In late June 1973, a small outbreak of equine encephalitis caused by eastern equine encephalomyelitis (EEE) virus occurred in the Republic of Panama. At least 100 horses were affected by the disease and 40 died. More than 1,700 human sera were obtained from areas of virus activity but no serological evidence for infection was found. Four isolates of EEE virus were recovered, one of which was from a small pool of Culex taeniopus mosquitoes. Serologic studies of infected horses and classification by the short incubation hemagglutination-inhibition test revealed that these isolates were South American strains. Our evidence suggests that another agent virulent for horses was active during this outbreak.
Present address: Clinical Research Center, Massachusetts Institute of Technology, 50 Ames Street, Cambridge, Massachusetts 02142.
Present address: Center for Disease Control, Atlanta, Georgia 30333.