Final answer:
The spread of disease to non-adjacent organs or parts is called metastatic or systemic infection. Infectious diseases can be communicable or noncommunicable; the latter includes genetic and environmental diseases. Epidemiology studies disease spread and impact, aiding public health.
Step-by-step explanation:
The spread of a disease from one organ or part to another non-adjacent organ or part is referred to as a metastatic disease when discussing cancer, or more broadly as a systemic infection in the case of pathogens. When an infectious disease like pertussis spreads from person to person, it's considered a communicable or contagious disease. However, not all infectious diseases are easily transmitted in this manner; some may be contracted from environmental sources or through animal vectors, known as zoonoses.
Noncommunicable diseases such as heart disease, stroke, and cancer are mainly caused by genetic and environmental factors, rather than pathogens. These diseases tend to be chronic, affecting individuals over an extended period. Understanding the nature of how diseases spread and their impact is essential, and the field of epidemiology plays a crucial role in public health by studying diseases in populations.
In the context of pathogens, when favorable conditions arise, such as transfer to an inappropriate body site or weakened immunity in an individual, some pathogens can cause disease. This is evident in cases like tetanus, where the pathogen is introduced to the body via a puncture wound, such as stepping on a rusty nail.