A number of signs may suggest that CHV is causing problems, but many of these signs are multifactoral and therefore it is important to try and make a definitive diagnosis.
CHV can be a significant cause of death in young puppies, and also smaller litter size and weight.
A number of problems have also been identified in adult dogs, such as infertility and abortion.
The unborn puppy: CHV attacks the placenta of the mother, starving the foetus of nutrients. This can lead to abortion, stillbirth or resorption of the foetus (seen by the breeder as infertility).
The newborn puppy: If the puppy is infected before birth and survives, it may be underweight at birth and have a weakened immune system, making it vulnerable to early puppyhood infections.
If the puppy is infected at or soon after birth, CHV is known to be one of the factors in “fading puppy syndrome”, in which the pup fails to suckle, cries constantly, loses weight and fades away despite intensive care, sometimes in a matter of a few hours.
Another sign is soft, yellow-green faeces, sometimes mistaken for parvovirus or coronavirus.
The abdomen is painful and there may be bleeding under the skin, or a rash on the belly.
Some puppies may show signs of brain damage, such as blindness or staggering.
The adult dog: in the dog, CHV can cause painful lesions on the genitals. In the bitch, there may not be any external signs, but the bitch seems infertile or gives birth to undersize and weak litters. Careful examination may sometimes reveal small blister-like lesions on the vaginal wall. In both males and females, CHV is also known to be one of the causes of kennel cough.
Gross pathology consists most notably of kidney changes - multiple subcapsular haemorrhages, and mottling and discoloration of the cortical parenchyma. Spleen and liver will contain discoloured and dark red areas, with a frail parenchyma. The lungs will be oedematous and have a heterogenous appearance with both reddish and grey areas. Haemorrhagic lesions are occasionally observed in the myocardium (heart).
There is often bleeding under the skin, especially around the abdomen.
CHV can be isolated from the lungs and kidneys of affected puppies, but is very labile and false negative results are common.
Serology is of limited value due to the high prevalence of the virus within the general population. A single negative or positive result is of little value. However, paired serum samples at 2-3 weeks interval showing a rise in antibody titre (seroconversion) will indicate active infection. The best time to take the samples (from the mother) is around the time of whelping.
PCR tests are available for identifying the virus from discharges or from affected pups. PCR will be negative when the virus is latent.