Histopathologic Diagnosis of Feline Herpesvirus
Erin Edwards, DVM, MS, DACVP and Jay Hoffman, DVM, PhD, DACVP
Feline herpesvirus is a highly transmissible, viral disease that is very common in cats. This disease is also known as feline viral rhinotracheitis and is included in core feline vaccines. Feline herpesvirus is frequently diagnosed at the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL). The most common laboratory methods of diagnosis include PCR and histopathology, while exposure to the virus can be demonstrated by measuring antibody response with the virus neutralization assay. This summer, two feline submissions demonstrated an array of respiratory histopathologic lesions that can be seen with herpesvirus infection. These cases were received two days apart but were completely unrelated and from two different states.
The first case was a 2-year-old cat belonging to a private owner. The submitted clinical history described recent respiratory distress and radiographs apparently showed a pneumonia with an interstitial pattern. A necropsy was performed by the submitting veterinarian and a set of fresh and formalin-fixed tissues were sent to TVMDL for histopathology and fungal culture.
The second case was a 2-week-old kitten from a humane society organization. This kitten was from a litter of six with a total of five deaths reported. Necropsy was performed by a referral laboratory and revealed an interstitial pneumonia. Lung samples were PCR-positive for feline herpesvirus and formalin-fixed samples were sent to TVMDL for histopathology.
The histopathologic lesions for both cats were similar, though different anatomic sites were affected. In the first case, the trachea and lung were severely affected and in the second case, the nasal cavity and lung were affected. Lesions included necrotizing bronchointerstitial pneumonia, necro-ulcerative rhinitis, and necro-suppurative tracheitis. Intranuclear viral inclusion bodies were found in scattered respiratory epithelial cells and were most prevalent in the trachea where there was also syncytial formation. These inclusions are diagnostic for feline herpesvirus.
Feline herpesvirus most commonly presents as an upper respiratory tract infection, but in severe cases it can affect the lower respiratory tract. This disease also commonly causes keratoconjunctivitis and can result in facial dermatitis. It is spread by direct contact and is often a problem in shelter environments. Young and immunosuppressed animals are most susceptible to clinical disease. Feline herpesvirus is typically not fatal and most cases are managed clinically. Once infected, cats will remain infected for life and recurrent disease flare-ups can be seen following bouts of stress. In severe cases, especially those affecting the lungs, this disease can be fatal.
Figure 1: Necrotizing bronchiolitis with many sloughed epithelial cells containing intranuclear viral inclusions (some are indicated by arrows). This image was the lung of the kitten in the second case.