Lyme disease is a bacterial illness spread by tick bites. The disease is widely known for causing a bull’s eye rash around the infected area, and although it commonly affects the skin, the disease can also affect joints and the cardiovascular and nervous systems. Although Lyme disease is known for its signature rash, not all Lyme disease victims present with the bull’s eye mark. For those who are infected and do not present with the rash, it’s difficult for doctors to detect the disease early on. This can be problematic, especially because antibiotic treatments are most effective in the early stages of the infection. A new study, however, suggests that the signature rash may be more useful than simply aiding in diagnosis. Researchers have developed a mathematical equation that captures the interactions between the bacteria that causes Lyme disease and the patient’s subsequent immune response. The study suggests that the rash may actually indicate the extent to which the infection will spread.
The findings can be found in the Biophysical Journal (published by Cell Press), where the study explains the connection between how the Lyme disease rash looks with the behavior of the bacteria in the body. By creating an equation that accounts for the growth and appearance of the rash, the researchers were able to predict factors of the disease such as densities of the bacteria in relation to the function of time during spreading. In patients with the bull’s eye rash, it seems as though the rash starts as small and uniform. Eventually, the immune system is activated, causing a strong immune reaction at the center of the rash. After approximately one week, the immune system clears most of the bacteria from the center of the rash. However, the immune system is not able to clear all of the bacteria entirely. Bacteria at the edge of the rash spread outward, which activates the immune response away from the edge of the rash. This causes the rash to grow, with the center of it becoming less red and inflamed. After some time, the bacteria returns to the middle of the rash, causing the bull’s eye pattern.
This information may help guide future research regarding how to treat Lyme disease patients. Now that researchers know that bacteria and immune cell populations change as the condition progresses, they are able to predict and track how the bacteria move through the body and how the bacteria and immune system are affected by various therapeutic strategies. The researchers then simulated the progression of various rash types during antibiotic treatment courses, and found that all rash types indicate that bacteria is cleared from the skin in roughly one week. However, the dynamics of rash disappearance varied depending on the type of rash. Bull’s eye rashes resolved after about one week of antibiotic treatment, while uniform rashes lasted around four weeks. The researchers believe that this discrepancy is due to inflammation, as uniform rashes are often more inflammatory. This also suggests that treatments should be altered depending on the type of rash the patient presents with.