The pathogen that is not classified according to modern classification among the options given is Elephantiasis.
Sleeping sickness is caused by the parasite Trypanosoma brucei.
Malaria is caused by the parasite Plasmodium.
AIDS is caused by the Human Immunodeficiency Virus (HIV).
Elephantiasis, on the other hand, is a condition caused by parasitic worms transmitted through mosquito bites and is not caused by a single pathogen or microorganism but rather by various species of parasitic worms.