play a unique role in Lyme disease ecology in the far-western United States. Lizards rather than mammals serve as the blood meal hosts for a large fraction of larval and nymphal western black-legged ticks (Ixodes pacificus-the vector for Lyme disease in that region) but are not competent reservoirs for the pathogen, Borrelia burgdorferi. Prior studies have suggested that the net effect of lizards is to reduce risk of human exposure to Lyme disease, a hypothesis that we tested experimentally. Following experimental removal of lizards, we documented incomplete host switching by larval ticks (5.19%) from lizards to other hosts. Larval tick burdens increased on woodrats, a competent reservoir, but not on deer mice, a less competent pathogen reservoir. However, most larvae fail!
ed to find an alternate host. This resulted in significantly lower densities of nymphal ticks the following year. Unexpectedly, the removal of reservoir-incompetent lizards did not cause an increase in nymphal tick infection prevalence. The net result of lizard removal was a decrease in the density of infected nymphal ticks, and therefore a decreased risk to humans of Lyme disease. Our results indicate that an incompetent reservoir for a pathogen may, in fact, increase disease risk through the maintenance of higher vector density and therefore, higher density of infected vectors.