The phrase "infectious agents" refers to tiny organisms such as bacteria, viruses, fungi, and parasites that can enter our bodies and cause diseases. These agents can spread from person to person and make us sick. Full definition
Their saliva can contain all kinds of infectious agents including viruses, bacteria and parasites (heartworm disease, malaria, etc.) contracted from prior victims. (drnelsonsveterinaryblog.com)
The other 10 to 20 % of cases are caused by a variety of other infectious agents, most of them viral. (vetinfo.com)
The best protection against infectious agents in our dogs is maintaining good health through preventive medicine, proper nutrition, adequate exercise, and good old TLC. (morrisanimalfoundation.org)