Canine Herpes Virus – Its Symptoms And Effects On Adult Dogs & Puppies

Ron Hines DVM PhD

Some Facts About Canine Herpes Virus

There are a lot of different herpes viruses. You know about the ones that affect humans: herpes simplex and the others that cause chickenpox, shingles, and mononucleosis. (ref) But canine herpes virus (CHV1) affects only dogs and wild canids. In most cases, CHV-1 just causes mild, transient upper respiratory tract infections in adult dogs (tracheobronchitis). In fact, some veterinarians include this herpes virus in their lists of the many causes of kennel cough. (ref)

Unfortunately, just like the cold sore herpes many of us harbor, the herpes virus of dogs has the same ability to hide dormant (sleeping/latent) in the body and take advantage of stress to reemerge (= recrudescence).

Exposure to canine herpesvirus-1 is extremely common in dogs. In one Norwegian study, 85.5% of 193 purebred breeding dogs sampled carried antibody evidence of exposure to the virus. (ref) A problem with just looking for antibodies against herpes virus as evidence of exposure is that those antibodies tend to drop to levels below test cut-off points during stress-free periods. So antibody-based tests underestimate the viruses’ true prevalence. I believe that that is the reason estimates of how common herpes infection is in dogs varies so greatly. (ref)  Like many viral diseases, exposure is probably more likely to occur in large breeding kennels, shelters and large-group housing situations than in individual household situations.

The canine herpes virus (CHV-1) would not rate nearly as much interest as it does if it was not for one of its peculiarities – when a new infection or a flare-up occurs during a female dog’s pregnancy, it can lead to abortion or sudden sever (fulminating) infections in the dog’s puppies (up through their 3rd week of age).  The canine herpes virus thrives and multiplies best at temperatures slightly lower than the normal body temperature of adult dogs (normal=101–101.5F 38-39C). Very young puppies have trouble maintaining that temperature. That, plus their lack of any residual antibodies against herpes virus imparted by prior exposure, make puppies particularly susceptible to severe herpes virus disease. Their incompletely developed immune system make the situation for them even worse. If the virus enters puppies during this defenseless period, it usually results in their death. (ref)

If My Adult Dog Has Herpes Virus, How Did It Catch it?

When a dog is first infected with the herpes virus, it sheds that virus in all its moist secretions: sneezes, coughs, vaginal secretions and semen. After it recovers from its initial infection, it often sheds the virus again when the dog is stressed. This usually occurs without any outward evidence of illness and can occur even when the shedding dog still has antibodies in its blood remaining from its initial infection or last relapse.

Veterinarians rarely if ever determine for sure how the virus entered your dog’s body. But most believe that exposure to the cough or sneeze of a virus-shedding dog accounts for many more instances of transmission than does sexual contact. Herpes virus is very fragile outside of the body. So it is unlikely that objects like water or food dishes transmit it.

When genital transfer occurs, it is usually from the mother to her own puppies as they pass through her birth canal. Since many of these female dogs are young and produce these star-crossed herpes puppies only on their first litter and never again, many believe that it is a female dog’s initial encounter with the herpes virus that is most likely to infect puppies. That has not been confirmed nor is it a hard and fast rule. All pregnancies are in themselves stressful and can reactivate sleeping virus. Some believe that the herpes virus can even infect these puppies while they are still in the uterus and cause spontaneous abortions. But herpes bouts in a mother dog can also cause fever; and fever in itself can cause miscarriages. 

What Are Some Signs That My Adult Dog Might Carry The  Herpes Virus?

The majority of dogs carrying canine herpes virus show absolutely no signs that they are sick.

The most common hints of the presence of CHV-1 in your adult dog are transient, mild, upper respiratory problems. Less commonly, blisters and ulcers (vesicular lesions) similar to cold sores and inflammation occur in the animal’s vaginal area, or on the prepuce and base of a male’s penis. Some dogs run fevers.

If those signs do occur, they often occur follow periods of stress such as increases in the number of dogs, boarding, or environmental changes in your home.

Herpes crosses the mind of veterinarians most frequently when dog owners complain of a lack of breeding success and/or stillborn or star-crossed puppies that die within their first 3 weeks of life.

Some vets have reported that on rare occasion, canine herpes inflammation has been limited to the eye (dendritic corneal ulcers and/or conjunctivitis). 

What Are The Signs Of Canine Herpes In Puppies?

If your mother dog experiences a rise in herpes virus numbers (relapse or primary herpes infection) near the end of her pregnancy, without a sufficient rise in her anti-herpes antibody level, it is common to loose all or some of the puppies during their first three weeks of life. Puppies born from mothers that have a decent antibody level against herpes are protected throughout this critical period. If the mother dog has adequate immunity herself, she will pass it along in her first milk (colostrum) in the form of anti-herpes antibody and immune cells that protect her offspring.

The signs of herpes virus disease are dramatically different in young puppies to what they are in adult dogs. As I mentioned, the critical period is from birth to three weeks of age. The most commonly described scenarios are puppies born apparently normal; only to die suddenly (a fulminating death in 1-2 days) after, at most a short period of listlessness. The first sign is often a lack of interest in suckling. Some affected pups whine continuously and appear uncomfortable. Pups might appear to be in pain due to tender or bloated tummies. There are reports of that. Their breathing is often fast and shallow. They might vomit back milk when you try to assist by bottle feeding them. Nose and eye discharges are not unusual. Some cases have reported pinpoint hemorrhages on the puppy’s gums; others an increased tendency to bleeding and seizures.

Young puppies, are not capable of running fevers. Their body mass (the source of their heat) is just not large enough in proportion to their skin area through which heat is lost. This is a major weakness of puppies in dealing with herpes. The virus reproduces much more rapidly at the puppy’s lower body temperature than it would in older dogs that can mount a fever.

As the disease progresses, the puppy’s temperature drops to subnormal levels (below 98F/ 36.7C). Subnormal temperature in a puppy is always a grave sign. And because things move downward at such a rapid rate, owners often do not recognize that the puppy is ill until it is gone. If the puppy is lost during its first few days, I believe that it was probably infected while still in the womb.

When CHV-1 occurs in somewhat older puppies, respiratory disease, more severe than in adults, can be part of the picture.  When the virus transfers to puppies while still in the womb but near birth, pups are often stillborn. When the virus transfer is earlier, the dog’s owner might just think their dog did not conceive.  That leaves some dog breeders mistakenly assuming that their dog (or stud) is infertile.

The protection maternal antibodies afford can be partial. If infected puppies do survive, they can be poor doers that suffer from multiple health issues including heart and nerve damage.

When a mother dog gives birth, it is quite possible for some of the puppies to become infected as they pass through the birth canal while others avoid infection. So some may thrive and some may not. It is also possible for the infected puppies to pass the virus to their littermates after birth. So there can be a second spike in puppy mortality 3-7 days after the first.

In all of these scenarios, the mother dog generally looks healthy and acts normally.

How Can My Veterinarian Be Sure That Canine Herpes Virus Is My Dog’s Problem?

None of the signs and symptoms of a Herpes-1 infection in adult dogs or puppies are distinctive enough to be sure herpes is the root of their problem. Antibodies, present in your adult dog’s blood confirm that at one point, your dog was exposed to CHV-1. But those antibodies are only present transiently. Many dogs carry them and remain disease free. Other dogs that do not produce them in sufficient amounts have Herpes-1 related issues but come up negative on the antibody tests. So these antibody tests have little value in predicting problem pregnancies or optimum times to breed.

The immune system of young puppies is rarely mature enough to produce the antibodies these tests look for. To tell your veterinarian much, blood samples need to be taken at several points in time during the illness and confirm that your dog’s antibody level against herpes virus is rising (three to four fold).

If the remains of puppies that die of herpes infection are sent out for autopsy, small (focal) hemorrhages and cell death (necrosis) in the lungs, liver, kidneys and elsewhere – as well as leaked fluids (serosanguinous effusions) in the chest and abdomen are also suggestive of the disease. Those tissue samples or the puppy’s remains must never have been frozen to be of value to pathologists. Thrombocyte counts are often low in puppies that die of canine herpes virus. But thrombocytes deteriorate upon death and by the time samples reach the lab that is unlikely to be verifiable.

For a positive diagnosis, tissue samples from a lost puppy or vaginal, nasal and oral swabs from an adult dog need to be sent to a central laboratory to search for the virus itself. Tagged artificially-created antibodies that bind only to the CHV-1 virus are used to confirm the viruses’ presence. (ref) A second test, the PCR test, will often detect the presence of the virus as well. (ref1, ref2) But the test is unlikely to be of value in detecting the dormant (“sleeping” latent) virus that all carrier dogs harbor. Those virus tend to hang out in two tangles of nerve (the trigeminal ganglia and lumbosacral ganglia) in quantities too small to be readily detected until the next flareup. (ref)

Attempts can also be made to grow and isolate the virus or to visualize them with electron microscopes – but that is only attempted in university settings.

What About Treatment For Canine Herpes Infections?

For infected young puppies, nothing has yet been found that slows or reverses the course of the disease. Treatment is generally unrewarding. Because the virus causes damage throughout the puppy’s body, even puppies that survive infection are often left with brain, kidney and liver problems.

Since most puppy owners rush in with the puppy(s) at death’s door, there is no time to send to the lab to even confirm the problem is herpes. So your vet may hope it isn’t herpes and proceed with life-supporting measures including warmth, tube feeding, oxygen and intravenous or subcutaneous fluids. Pups tend to perk up a bit with this care – but they fade back down shortly thereafter.

Although elevated temperature kills this herpes virus, treating the puppy with elevated temperature has not proved effective in saving infected pups. There are those that disagree – particularly when puppies not yet ill are separated into isolettes where ambient and body temperature can be accurately adjusted (95°F /35°C, 50% relative humidity).

There are also reported cases of puppies being saved by giving them blood serum from adult dogs that recently recovered from a herpes virus episode. Blood serum from adult dogs in that situation might contain enough antibodies to neutralize the herpes virus. Others reported that the antiviral drug, vidarabine, saved some puppies and still others have attempted to use acyclovir – since it is commonly given to humans with herpes virus flare-ups.

I do not suggest you attempt to treat sick puppies suffering from infection with canine herpes virus. If puppies survive infection they are usually left with nervous system and heart damage. I believe that it is considerably kinder to just put them down.

Veterinarians have little specific to offer you once an adult dog has become a CHV-1 carrier. We dispense medications to help with respiratory and eye issues when they occur. That, rest and TLC are all most adult dogs need to get over the active stage of herpes infection or a relapse. Remember that the vast majority of dogs that become infected will go through a mild initial upper respiratory tract illness that lasts a week or two and then are never visibly sick again.

What About Anti-Herpes Vaccinations?

In 2003, Merial, now a division of Boehringer Ingelheim, introduced an inactivated (sub-unit) canine herpes vaccine that appeared to boost antibody protection in adult dogs for about 60 days. The thought was, give the vaccine just before breeding and the dog will be less likely to be shedding herpes virus during and just after pregnancy. It was also hoped that some of that increased antibody would be passed on to the puppies in the first milk (colostrum). This vaccine is called Eurican® Herpes 205. Although studies on its effectiveness were minimal, It appeared to have positive effects and the EMA approved its use in Europe. (ref)

The first injection of Eurican® Herpes 205 is given when the female is bred. The second is given 6-7 weeks later. The process must be repeated every time the dog is bred since the immunity it hopes to imparts is temporary. It might be good insurance in first-time breeders and repeat problem breeders. Because the vaccine does not contain complete herpes virus, it is said not to interfere with PCR-based diagnostic tests. Living in America, I have no experience administering it. The vaccine has never been available in North America – probably because the USDA would require more extensive testing of its efficacy that the EMA did. The vaccine is probably not going to be a big enough money earner to warrant that.

Vaccine companies have been attempting to develop a vaccine to reduce human herpes simplex flare-ups since the 1920s. None have ever proven effective. The latest human herpes vaccine, VCL-HB01, failed its phase 2 clinical trials in June of 2018 and further studies on its use were discontinued.

What Can I Do To Lessen The  Likelihood That My Dog Will Be Exposed To Canine Herpes Virus?

Herpes is not a tough virus like parvo that persists in the environment. It is quickly killed by most common household disinfectants. Temperature over 104 F kills the virus, as does exposure to bright sunlight.

At dog shows and other community areas with many dogs, keep some sanitizing paper towels at hand. Any that claim to kill the flu virus are fine. Disinfect your hands before touching other dogs or allowing your dog to be handled by others. Good disinfectants for herpes, listed in order of effectiveness are 70% isopropyl alcohol mixed 50-50 with water, 0.5% Lysol, Listerine mixed 50-50 with water and household bleach diluted 7 tablespoons-full in 1 quart of water (=~2000ppm). (ref)

Keep your dog on a short leash when visiting high dog-traffic areas. Keep the pet’s head up and do not let it sniff other dogs. In calm air, virus in coughs and sneezes travel about 6 feet.

In grooming establishments, cages and kennels need to have solid partitions and be disinfected between animals.

Isolating your pregnant dog during the critical susceptibility period (3 weeks before to 3 weeks after its due date) is advisable – particularly if it is her first pregnancy.

Should I Breed My Female Dog Again?

Yes, if that is your desire.

If there were good reasons for you to breed your dog before you learned that she harbored the CHV-1 virus, there is no reason not to breed her again. Baring some unanticipated breakthrough, we are not going to eliminate canine herpes virus from the dog population any more than we can now eliminate human herpes simplex virus.

Wait a year, build up your dog’s health and breed her again to a different healthy stud – one that already carries anti-herpes antibodies.

If the second try is still a problem litter, retire the breeder.

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