In an attempt to evaluate the activity of the Western equine encephalitis virus within Minnesota, the pigeon sentinel station technique was utilized in each of four areas during the summers of 1958 and 1959. Each summer, before Culex tarsalis Coquillett emerged in appreciable numbers, 240 juvenile pigeons, shown to be free of antibodies for WEE, were divided into four groups of 60 and released into a flight cage in each study area. The birds were bled at monthly intervals and the samples were sent to the Rocky Mountain Laboratory for serological study.
The locations of the stations and the respective percentages of birds with antibodies for the WEE virus in 1958 and 1959 are as follows: (1) Crookston, 68.3 and 23.9%; (2) Fergus Falls, 67.6 and 22.8%; (3) Buffalo, 34.1 and 31.7%; (4) Spring Lake, 0.0% in 1958, with station not utilized in 1959; and (5) Sherburn, the station established in 1959, 1.7%. A total of 105 pigeons showed evidence of WEE infection during the 2 years; of these, only 19 were positive at the July bleeding, 41 more became positive by the August bleeding and 45 additional birds were positive at the final bleeding in September or October. At the Buffalo station, two pigeons which were negative for WEE showed antibodies for St. Louis encephalitis.
School of Public Health, University of Minnesota, Minneapolis 14, Minnesota.
Rocky Mountain Laboratory, Hamilton, Montana.
Department of Entomology and Economic Zoology, University of Minnesota, St. Paul 1, Minnesota.