Negri bodies are eosinophilic, sharply outlined, pathognomonic inclusion bodies (2–10 μm in diameter) found in the cytoplasm of certain nerve cells containing the virus of rabies, especially in pyramidal cells[1] within Ammon's horn of the hippocampus. They are also often found in the Purkinje cells[1] of the cerebellar cortex from postmortem brain samples of rabies victims. They consist of ribonuclear proteins produced by the virus.[2]
They are named for Adelchi Negri.[3]
Adelchi Negri, an assistant pathologist working in the laboratory of Camillo Golgi, observed these inclusions in rabbits and dogs with rabies. These findings were presented in 1903 at a meeting of the Società Medico-Chirurgica of Pavia. The American pathologist Anna Wessels Williams made the same discovery,[4] but because Negri published his results[5] first, the bodies bear his name.
Negri was convinced the inclusions were a parasitic protozoon and the etiologic agent of rabies. Later that same year, however, Paul Remlinger and Rifat-Bey Frasheri in Constantinople and, separately, Alfonso di Vestea in Naples showed that the etiologic agent of rabies is a filterable virus. Negri continued until 1909 to try to prove that the intraneuronal inclusions named after him corresponded to steps in the developmental cycle of a protozoan.
In spite of his incorrect etiologic hypothesis, Negri's discovery represented a breakthrough in the rapid diagnosis of rabies, and the detection of Negri bodies, using a method developed by Anna Wessels Williams, remained the primary way to detect rabies for the next thirty years.[6]