Lyme Handbook

Excerpted from  Associated Content  ( Posted: 11/15/2006 ) 

The herxheimer reaction, nicknamed “herx” or otherwise referred to as Jarisch-Herxheimer (J-H) is a phenomena originally observed in the treatment of syphilis, but later found in other illness. In general terms, it is described as a temporary increase of symptoms when anti-syphilitic drugs (antibiotics) are administered. What is known or speculated about Lyme disease herxheimers are based heavily on the reactions seen in syphilis. This is due to the fact both diseases are caused by a bacteria known as a spirochete, the former being Treponema pallidum, the latter Borrelia burgdoferi (B.b). However the herxheimer reactions in Lyme disease are not identical to those seen in syphilis, especially in terms of timing, frequency and duration as noted below.

In Lyme disease it is thought that the cause of herxheimers are the result of endotoxin release, that is toxin within the spirochete that are released as the B.b are killed or broken down. This may be a result of the toxin(s) itself or the body’s immune response to such. 

To  read more: http://www.associatedcontent.com/article/87765/lyme_disease_what_is_a_herxheimer_reaction.html?cat=5