BOSTON — A new species of bacteria is causing Lyme disease, adding to worries that the infection will continue its relentless escalation across the United States. Lyme is already the most common tick-borne disease in North America, with new cases peaking every June and July.
“In summary, the news is largely bad,” Paul Mead of the U.S. Centers for Disease Control and Prevention said June 19 at a joint meeting of the American Society for Microbiology and the Interscience Conference on Antimicrobial Agents and Chemotherapy. Not only is the prevalence of Lyme disease increasing, another tick-borne illness — Rocky Mountain spotted fever — is cutting a deadly path through Mexico.
Public health officials began collecting data on Lyme disease in 1991. Since then, it has spread in all directions from two U.S. epicenters, one in the Northeast and one in the Upper Midwest, according to data Mead presented at the meeting and published last year in Emerging Infectious Diseases. In the early 1990s, 43 Northeast counties had a high incidence of the disease. Today, 182 do. About 30,000 to 35,000 Lyme disease cases are reported each year in the United States, up from around 11,000 cases in 1995, the CDC reports.
Until recently, only one bacterium in North America was known to cause the disease: Borrelia burgdorferi. (In Europe, two other species are more common.)This year, researchers at Mayo Clinic testing blood and synovial fluid samples from people infected with Lyme disease discovered six infections that did not trace to B. burgdorferi. In addition to a rash, fever and other classic Lyme symptoms, those patients also experienced confusion, nausea and vomiting. “Not so typical for Lyme disease,” Mead observed.
A previously unknown species of Borrelia was causing the disease, the Mayo team reported in the May issue of Lancet Infectious Diseases. Infections from the newly named Borrelia mayonii appear to cause unusually high concentrations of bacteria in the blood. The patients recovered after receiving the same antibiotics that treat Lyme disease. As of now, samples taken from ticks show that B. mayonii is only found in the Upper Midwest.
How this new Lyme culprit will affect the spread of disease is unknown, said Peter Krause, an epidemiologist at Yale University who was not involved in that research. “Is this going to spread rapidly? Is it going to increase the number of cases? Or is it going to remain uncommon? It’s too early to know.”
Also during the meeting, Gerardo Alvarez-Hernandez of the University of Sonora in Hermosillo, Mexico, described an epidemic of Rocky Mountain spotted fever that is largely affecting that country’s children.
Rocky Mountain spotted fever was first reported in Mexico in 2009, but the full scope of its incidence is unknown because Mexico does not have the resources for more accurate reporting. However, Alvarez-Hernandez’s studies in Sonora have found that about 20 percent of children hospitalized for Rocky Mountain spotted fever will die, largely, he said during the meeting, because they don’t get antibiotics in time to help. U.S. fatality rates are less than 1 percent.
There’s another difference, too: Most U.S. cases occur in temperate climates (North Carolina, Oklahoma, Arkansas, Tennessee and Missouri), where Rocky Mountain spotted fever is spread by a tick that lives on deer, dogs and livestock. But in Mexico’s desert region, the disease is mostly spread by a tick that prefers domestic dogs. “We have close interactions between ticks, dogs and children,” Alvarez-Hernandez said.