Canine Herpesvirus and Rabies

Canine Herpesvirus and Rabies Viral and Chlamydial Diseases ;Canine Parvovirus;Canine Coronavirus in dogs;Treatment is largely supportive;Canine Distemper breeding Canine herpesvirus;rabies;vaccine product
Canine Herpesvirus and Rabies

- Canine Herpesvirus
Etiology. Canine herpesvirus (CHV) infection causes a generalized hemorrhagic disease with a high mortality rate in newborn puppies less than 2 weeks of age. In adult dogs, CHV causes a persistent, latent infection of the reproductive tract with recrudescence and shedding during periods of physiologic stress.

Clinical signs. Clinically affected puppies do not suckle, cry persistently, become depressed and weak, and fail to thrive.

Petechial hemorrhages of the mucous membranes and erythema of sparsely haired regions such as the caudal abdomen and inguinal area are evident. Older puppies, aged 3-5 weeks, develop less severe clinical signs and are likely to survive with neurologic sequelae such as ataxia and blindness resulting from reactivation of latent infection. Infection in adult dogs may result in stillbirths, abortions, and infertility. Lesions in adult bitches include raised vesicular foci in the vaginal mucosa, accompanied by mild vaginitis. Adult males have preputial discharge due to vesicular lesions at the base of the penis and on the preputial mucosa.

Epizootiology and transmission.
Transmission occurs during passage of puppies through the birth canal or venereally in adult
dogs. Puppies can also be horizontally infected by littermates.

Entire primiparous litters may be lost, with subsequent litters protected by the colostral antibody.

Pathologic findings. Pathologic findings include multifocal ecchymotic hemorrhages of the kidneys, liver, lungs, and gastrointestinal tract. Basophilic intranuclear inclusions in necrotic areas of parenchymal organs are characteristic findings.

Diagnosis and differential diagnosis. Diagnosis of canine herpesvirus infection in adult dogs is based on a history of reproductive infertility and the presence of genital vesicular lesions.

Differential diagnoses for stillbirths, abortions, and infertility include canine brucellosis, canine distemper virus and parvovirus infections, and pyometra. The diagnosis in infected puppies is usually made based on clinical history and characteristic lesions (multifocal systemic hemorrhages) (Carmichael and Greene, 1998). Differential diagnoses for the disease in neonates would include canine ehrlichiosis and causes of disseminated intravascular coagulation, including bacterial endotoxemia.

Prevention and treatment. A vaccine is not available, and there is no effective curative treatment. Supportive therapy is unrewarding, and death usually ensues within 48 hours infected neonates. In general, adult bitches that have multiple abortions, stillbirths, or persistent infertility should be culled from the breeding colony. Examination of these animals may reveal raised vesicular lesions on the vaginal mucosa. Adult male dogs that have vesicular lesions on the base of the penis and preputial mucosa should be similarly culled.

Research complications. Canine herpesvirus infection in adult dogs would obviously interfere with production operations, and affected animals should be culled based on the criteria noted above in the discussion of prevention and treatment.

Because of the severity of clinical illness in puppies, such animals should be humanely euthanatized.

- Rabies:
Etiology. Rabies virus is a member of the rhabdovirus family and is essentially contagious to all species of warm-blooded animals.
Clinical signs. Clinical progression of neurologic disease occurs in three stages. The first, or prodromal, the stage is characterized by a change in species-typical behavior. 

The loss of the instinctive fear of humans by a wild animal is a classic sign of impending rabies. In the second, or furious, stage animals are easily excited or hyperreactive to external stimuli and will readily snap at inanimate objects. The third, or paralytic, the stage is characterized by incoordination and ascending ataxia of the hindlimbs due to viral-induced damage of motor neurons. Death usually occurs within 2-7 days of the onset of clinical signs, due to respiratory failure.

Epizootiology and transmission. Wild animals such as raccoons, skunks, and bats are common reservoirs of infection for domestic animals, which in turn are the principal source of infection for humans. Transmission occurs primarily by contact of infected saliva from a rabid to a naive animal (or human), usually via bite wounds.

Pathogenesis. The incubation period for rabies is generally 3-8 weeks from the time of exposure to the onset of clinical signs but can range from 1 week to 1 year. Bites of the head and neck typically result in shorter incubation periods because of the proximity to the brain. Following infection, the virus migrates centripetally via peripheral nerve fibers to the central nervous system and eventually to neurons within the brain, resulting in neurologic dysfunction. On reaching the brain, the virus migrates centrifugally to the salivary glands, thus enabling shedding and subsequent transmission.

Diagnosis and differential diagnosis. Diagnosis of rabies is based on clinical signs; differential diagnoses include pseudorabies, canine distemper, bacterial meningitis, and toxicants that affect neurologic function. Definitive diagnosis is based on fluorescent antibody demonstration of the virus in Negri bodies of hippocampal cells.

Prevention and treatment. Puppies should be vaccinated at 4- 6 months of age, "bolstered" in 1 year, then vaccinated annually or triennially, depending on state and local laws and which vaccine product is used. Treatment of rabies is not recommended, because of the risk of human exposure.

Research complications. In a research setting, dogs are often not vaccinated for rabies, because of the low incidence of exposure to wild-animal reservoirs. A healthy, purpose-bred dog that bites a human in a research facility should be quarantined For 10 days and a note of signs of rabies.

This quarantine interval is based on the knowledge that dogs do not shed rabies in the saliva for more than a few days before the onset of neurologic disease.

A random-source dog with an unknown vaccination history that bites a human should be immediately euthanized. The brain should be examined for rabies virus to determine if the dog was infected, and if the test is positive, postexposure immunization should be initiated for the human patient. A rabies vaccine licensed for use in humans is available, and immunoprophylaxis is recommended for animal care and research personnel who may have high work-related risks of exposure.

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