infectant

An infectant is an agent capable of causing infection in a host. In many contexts the term is synonymous with infectious agent or pathogen, though some usages distinguish an infectant as any entity that can initiate infection, including certain nonviable or poorly characterized materials. Infectants can be living organisms—bacteria, viruses, fungi, and parasites—or non-living agents such as prions, which cause disease by protein misfolding.

Infection occurs when an infectant gains access to a host, overcomes defenses, and establishes replication or persistence. Virulence factors, such as toxins, adhesins, and immune evasion mechanisms, influence the likelihood and severity of disease. Transmission routes include contact, inhalation of droplets, vectors, contaminated food or water, and vertical transfer from mother to offspring.

Examples of infectious agents include bacteria such as Staphylococcus aureus and Escherichia coli; viruses such as influenza and SARS-CoV-2; fungi such as Candida albicans; parasites such as Giardia and Plasmodium; and prions responsible for certain neurodegenerative diseases.

Control and prevention focus on reducing exposure and transmission: hand hygiene, vaccination, barrier methods, and environmental disinfection, as well as sterilization of medical and laboratory equipment. In clinical and public health contexts, diagnosing an infection involves detecting the infectant or the host response, using microbiological, molecular, or serological methods.

Note: The term infectant is less common than pathogen or infectious agent; precise terminology depends on context and field.