Sialodacryoadenitis Virus
Also known as: SDAV
Introduction
Rats are the natural hosts for the highly contagious coronavirus sialodacryoadenitis virus.
It causes a non-fatal inflammation of salivary and lacrimal glands.
The disease is seen worldwide, primarily in young rats. It can occur as an epizootic in a naive colony, with a large number of rats developing lesions, or enzootically with only a few animals developing signs.
Transmission is by direct contact and fomites. Transmission between rats is extremely rapid, with the respiratory tract being the primary portal of entry. Infected animals secrete the virus for approximately 7 days. The virus is excreted via ducts of the salivary, lacrimal and Harderian glands.
Healthy, naive rats of both sexes and all ages are susceptible to infection. Young animals, 2-4 weeks of age and with no maternal antibody, develop more serious forms of the disease with the highest mortality.
Clinical signs
In a colony, clinical signs can be seen for several weeks during an epizootic. In individual animals, they should only last about one week.
Signs include: squinting, photophobia, blinking and eye rubbing followed by sneezing and cervical swelling withing 3-5 days post infection.
There is decreased lacrimation which then leads to: suborbital or periorbital swelling, prominent or bulging eyes and often chromodacryorrhea (red porphyrin-pigmented tears) and ophthalmic lesions.
Rats usually remain appetant and active.
Some strains may cause an interstitial pneumonia in young rats and disease may be exacerbated by concurrent Sendai virus infection.
Diagnosis
Diagnosis is primarily based on gross clinical signs and gross pathology.
Post-mortem findings include: large, oedematous and pale glands, including the salivary, Harderian or lacrimal glands, either affected individually or as a group. These glands may become permanently scarred.
Keratitis sicca may be observed as well as corneal ulceration.
Viral antigen can be found in the respiratory epithelium, lacrimal and salivary glands and lymph nodes.
Serum antibodies can be detected by ELISA testing.
Signs may be mimicked by Sendai virus, corona virus and secondary bacterial infection with Pasteurella pneumotropica and Mycoplasma pulmonis.
Treatment
Nursing support is vital, by providing a warm, comfortable environment, tasty food treats, ophthalmic lubricant and fluids.
Antibiotic treatment during the acute phase of the infection may alleviate the effects of secondary ophthalmic trauma and bacterial infections.
Laboratory rats are rarely treated and are humanely culled. Alternatively, the infection is actively spread throughout the facility and the outbreak is allowed to take its course. Following seroconversion of all animals the breeding program can resume.
Prevention
Susceptible colonies can be isolated and quarantined. The disease usually produces no long-term disability.
Rats which clear the infection can become reinfected with a different strain as there is little interstrain cross-protectivity.
In the laboratory setting, prevention of the disease is by the procurement of disease-free rats. Non-essential personnel should be avoided and movement restricted within the facility due to the highly contagious nature of the virus.
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References
Harkness, J. (2010) Harkness and Wagners Biology and Medicine of Rabbits and Rodents John Wiley and Sons
Baker, D. (2003) Natural pathogens of laboratory animals ASM Press
Carlyle Jones, T. (1997) Veterinary Pathology Wiley-Blackwell