Canine Herpesvirus-1 and reproductive problems

Stefaan Van Poucke D.V.M.

The Veterinary Practice

Millennium Way, Braintree, Essex

Canine herpes virus-1 can cause a fatal haemorrhagic disease in puppies less than 3 weeks old. Less well known is the effect of herpesvirus on fertility and pregnancy losses.

In the UK up to 80% of dogs are positive for canine herpes virus-1. Almost all dogs with regular contact with other dogs will have been exposed, especially in larger kennels, kennels with bad hygienic conditions and kennels with a history of kennel cough. Just like herpes virus infections in humans (e.g cold sores), adults can be healthy carriers which can reactivate or restart shedding following a period of stress such as pregnancy. Infection in adult dogs is mostly very mild and in the majority of time this goes unnoticed. It can cause self limiting lesions on the genitalia of sexually active dogs. They can be seen as small blisters in the vagina or on the prepuce. Herpes in dogs is not just a venereal disease but is often also passed on through oronasal contact. There is also an important link between canine herpes infection and a history of kennel cough.


Fading puppy syndrome

Infection with the virus in newborn puppies less than 3 weeks of age can result in sepsis and death. Older puppies show no or only mild clinical signs but can become carriers and may start shedding the virus around puberty. Treatment of young puppies which are showing clinical signs of infection is very disappointing and the mortality rate can be very high. Your veterinary surgeon can diagnose the disease by virus isolation at post mortem examination of a dead puppy. Once a diagnosis is made the other puppies can be treated. The environmental temperature should be raised over 38 °C as young puppies cannot mount a fever very effective. Antibiotics will not work against herpes but can be given to treat a secondary bacterial infection. Hyper-immunisation of affected puppies and treatment with antiviral drugs such as acyclovir has been reported.


Reproductive problems

What is not so well known is the effect of herpes virus on fertility and pregnancy losses. The virus has shown reproductive failure in bitches which were infected or reactivated during the season or pregnancy. Reproductive failure is characterized by infertility (not getting pregnant), resorption (early abortion), abortion, stillbirth or poorly developed puppies. To find out if herpes virus is the possible cause for poor fertility or pregnancy losses, two blood samples can be taken 2 weeks apart around the suspected time of whelping. A changing herpes titer is suggestive that herpes infection may be the underlying cause.

To minimize the risk of reproductive problems it is especially important to avoid contact of pregnant bitches with other dogs, so quarantine the bitch from 3 weeks prior to breeding to 3 weeks after whelping. It is also important to implement strict hygiene of the kennels and vaccination of the pregnant bitch. A vaccine is available in the UK (Eurican Herpes, Merial) for active immunization against canine herpes virus. The recommended vaccination scheme is a first vaccination at the time of mating followed by a booster 6-7 weeks later to achieve maximum protection around whelping. Some reproductive specialists advice first vaccination one month before the season, followed by a booster at the time of mating. This is followed by a blood test to check for adequate protection at mid-pregnancy and if the levels are not high enough a third booster is given. The benefit of the latter vaccination scheme is to give protection against possible fertility problems around the season. This vaccine has shown higher pregnancy rates but also improve birth weight, weaning rate and litter sizes.

So pregnancy losses in dogs are important problems for breeders in the UK and canine herpes virus infection may play an important role in this.