The tick is considered the vector in the chain of infection.
Generally, vector organisms are organisms that are capable of transmitting disease pathogens from infected organisms to uninfected ones either directly or indirectly as a result of their activities.
Ticks are parasites that feed on the blood of vertebrate animals such as deers and humans. When they feed on the blood of animals with certain infections, the pathogens for such infections are sometimes carried in the guts of the parasites and these are transferred to the bloodstream of the next animal that would be their host.
All of life can be divided into three domains, based on the type of cell of the organism: Bacteria: cells do not contain a nucleus. Archaea: cells do not contain a nucleus; they have a different cell wall from bacteria. Eukarya: cells do contain a nucleus.
