Chapter 10 - The tick microbiome

Abstract

What is the tick microbiome? The simple answer is that it is the totality of microorganisms associated with a particular tick. However, this encapsulates enormous complexity that encompasses everything from viruses to multicellular organisms such as nematodes. It can include microorganisms that reside on the surface of the tick, within its organs and cells, and even within cellular organelles such as the mitochondria. The study of the tick microbiome began with the discovery of known vertebrate pathogens that were transmitted by ticks such as Babesia and Rickettsia species. This has been driven in recent decades by innovations in genetic sequencing technologies, enabling the ability to identify and discriminate between pathogens and their nonpathogenic relatives. This has now expanded to the discovery of a host of microorganisms that exist within ticks but have no apparent interaction with the vertebrate host on which the tick feeds. The study of the tick microbiome has now come full circle with researchers now asking what associations and effects does the microbiome have with known pathogens and do they influence transmission? Further questions remain on the viability of these putative microorganisms outside of the tick and their mechanism of transmission within and between ticks. Although the significance of these discoveries is widely debated, it is clear there are many organisms that coexist exclusively within ticks.