Armstrong – Table of Contents

be positive for virus. Eight mice were trapped in the row of houses directly across the
street from the patient but Armstrong was not successful in recovering virus from any of
them. With tongue-in-cheek, Armstrong observed, “It appears that an open street is not
readily traversed by gray mice.”
Armstrong expanded surveillance of the mouse population of Washington, DC.
He trapped more than 400 mice, including those already mentioned, from various parts of
the city. Of the 400 mice captured, 365 survived for examination. He recovered the virus
from 64 of a total of 303 gray mice, or, approximately 1 out of every 5 mice examined
was a carrier of the virus. The mice examined came from 76 different homes while the
infected mice came from 34 dwellings. Thus, 44 per cent of the mouse-infested homes
studied were harboring mice infected with LCM. From these 34 infested homes a total of
122 mice were examined of which 64, or 52.4 per cent, were active carriers of the virus.
All four of the DC patients were located in association with clusters of the 34 houses that
harbored infected mice.
Armstrong staved off criticism (33) of the use of white laboratory mice to isolate
LCM in view of several reports that indicated some stocks of white mice had been
spontaneously infected with the virus. He showed that he used the same stock of white
mice with other viruses and did not encounter LCM. He also used numerous random
controls. As a further check on the reliability of using white mice to isolate LCM,
Armstrong did immunity studies in gray mice trapped in infected and non-infected
homes. He injected 62 mice from infected homes intracerebrally using stock laboratory
virus (LCM). In this group 41 of 62 survived, indicating 66 per cent immunity. He next
injected 47 mice from non-infected homes. Only 5, or 10.6 per cent survived. Twelve