Differential diagnosis of feline herpesvirus
Respiratory signs
If feline herpesvirus replicates in the nasal mucosa and tonsils, it materialises as rhinotracheitis or cat flu. The clinical signs vary considerably, including sneezing, anorexia, fever, weakness, excessive drooling.
Feline viral rhinotracheitis may also be caused by feline calicivirus. Feline herpesvirus infection generally triggers more severe signs, but the clinical picture is similar.
Cats usually recover completely, although some may suffer chronic rhinitis. Problems tend to be caused by secondary bacterial infections.
Feline calicivirus produces moderate signs of cat flu, in fact sometimes it only causes ulcers on or around the tongue, palate or nose.
Ocular signs
Feline herpesvirus is the most frequent cause of eye disease in cats. The main ocular condition associated with FHV is bilateral conjunctivitis in kittens and young cats.
Dendritic corneal ulceration is a pathognomonic consequence of FHV infection in cats. These ulcers can be stained with rose bengal dye.
Feline herpesvirus carrier status
Feline herpesvirus can install itself permanently, so cats develop a chronic carrier state. Stress is the main trigger of the disease when it is present in this latent state. Treatment with corticosteroids or other immunosuppressants may also reactivate the virus. So FHV carrier cats once again become a potential source of infection during such therapy.
Cats with feline herpesvirus shed the virus in nasal, oral and conjunctival secretions for approximately 3 weeks. Infection requires direct contact with the virus.
Diagnosis of feline herpesvirus
Samples of nasal, oral or conjunctival secretions should be collected with a swab. Corneal scraping or even biopsy samples may also help. The samples undergo PCR analysis, which is the only means of determining whether the infection is in fact caused by feline herpesvirus or another microorganism.
Clinical course of feline herpesvirus infection
The following gives the timeline for the signs of herpesvirus infection (1)
The first contact with feline herpesvirus, also known as primary infection, produces the following clinical signs:
- Upper respiratory disease
- Bilateral conjunctivitis, with a lot of serous or purulent discharge
- Severe corneal ulceration
In the event of a secondary infection or if feline herpesvirus is reactivated from the asymptomatic carrier state, the signs will be milder than the first infection:
- Minimal respiratory signs
- Chronic unilateral conjunctivitis
- Chronic epiphora
- Stromal keratitis
- Keratoconjunctivitis sicca
