Canine herpesvirus – symptoms and protecting puppies

Overview

CHV-1 belongs to the herpesviruses, which can remain dormant, or latent, after infection. Latent virus may reactivate intermittently without visible illness. This maintains circulation of the virus in the dog population.

Canine herpesvirus occurs worldwide.

Exposure is common in dogs. Antibodies were present in 40% of dogs tested in the Netherlands. In Britain, the corresponding proportion among tested dogs was 88%.

Antibodies indicate previous exposure, rather than how many dogs are currently ill. The most serious form involves newborn puppy deaths. People cannot acquire infection from this canine herpesvirus.

Causes

Close contact spreads the virus

Transmission is mainly direct from an infected dog to another. The respiratory route is the main route in adults. Even nose-to-nose contact on an ordinary walk may transmit infection.

A bitch may shed virus in both nasal and vaginal secretions. Ill puppies can shed large amounts. Spread through mating is possible but less common than respiratory transmission.

A puppy can become infected before birth. Virus can also be acquired in the birth canal or soon afterwards through the dam's nasal secretions. Another infected dog may also introduce it to the litter.

The incubation period, from infection to symptoms, is usually 3–7 days. Infection in early pregnancy may cause embryonic death and resorption. Infection late in pregnancy may instead cause premature birth.

After oral or nasal infection, virus multiplies in nasopharyngeal surface cells and tonsils within 24 hours. This local phase may be followed by spread into the bloodstream within infected white blood cells.

Chilling helps the virus spread

A puppy's temperature regulation is immature during the first 4 weeks, requiring a sufficiently warm environment. At a low body temperature, virus can spread from the mouth and throat into the bloodstream. It can then reach several organs.

Stress, corticosteroid treatment or immunosuppressive disease may reactivate latent virus. During reactivation, the dog may again shed virus from nasal or genital mucous membranes.

Risk factors

Very young puppies have the highest risk of severe disease. Herpes-associated newborn deaths concentrate in the first 2 weeks of life. In puppies over 4 weeks old, respiratory infection usually causes mild signs.

Puppies whose dam first becomes infected late in pregnancy are particularly at risk. She may not have time to develop enough antibodies to protect them through colostrum. Even with a vaccinated dam, a puppy that suckles poorly receives little colostral protection.

Unfamiliar kennels, shows and new dog contacts increase exposure opportunities for a pregnant bitch. A dog with kennel cough, or one that has recently had it, may also spread herpesvirus.

Typical symptoms

Infection in a bitch may appear as abortion or stillborn puppies. Newborn illness may begin simply with reduced suckling and subdued behaviour. Signs can progress rapidly even when they initially seem mild.

A bitch may also have a smaller-than-usual litter or puppies born weak. An affected puppy's weight may start falling as appetite declines.

• The puppy is sleepy and does not seek to suckle.

• The puppy vocalises constantly and has a tender abdomen.

• Thick discharge runs from the nose.

• Breathing becomes difficult.

• The puppy passes soft grey-yellow or greenish faeces.

• Small haemorrhages may be visible on mucous membranes.

• Severe disease involves seizures or paddling limb movements.

An adult dog may have only a mild cough or runny nose. Ocular herpes infection can cause squinting, recurrent eye discharge or conjunctivitis. Blisters may occur on genital mucous membranes.

Complications and consequences

The outlook for a litter can be poor

A severely affected newborn may die within 24–48 hours of the first signs. Severe herpes infection can kill the entire affected litter. Some puppies surviving the acute phase develop permanent central nervous system damage.

An affected puppy can also become blind. Adult eye infection may involve a corneal ulcer. The outlook is usually better for older puppies and adults when signs are mild.

A surviving puppy may have permanent kidney damage even after the acute life-threatening illness has passed.

Losing one litter does not mean every future litter from the bitch will die of herpes. Antibodies from previous infection may protect the next litter through colostrum. Colostral protection may prevent severe disease even without preventing later infection.

Diagnosis at the vet

Other diseases cause similar signs

The vet assesses the puppy's condition and the pattern of signs across affected puppies. Investigations distinguish herpes from other causes of puppy deaths. Alternatives include bacterial infections, brucellosis and toxoplasmosis.

Maternal mastitis can also be associated with a puppy's bacterial infection. Examination checks the puppy's suckling reflex and mucous membranes. Congenital problems such as a cleft palate are also sought.

PCR looks for virus; antibody testing looks for exposure

PCR can demonstrate herpesvirus genetic material. Samples may be an organ sample from a puppy or a respiratory or genital mucosal swab from an adult. The usefulness of an adult mucosal swab depends on whether virus is being shed at collection.

Antibodies in an unvaccinated dog's blood show that it has encountered the virus. An antibody test does not show whether the dog is infectious at that moment. With latent infection, antibodies are not always detectable even though virus remains in the body.

Antibody testing cannot distinguish rises caused by vaccination from those caused by infection. Levels measured by virus neutralisation may decline within around 2 months of infection. PCR is recommended in acute infection because antibody levels may be low.

In some situations, antibody levels are compared in blood samples taken 2 weeks apart. Interpreting a single level requires information on infection timing.

Examining a dead puppy helps assess the rest of the litter

A post-mortem examination can confirm the cause of a sudden puppy death. Herpes infection may produce tiny pinpoint haemorrhages in internal organs. Organ samples can undergo PCR testing for the virus.

On tissue microscopy, viral changes within cell nuclei, called inclusion bodies, may suggest herpes infection.

Treatment

A puppy needs prompt supportive care

Treatment outcomes in affected newborns are often poor because disease progresses rapidly. Veterinary intensive care may include controlled warming, fluids and supplemental oxygen. Low blood sugar is also corrected if necessary.

A newborn that fails to suckle can rapidly develop low blood sugar even after a short fast. Chilling also impairs immunity, suckling and digestion. Gut movement may stop in a hypothermic puppy, increasing feeding-related reflux and aspiration risk.

A chilled newborn is warmed slowly, usually over 30–60 minutes. A heat lamp placed too close or an excessively hot warming pad can cause overheating and burns. The usual rectal temperature during the first week of life is 35–37.2°C.

Keeping a newborn warm provides support, but raising temperature alone after signs begin does not repair existing internal organ damage.

Antiviral use requires veterinary supervision

There is no established antiviral treatment for neonatal herpes infection demonstrated to be safe. Aciclovir, for example, can cause severe poisoning and kidney damage in dogs. Do not therefore treat a puppy at home with a human herpes medicine.

An adult dog's eye signs may be treated with topical antivirals at the vet's discretion. A secondary bacterial eye infection may need a topical antibiotic. Eye pain is treated too.

Mild adult signs may disappear without specific medication. However, the end of symptoms does not mean the virus has left the body.

Prevention

Restrict a pregnant bitch's contact with unfamiliar dogs during the final 3 weeks of pregnancy. Continue the same protection for 3 weeks after birth. Keep newborn puppies away from adult dogs other than their own dam during this vulnerable period.

Good hand hygiene and a clean puppy environment reduce infection risk. Herpesvirus is relatively fragile in the environment and does not survive long outside a dog. Restricting matings alone does not eliminate the virus because other close contact is the main transmission route.

Excluding an antibody-positive dog from breeding is not by itself an effective way to eliminate this common virus from the dog population.

Where a vaccine is available, breeding bitches can be vaccinated against herpesvirus to protect their puppies. Vaccine-induced maternal antibodies pass to puppies through colostrum. The aim is to protect newborn puppies, rather than vaccinate them directly.

Adequate colostrum intake is essential for protection. Protection matters particularly before 3 weeks of age, when infection can be fatal. The need to vaccinate a bitch is assessed individually with the vet.

Important for dog owners

Weigh puppies and record their condition daily. A healthy puppy feeding well is usually quiet and sleeps between feeds. Usual daily weight gain is around 5–10% of bodyweight.

Alongside puppy monitoring, check the dam's appetite, condition, mammary glands and post-birth discharge daily.

Record each puppy's birth time, weights, suckling and the time of first signs separately. Tell the vet about maternal vaccinations, mating and dog contacts, and previous litter losses. Discuss the whole litter even if only one puppy looks ill. Arrange examination of a dead puppy and sample delivery before transport.

Colostral antibodies can be absorbed from the intestine into the bloodstream for at most around 24 hours after birth. Absorption is most efficient during the first 4 hours. Successful suckling immediately after birth therefore needs particular monitoring.

Frequently asked questions

Can a dog without symptoms spread herpesvirus?

Yes: latent infection may reactivate without obvious signs. Virus may then be shed again from respiratory or genital mucous membranes. A healthy-looking adult is therefore no guarantee that a litter cannot be exposed.

Does a positive antibody result mean the dog is infectious?

No: in an unvaccinated dog, antibodies indicate previous contact with the virus rather than directly measuring current shedding. Conversely, antibodies may go undetected in a dog carrying a longstanding latent infection. Results are assessed alongside signs and exposure information.

Does a puppy gain protection from its dam's herpes vaccination?

Vaccination aims to increase maternal antibodies, which the puppy receives in colostrum. The puppy therefore needs enough of its mother's first milk immediately after birth. A poorly suckling puppy does not receive equivalent protection simply because the dam was vaccinated.

Can the bitch's future litters survive?

Yes: maternal antibodies formed after herpes infection can protect later litters through colostrum. A previous litter loss does not mean the same will happen every time. However, latent virus can remain in the bitch's body.

Can canine herpes spread to people?

Canine herpesvirus does not infect people. However, brucellosis and toxoplasmosis, for example, can also cause puppy deaths and carry human infection risks. The cause of a sudden puppy death should therefore be investigated rather than assumed to be herpes from symptoms alone.