A scourge for breeding

Canine herpesvirus, which causes reproductive problems in bitches, remains in the body and can reactivate at certain times of life. Males and females can become infected during gestation, at birth or during mating. Sanitary measures are in place to limit the spread of the virus.

Herpesvirosis is increasingly cited by breeders and veterinarians for its impact on canine fertility. While it's true that canine herpesvirus infection leads to reproductive disorders - neonatal mortality, infertility, abortions, stillbirths - it's worth remembering that infertility can result from a variety of factors (management of breeding periods, diet, hygiene, living conditions, etc.). Advances in diagnostic methods have improved veterinarians' knowledge of the infectious agents responsible for reproductive disorders in the canine species, which until recently were considered secondary. Taking these infectious agents into account - some already known, others more recent (herpesvirus, Brucella canis...) - represents a step forward in the treatment of infertility in the bitch.
Canine herpesvirus (CHV) is a DNA virus specific to dogs. Like all herpesviruses, it has the particularity of remaining in the organism it infects for long periods of latency. Once the infection has healed, the virus can reactivate in response to stress in the body, once again causing symptoms (in humans, the varicella virus remains in the body for life, and can later cause shingles).

Three routes of contamination

HVC is present in many countries. In France, its incidence is not precisely known. The virus is transmitted to dogs via three routes:
oronasal (puppies are contaminated by their mothers at birth through secretions), venereal (during mating), and via the placenta (puppies become contaminated during gestation).
All genital secretions of infected individuals, as well as runts, foetal envelopes and excretions of sick puppies, contain the virus and are therefore infectious. This is important to protect healthy dogs from these contaminants. HVC causes a disease - herpesvirosis - encountered mainly in breeding communities, but it also infects private dogs. The disease is often inapparent in healthy adults. The virus has an affinity for mucous membranes.
Depending on where it enters the body, it develops in the nasal, pharyngeal or genital mucosa. It either enters a latent phase, or spreads throughout the body via the bloodstream; some dogs can also eliminate the virus for good. This evolution is conditioned by the immune response of the infected dog. When the immune response is good, the infection can remain latent for several months.

Neonatal mortality

If the immune response is inadequate, CVH infects organs such as the liver, spleen, heart and kidneys, where it causes haemorrhaging. This is particularly true of puppies under three weeks of age. In older puppies, the virus causes local symptoms: rhinitis, pharyngitis, conjunctivitis. Herpesvirosis should be suspected in a kennel when mortality is observed in puppies under three weeks of age, and when infertility is observed in bitches. A clinical examination can help guide the diagnosis if the veterinarian observes vesicles on the vaginal mucosa. Necropsy of newborn puppies shows characteristic lesions of affected organs when CVH is involved. Laboratory diagnosis enables the virus to be identified with certainty. It uses several techniques applied to the organs of newborn puppies, to vaginal or preputial swabs, and also to tonsils. Blood tests are of little use in diagnosing canine herpesvirosis, as CVH is not very immunogenic (it does not trigger a strong immune response in the body) and a carrier dog may have negative serology. Furthermore, infected puppies die very quickly, and have no time to synthesize antibodies.

Exclude infected breeding stock

Preventing herpesvirosis means excluding infected dogs and bitches from breeding, after accurate diagnosis by a veterinarian via the laboratory. Exchanges of breeding stock should be limited. In the event of transmission of the virus via semen, the use of frozen semen is not without danger. Sanitary measures, recommended by the practitioner, can limit the spread of the virus (in particular, isolation of the mother-to-be at the end of gestation and during the first weeks of breast-feeding, control of general hygiene and care of newborns).
Fortunately, HVC is fragile and sensitive to disinfectants, ultra-violet rays and heat. Premises must therefore be regularly and correctly disinfected, using suitable products, to reduce the viral load.

Causes infertility in bitches

In pregnant bitches, infection with canine herpesvirus (CHV), or its reactivation due to reduced immunity during gestation, can cause damage to the uterus. The virus causes early embryonic death, fetal resorption, fetal mummification, abortion and stillborn puppies. Embryonic death, resorption and fetal mummification lead the breeder to believe that the bitch remains empty after mating, when in reality she was full but the fetuses did not develop.

Discreet symptoms and latency in adults

Infection of healthy adult dogs with canine herpesvirus (CHV) causes discreet symptoms. Typical herpesvirus lesions, known as vesicles, can be seen on the mucous membranes, ulcerating and healing within 1-2 weeks. HVC remains latent in the body after symptoms have disappeared. It is reactivated by stress - heat, gestation, illness, etc. - and excreted again by the dog or bitch, which may infect others when mated.
Blood tests are of little use in diagnosing canine herpesvirosis: a carrier dog may have negative serology...

Merial press release. Diffusion Biokema.
Courtesy Chiens 2000.
Méd. Vét. Valérie Duphot.