Wednesday, June 25, 2014

Troublesome Ticks

Ticks are ever present during North Carolina summers, and they bring with them the risk of tick-borne illnesses. Many of us have known since childhood to be on alert for symptoms of Rocky Mountain spotted fever, but fewer of us in this state have been aware that Lyme disease is a real threat.

For years, public health officials assumed that Lyme disease is a New England and mid-western illness that those of us outside the Northeast don't have to worry about. However, statistics show that the risk has started to move South and, perhaps, has been here for a while. Lyme disease is the most commonly reported vector borne illness in the United States: in 2012, it was the 7th most common Nationally Notifiable disease.

A Centers for Disease Control and Prevention (CDC) map indicates reported cases of Lyme Disease throughout North Carolina in every year of the last decade. And, the North Carolina Public Health department reports that last year, there were 173 (39 confirmed and 134 probable) incidences of Lyme disease in our state. The number for the past five years combined is 601. Four North Carolina counties Guilford, Alleghany, Haywood, and Wake—are considered endemic for Lyme disease (this means a county has two or more diagnoses of Lyme disease originating from ticks within the county).

It's essential to note that these statistics only represent cases diagnosed by the strict CDC criteria. According to Dr. Scott Taylor, DVM, a veterinarian who acquired Lyme disease, the “CDC criteria was established for an epidemiological survey, which was designed to study the distribution of Lyme disease. The two-step method of the CDC uses a screening immunoassay (ELISA) for all patients followed by a more sensitive and specific Western Blot only if the screening test was positive.

 

Unfortunately, this approach was originally intended for surveillance of Lyme disease in potentially asymptomatic patients, not for diagnostic purposes in patients with symptoms that are potentially related to Lyme disease. This criteria was not intended to be used as a standard for the clinical diagnosis of Lyme disease; the CDC has clearly stated this. Unfortunately, (many) health officials and physicians continue to use these criteria for the clinical diagnosis of Lyme disease.” To reiterate, the CDC states clearly, that the diagnosis of Lyme disease is a clinical diagnosis. That means the physician decides whether the patient has Lyme after reviewing the patient’s history, symptoms, progression of illness and tick exposure record and physical exam.


And lab tests may be falsely negative for other reasons. Again Dr. Taylor explains “The causative agent, Borrelia burgdorferi, Bb, is a type of spirochete (, a snake like bacteria, similar to syphilis). When Bb was first discovered in 1982 it was thought that there was just one strain. Since then, (five subspecies and) about 100 U.S. and 300 worldwide strains of the bacterium have been discovered.” Lab tests only test for the original Bb. There are more strains of Bb in the Southeastern United States than thought before.  So if you are infected with a different strain, your tests may be negative even though you do have Lyme.