Behavioural changes in the rat following infection with varicella-zoster virus

Researchers investigated whether rats infected with varicella-zoster virus (VZV) develop sensory abnormalities similar to post-herpetic neuralgia (PHN), a chronic pain condition in humans following shingles. Male Wistar rats were injected with VZV-infected cells in one hind paw footpad, while control rats received mock-infected cells. Behavioral tests measuring withdrawal responses to mechanical stimulation (using von Frey filaments) and noxious heat were performed before infection and up to 33 days post-infection. VZV-infected rats showed significant and sustained decreases in withdrawal thresholds in the injected paw only, indicating mechanical allodynia and hyperalgesia persisting for the entire observation period. Control rats showed no such changes. Immunohistochemical analysis confirmed VZV protein (IE 63) expression in dorsal root ganglia of infected animals without inflammatory infiltrates or neuronal death. This rat model successfully reproduces sensory abnormalities associated with PHN and may be useful for investigating the mechanisms underlying this chronic pain syndrome.

Key findings

• Rats infected with VZV in the hind paw developed sustained mechanical allodynia and hyperalgesia in the injected limb lasting up to 33 days post-infection
• Sensory abnormalities were specific to the infected limb, with no changes observed in the contralateral paw or in mock-infected control rats
• VZV protein (IE 63) was detected in dorsal root ganglia of infected rats without evidence of inflammatory infiltrates or neuronal death
• This rat model reproduces pain-related behavioral changes similar to human post-herpetic neuralgia and provides a platform for investigating underlying mechanisms