infective

Infective describes something that is able to cause infection or transmit it to another host. The word is common in biology and medicine, where the focus is on whether a germ, parasite, person, animal, object, or stage of an organism can start an infection.

Think about the difference this way: something can be infected, meaning it already contains harmful organisms, without always being infective in the sense of passing the infection on. It is infective when it can actually start infection in another organism. A mosquito carrying malaria parasites can be infective. A contaminated needle can be infective because it may transmit diseases such as HIV or hepatitis. In parasitology, an "infective stage" is the stage at which a parasite is ready to enter and infect a new host.

The term is not limited to living things. Blood, food, water, soil, or medical equipment may be described as infective if they contain organisms that can cause infection. In veterinary medicine and microbiology, the word is also used for organisms or materials that remain able to infect after leaving one host and before entering another.

You'll often encounter the word in fixed medical names such as "infective endocarditis," which is an infection of the inner lining of the heart. In everyday English, people often choose infectious when talking about diseases that spread easily, but infective is still useful when the main idea is the power to cause infection. Understanding infective helps clarify how disease moves from one host, surface, or organism to another.