organisms can be simultaneously transmitted with one tick bite, and we do not have reliable blood tests for all of these bacteria and parasites. These infections can therefore go undetected and lead to a "Lyme-like illness".

From
Dr. Richard Horowitz 

Lyme disease is spreading worldwide. In this study recently published in Infection, Genetics and Evolution, scientists have confirmed that Ixodes scapularis ticks from across five Midwestern States contain multiple infectious agents apart from Lyme disease, including newer Borrelia species, such as Borrelia miyamotoi, and other Babesia species, such as Babesia odocoilei. These organisms can be simultaneously transmitted with one tick bite, and we do not have reliable blood tests for all of these bacteria and parasites. These infections can therefore go undetected and lead to a "Lyme-like illness". The MSIDS model discussed in my book discusses in detail how the majority of patients affected with Lyme disease suffer from overlapping co-infections, contributing to chronic persistent illness.
http://www.sciencedirect.com/science/article/pii/S1567134814002068