1. Pathogen

Feline herpes virus type 1 belongs to the family Herpesviridae, subfamily Aherpesvirinae, and is an enveloped linear double-stranded DNA virus. It has weak resistance to the outside world and is sensitive to acids and lipid solvents. It is inactivated at 56°C for 4 to 5 minutes, but it can sustain infection for 5 months at 4°C.

2. Epidemiology and pathogenesis

This disease mainly affects felines, among which young cats aged 2 to 6 months are susceptible, with an incidence rate of up to 100% and a fatality rate of 100%. 20%~50%. The virus is transmitted through direct contact and droplets, and enters the body through the mouth, nose, knots and other channels, causing lytic infection of nasal mucosal epithelial cells and spreading to the conjunctiva, throat, trachea, and bronchi, causing local multiple necrosis. Detoxification begins 24 hours after infection and continues for the same number of days. In addition, the virus can also replicate and proliferate in Shenqingyuan cells. Even after recovery, the virus can still lurk in the trigeminal ganglia of cats, causing chronic latent infection. During the latent period, the virus only retains its genome, evading immune surveillance to the greatest extent, making the virus latent for a long time without any risk. cleared by the body. As a result, about 80% of cats infected with the virus will carry the virus for life. When the cat encounters stress factors such as estrus, childbirth, lactation, environmental changes, and steroid drugs that induce virus reactivation, the virus can be reactivated and detoxified. Exciting and intermittent dispersion of poison. Therefore, the sources of infection include cats in the acute infection stage and cats with chronic latent infection. In addition, the disease can also be transmitted vertically, causing fetal death or being infected after birth. In addition, herpes viruses have developed an immune evasion mechanism during evolution, evading humoral immunity through syncytia, and evading the body's cellular immunity through molecular mimicry on the virus surface during acute infection.

3. Clinical symptoms and diagnosis

Mainly causes acute upper respiratory tract diseases and Eye diseases. Mucosal surface erosions and ulcers, rhinitis, and conjunctivitis often occur in young cats, among which corneal dendritic ulcers are considered diagnostically specific. Typical symptoms include fever, anorexia, serous ophthalmic and nasal discharge, conjunctival congestion, and sneezing. It may also cause primary pneumonia and viremia, followed by systemic symptoms and death. It is often mixed with calicivirus, chlamydia, Bosella, Staphylococcus and other mixed infections to cause multi-pathogen respiratory syndrome. The upper respiratory tract symptoms caused by these pathogens are similar, and it is difficult to diagnose through clinical symptoms. Laboratory testing is required for diagnosis.

3.1 Virus isolation

Feline herpes virus can proliferate in F81 cells and produce cytopathic effects, so this method can accurately reflect the presence of viruses with the ability to proliferate. However, feline herpes virus has weak resistance to the environment, requires high virus preservation and is time-consuming; more importantly, the detection results of viruses isolated from asymptomatic carrier cats have no diagnostic significance, resulting in this method not being commonly used in clinical diagnosis.

3.2 Serology

Although it can be diagnosed by detecting antibodies in serum through serum neutralization test or ELISA, it cannot distinguish between vaccine and wild virus antibodies, and the antibody titer and symptoms are not present. There is a positive correlation, so serological tests are of little diagnostic significance.

3.3 Molecular biology

Including pavement PCR, nested PCR, real-time fluorescence quantitative PCR technology, etc., can be used to detect cat nasal branch. However, the sensitivity of this method is too high, and the detection results may not be related to the disease state. A positive PCR result may represent a small amount of viral shedding or latent virus infection, but does not necessarily mean that the current symptoms are caused by the herpes virus. The virus concentration information detected by fluorescence quantitative PCR, such as high virus concentration in nasal or eye secretions, represents active virus replication, which may be related to clinical symptoms. For example, low concentration represents latent infection. However, existing PCR methods cannot distinguish between vaccine virus and wild virus infection, so the results still need to be judged and analyzed with caution.

4. Prevention and treatment

4.1 Lysine

Lysine was once the recommended prescription for the treatment of rhinorrhea in pet clinics, but clinical trials have proven that in cats with chronic herpes disease, only lifelong daily use of lysine may be beneficial, and only in acute attacks or Treatment of upper respiratory tract inflammation and eye diseases caused by herpes virus infection during the relapse period is ineffective and may even enhance the replication of herpes virus in cats. So this is only an auxiliary treatment. In order to better control the disease, antiviral drugs may be necessary.

4.2 Interferon

Although relevant clinical studies have proven that interferon has therapeutic effects, interferon has not yet been approved for clinical use in pets, and more research is needed. Clinical treatment trial to further evaluate the therapeutic effect of interferon on nasal branch in cats.

4.3 Nucleotide anti-herpes virus drugs

This type of acyclic nucleoside analogs are usually used for systemic treatment of human herpes A virus, including acyclovir, more Aciclovir, penciclovir (and its prodrug famciclovir) require three phosphorylation steps to be activated. The first step must be absorbed by the herpes virus and then catalyzed by intraviral thymus kinase. The last two steps require phosphorylation by the host kinase to form a triphosphate compound, which inhibits DNA polymerase and blocks DNA replication to achieve antiviral effects. However, the host is different. It will directly affect the efficacy of the medicine. For example, although acyclovir is effective in the treatment of feline rhinophyma, its antiviral efficacy and bioavailability are low, and increasing the dose causes bone marrow suppression and nephrotoxicity, which limits its use. Famciclovir is currently the most widely used cat nasal branch drug and is the prodrug of the active compound penciclovir. However, famciclovir requires deacetylation to be converted into penciclovir, which cannot be converted in cats, so the dose can only be increased to achieve therapeutic effects. . This inevitably increases the risk of side effects.

4.5 Vaccine

Vaccine immunity is an important means, but the current vaccine cannot completely prevent viral infection. It can only reduce the viral load latent in the trigeminal nerve and reduce virus shedding. In terms of treatment, the therapeutic drugs for feline nasal branch mainly include lysine, interferon, and nucleotide anti-herpes virus drugs such as acyclovir, famciclovir, and penciclovir. However, it is also due to the lack of diagnostic methods that the evaluation of drug effects is controversial.

5. Conclusion

Although feline rhinophyma is not a serious infectious disease, it has the characteristics of life-long virus carrying, chronic latent infection and recurrence after infection, so there is currently no simple test method. This latent state can be measured, which makes clinical diagnosis and treatment difficult. In short, the research on feline nasal branch is still in its early stages, but as more diagnostic methods are applied to pets and current available drugs are continuously tested, there is hope that a definite and effective solution for the diagnosis and treatment of feline nasal branch will emerge in the future.