There’s a good chance your dog has herpes, but it’s not what you might initially think. There is a generally higher prevalence in kenneled dogs versus household pets, but Dr. James Evermann, Ph.D., professor emeritus of Veterinary Clinical Sciences at Washington State University and a canine herpes expert says that infection rates vary from 15% to 100% based on surveys conducted studying antibodies in the blood serum. So what is it, and how do dogs get it?
What is Canine Herpesvirus?
Canine herpes (CaHV-1, or CHV for short) is separate from human forms of herpes. Neither form of CHV can be transmitted from one species to the other. Canine herpesvirus only occurs in domestic and wild canids (like foxes and coyotes). Surveys worldwide have estimated how often it’s prevalent in different countries, from 88% of dogs in the United Kingdom to 22% in Japan.
The prevalence of the disease also depends on dogs’ proximity to other dogs, and Dr. Evermann explains that there is a generally higher prevalence in kenneled dogs versus household pets.
How is CHV Transmitted?
Canine herpesvirus is most commonly transmitted through the nose and mouth, and, less commonly, through the eyes and genitals. In adults and puppies older than three weeks of age, CHV usually presents as a mild upper respiratory disorder. However, it can also cause mild genital, ocular, and neurological disorders in dogs.
Generally, you won’t even notice it if your dog is infected. Your dog may have a discharge from the eyes or nose. Male dogs may exhibit inflammation of the penis or prepuce (foreskin), while females may exhibit inflammation of the vulva. The signs may be so mild they go unnoticed. In pregnant females, CHV may cause loss of litters. But it’s in newborn puppies that canine herpes wreaks its most damage.
Puppy CHV Infections
Puppies can become infected before birth, while passing through the birth canal, or as a result of their dam licking them. Infected puppies quit nursing, begin crying from abdominal pain, become increasingly ill, and often die within 48 hours after first exhibiting symptoms. After the age of three weeks, puppies will be unaffected by CHV or, like adults, will only be mildly affected by the virus. Why the difference?
Canine herpesvirus can’t replicate itself effectively in temperatures above about 98.6° F. If a puppy is under the age of three weeks, its body temperature will be below that temperature threshold. As a result, the virus can replicate and thrive in young dogs of that age. Placing exposed puppies in an incubator with a temperature above 98.6° F has been credited with saving these young animals as long it’s done before they show any signs. However, once a puppy exhibits signs of CHV, the success rate of them surviving after being placed in an incubator is very low. In addition, those that do survive are generally plagued for life with heart or neurological problems.
If a dam has been exposed to CHV at least three weeks before whelping, has developed immunity to it, and is no longer showing any signs, her puppies will become passively immune to CHV by nursing from her. Dr. Evermann stresses that puppies must ingest adequate amounts of colostrum (the first milk produced by a dam) to acquire passive immunity. But puppies that nurse from dams showing signs of CHV, or dams that are seronegative (that is, who have not been exposed to CHV), are still at risk if they are then exposed to the virus. That exposure could come from their dam, other dogs, human hands, or other objects that have recently been in contact with a dog with the virus.
Adult CHV Infections
Dr. Evermann has identified several risk factors that can increase the possibility of CHV infection in adults—larger kennels, poorer hygiene, and kennel cough. The infection in adults may have several different signs, some of which are more obvious than others.
In adult dogs, CHV can spread in areas around the nose and mouth, such as the membranes lining nasal cavities, pharynx, and tonsils. It generally causes signs of a mild upper respiratory tract infection, such as a runny nose or intermittent cough. In immunocompromised dogs (those that have a weakened immune response), such as dogs receiving chemotherapy or corticosteroids, signs may be much more severe.
Infected adults may exhibit mild signs of the disease on the eye’s surface, including the cornea (the clear outer surface at the front of the eye) and the conjunctiva (the thin membrane that covers the eye and inner surfaces of the lids). Owners may notice their dogs have inflamed eyelids, reddened conjunctiva, corneal lesions, or eye discharge. The discharge starts as clear tears and eventually turns into thicker mucus that can even become bloody as the infection progresses. The discharge can affect both of your dog’s eyes, which will often appear to cause pain in your pet, especially in response to bright light.
The condition usually goes away on its own, though it may recur. Recurrence most often occurs in dogs that are immunocompromised, which can happen from taking immunosuppressive drugs. These drugs, which can include topical or systemic cyclosporine or corticosteroids, often bring on a recurrence. In one study, 83% of dogs receiving an immunosuppressive drug had recurring signs of CHV in their eyes.
As with human herpes viruses, canine herpesvirus doesn’t go away just because its outward signs do. Instead, it lays dormant in the body. When CHV is dormant, your dog does not show any signs of being ill with the virus and does not shed the virus (when the virus reproduces and can spread from an infected dog). However, the CHV virus may reactivate with or without clinical signs, either spontaneously or after exposure to immunosuppressive drugs.
How Do You Detect CHV?
Although antibody testing was once the norm for CHV detection, now polymerase chain reaction (PCR) testing is preferred. Dr. Evermann notes that antibody testing “is less sensitive than PCR-based testing, but can provide information on a population of dogs by way of screening 10% of the kennel. This may help detect prior CHV exposure and assist in determining the risk category. It may also assist in determining if a dog is a carrier of CHV. A carrier dog is defined as one not showing disease symptoms, but latently infected, and potentially capable of shedding concurrent with stress.” This means that a carrier dog might carry the virus dormant in their system without exhibiting symptoms, though stress might cause the virus to begin to shed.
Newly infected dogs exhibiting signs of CHV will shed the virus for various periods of time, from days to weeks. Dogs with recurrent episodes also shed the virus, though probably for shorter periods. The virus can be shed from all mucosal surfaces. A previously exposed pregnant dam can have a recurrence and infect her puppies.
How Do you Treat CHV?
Treatment of puppies already showing signs is generally not effective, although some treatments may be helpful for puppies not yet showing signs. In adults, treatment of respiratory and genital CHV generally can relieve symptoms, as no specific treatments address the virus. Ocular CHV is often treated successfully with antimicrobials designed to fight secondary bacterial infections, ocular atropine to increase comfort, and the antiviral drugs idoxuridine or trifluridine.
Is there a Vaccine for CHV?
A vaccine is available in Europe, but not in North America. But it really isn’t adequate for treating CHV. “The vaccines available in Europe are inactivated and may provide some short-term protection,” explains Dr. Evermann. “However, these vaccines require regular re-vaccination of dams for some protection to the puppies via colostrum.”
Precautions to Prevent CHV
Evermann suggests instead that precautions are the best means of preventing CHV at present. “In lieu of vaccination, awareness of CHV infections in the dog populations is very important.” Pregnant dams that have not been exposed to the virus or lack immunity can be very susceptible to getting infected by dogs that are shedding the CHV virus and carriers. He adds, “The risk of infection and disease in pups from recently infected dams, pre-whelping—three weeks—and post-whelping—three weeks—is high. This six-week caution period allows for selective quarantine, especially in dams with unknown history of past CHV infection.”
Previously, it was thought that as long as the dam and every dog she was in contact with had been exposed to CHV, the puppies would be safe. But with the discovery that the virus and shedding can be reactivated, the current recommendation is that dam and puppies should be quarantined, regardless of exposure history.