The incidence of infection is high. The disease is not fatal, and is generally subclinical. The rats may exhibit a porphyrin oculonasal discharge. The submaxillary salivary gland may be palpably enlarged due to sialoadenitis. Dacryoadenitis may cause exophthalmos, which can lead to keratitis and corneal ulcers.
Symptomatic rats are at a greater risk for inhalation anesthesia.
Chronic exophthalmos can result in exposure keratitis. Chronic lesions include replacement of acini with fibrous connective tissue and an infiltration of lymphocytes. Similar lesions are present in the lacrimal and Harderian glands. No carrier state exists, and recovered rats are free of virus and are immune. Cessation of all breeding activity in a production colony for 60 days and concomitant removal of all suckling and weanling animals or intentional exposure of these young rats by frequent mixing will eliminate the infection in the colony.