1254 



MANUAL OF DETERMINATIVE BACTERIOLOGY 



sional excitability followed by incoor- 

 dinatedactionof limbs, disturbed equilib- 

 rium, grinding of teeth, paresis and varied 

 paralyses; frequently inability to swal- 

 low, paralysis of lips and bladder, amauro- 

 sis ; case fatality about 50 per cent ; 

 recovery without sequelae in mild cases ; 

 death within 3 to 8 days in severe cases. 

 In man (childi'en particularly vulnera- 

 ble), a profound, acute, disseminate and 

 focal encephalomj'elitis characterized by 

 intense vascular engorgement, perivascu- 

 lar and parenchymatous cellular infiltra- 

 tion and extreme degenerative changes in 

 the nerve cells. In chick embryo, ex- 

 cessive increase of virus continuing until 

 just before host's death, virus being found 

 eventually throughout the egg but most 

 concentrated in the embryo ; vaccines 

 made from virus grown in chick embryo 

 and then inactivated are especially effec- 

 tive because of the high titer of virus 

 represented in them ; increased resistance 

 with age characteristic of chorioallantoic 

 membrane as well as of hatched chick ; 

 rounded acidophilic masses occur usually 

 near periphery of nucleus in embiyonic 

 nerve cells; no such inclusions are found 

 as a result of infection with Borna disease 

 virus or poliomyelitis virus. 



Transmission : Experimentally by tick, 

 Dermacenlor andersoni Stiles {IXODl- 

 DAE), passing through eggs to offspring ; 

 this tick is infective to susceptible ani- 

 mals on which it feeds as larva, nymph or 

 adult . Experimentally by Aedes acgypii 

 L. (to guinea pig and horse, preinfective 

 period 4 to 5 days ; insects retain virus for 

 duration of life; not to eggs of infected 

 mosquitoes; not passed from males to 

 females or by males from female to fe- 

 male), A. albopictns, A. atropalpvs, A. 

 cantator, A. dorsalis, A. nigromacrdis, A. 

 sollicilans, A. taeniorhynchus , A. triseria- 

 tus, and A. vexans {CULICIDAE). 

 Triatoma sanguisxiga (Le Conte) {RE- 

 DUVIIDAE) has been found infected 

 in nature and has transmitted virus ex- 

 perimentally to guinea pigs. The Ameri- 

 can dog tick, Dermncentor variabilis Say 

 [IXODIDAE) has been infected by 



inoculation, not by feeding; it has not 

 been shown to transmit. 



Serological relationships : Neutralizing 

 antibodies are formed as a result of vac- 

 cination with inactive, formolized virus; 

 antigenicity of formalin-inactivated virus 

 as well as of active virus is blocked in the 

 presence of antiserum. In rabbit, cere- 

 bral resistance is coincident with pres- 

 ence of neutralizing antibody in spinal 

 fluid. In guinea pig, therapy with spe- 

 cific antiserum ineffective if begun after 

 onset of encephalitis ; effective if begun 

 within 24 to 48 hours of peripheral inocu- 

 lation. No cross neutralization reaction 

 with lymphocytic choriomeningitis virus, 

 Japanese B encephalitis virus or St. Louis 

 encephalitis virus. Constituent strains 

 (typical Western and Eastern) do not 

 give cross neutralization reactions, but 

 do show the presence of common antigens 

 by cross reactions in complement fixation 

 not shared with such other viruses as 

 Japanese B encephalitis virus, St. Louis 

 encephalitis virus. West Nile encepha- 

 litis virus, lymphocytic choriomeningitis 

 virus. Sera of human cases may be nega- 

 tive by complement fixation tests a few 

 days after onset, yet strongly strain- 

 specific during second week of illness. 



Immunological relationships : Young of 

 immunized guinea pigs are immune to 

 homologous strain at least a month after 

 birth. No cross immunity between 

 Western and Eastern strains of equine 

 encephalitis virus. 



Thermal inactivation : At 60° C, not at 

 56° C, in 10 minutes. 



Filterability : Passes collodion mem- 

 branes 66, not 60, millimicrons in average 

 pore diameter. Passes Berkefeld V, N, 

 and W, finest Handler, and Seitz filters. 



Other properties : Inactivated below 

 pH 5.5. Viable at least a year, dry in 

 vacuum. Particle diameter estimated 

 from filtration experiments to be 20 to 30 

 millimicrons. Electron micrographs 

 show particles as spherical or disk- 

 shaped, about 39 millimicrons in diameter 

 with round or oval region of high density 

 within each; older preparations show 



