News You Can Use: Map Shows Where Dogs & Humans Are at High Risk of Lyme Disease This Summer

Map Shows Where Dogs & Humans Are at High Risk of Lyme Disease This Summer

Lyme is a growing threat as we move into warmer weather in the US. Researchers have said this year could be one of the worst for this tick-borne disease, as a skyrocketing mouse population and warmer temperatures increase the risk.

Knowing where this risk is highest is going to be important in protecting ourselves, and our pets, from this dangerous infection. To that end, a University of Georgia parasitologist and a mathematician at Clemson University joined efforts to create a forecast map to help veterinarians — and humans — avoid Lyme disease this summer.

Lyme disease, the most common zoonotic tick-borne disease in the US and Europe, is an infection caused by a type of bacteria called a spirochete, in this case, from the family Borrelia burgdorferi.

Colored scanning electron microscope image of B. burgdorferi spirochetes, a type of bacteria. Image by Janice Haney Carr/CDC

B. burgdorferi and its associated strains reside in reservoir hosts like white-footed mice and other rodents. The primary vector of Lyme disease is the black-legged tick, which feeds on infected rodents. The reservoir host is where the spirochetes principally reside, while the vector is the means by which the infection is transmitted. In this case, ticks take blood meals on animals, like humans and dogs, and transmit Lyme disease far and wide.

Lyme disease is spread by black-legged ticks of the eastern and western variety, and while the northeastern US is hardest hit, Lyme disease has spread across the country. Once considered easily treatable with antibiotics, healthcare providers are trying to understand why some people acquire and suffer chronic symptoms after infection with Lyme disease.

Research reveals that ticks can carry multiple pathogens, and some of those, like the Powassan virus, have recently spread into black-legged ticks — creating the disturbing possibility of extremely serious coinfection (the unfortunate condition of being infected by more than one pathogen at a time).

Historical cases reported in the US from 1990 to 2015, according to the Lyme Disease Association (compiled from CDC data). Image via CDC

All of this troubling news creates an incentive to create predictive tools to understand what areas will be hard hit by Lyme disease. A study published in PLOS One offers a model to suggest what areas of the county are at highest risk in the summer of Lyme disease for dogs. Where there are dogs — there will be humans — and the forecast map could help both.

B. burgdorferi antibody prevalences in domestic dogs for an average year during 2011 to 2015. Image by Watson et. al/PLOS ONE

The researchers who created this model used data from 11,937,925 dogs tested for antibodies to B. burgdorferi collected from 48 US states between 2011 and 2015. Using mathematical modeling, the scientists created a forecasting tool that combines the serologic test results with other factors associated with Lyme disease, including:

  • forest cover
  • elevation
  • surface water
  • median household income
  • population density
  • temperature and relative humidity
  • rainfall

An organization involved with the research, the Companion Animal Parasite Council, helped organize the study to better understand and provide information to vets on parasitic infections in pets. The council reports approximately four million dogs were tested for Lyme disease in 2015, with 250,880 dogs testing positive for antibodies to B. burgdorferi.

Lyme disease hits dogs just as hard as it does humans, with fever, loss of appetite, neurologic, renal, cardiac, and skin troubles. The incubation period for Lyme disease in dogs is between two to five months, which is longer than in humans. Symptoms may include:

  • fever
  • general feeling of being unwell
  • lameness
  • swollen lymph nodes

Scientists sought to evaluate and combine time and space drivers of canine Lyme disease using a Bayesian hierarchical modeling process. Bayesian refers to a theory of probability used for creating statistical models developed by the Reverend Thomas Bayes in the 1700s.

While working on their model, the authors noted the heavy prevalence of positive antibody results in the Northeast. Other predictions of the model include:

  • Movement of ticks and Lyme disease through California, Idaho, Colorado, New Mexico, and North Dakota, that marks a north and westward expansion of the infection.
  • Convergence of Lyme disease in dogs in the Great Lakes region, including Indiana, Ohio, Illinois, Kentucky, and Michigan.

The researchers recommend care for dogs; including:

  • annual testing for Lyme disease
  • annual use of tick and mite killing medications
  • vaccination against Lyme disease

In a press release, parasitologist Michael Yabsley of the University of Georgia noted:

Dogs really are the canary in the coal mine for human infection. Our research team has evidence that the relationship between canine disease and human disease is strong.

While the report is limited to results from dogs under veterinary care, researchers believe the numbers in the report are lower than in the actual population. While dogs are generally out beating the bush more than their human counterparts, their owners are generally not too far behind — leaving both dog and dog-person at greater risk for Lyme disease as the ticks and disease continue to spread across the country.

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Cover photo by Kaldari/Wikimedia Commons

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