These bloodsuckers are more than just an annoyance. The ticks can carry Borrelia burgdorferi, the bacterium that causes Lyme disease. The first symptoms are typically mild—a rash that looks like a bull’s-eye, followed by fever, headaches and fatigue. But, if left untreated, the disease can cause temporary facial paralysis, shooting pains, bouts of arthritis and even speech and memory problems. Lyme disease is the most common tick-borne illness in the Western world, with approximately 30,000 cases reported annually in the US. But the number of people infected could be far higher. Last summer, the US Centers for Disease Control and Prevention (CDC) released a preliminary estimate based on insurance claims, lab results and population surveys that indicates roughly 300,000 people are diagnosed with the disease each year. (The gap may be because many Lyme diagnoses go unreported.) In Europe, estimates range between 65,000 and 85,000 cases per year.