Guarnieri bodies, also known as Negri bodies, are distinct cytoplasmic inclusions found in nerve cells infected with the rabies virus. These structures were first described by Adelchi Negri in 1903 and later named after his mentor, Giuseppe Guarnieri. These eosinophilic cytoplasmic inclusions serve as diagnostic markers for rabies infection. Besides the term Guarnieri bodies, these intracytoplasmic inclusions are also commonly referred to as Negri bodies. Identified under microscopic examination of brain tissue, they appear as round or oval structures containing aggregates of viral nucleoproteins. The presence of Guarnieri bodies in neurons is a characteristic finding in cases of rabies, aiding in the definitive diagnosis of the disease.