Dogs get herpes through direct contact with an infected dog’s bodily fluids, primarily nasal secretions, saliva, and genital discharges. The virus, called canine herpesvirus-1 (CHV-1), spreads during nose-to-nose greeting, mating, sneezing, and from mother to puppy during birth. Roughly 30% of dogs in some populations carry antibodies to the virus, meaning exposure is common, though most adult dogs show few or no symptoms.
How Dogs Transmit the Virus
CHV-1 passes between dogs through three main routes: respiratory, genital, and from mother to newborn. The respiratory route is the most common in everyday life. When an infected dog sneezes, coughs, or simply touches noses with another dog, the virus transfers through nasal and oral secretions. This makes places where dogs congregate, like kennels, dog parks, and boarding facilities, natural hotspots for spread. CHV-1 has been isolated from lung and tracheal tissue and is considered a contributing agent in kennel cough.
Genital transmission happens during mating. Infected females can develop small fluid-filled blisters in the vaginal area, and these lesions frequently appear at the start of the heat cycle, making venereal spread particularly likely during breeding. Males can carry and shed the virus too, often with little more than mild redness at the base of the penis and a watery discharge from the eyes or nose. That discharge appears to be one of the major ways the virus reaches females and, eventually, their puppies.
The third route is the most dangerous. Puppies can become infected as they pass through the birth canal of an infected mother or through contact with her nasal secretions shortly after birth.
Why It’s Mild in Adults but Deadly in Puppies
In adult dogs, CHV-1 typically causes nothing more than a mild respiratory illness or subtle genital irritation that clears up on its own. Many infected adults never show signs at all. The virus can cause nasal inflammation, conjunctivitis, and occasionally a deeper eye condition called keratitis, but these are generally short-lived.
Newborn puppies face an entirely different outcome. CHV-1 replicates most efficiently at lower body temperatures, and neonatal puppies can’t regulate their own temperature well. Their cooler bodies provide ideal conditions for the virus to multiply rapidly and spread to multiple organs. In affected litters, mortality rates often reach 100%. Deaths occur most commonly between 1 and 3 weeks of age, occasionally up to one month, and rarely in puppies as old as 6 months. This pattern of sudden puppy loss is sometimes called “fading puppy syndrome,” where seemingly healthy newborns stop nursing, cry persistently, and deteriorate within hours.
Latency and Reactivation
Like human cold sores (caused by a related herpesvirus), CHV-1 never fully leaves the body. After the initial infection, the virus travels along sensory nerves and settles into clusters of nerve cells called ganglia, where it goes dormant. A dog can carry the virus silently for years.
Certain stressors can wake the virus back up and trigger a new round of shedding, meaning the dog becomes contagious again without necessarily showing symptoms. Known triggers include stress, surgery, trauma, hormonal fluctuations, and the use of immunosuppressive medications like corticosteroids. Research from the American Journal of Veterinary Research found that systemic corticosteroid treatment repeatedly caused viral reactivation and shedding in latently infected dogs. This is especially relevant for pregnant dogs: the stress and hormonal shifts of pregnancy can reactivate a dormant infection at exactly the wrong time.
Reproductive Consequences
For breeding dogs, CHV-1 carries reproductive risks beyond neonatal death. Infections during pregnancy can cause abortions, stillbirths, and infertility. A female dog who was infected years earlier and showed no symptoms might reactivate the virus during pregnancy and pass it to her litter during or immediately after birth, with no warning signs beforehand.
Males contribute to the cycle as well. An infected stud dog can appear completely healthy while shedding virus from genital or nasal secretions, introducing CHV-1 to a previously unexposed female during breeding.
Signs to Watch For
In adult dogs, symptoms are often so mild they go unnoticed. When they do appear, they include:
- Respiratory signs: sneezing, nasal discharge, mild cough
- Eye problems: watery or mucus-like discharge from the eyes, redness, corneal inflammation
- Genital lesions: small blisters or redness on the vulva or at the base of the penis, sometimes with a pus-like discharge in females
In puppies under three weeks old, the signs are more alarming: loss of appetite, persistent crying, weakness, difficulty breathing, soft yellowish-green stool, and rapid decline. By the time symptoms appear in a newborn puppy, the infection has often already become systemic.
How Vets Diagnose CHV-1
Two main tests are used, and they answer different questions. PCR testing detects the virus’s actual DNA in a swab or tissue sample, confirming an active infection. The catch is that the sample has to come from a site where the virus is present, so a negative result doesn’t always rule out infection if the wrong area was swabbed.
Antibody (serology) testing checks whether a dog’s immune system has responded to the virus at some point. A positive result means the dog was exposed or infected but doesn’t distinguish between a current active infection and one that happened months or years ago. For breeding programs, antibody testing helps identify which dogs carry the virus, while PCR is more useful when a dog is actively sick or when investigating puppy losses.
Prevention for Breeders
A vaccine called Eurican Herpes 205 is available in parts of Europe and some other markets, though not in the United States. It’s designed specifically for pregnant dogs and follows a two-dose schedule: the first injection is given during heat or 7 to 10 days after mating, and the second injection is given 1 to 2 weeks before the expected whelping date. The vaccine needs to be repeated with each pregnancy.
Beyond vaccination, practical steps make a significant difference. Keeping pregnant dogs isolated from other dogs during the last three weeks of pregnancy and the first three weeks after whelping reduces exposure risk. Maintaining warm whelping areas is critical because the virus thrives at the lower body temperatures typical of newborn puppies. Keeping the whelping box consistently warm helps limit viral replication even if exposure occurs. CHV-1 is a fragile, enveloped virus, meaning it doesn’t survive well outside the body and is easily killed by common disinfectants, so keeping whelping areas clean provides an additional layer of protection.
Can Dogs Give Herpes to Humans?
CHV-1 is species-specific. It does not infect humans, cats, or other animals. Similarly, human herpes simplex viruses (HSV-1 and HSV-2) do not infect dogs. The two viruses belong to the same broader family, which is why they share some behavioral traits like latency and reactivation, but they are distinct viruses with different host ranges.