The first, colonization, has fever and coughing and lasts about 10 days. The first stage is usually thought to be a cold and is the highly infectious stage. It is here that the ciliated cells of the respiratory epithelium are destroyed. The second stage, toxemic, is characterized by the dry nonproductive cough, or paroxysmal cough. In the absence of ciliary activity, coughing becomes the only mechanism of clearing mucus, bacteria, and inflammatory debris from the respiratory tract.
Symptoms can continue for months at which time the bacteria have been cleared.
S3 binds to a ganglioside found primarily on phagocytic cells. The Ptl proteins are closely related to 9 of 11 VirB proteins from A. tumafaciens involved in transfer of DNA into plant cells. This system has apparently been adapted from the transport phase of conjugal transfer and is grouped with members of the type IV secretion system. There is no requirement for endocytosis or acidification. S1 is apparently delivered without internalization of the B-subunits.