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Although the majority of Lyme infections in the United States occur in the Northeast, incidence of the disease is growing across the country. Changes in climate and the movement of infected animals may be partly to blame. (Credit: Ervic Aquino)


San Francisco Bay area crawling with infected ticks

Ticks infected with the bacterium that causes Lyme disease and a newly identified human pathogen are widespread in the San Francisco Bay Area.

A study to be published in the March issue of the journal Emerging Infectious Disease details how researchers found the bacterium Borrelia miyamotoi, as well as B. burgdorferi, the bacterium that causes Lyme disease, in ticks they sampled throughout the area.


The researchers were surprised to find ticks infected with one or both bacteria in nearly every park they examined. The findings raise the question of whether B. miyamotoi has gone undetected in California residents.

The research results are “an important step toward dispelling the perception that you cannot acquire Lyme disease in California,” says Ana Thompson, the executive director of the Bay Area Lyme Foundation.

B. miyamotoi has been known for some time to infect ticks; the first known human case of B. miyamotoi infection in the United States was discovered in 2013. Beyond Lyme-like symptoms such as fever and headache, little is known about its potential health effects.

Lyme disease, named for Lyme, Connecticut, where the illness was first identified in 1975, is transmitted to humans via the bite of a tick infected with B. burgdorferi. In California, the culprit is the western black-legged tick and the primary carrier is the western gray squirrel. On the East Coast, the culprit is the black-legged tick and the white-footed mouse is the main carrier.

Lyme can be difficult to diagnose, but its early symptoms include fever, headache, fatigue, and sometimes a telltale rash that looks like a bull’s-eye centered on the tick bite. If left untreated, the infection can cause a range of health problems, from arthritis and joint pain to immune deficiencies and a persistent cognitive fog.

Most people recover with antibiotic treatment, but for unknown reasons some patients who suffer from a variety of Lyme-like symptoms find no relief from the normally prescribed therapy.

Difficult to diagnosis

Although the majority of Lyme infections in the United States occur in the Northeast, incidence of the disease is growing across the country. Changes in climate and the movement of infected animals may be partly to blame.

Last summer, the Centers for Disease Control and Prevention reported that as many as 300,000 Americans contract Lyme disease annually, a rate 10 times higher than previously reported. The new figure, the result of national laboratory surveys and a review of insurance information, reflects what has long been suspected: Lyme is not well diagnosed or reported by many doctors.

When someone is infected, it can take weeks before blood tests detect antibodies. Adding to the diagnostic headache, tests have been known to return false positives and false negatives. Current testing capabilities also have a hard time determining whether the infection has been cured.

An interdisciplinary Lyme Disease Working Group at Stanford School of Medicine is exploring ways to improve diagnostic tests and medical understanding, evaluate the effectiveness of innovative therapies, expand clinical services, and build greater public awareness.

Dan Salkeld is a research scientist at Colorado State University and a former lecturer at Stanford University who still does disease ecology research at the Stanford Woods Institute. He started this tick research with Stanford Woods Institute Senior Fellow Eric Lambin while teaching a course in conservation medicine at Stanford.

Aided by his Stanford students, Salkeld’s initial research focused on assessing the risk of Lyme disease at the university’s Jasper Ridge Biological Preserve and in the neighboring towns of Portola Valley and Woodside.

Salkeld and his fellow researchers went on to test 12 Bay Area recreational areas. They found B. burgdorferi in about 2 percent of adult ticks, an expectedly low rate of infection for the region, according to Salkeld. By comparison, about 35 percent of adult ticks in the Northeast United States carry the bacterium.

Salkeld was surprised to find ticks infected with B. burgdorferi not only in woodlands but also in grassland chaparral habitat far from wooded areas. He was more surprised to find that ticks were infected with B. miyamotoi at slightly higher rates than those infected with B. burgdorferi.

The Bay Area Lyme Foundation funded Salkeld’s research.

Source: Stanford University

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