Key Instruction Points
Treat all animals as if they may have zoonotic disease
Consider periodic testing of animal colonies, regardless of source
In 1989, a 23-year-old employee at a research institution was hospitalized for viral meningitis. Her symptoms included fever, abdominal pain, myalgia, malaise, fatigue, severe headaches, chest pain, difficult breathing, coughing, vomiting, and hair loss. Her illness lasted eight weeks and was determined to be caused by viral meningitis (inflammation of the lining of the brain and spinal cord) caused by lymphocytic choriomeningitis virus (LCM).
The patient worked at a research laboratory that develops drugs and diagnostic tests using animals. Part of this effort involved use of a tumor cell line that could not be maintained in tissue culture. The tumor cells had been maintained for 20 years by injection into the cheek pouches of hamsters. (Hamster cheek pouches are immunologically protected. Tumors will grow there without rejection.) For the past few years the tumor had been injected into nude mice. (Nude mice, like AIDS patients, are deficient in T lymphocytes. They do not reject transplanted tissues, even from other species.) A follow-up investigation revealed that the tumor line had been infected with LCM virus since 1975. Almost 20 percent of the cell lines maintained by the company were infected. Apparently, the switch to using nude mice had increased the employee exposure. Employees who worked with nude mice were tested; 26 percent had evidence of infection with LCM. Several other workers had recovered from illnesses that were likely due to LCM. Changing bedding, changing water bottles, and cleaning cages were the activities most associated with infection.
LCM is one of the few zoonotic diseases of concern in modern rodent research facilities. It has been eliminated from commercial rodent breeding colonies although it is found in wild mice. LCM can be introduced into research facilities by wild mice, or by the introduction of infected tissues. Standard steps used in well run programs reduce the risk of LCM. These include exclusion of wild rodents, careful evaluation of animals and animal tissues from other than commercial breeders, and implementing testing programs within the facility.