This negatively-stained transmission electron micrograph (TEM) revealed the presence of La Crosse (LAC) encephalitis virus ribonucleoprotein particles (RNP). LAC virus is a member of the Bunyaviridae virus family, California serogroup. This is an arbovorus, which means that transmission occurs through the bite of an infected arthropod, which in this case, is the treehole mosquito, Aedes triseriatus . LAC can also be transmitted through the bite of infected vertebrates including chipmunks and sq