Borrelia burgdorferi, the cause of Lyme Disease
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"Home is where the heart is..." - Proverb

No wait... "Home is where the HOST is..."

Borrelia burgdorferi is an endoparasitic species and therefore its main habitat and nutrition is in host tissue.  An endoparasite is a parasite that lives within the cells and tissues of its host (Singleton, P., & Sainsbury, D., 2006).  The most prominent organism in which B. burgdorferi infects is the Ixoidid tick species, which are ticks that have a hard outer covering .  Ixoidid ticks are most commonly found in the northern hemisphere and in wooded areas and therefore, the species B. burgdorferi is most apparent in these areas as well.  Ixoidid ticks are exoparasites and generally attach to intermediate sized mammals such as deer, rabbits, mice and also some species of birds.  Ticks also accidentally attach to humans while waiting for a deer to attach to, making humans secondary hosts of Ixoidid ticks (O'Connel, S., 2005).

Ixodes tick and Borrelia burgdorferi              

B. burgdorferi species reside in the midgut of Ixoidid ticks.  While the tick slowly feeds on blood meal, B. burgdorferi multiply and disperse within the tick through the hemolymph.

 However, B. burgdorferi bacteria not only reside in the tissues of Ixoidid ticks but change habitats when infecting one of their secondary hosts - small- to medium-sized mammals including humans.  This bacteria species is transmitted to other hosts through the saliva of a tick.   B. burgdorferi then can spread through the bloodstream and lymphatic system to a variety of tissues and has the potential to infect the circulatory, muscle, skeletal, and nervous systems (Schnarr, S., Franz, J., Krause, A., & Zeidler, H., 2006).  The actual life cycle of B. burgdorferi is discussed in the "Reproduction" section of this web page.

In order to get into a mammalian host, B. burgdorferi  is dependent upon the Ixoidid tick population.   Therefore, part of the ecological niche of this bacteria species is the presence of Ixoidid ticks (specific tick species fluctuate depending upon region).  Once B. burgdorferi infects a mammalian host, it remains within that host for life; however some mammals seem to be unaffected by this endoparasite (see "Other Facts" section of this web page). Mammalian hosts are considered "animal reservoirs" for B. burgdorferi  (Coburn, J. & Kalish, R., 2000).   A large population of these mammals need to be infected so that in turn, ticks will feed on them, become infected, and the cycle of B. burgdorferi can continue.  Therefore, some ecological niches of B. burgdorferi include, moderate temperatures generally in forested areas, the midgut of Ioxidid ticks, and intermediate sized mammals that live in close proximity.  Additional niches can be found in the "Adaptation" section of this web page.


This is the distribution of the Ixodes tick species who transmit the Borrelia burgdorferi species which in turn causes Lyme Disease.





More specifically, the hosts that ticks infect include:                                                                                                                    The white-footed mouse is the primary host of an Ixoidid tick


* Mice, (generally white-footed mice) rabbits, quail, songbirds, foxes, squirrels, and other rodents which all act as primary hosts for ticks




The white-tailed deer is the intentional secondary host of an Ioxidid tick.                                                                                                                                                 Humans are an incidental host of Ioxidid ticks.

* Ultimately, ticks want to attach to white-tailed deer as their secondary hosts; however, often ticks incidentally attach to humans passing by. 






The following is a lifecycle of a tick that exhibits the variety of hosts that the ticks attaches to at various points in its growth and development.