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

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

Ron Hines DVM PhD

Read about Kennel Cough In Your Dog 

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. (read here) But canine herpes virus (CHV1) affects only dogs and wild canids. In most cases, CHV1 just causes mild, transient upper respiratory tract infections in adult dogs (tracheobronchitis) similar to kennel cough. In fact, some veterinarians include this herpes virus in their lists of the many causes of kennel cough. 

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. (read here) 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. (read here)  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 (CHV1) 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 life).  The canine herpes virus thrives and multiplies best at temperatures slightly lower than the normal body temperature of adult dogs (normally 101–101.5 F / 38-39 C). 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. The puppies’ incompletely developed immune system make the situation for them even worse. If the herpes virus enters puppies during this defenseless period or even before they were born, the virus directly, or in combination with other factors, often results in their death. (read here)

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 CHV1 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 scenario are puppies born apparently normal; but suddenly experiencing an abrupt (“fulminating”) death 1-2 days later. At the most, death might be preceded by a short period of listlessness. The first sign is often a puppy with a lack of interest in suckling. Some affected pups whine continuously and appear uncomfortable. Others appear to have tender or bloated tummies. The pup’s 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 have reported pinpoint hemorrhages on their puppy’s gums; others an increased tendency for bleeding or 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. If the disease progresses, the puppy’s temperature drops to subnormal levels (below 98 F / 36.7 C). Subnormal temperature in a puppy is always a grave sign. Because things move downward at such a rapid rate, dog owners often do not recognize that the puppy is in trouble until it is gone. When a puppy is lost during its first few days, I believe that it was probably infected with the virus while it was still in the womb.

When CHV1 occurs in somewhat older puppies, respiratory signs, 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 the maternal antibodies of the mother afford to their puppies through their first milk (colostrum) can be only partial. If these partially-protected but infected puppies do survive, they sometimes remain “poor doers” that continue to suffer from multiple health issues including stunted growth, 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 remains 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 CHV1. 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 CHV1 virus are used to confirm the viruses’ presence. (read here) A second type of test, the PCR test, can detect the actual presence of the herpes virus in the puppy. (see here) But the PCR test is not of much value in detecting dormant (“sleeping” latent) virus that all herpes carrier dogs harbor. That is because there is not enough virus material in those dogs for the PCR test to detect between flareups. Those sleeping herpes virus tend to hang out (reside) in two tangles of nerve (the trigeminal ganglia and lumbosacral ganglia) in quantities too small to be readily detected until the dog’s next flareup. (read here) Attempts can also be made to grow and isolate the virus or to visualize them using an electron microscope – but that is only attempted in university research settings.

What About Treatment Options For Canine Herpes?

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 (pediatric incubators) 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 obtained from an adult dog – particularly a kenneled dog – 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 that medication is commonly given to humans with herpes virus flare-ups. Unfortunately there can be down sides to heroic treatment of sick puppies suffering from infection with canine herpes virus. If the puppy(s) survive infection they are frequently left with permanent nervous system and/or heart damage. 

Veterinarians have little to offer you once your adult dog has become a confirmed CHV1 carrier. We can dispense medications to help with any respiratory or eye issues. That plus rest and TLC are all the majority of 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 with canine herpes will go through a mild initial upper respiratory tract illness that lasts a week or two and then are never visibly sick again. Most of those dogs still carry “sleeping” (dormant) living herpes virus deep within their nervous system. But they are extremely unlikely to pass those virus on to their puppies unless they are faced with major stress during or just after pregnancy.  

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 that if they gave the vaccine just before breeding, the dog would 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. I do not believe that Boehringer ever requested permission to market the product in North America but I could be wrong. The vaccine would probably not earn the Company enough money to justify the effort.

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. 

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 parvovirus that persists in the environment. It is quickly killed by most common household disinfectants. Temperatures over 104 F/40 C kill the virus, as does prolonged exposure to bright sunlight.

At dog shows and other community areas shared by many dogs, keep some pre-moistened sanitizing paper towels on hand. Any that claim to kill the flu or COVID virus will kill herpesviruses. Disinfect your hands before touching other dogs. Don’t allow your dog to be handled by onlookers or mingle with other dogs. Its not that humans spread dog herpes virus or that human herpes virus infect dogs. Its because people who are inclined to pat your dog are inclined to pat multiple dogs.  Good disinfectants for herpes, listed in order of effectiveness are 70% isopropyl alcohol (can be mixed 50-50 with water), 0.5% Lysol™, Listerine™ mixed 50-50 with water and household bleach (diluted 7 tablespoons-full (104 ml) in 1 quart (946 ml) of water (=~2000 ppm). (read here)

Keep your dog on a short leash when visiting high dog-traffic areas. Keep the pet’s head up and restrain it from sniffing other dogs. In calm air, virus in coughs and sneezes travel about 6 feet. In grooming establishments, cages and kennels should have solid partitions and be thoroughly 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.

If I Experienced a Herpes Star-Crossed Litter Should I Breed My Dog Again?

Yes, if you are motivated to do so.

If there was good reason to breed your dog before you learned that she harbored the CHV1 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 currently eliminate human herpes viruses. Wait about a year, build up your dog’s health and breed her again to a different proven healthy stud. The only ethical thing to do is to inform the stud’s owners of the situation even though most adult dogs have already been exposed. In Italy, only about a third of kennels did not have virus-exposed dogs. There is no data on the percentage that carry the virus in the United States. (read here) If your second attempt still produces a problem litter, permanently retire the breeder.

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