1252 



MANUAL OF DETERMINATIVE BACTERIOLOGY 



rat. MUSCICAPIDAE—Tiirdus mi- 

 gratorius L.,Tohm. PHASIANIDAE— 

 Gallus gallus (L.), chicken; Lophortyx 

 calif ornica, California quail. PICIDAE 

 — Asyndesmus lewis, Lewis woodpecker; 

 Colaptes cafer (Gm.), red-shafted flicker. 

 STRIGIDAE— Bubovirginianus (Gm.), 

 great horned owl. S UIDAE—Svs scrofa 

 L., pig. Experimentally, white mouse 

 (some substrains of the Swiss white 

 mouse are genetically more readily in- 

 fected than others); Macacus rhesvs; 

 pigeon (inapparent infection) ; chick 

 embryo and to a limited extent the young 

 hatched chick. 



Insusceptible species : Laboratory rab- 

 bit, Cebus monkey, guinea pig, rat. 



Geographical distribution : L'nited 

 States. 



Induced disease : In man, during sum- 

 mer and fall, about 9 to 21 days after ex- 

 posure, headache, high fever, rigidity of 

 neck, tremors; encephalitis, usually with 

 fever; some patients become drowsy, 

 others sleepless or delirious; usual se- 

 quelae headaches, irritability, some loss 

 of memory, and drowsiness ; neutralizing 

 antibodies maintained in vivo at least 

 2^ years after occurrence of disease. 

 Experimentally, in susceptible strains of 

 white mouse inoculated by intracerebral 

 injection, after 3 to 4 days, coarse tremors, 

 convulsions, prostration, death; perivas- 

 cular accumulations of mononuclear leuco- 

 cytes throughout brain, stem, cord, and 

 pia, with destruction of pyramidal cells 

 in the lobus piriformis and cornu Am- 

 monis ; subcutaneous and intraperitoneal 

 injections immunize against subsequent 

 infection by intracerebral inoculation, 

 virus reaching only blood and spleen in 

 the process of immunization unless an 

 excessive dose is given; some substrains 

 of the White Swiss mouse are relatively 

 resistant to infection, requiring inocula- 

 tion with about 1000 times the minimal 

 infective dose for highly susceptible 

 strains and when infected proving rela- 

 tively poor sources of virus for subinocu- 

 lation; highly susceptible substrains of 

 the White Swiss mouse lack a single 



major, dominant, genetic factor that is 

 present in resistant substrains. 



Transmission : By mosquito, Cnlex tar- 

 salis Coquillett {CULICIDAE), prob- 

 ably extensively; this insect has been 

 collected in nature carrying the virus. 

 Experimentally, by larvae of American 

 dog tick, Dcrmacentor variabilis (Say) 

 ilXODIDAE); by mosquito, Culex 

 pipiens Linn., var.pallans Coq. (CULI- 

 CIDAE). To mice, by feeding on in- 

 fected tissues. 



Serological relationships : Human anti- 

 sera may neutralize virus after clinical 

 and subclinical attacks. 



Immunological relationships : Specific 

 intracerebral immunity after vaccination 

 by subcutaneous or intraperitoneal injec- 

 tion in mice appears early (about 1 week 

 after vaccination) and disappears before 

 humoral antibody titer reaches its max- 

 imum. 



Thermal inactivation : At 56° C in 30 

 minutes. 



Filterability : Passes Berkefeld V and 

 N filter candles and collodion membranes 

 66 millimicrons in average pore diameter. 



Other properties : Storage in human 

 brain tissue in glycerine inactivates this 

 virus in about 32 days. Diameter of 

 infective particle calculated from filtra- 

 tion data as about 20 to 33 millimicrons. 

 In storage, rabbit and sheep sera act to 

 some extent as preservatives. At 4° C, 

 after drying in vacuo while frozen, viable 

 in apparently undiminished titer for at 

 least 17 months. 



Literature : Bang and Reeves, Jour. 

 Inf. Dis., 70, 1942, 273-274 ; Bauer et al., 

 Proc. Soc. Exp. Biol, and Med., 31, 1934, 

 696-699; Blattner and Cooke, Jour. Inf. 

 Dis., 70, 1942, 226-230; Blattner and 

 Heys, Proc. Soc. Exp. Biol, and Med., 

 48, 1941, 707-710; Cook, .Jour. Inf. Dis., 

 63, 1938, 206-216; Cook and Hudson, 

 ibid., 61, 1937, 289-292; Elford and 

 Perdrau, Jour. Path, and Bact., 40, 1935, 

 143-146; Hammon and Howitt, Am. Jour. 

 Hyg., 35, 1942, 163-185; Hammon et al.. 

 Science, 94, 1941, 305-307, 328-330; Jour. 

 Inf. Dis., 70, 1942, 263-266, 267-272, 278- 



