Life Cycle

Fig.16. Ixodid Tick and
B. burgdorferi

B. burgdorferi circulates between lxodes ricinus ticks and a large variety of mammalian hosts, usually small rodents, in a zoonotic cycle 

(zoonosis: an infectious disease that can be transmitted between species).

The lifecycle of B. burgdorferi is closely related to that of its primary host, the Ixodes ticks.

The ticks are the bacterium’s vector: an organism that has been previously infected by B. burgdorferi and acts as its carrier and transmitter. 

The infected mammals are the reservoir, a “holding area” for these spirochetes.

Fig.17. Seasonal 2-Year Lifecycle
of a Deer Tick

The hatching of a tick larva in early summer marks the start of this pathogenic species’ lifecycle. 

The larva attaches to and bites into a host that has been previously infected by B. burgdorferi, allowing the bacterium to enter the tick’s bloodstreams.

B. burgdorferi continues to flow through the blood to all parts of the tick’s body, such as the heart, brain, muscles, bones, and eventually into its gut.

Once in the tick’s gut, B. burgdorferi attaches to the lining of the gut using its surface proteins, creating colonies of the bacterium. 

It then penetrates the gut wall and multiplies in the spaces between the tick’s cells. These colonies of B. burgdorferi remain in this state until the next time the tick feeds.

 When it does, the B. burgdorferi reactivates and enters the tick’s hemolymph to its salivary glands. 

It is through the tick’s saliva that the spirochetes can be transmitted to a new host.

Once in a mammalian host, the bacterium remains in it for the rest of its life.

Fig.18. Relative Sizes of Ixodes Ticks
at Different Stages

An Ixodes tick’s two-year long life cycle can be divided into three stages: larva, nymph, and adult. At each stage, the tick must take a “meal” and it is during this time that B. burgdorferi is transmitted between species.

After growing into a nymph from a larva, the tick will detach itself from the host. The nymph stage is the dormant stage of the tick’s life, and it is in this nymph stage that it remains through the winter. 

The next spring, the adult tick reproduces and 

once again a B. burgdorferi lifecycle begins.

Fig.19. The Lifecycle of a B. burgdorferi and its Interconnected Organisms

Although B. burgdorferi is known to negatively affect some animals, including humans, 

through evolution, their primary hosts, the Ixodid ticks have developed tolerance to this pathogen. 

The ticks’ ability to withstand B. burgdorferi allows the two organisms to form a stable symbiotic relationship.