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An adult deer tick (Source: Wikipedia)

Look out, San Francisco. As springtime approaches and Golden Gate Park beckons, scientists say the ticks that infest much of Northern California are carrying not only Lyme disease but also a new, previously unknown pathogen.

A study to be published in the March issue of the journal Emerging Infectious Disease details how researchers including Dan Salkeld, a research associate at the Stanford Woods Institute for the Environment, found the bacterium, Borrelia miyamotoi, as well as Borrelia 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. They also represent "an important step toward dispelling the perception that you cannot acquire Lyme disease in California," said Ana Thompson, executive director of the Bay Area Lyme Foundation.

Known for some time to infect ticks, the first known human case of B. miyamotoi infection in the U.S. was discovered in 2013. Beyond Lyme-like symptoms such as fever and headache, little is known about its potential health impacts. In the Bay Area, low awareness of tick-borne diseases such as Lyme could heighten the risk of infection with B. miyamotoi for users of the region's extensive natural areas and trails.

"People who have difficulty getting diagnoses – maybe this is involved, " Salkeld said.

Lyme disease

Lyme disease, named for Lyme, Conn., 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, it's 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 proscribed therapy.

Although the majority of U.S. Lyme infections 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. 

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.


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