Here's some valid information:
http://edis.ifas.ufl.edu/vm013
Disease and Eggshell Quality:
Not all diseases which affect chickens cause a decline in eggshell quality. However, egg production will usually decline. An example of a disease that can affect the numbers of eggs and not necessarily the quality is infectious laryngotracheitis. Other common viral diseases such as egg drop syndrome (EDS), avian influenza (AI), Newcastle disease (ND) and infectious bronchitis (IB) may produce severe effects on eggshell and internal quality. Many times the total number of eggs is not influenced even though the egg records indicate a drop in total collectable eggs. This is due to the increase in non-collectable eggs (shell-less or ultra-thin shells) that are lost under the cages. This is a common occurrence with EDS.
It has been established that the EDS virus affects only the shell gland but with ND and IB every portion of the reproductive tract can be affected. If one disease had to be singled out as being the one responsible for the majority of the economically significant production losses in egg layers it would have to be Infectious bronchitis. Infectious bronchitis virus, a coronavirus, has a preference for the mucus membranes of the respiratory and reproductive tracts. The kidney is also affected by certain IB virus strains. Not only is eggshell quality affected but internal quality also declines. Watery whites are very common and can persist for long periods after egg production returns. Also, an IB outbreak can result in a pale colored shell in brown shell.
http://edis.ifas.ufl.edu/vm013
Disease and Eggshell Quality:
Not all diseases which affect chickens cause a decline in eggshell quality. However, egg production will usually decline. An example of a disease that can affect the numbers of eggs and not necessarily the quality is infectious laryngotracheitis. Other common viral diseases such as egg drop syndrome (EDS), avian influenza (AI), Newcastle disease (ND) and infectious bronchitis (IB) may produce severe effects on eggshell and internal quality. Many times the total number of eggs is not influenced even though the egg records indicate a drop in total collectable eggs. This is due to the increase in non-collectable eggs (shell-less or ultra-thin shells) that are lost under the cages. This is a common occurrence with EDS.
It has been established that the EDS virus affects only the shell gland but with ND and IB every portion of the reproductive tract can be affected. If one disease had to be singled out as being the one responsible for the majority of the economically significant production losses in egg layers it would have to be Infectious bronchitis. Infectious bronchitis virus, a coronavirus, has a preference for the mucus membranes of the respiratory and reproductive tracts. The kidney is also affected by certain IB virus strains. Not only is eggshell quality affected but internal quality also declines. Watery whites are very common and can persist for long periods after egg production returns. Also, an IB outbreak can result in a pale colored shell in brown shell.