No cosmetologist, manicurist, aesthetician, or instructor who knowingly has an infectious or contagious _______ , or parasitic infection can give services in a shop.

In the context of Tennessee cosmetology laws, the correct term to use is "disease." The law prohibits professionals in these roles from providing services if they knowingly have an infectious or contagious disease. This terminology highlights the severity and the potential public health implications associated with such conditions when performing personal services that could spread infections to clients.

Using "disease" specifically encompasses a wide range of medical conditions that can be infectious or contagious, thereby emphasizing the responsibility that practitioners have in maintaining a safe and sanitary environment in their establishments. This distinguishes it from terms like "condition," "disorder," or "infection," which may not adequately capture the seriousness or transmissibility of the ailments being referred to in this context.