Final answer:
Viruses are the exception to typical cell structure among pathogens because they consist of nucleic acid surrounded by a protein coat without a cellular structure, whereas other pathogens like bacteria, fungi, and protists have cellular structures.
Step-by-step explanation:
Among bacteria, fungi, viruses, and protists, the pathogen that is an exception to the rule of typical cell structure is viruses. Viruses consist of a central core of nucleic acid either DNA or RNA, usually surrounded by a protein coat and sometimes by a lipid envelope derived from the host cell. Unlike bacteria, fungi, and protists, viruses do not have a cell structure; they are not composed of cells at all. Whereas bacteria are prokaryotic, fungi and protists are eukaryotic, and viruses are considered acellular.
For example, the common cold is caused by a virus (typically a rhinovirus), while athlete's foot is caused by a fungal pathogen. Different types of antigens associated with these pathogens can be the key to their identification and subsequent treatment. While bacteria possess antigens associated with structures like capsules and cell walls, viruses have antigens associated with their capsids and envelopes. In the discussion of pathogens, it is significant noting that viruses require a host cell to replicate, distinguishing them from other pathogens with more autonomous cellular structures.