Tick season is upon us, and two researchers have suggested that it may be a particularly active one in Marin and the Bay Area.

Dan Salkeld, a Colorado State University research scientist who conducted field research in early May in West Marin, observed a higher than usual number of ticks. “This is a really different year [compared to last year],” he said. 

Last May, in surveying parks around Marin, he found the prevalence of Lyme—the spiral-shaped bacterium that can have life-altering consequences for many people—varied in tick samples from 0 to 12 percent. This year, he observed more ticks in the field but has not yet tested for Lyme and other bacteria. 

An assistant professor at San Francisco State University, Andrea Swei, said her students were recently in the field collecting tick samples and noted the high number. While it was hard to draw conclusions before an analysis was complete, she said, “it does seem like a ticky year.” An increase would not be surprising, she added, given the rainy winter two years ago that may have caused a spike in reproduction.

Across the country, cases of Lyme disease reported by doctors reached more than 36,000 in 2016, up from about 20,000 in 2004, according to a Centers for Disease Control report released on May 1. Yet the C.D.C. said the actual number may well exceed 300,000 cases a year, based on insurance claims and laboratory results. More than 95 percent of cases occur in Northeastern states. 

In Marin County, just three cases were reported to the C.D.C. each year for 2014, 2015 and 2016. Reports for California, which likely underrepresent the actual number of Lyme disease cases, typically fall in the range of 100 per year and have been stable for the past several years. 

April to June is a higher-risk time period for contracting Lyme from nymphs, the immature ticks that typically carry the bacteria at two times the rate of adult ticks. Adults, which are more active from November to January, are found in tall grasses, while nymph populations are concentrated in dense, woody areas, particularly in oak woodlands. 

According to the C.D.C., Lyme is contracted most often in the first week of July, though because of California’s mild weather, people can contract tick-borne diseases year-round. The ticks are infected with Lyme by small rodents, such as Western gray squirrels and wood rats, then latch onto deer to multiply and spread.  

Precautions such as tucking long pants into socks, spraying insect repellent on skin or clothes, checking skin before driving away after a hike and tumbling clothes in a dryer can all dramatically reduce your chance of contracting Lyme from these poppy seed-size critters. 

The Lyme bacteria has been present in tick and animal populations of Europe and the U.S. for thousands of years, but deforestation of the East Coast increased human exposure. 

Scientists in the United States first identified Lyme in the 1970s, after two mothers alerted health authorities to an unusual spate of juvenile rheumatoid arthritis in and around the town of Lyme, Connecticut. 

An early sign of a tick bite is a bull’s-eye rash, though it does not always appear and can be hard to spot. Flu-like symptoms like fever, headaches and general aches may also signal early stages of Lyme, especially if experienced in mid-summer. 

At this early stage, the majority of patients get better with a course of antibiotics, according to the C.D.C. However, left untreated, Lyme disease can manifest months later with sore, swollen joints, neurological symptoms such as numbness or blurry vision, and cardiac issues.

Some people who test positive for Lyme antibodies in their blood might experience no symptoms at all, as is the case for Inverness resident Jessica Dietrich. She tested positive for Lyme last year but has not experienced any classic Lyme symptoms or undergone treatment.

Not so for 17-year-old Ruby McCracken of Bolinas. When Ms. McCracken started experiencing joint pain in her early teens, her mother, Pamela Springer, put it down to growing pains. But the pain continued and Ms. McCracken began to suffer from strong anxiety that made it difficult to attend school. 

The local clinic referred her to a counsellor for anxiety and depression, but after months of visits and little improvement, her father suggested they visit a Lyme specialist. In May 2017, Ms. McCracken tested positive for Lyme and a co-infection of Babesiosis. She immediately started taking antibiotics and an antiprotozoal, as well as mineral and herbal extracts. The treatments have been costly, adding up to about $20,000, but have been offset by fundraisers and private donations. 

After taking the antibiotics for nine months, Ms. McCracken’s health has seen some improvement. But like other Lyme sufferers, it has not been an easy or predictable recovery. After missing school all last year, Ruby went back in January. 

Still, Ms. Springer said, “She is still not getting to school as much as she wants,” and she no longer speaks of wanting to go to university and study marine biology. “That’s not what I dreamt for my kid,” Ms. Springer said. 

Bay Area doctors who specialize in Lyme disease, such as Dr. Christine Green and Dr. Raphael Stricker, both told the Light that their patient loads suggest a Marin and California case count that is significantly higher than C.D.C.’s records.

The health agency recommends doctors use a two-step test involving the enzyme immunoassay followed by a Western blot test, yet Dr. Stricker pointed to research that suggests this protocol will only give accurate results 50 percent of the time. 

Dr. Stricker said co-infections that often occur with Lyme can make it more difficult to treat, and said more sensitive diagnostic tests are needed to help explain why symptoms continue after treatment. 

The Infectious Diseases Society of America recommends a single course of antibiotics to treat Lyme but, over the years, a growing collective of doctors and patients struggling with long-term symptoms have pushed for a revision of this protocol. 

Some patients experience serious symptoms after receiving antibiotic treatment, possibly due to a sustained immune response or antibiotic-resistant bacteria. So far, explanations for long-term Lyme disease symptoms have lacked strong scientific evidence, but this may be changing. 

Studies conducted over the past four years on rhesus macaque primates at the Tulane National Primate Research Center showed the Lyme bacteria, Borrelia Burdolferi, could survive after a course of antibiotics. A 2018 study of 12 human patients who had undergone antibiotic treatment found the bacteria present in seven of the patients.