Microscopic analysis of Rickettsial co-infection in the Gulf Coast tick, Amblyomma maculatum

Ticks can pass a variety of organisms to humans, resulting in mild flu-like illnesses or more severe diseases that may be fatal if not treated. One group of tick-borne organisms of interest to us are rickettsiae, which cause an illness known as spotted fever rickettsiosis. The ticks that transmit rickettsiae to humans may also pass these organisms to animals and to other ticks, which allows for these organisms to continue to circulate in nature. In some cases, two rickettsiae will utilize the same tick host, and occasionally this presents itself as co-infection of the bacteria. Co-infection can then lead to altered distribution of the bacteria in the tick tissues and impact the modes of transmission of one or both bacteria. In this study, our goal was to locate two species of rickettsial bacteria, one that causes disease and one that is not known to, in infected ticks using two different microscopy methods. We found that, while we could tell the two species apart using fluorescence microscopy, and identify whole bacteria in specific tissues using electron microscopy, we had to rely on DNA testing to screen samples, and found inconsistent results. These techniques would likely be inefficient if pursued on a larger scale, which leads us to suggest an alternative technique for future studies