Final answer:
A parasitic infection caused by a protozoan entering through the nose is Primary Amoebic Meningoencephalitis (PAM), linked to the protozoan Naegleria fowler.
Step-by-step explanation:
A human parasitic infection caused by a protozoan that enters through the nose is called Primary Amoebic Meningoencephalitis (PAM). This condition is often associated with the protozoan Naegleria fowler, which is found in fresh water sources such as ponds, lakes, and rivers.
This protozoan makes its way to the brain by entering through the nasal mucosa during activities like swimming or diving in contaminated water. PAM, while rare, is often fatal due to the inflammation and destruction of brain tissue caused by the organism.