pathogen
Concise Oxford English Dictionary © 2008 Oxford University Press:
pathogen /ˈpaθədʒ(ə)n/
▶noun Medicine a bacterium, virus, or other microorganism that can cause disease.
– derivatives
pathogenic adjective,
pathogenicity noun,
pathogenous /pəˈθɒdʒɪnəs/ adjective.
pathogenic adjective,
pathogenicity noun,
pathogenous /pəˈθɒdʒɪnəs/ adjective.
'pathogen' also found in these Oxford entries:

