{"id":10138,"date":"2016-04-28T18:12:22","date_gmt":"2016-04-28T18:12:22","guid":{"rendered":"http:\/\/phosdev.com\/todaysveterinarypractice\/?p=10138"},"modified":"2022-02-15T21:34:54","modified_gmt":"2022-02-15T21:34:54","slug":"observations-in-ophthalmology-runny-eyes-feline-herpesvirus-infection","status":"publish","type":"post","link":"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/ophthalmology\/observations-in-ophthalmology-runny-eyes-feline-herpesvirus-infection\/","title":{"rendered":"Runny Eyes: Feline Herpesvirus Infection"},"content":{"rendered":"

Feline herpesvirus type 1 (FHV-1) is the most frequent cause of conjunctivitis and keratitis in domestic cats. Serologic studies show that FHV-1 is widespread worldwide, with reported exposure rates up to 97%.1<\/sup> Diagnosis and treatment of the ocular manifestations of FHV-1 can be difficult and frustrating, with recurrence common in infected animals.<\/p>\n

Young and adolescent cats are most at risk for acute primary disease, and the vast majority of these cats become persistently infected. This article reviews common clinical presentations of FHV-1 and provides a systematic approach to diagnosis and treatment for the general practitioner.<\/p>\n

Feline Conjunctiva & Cornea<\/h2>\n

The inner lining of the feline eyelid consists of a mucous membrane called the palpebral conjunctiva<\/em>. This conjunctiva becomes confluent with the bulbar conjunctiva<\/em> at a junction called the fornix<\/em>. The bulbar conjunctiva is adhered to the globe tightly at the limbus<\/em>, where it becomes continuous with the corneal epithelium<\/em>.<\/p>\n

The conjunctiva prevents desiccation of the cornea, increases mobility of the eyelids and globe, and provides a physiologic barrier against microorganisms and foreign bodies through local mucosa-associated lymphoid immunity. The conjunctival fornices house a high concentration of goblet cells, which are apocrine secretory cells that produce mucin for the tear film.2<\/sup><\/p>\n

The feline cornea is comprised of 5 layers (Figures 1 and 2<\/strong>)3<\/sup>:<\/p>\n

    \n
  1. The outermost epithelium<\/strong> is a stratified, squamous, nonkeratinized layer consisting of 6 to 10 cell layers.<\/li>\n
  2. The epithelial basement membrane<\/strong> anchors the corneal epithelium to the underlying stroma.<\/li>\n
  3. The corneal stroma<\/strong>, which comprises parallel lamellar collagen fibrils, constitutes 90% of corneal thickness.3<\/sup> Corneal sensory nerves, located in the anterior stromal layer, are branches of the ophthalmic division of the trigeminal nerve.<\/li>\n
  4. Descemet\u2019s membrane<\/strong> is an acellular layer of collagen fibrils between the stroma and the inner corneal endothelium.3<\/sup><\/li>\n
  5. The endothelium<\/strong> is a single cell layer that functions to maintain relative corneal dehydration, called deturgescence<\/em>, by preventing imbibition of fluid from the aqueous humor.<\/li>\n<\/ol>\n
    \"FIGURE<\/a>

    FIGURE 1. Anatomy of the feline corneal epithelium and stroma. Illustration by Lisa Wirth, VMD<\/em><\/p><\/div>\n

    \"Figure<\/a>

    Figure 2. Anatomy of the feline cornea. Illustration by Lisa Wirth, VMD<\/em><\/p><\/div>\n

    Pathogenesis of FHV-1<\/strong><\/h2>\n

    FHV-1 is a double-stranded DNA alphaherpesvirus that induces damage to mucosal epithelial cells during replication. Alphaherpesviruses are characterized by their short replication cycle, rapid cell-to-cell spread, tendency to induce cell lysis, and persistence in the sensory ganglia of their host.4<\/sup><\/p>\n

    Clinically, members of this subfamily tend to cause acute lytic disease followed by periods of latency and intermittent recrudescent disease.4<\/sup> Following exposure to FHV-1, more than 80% of cats become persistently infected, a state characterized by latent infection in the trigeminal ganglia with intermittent periods of virus shedding. Of these, 45% shed the virus spontaneously or as a result of stress, and about 70% shed the virus in response to corticosteroid administration.4,5<\/sup><\/p>\n

    Periods of stress and immunocompromise can activate recrudescent clinical disease, leading to viral replication and migration from the sensory ganglia, down the sensory axons to epithelial tissues. FHV-1 preferentially infects mucoepithelial cells of the tonsils, conjunctiva, and nasal mucosa, but significant infection of corneal epithelial cells is also present.4,5<\/sup><\/p>\n

    Primary infections occur most frequently in kittens and adolescent cats, as maternal antibodies decline around 8 weeks of age.5<\/sup> The main source of transmission between cats is through direct contact or aerosolization of virus particles.6<\/sup> Nasal, oral, and conjunctival routes of infection have been demonstrated, and the virus is shed primarily in secretions from these body systems for 1 to 3 weeks following infection.6<\/sup><\/p>\n

    FHV-1 produces disease by 2 different mechanisms:<\/p>\n

      \n
    1. Cytolytic disease<\/strong>, or cell rupture, can occur during primary infection or following viral reactivation from latency.<\/li>\n
    2. Immune-mediated disease<\/strong> is characterized by inflammation and can be an uncommon response to infection with FHV-1.<\/li>\n<\/ol>\n

      Ocular Manifestations of Disease<\/strong><\/h2>\n

      Conjunctivitis<\/strong><\/h3>\n

      Primary FHV-1 infection and viral replication will result in conjunctivitis, while latently infected cats that chronically or periodically shed the virus do not demonstrate clinical signs.<\/p>\n

      Acute conjunctivitis occurs in conjunction with rhinotracheitis following a 2- to 6-day incubation period in neonatal and adolescent cats.5,7<\/sup> The conjunctivitis is usually bilateral (but can be unilateral) and is characterized by hyperemia, serous to mucopurulent ocular discharge, and a variable degree of chemosis (Figure 3<\/strong>). Areas of conjunctival ulceration may develop secondary to necrosis of the conjunctival epithelium.<\/p>\n

      Clinical signs tend to resolve within 10 to 20 days postinfection. Chronic or recurrent conjunctivitis, due to latency and recrudescence, may occur in normal cats but is most likely in cats with severe viral infections or those that are immunosuppressed.6,7<\/sup><\/p>\n

      \"FIGURE<\/a>

      FIGURE 3. Conjunctivitis; note the hyperemia, chemosis, and mucopurulent discharge.<\/p><\/div>\n

      Diagnosis<\/em><\/strong>
      \nFHV-1 should be considered in any cat presenting with upper respiratory signs in conjunction with conjunctivitis. The following tests can aid in diagnosis:<\/p>\n