By Dr. Tracy Satchell, DVM, MS
Note to Reader: This blog post has 2 parts; the first part briefly discusses the feline herpes virus and upper respiratory disease, and the second part touches on a research paper that was recently published about the isolation of gammaherpesvirus in cats. Little is known about gammaherpes in cats and this virus is not known to be a cause of feline upper respiratory disease.
Part 1 – Love vs. Herpes
“What’s the difference between love and herpes?”, asked Dr. Stämpfli, a brilliant yet intimidating large animal internal medicine specialist, as I walked into the Ontario Veterinary College (OVC) teaching hospital barn.
I was there for an exam, one of about a dozen assessments that all third year OVC students tackled at the end of the year, even if you were never going to voluntarily touch a cow or horse again.
Not surprisingly, this initial question caught me off-guard. Dr. Stämpfli was exceptionally tall, lean, and had a pronounced Swiss accent. His face was expressionless as he stood silently waiting for my response. I stared wide-eyed at him for a moment as my brain went down the list of differential diagnoses relating to bovine herpes virus and… love?
After what felt like an eternity, but was likely only a few seconds, I realized this was not an exam question, but a joke. I was wearing my standard issue blue coveralls and sported an impressive cold sore on my lower lip.
I smiled and replied, “I don’t know, what’s the difference?”
His answer (insert lovely Swiss accent here), “Herpes is forever.”
Herpesvirus is Everywhere
Herpes is ubiquitous in vertebrate species, infecting every species of mammal and bird, and even insects, fish, reptiles, amphibians, and mollusks [1]. Fortunately, herpesvirus is species-specific, meaning it cannot replicate outside of its preferred host species, and will not spread from one species to another. For example, feline herpes cannot infect dogs and can only be transmitted to other cats.
Herpesvirus is Forever
Dr. Stämpfli’s icebreaker might have flopped, but my professor was correct; infected animals carry herpes for life. Herpesviruses establish latency, a persistent life-long infection that can be reactivated by stress [2]. “Cold sores” in humans are caused by herpes simplex type 1, and can be brought on by the stress of proving that you know how to perform a physical examination on a cow.
Feline Herpes
The Herpesviridae family is subdivided into three subfamilies: Alpha-, Beta-, and Gamma-herpesvirinae [3]. Feline Herpesvirus-1 (FHV-1) is an alphaherpesvirus and commonly leads to upper respiratory and ocular disease in cats, manifesting in symptoms such as lethargy, decreased appetite, fever, sneezing, and ocular and nasal discharge [4]. Studies have shown that up to 97% of cats are seropositive for FHV-1, indicating widespread exposure [5]. In shelter cats, stress reduction is imperative to decreasing the incidence of upper respiratory disease caused by herpes recrudescence.
Vaccination
Despite many shelter cats receiving vaccinations to prevent upper respiratory disease, many herpes infections occur in younger cats before vaccine-induced immunity has been acquired [2]. Vaccination for FHV-1 produces non-sterile immunity, so vaccines help to prevent or minimize clinical signs but may not prevent infection [4] [6]. Vaccinated cats or kittens that are exposed to herpesvirus develop milder signs of disease and shedding is decreased compared to unvaccinated cats [7].
A Brief Review of Feline Upper Respiratory Disease [7b]
In shelter cats, 80-90% of feline upper respiratory infections are caused by the herpesvirus and the calicivirus. Other possible agents include Chlamydophila felis, Mycoplasma spp., Bordetella bronchiseptica, and potentially some Streptococcus spp. These infectious agents are primarily spread via fomites and droplet transmission (5 feet or less), or via reactivation of latent herpesvirus due to stress.
An achievable goal is for less than 5% of cats to develop URI while in shelter care. Preventing URI should focus on stress reduction by providing appropriate housing (adequate floor space, double-sided compartments, access to a hiding space, avoiding overcrowding), limiting movement within the shelter (spot-cleaning, reduced movement from kennel-to-kennel), reducing length of stay (managing intake, fast-tracking, adoption driven capacity, Shelter-Neuter-Return for community cats), and routine cleaning and disinfection.
It is often cost-prohibitive and impractical to determine the causative agent(s) of URIs in the shelter. Clinical signs can be used as a starting point: calicivirus is more likely to cause oral ulceration, herpesvirus is associated with keratitis and dendritic corneal ulcers, while Chlamydia and Mycoplasma are more commonly associated with conjunctivitis alone.
Treatment of upper respiratory disease typically aims at treating secondary bacterial infections, and as such, antibiotics can be discontinued once clinical signs resolve. Not all cats will require antibiotics and treatment should be based on evidence of a secondary bacterial infection. Signs of a secondary infection include sneezing, congestion, or squinting with mucoid (green, yellow, or bloody) nasal or ocular discharge. Cats with clear ocular or nasal discharge should not be treated with antibiotics but instead monitored daily for changes in their clinical signs.
Since the clinical signs of URI are highly variable, it is difficult to provide a comprehensive summary of all treatment options. Thankfully, the UC Davis Koret Shelter Medicine Program has an excellent sample URI treatment protocol available here: https://www.sheltermedicine.com/library/resources/uri-sample-treatment-protocol
There are also numerous additional resources for feline herpesvirus:
- Feline Upper Respiratory Infection aka URI from the UC Davis Koret Shelter Medicine Program (includes video and lecture slides at bottom):
https://www.sheltermedicine.com/library/resources/feline-upper-respiratory-infection-aka-uri
- Feline Respiratory Infections in Animal Shelters from Maddie’s Shelter Medicine Program of the University of Florida:
https://sheltermedicine.vetmed.ufl.edu/files/2017/01/Feline-respiratory-infections-in-shelters.2018.pdf
- Feline HerpesVirus (FHV) Infection from International Cat Care:
https://icatcare.org/advice/feline-herpesvirus-fhv-infection/
- Upper Respiratory Disease Handout for clients from Veterinary Partner: https://veterinarypartner.vin.com/default.aspx?pid=19239&id=4951489
- Viral Conjunctivitis Handout for clients from Veterinary Partner:
https://veterinarypartner.vin.com/default.aspx?pid=19239&id=4951824
Part 2 – Feline Gammeherpes Virus
Recall that there are three flavors of herpesvirus: alpha, beta, and gamma. Recently, I participated in a research study that isolated feline gammaherpesvirus 1 (FcaGHV1) for the first time in Canada [8]. FcaGHV1 was first described in 2014 [9] and further research found this virus to be widely endemic in domestic cats throughout the world [10] [11] [12], but cats in Canada had yet to be tested.
My role in the study primarily involved collecting saliva samples from shelter cats undergoing spay/neuter procedures while under anesthesia. Subsequently, these samples were transported to the researchers’ laboratories for detailed analysis. The study aimed to assess the prevalence of gammaherpesvirus among this specific population, identify potential risk factors, and conduct sequencing of the viral DNA.
The article is available online here.
Summary of Results:
- Approximately 20% of domestic cats tested positive for FcaGHV1 DNA in their saliva, with intermittent shedding contributing to potential underestimation.
- Shedding can persist over an extended period, as evidenced by consistent positivity in multiple saliva samples collected from an infected cat over two months.
- Feral cats may exhibit higher viral loads in saliva, potentially due to increased stress and overall health challenges [13]. However, there were only 4 positive feral cats in this study.
- In contrast to other studies, cat age and sex were not associated with the occurrence or level of FcaGHV1 shedding. Multiple studies have found that seropositivity is associated with male sex [11] [14] [15] and co-infection with FIV and hemotropic mycoplasma (previously called Mycoplasma haemofelis) [12] [10].
- Notably, most cats tested in our study were young, suggesting a need for further investigation into the virus’s dynamics across different age groups.
While this study provides valuable insights, it’s essential to recognize its limitations, including the small sample size of feral cats and the absence of screening for certain co-infections, such as FIV.
Conclusion
I thoroughly enjoyed the opportunity to participate in this research project but deriving clinically significant conclusions proves challenging due to the limited overall understanding of gammaherpesvirus in cats. To date, the potential association between this virus and clinical disease remains uncertain. Nevertheless, ongoing research endeavors may shed further light on the impact of gammaherpesvirus infection on feline health.
Works Cited
[1] Maclachlan, N. J., Dubovi, E. J. Fenner’s Veterinary Virology. Academic Press, 2010.
[2] Rothrock, K. Brister, J. (Ed). VINcyclopedia of Diseases. 16 January 2020. <https://www.vin.com/doc/?id=5419219&pid=6076fe1bc3e-045a-43c2-9a17-45d06e4ea7c7.1710179001>.
[3] Payne, Susan. Viruses: From Understanding to Investigation. Academic Press, 2017.
[4] Gaskell R.M., Dawson S., Radford A. Feline Respiratory Disease. Infectious Diseases of the Dog and Cat, 3rd ed. St. Louis: Elsevier Saunders, 2006.
[5] Glaze, M.B. “British Small Animal Veterinary Congress Conference Proceedings.” 2008. Veterinary Information Network. <https://www.vin.com/doc/?id=3862864>.
[6] Summers, S. C., Ruch-Gallie, R., Hawley, J. R., Lappin, M. R. “Effect of modified live or inactivated feline herpesvirus-1 parenteral vaccines on clinical and laboratory findings following viral challenge.” Journal of feline medicine and surgery 19.8 (2017): 824-830.
[7] Jas, D., Aeberle, C., Lacombe, V., Guiot, A. L., & Poulet, H. “Onset of immunity in kittens after vaccination with a non-adjuvanted vaccine against feline panleucopenia, feline calicivirus and feline herpesvirus.” The Veterinary Journal (2009): 86-93. University of California Davis “Feline Upper Respiratory Infection aka URI” 2015. Koret Shelter Medicine Program. <https://www.sheltermedicine.com/library/resources/feline-upper-respiratory-infection-aka-uri#Etiologic >.
[8] Hill, M. A., Satchell, T., Troyer, R. M. “Detection of Felis catus Gammaherpesvirus 1 in Domestic Cat Saliva: Prevalence, Risk Factors, and Attempted Virus Isolation.” Pathogens (2024): 111.
[9] Beatty, J.A., et al. “Felis catus Gammaherpesvirus 1; a Widely Endemic Potential Pathogen of Domestic Cats.” Virology 460-461 (2014): 100-107
[10] Ertl, R., et al. “Prevalence and Risk Factors of Gammaherpesvirus Infection in Domestic Cats in Central Europe.” Journal of virology (2015): 146.
[11] McLuckie, A., et al. “High Prevalence of Felis catus Gammaherpesvirus 1 Infection in Haemoplasma-Infected Cats Supports Co-Transmission. .” The Veterinary Journal 214 (2016): 117-121.
[12] Norris, J. M., et al. ” Prevalence of feline immunodeficiency virus infection in domesticated and feral cats in eastern Australia.” 9.4 (2007).
[13] Troyer, R. M., Beatty, J. A., Stutzman-Rodriguez, K. R., Carver, S., et al. “Novel gammaherpesviruses in North American domestic cats, bobcats, and pumas: identification, prevalence, and risk factors.” Journal of virology 88.8 (2014): 3914-3924.
[14] Novacco, M., et al. “Prevalence, Geographic Distribution, Risk Factors and Co-Infections of Feline Gammaherpesvirus Infections in Domestic Cats in Switzerland.” Viruses 11.8 (2019): 721.