Canine Herpesvirus Infection

1 Canine Herpesvirus Infection

Epidemiology

Canine herpesvirus infects only dogs, causing an acute fatal respiratory disease in puppies under 2 weeks old, with a mortality rate up to 80%. Older puppies show mild or inapparent signs; adult dogs show no obvious signs, occasionally mild rhinitis, tracheitis or vaginitis. Sick and recovered dogs are the main source; infected dogs shed the virus in saliva, nasal discharge and urine. Puppies are mainly infected by contact with the infected bitch’s vagina during birth or by inhaling her virus-laden droplets; infection also spreads among puppies by mouth and throat.

Clinical symptoms

In newborn puppies under 21 days the infection is fatal. Early signs are dementia, depression, anorexia, weakness, labored breathing, abdominal tenderness and yellow watery stools. Some show rhinitis with serous nasal discharge and widespread petechial bleeding on the nasal mucosa. Skin lesions are red papules on the groin, the bitch’s vulva and vagina, and the male’s prepuce and mouth. The puppy finally loses consciousness, with opisthotonos and seizures. Most die within 24-48 hours of signs appearing. Recovered puppies may show permanent opisthotonos and seizures.

Dogs 21-35 days old mainly show nasal discharge, sneezing and a dry cough and other upper-respiratory signs lasting about 14 days, then improving. Mixed infection can cause fatal pneumonia. Genital infection in bitches is marked by diffuse vesicular lesions of the vaginal mucosa. Pregnant bitches may abort or produce stillborn puppies. Males show penile and preputial lesions with increased discharge.

Pathological changes

In fatal neonatal infection the parenchymal organs, especially liver, kidney and lung, show diffuse hemorrhage and necrosis; serous or mucous effusion is seen in the chest and abdomen; lungs are congested and edematous with enlarged hilar lymph nodes; spleen is congested and enlarged; intestinal mucosa shows petechial bleeding; jaundice and non-suppurative encephalitis occur occasionally.

Differential diagnosis

(1) Canine herpesvirus infection vs. canine toxoplasmosis

Both show nasal discharge, cough, sneezing, vomiting, incoordination and abortion in bitches.

Difference: toxoplasmosis cases have fever and reduced red and white blood cell counts. At necropsy the lungs show gray-white nodules and the heart muscle has necrotic foci; smears of cadaver tissue stained with Giemsa or Wright’s stain reveal trophozoites.

(2) Canine herpesvirus infection vs. canine distemper

Both show anorexia, lethargy, sneezing, nasal discharge, dry cough, vomiting and conjunctival inflammation.

Difference: herpesvirus cases have no fever; distemper is biphasic, with conjunctival and corneal inflammation, purulent discharge and marked neurological signs, and reduced white cells. Viral-antigen testing by immunofluorescence on blood leukocytes, conjunctiva, and liver and spleen smears detects distemper virus.

(3) Canine herpesvirus infection vs. canine tuberculosis

Both show a dry cough and mucous or purulent nasal discharge and other upper-respiratory signs.

Difference: tuberculosis cases show obvious progressive emaciation, fever, usually a chronic course, and nodules on the reproductive organs and skin.

(4) Canine herpesvirus infection vs. canine cold, laryngitis, bronchitis, pneumonia

Cold, laryngitis, bronchitis and pneumonia all show cough, nasal discharge, depression and anorexia but are not contagious.

(5) Canine herpesvirus infection vs. canine cryptococcosis

When Cryptococcus invades the lungs it causes cough, sneezing, increased eye discharge or skin infection and labored breathing. After nervous-system involvement it causes ataxia and movement disorders.

Difference: when a dog shows respiratory and nervous signs with skin edema, cryptococcosis is more likely; examine material (urine, pus, feces, blood) on a slide stained with methylene blue to see round thick-walled organisms.

(6) Canine herpesvirus infection vs. canine aspergillosis

When Aspergillus invades the nasal cavity and sinuses the dog sneezes and has serous or mucoid nasal discharge.

Difference: herpesvirus cases have the specific signs of labored breathing, vomiting and diarrhea. Also, examine nasal discharge or pus with one drop of 20% potassium hydroxide under a coverslip; branched septate hyphae with chained conidia at the hyphal-tip vesicles indicate aspergillosis.

Notes

A preliminary diagnosis is based on the acute onset and high mortality in newborn puppies, and diffuse hemorrhage and necrosis of the parenchymal organs (liver, kidney, lung); confirmation needs etiological examination.

Prevention and treatment

(1) Prevention

1. Immunization. Naturally recovered and artificially infected dogs both produce low-level neutralizing antibodies that protect against infection.

Injecting newborn puppies intraperitoneally with serum from a bitch that has neutralizing antibodies can prevent infection and death. Because infected kennels usually develop immunity, a litter that has had the disease is rarely infected later. An inactivated vaccine with adjuvant given several times can induce a certain antibody level in bitches.

2. Disinfect the kennel, strengthen husbandry, and isolate and treat sick dogs promptly.

(2) Treatment

The treatment principle is to raise resistance, raise environmental temperature and prevent secondary infection.

1. During outbreaks, inject 1-2 mL of hyperimmune serum into puppies intraperitoneally to reduce deaths.

2. For dogs with respiratory signs, use broad-spectrum antibiotics to prevent secondary infection.

3. Interferon: 100,000-200,000 IU per dose, subcutaneously or intramuscularly, every 2 days.

4. Raising the environmental temperature helps recovery. Place the dog in an incubator or use a heater, preferably 35-38°C with 50% humidity.