A biopsy from an external nose lesion on a 13-year-old domestic longhair male neutered cat was submitted to our laboratory. Histopathology identified a severe ulcerative necrotising dermatitis with numerous intranuclear inclusion bodies. These histological changes, in combination with the anatomical location are consistent with a herpesvirus infection.

Feline herpes virus ulcerative dermatitis is a rare feline skin disease caused by feline herpes virus 1. Feline herpesvirus 1 is known to cause mainly upper respiratory tract infection (Feline Viral Rhinotracheitis) and it is associated with many clinical symptoms which include: sneezing, nasal discharge, conjunctivitis, mouth ulcers and sometimes fever. In more severe cases breathing may be affected and secondary bacterial infection can develop.

This virus is highly contagious and spreads through direct contact between infected cats or via contaminated surfaces. Once the cat is infected, the virus remains in the body in a latent state, and presence of the virus has been demonstrated in the trigeminal ganglion. Following immunosuppression, the virus can start replicating again and lesions may occur.

In rare instances this virus can cause ulcerative dermatitis, particularly of the face, however, lesions have also been reported on the pinna and flank.

Clinically these lesions are characterised by vesicles, ulcers and crust formation which are variably pruritic. This is a non-specific clinical presentation, and differentials include: hypersensitivity to insect bites, eosinophilic granuloma complex lesions, pemphigus foliaceous, adverse drug reactions and even neoplasia.

Histopathology of this lesion can help distinguish between these entities. On histological examination these lesions are characterised by severe epidermal necrosis and ulceration which often extend into the wall of the underlying hair follicles. The inflammatory infiltrate is usually characterised by significant numbers of eosinophils, however, neutrophils may predominate on occasion. Intranuclear inclusion bodies, when identified, are diagnostic. These are usually observed in the areas of epithelial necrosis.

Figure 1: On low power the segmental epidermal necrosis and ulceration are evident (blue arrow).

Figure 2: The necrosis extends into the wall of hair follicles which are multifocally heavily infiltrated by mixed inflammation (blue circle area).

Figure 3: Large intranuclear inclusion bodies with associated chromatin margination are observed (blue arrow).

In the case presented here, inclusion bodies were readily identified, and the diagnosis was straightforward, however, herpes virus inclusion bodies may be difficult to detect or completely absent. In these cases, PCR testing may be useful. However, it is important to bear in mind that a previous vaccination with live vaccine may produce a false positive PCR result. This is due to virus latency and the fact that the PCR currently available in unable to distinguish between field and vaccination strains. Immunohistochemistry for feline herpes virus is also available commercially and it is considered the gold standard to confirm the diagnosis.

In summary, feline herpes virus 1 is a lifelong infection which is usually associated with mild disease, and it is largely prevented by vaccination. In rare cases infection becomes more severe and supportive care is required. Skin lesions associated with this infection are rare, however, they do occur, and, in these cases, histopathology is a very useful tool to identify it.

References

Persico, P., Roccabianca, P., Corona, A., Vercelli, A. and Cornegliani, L. (2011), Detection of feline herpes virus 1 via polymerase chain reaction and immunohistochemistry in cats with ulcerative facial dermatitis, eosinophilic granuloma complex reaction patterns and mosquito bite hypersensitivity. Veterinary Dermatology, 22: 521-527. https://doi.org/10.1111/j.1365-3164.2011.00984.x

Sánchez MD, Goldschmidt MH, Mauldin EA. Herpesvirus dermatitis in two cats without facial lesions. Vet Dermatol. 2012 Apr;23(2):171-3, e35. doi: 10.1111/j.1365-3164.2011.01031.

Porcellato I, Luciani L, Marenzoni ML, Santagostino SF, Sforna M, Mechelli L, Brachelente C. Feline herpesvirus ulcerative dermatitis: an atypical case? Vet Dermatol. 2018 Jun;29(3):258-e96. doi: 10.1111/vde.12537

Parzefall, Matiasek, Evidence of feline herpesvirus-1 DNA in the vestibular ganglion of domestic cats, The Veterinary Journal, Volume 184, Issue 3, 2010, Pages 371-372, ISSN 1090-0233, https://doi.org/10.1016/j.tvjl.2009.03.030.