Systematic Veterinary Bacteriology and Mycology

PATHOGENESIS

• Infection is mainly by inhalation of dust. Primary cutaneous infections are rare. Infection is initiated by inhalation of the arthrospores.
• Relevant cell products include protea­ses, T suppressor cell activator, and leukotactic agents. Leukocytes in vitro encourage arthroconidial metamor­phosis to spherules.
• The agent triggers an inflammatory response in the lung, is engulfed but not killed by phagocytes and is con­veyed to the lymph node, where another inflam­matory focus develops.
• Inflammation is stimulated in part by a potent serine protease, which is liberated during the growth of the fungus in vivo (digests elastin, collagen, and immunoglobulins).
• Normally, cell-mediated immune responses arrest the process at this stage following stimulation of TH -1, lymphocytes that activate macrophages.
• With inadequate cell-mediated immunity, dissemination can occur to bones, skin, abdominal viscera, heart, genital tract, and eye (and rarely in animals to brain and meninges).