Natural 



PROPOSED PATHWAYS OF SHELL DISEASE 



\ 



Cuticular abrasion or 

 mechanical disruption. 



Invasion and proliferation 

 by chitinoclastic organisms, 



Pitting and erosion of cuticle 

 and perforation of shell in 

 advanced cases. 



Secondary infection of 

 underlying tissues. 



Stress- Induced 



Immunosuppression and 

 physiological/biochemical 

 disturbances in chitin 

 synthesis and mineral 

 deposition, especially in 

 areas of setal pores. 



Invasion by chitinolytic 

 organisms, often with 

 bilateral configuration. 



i 



Host responses include 

 formation of hemocytic plug, 

 deposition of melanin and 

 increased chitin formation. 



i 



Calcified areas may become 

 friable and eventually 

 perforate, forming the so- 

 called "ulcerative" stage, 



Figure 7 . 



Dual pathway of shell disease, based on a proposal 

 by R.A. Bullis (unpublished). 



24 



