Canine herpesvirus and puppies.
Canine herpesvirus (CHV) is specific to domesticated and wild dogs. As with other herpesviruses, CHV becomes latent and is carried by the affected individual for life, though they may not show any clinical signs. The infection may flare up and become a clinical problem during periods of stress or immunosuppression.
Dogs are infected in one of the following ways:
- In fetuses, across the dam’s placenta
- In new born pups through contact with the birth canal
- During mating
- Via the respiratory route
CHV is a virus that grows best at a temperature slightly below the normal core temperature of a dog, meaning that it is usually restricted to the nasal passages where the temperature is lower. If a puppy is chilled or has few maternal antibodies, it is more susceptible to widespread infection.
A puppy may acquire protective antibodies against CHV from the mother across the placenta as well as in the colostrum. The bitch will only have antibodies to pass on if she has either been exposed to the virus or if she has been vaccinated recently against it
Vaccination has not been shown to give lasting immunity; live vaccines might be more effective, but could result in a lifelong carrier status.
If a fetus is exposed while in utero, the effects will depend upon the stage of pregnancy – those infected earlier are unlikely to survive to term, though pups infected later may also be aborted, mummified, stillborn, premature or born weak. Some pups may be born apparently normal but succumb within 9 days of birth.
If a newborn pup is exposed to CHV, the virus first reproduces in the nose and the tonsils; then it travels through the blood and spreads to other organs. The virus can affect blood clotting, causing bleeding problems within the organs.
These pups infected after birth may become acutely affected with a fatal illness between the age of 1 and 3 weeks. Affected pups often fail to suckle and may cry persistently. Some may have a nasal discharge and some develop pinpoint bleeding on their gums.
Puppies that have antibodies from the dam are not completely protected, but are less likely to develop a severe infection. A bitch may give birth to a severely affected litter and then, because she develops antibodies against CHV, may have normal litters subsequently.
Pups infected after 3 weeks old are less likely to have a severe infection, but instead show milder signs of upper respiratory tract infection and sometimes genital lesions.
Infected dams seldom show any signs of a problem until they lose a litter.
Prevention is currently largely based around management, such as keeping puppies warm to reduce the likelihood of systemic infection. Routine testing is not carried out, even when pups are lost, so there are no concrete data on how many puppies are lost to CHV every year.
Currently the main tests available for CHV are:
- Blood tests for antibodies (‘serology’)
- Viral isolation
Virology simply proves exposure to the virus but not whether it is a clinical problem; viral isolation requires live virus to grow in cell culture.
PCR (polymerase chain reaction) is a technique that can be used to detect CHV DNA. This has been done on tissue samples but, in theory, could be applied to nasal swabs from live dogs.
A new study being carried out by Ben Harris at The Queen’s Veterinary School Hospital, Cambridge University, aims to investigate this possibility: Having received funding from the Kennel Club Charitable Trust and endorsement from the Irish Setter Joint Breed Health Committee, Ben and his colleagues will be inviting owners of Irish Setters to submit swabs from dams and puppies to look for CHV DNA. The study is restricted to this breed to reduce complicating factors such as whelping problems as much as possible.
Article supplied by Ed Hall our Breed Health Co ordinator.
Update on Ben's study January 2013
Ben thanks all breeders who supplied DNA samples. He is is now working with these samples but, unfortunately, it is taking longer than anticipated to get results.