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Canine herpesvirus is a fatal, viral infection of puppies worldwide. It also may be associated with upper respiratory infection or a vesicular vaginitis or posthitis in adult dogs. Only canids (dogs, wolves, coyotes) are known to be susceptible.


Etiology:

The disease is caused by an enveloped DNA canine herpesvirus (CHV), which is sensitive to lipid solvents and most disinfectants. CHV is relatively unstable outside the host.
Transmission usually occurs by contact between susceptible puppies and the infected oral nasal, or vaginal secretions of their dam or oral or nasal secretions of dogs allowed to commingle with puppies during the first 3 wk of life. In utero transmission may occur.
Infection of newborn susceptible puppies results in replication of CHV in the surface cells of the nasal mucosa, pharynx, and tonsils. If the pups become hypothermic, viremia and invasion of visceral organs occur.

Clinical Findings:

Deaths due to CHV infection usually occur in puppies 1-3 wk old, occasionally in puppies up to 1 mo old, and rarely in pups as old as 6 mo. Typically, onset is sudden, and death occurs after an illness of ≤24 hr. Older dogs exposed to or experimentally inoculated with CHV may develop a mild rhinitis or a vesicular vaginitis or posthitis. In utero infections may be associated with abortions, stillbirths, and infertility.

Lesions:
The characteristic gross lesions consist of disseminated focal necrosis and hemorrhages. The most pronounced lesions are seen in the lungs, cortical portion of the kidneys, adrenal glands, liver, and GI tract. All lymph nodes are enlarged and hyperemic, and the spleen is swollen. Lesions may also occur in the CNS. The basic histological lesion is necrosis with hemorrhage in the adjacent parenchyma. Most often there is no inflammatory reaction. Single, small, basophilic, intranuclear inclusion bodies are most common in areas of necrosis in the lung, liver, and kidneys; occasionally, they occur as faintly acidophilic bodies located within the nuclear space.



Diagnosis:
CHV infection may be confused with infectious canine hepatitis ( Infectious Canine Hepatitis: Introduction), but it is not accompanied by the thickened, edematous gallbladder often associated with the latter. The focal areas of necrosis and hemorrhage, especially those that occur in the kidneys, distinguish it from hepatitis and neosporosis ( Neosporosis: Introduction). CHV causes serious disease only in very young puppies. The rapid death and characteristic lesions distinguish it from canine distemper ( Canine Distemper: Introduction). The virus can be isolated from fresh lung, liver, kidney, and spleen by cell culture techniques. The tissues should be submitted to the laboratory refrigerated but not frozen.


Control:
No vaccine is available. Infected bitches develop antibodies, and litters subsequent to the first infected litter receive maternal antibodies in the colostrum. Puppies that receive maternal antibodies may be infected with the virus, but disease does not result.

Removal of puppies from affected bitches by cesarean section and rearing them in isolation has prevented deaths under experimental conditions. However, infections have been noted even in puppies delivered by cesarean section. Deaths may be reduced when infected puppies are reared in incubators at increased temperatures (95°F [35°C], 50% relative humidity) and given adequate fluids and supportive therapy. The prognosis of puppies that survive neonatal infections of CHV is guarded because damage to lymphoid organs, brain, kidneys, and liver may be irreparable.