Which of the following is a host-related disease determinant?

• A. Age
• B. Transmission route
• C. Environmental humidity
• D. Viral mutation rate

Answer: (A)

Host-related determinants are characteristics of the person that influence how susceptible they are to infection or how severe the disease may be. Age fits this because it directly affects immune function and exposure patterns: very young children often have developing immune systems and frequent close contact in settings like daycare, while older adults may have waning immunity and more comorbidities, increasing both susceptibility and risk of severe disease. These age-related differences shape who gets infected and how severe their illness tends to be.

In contrast, how a pathogen spreads between people (the transmission route) is about exposure pathways rather than a trait of the host. Environmental humidity relates to conditions outside the host that affect pathogen survival and transmission, not the person themselves. Viral mutation rate concerns changes in the pathogen’s genome, not host characteristics.