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standard biologic specimens containing infectious ebov commonly generated in high - level biocontainment operations were inactivated by several methods of chemical treatment ( figure ; table ; technical appendix ) . for in vitro testing , we used wild - type ebov expressing enhanced green fluorescent protein ( ebov - egfp ) ( 7 ) , which allows for cytopathic effect ( cpe ) and fluorescence as simple readout parameters . for in vivo testing , we used mouse - adapted ebov ( ma - ebov ) ( 8) infection of balb / c mice . virus stocks were grown in vero e6 cells and titrated by using a 50% tissue culture infectious dose ( tcid50 ) assay ( 9 ) .
infected cells were produced by infecting vero e6 cells at a multiplicity of infection of 0.01 .
cells were harvested at cpe of 75% , pelleted , and resuspended in 6 ml dulbecco s phosphate - buffered saline ( dpbs ) ; 1 ml aliquots were stored at 80c .
samples were chemically treated according to the specific testing parameters and dialyzed or run over detergent - removal columns to remove inactivating reagents . in brief
, samples were dialyzed by using a 10-kda molecular weight cutoff ( spectrum laboratories , lawrenceville , ga , usa , or fisher scientific , pittsburgh , pa , usa ) and using dpbs over a stir plate at 4c ( > 500-fold exchange volumes , 5 changes over 3248 h ) ; detergent was removed by using detergentout gbs105000 columns ( g - biosciences , st .
avl140 , 140 l buffer avl ( qiagen , valencia , ca , usa ) + 560 l sample ; avl100 , 100 l buffer avl + 600 l sample ; rlt600 , 600 l buffer rlt ( qiagen ) treatment of cells ; rlt800 , 800 l buffer rlt treatment of cells ; + ethanol , after a buffer avl or buffer rlt inactivation contact time of 10 min , addition of 100% or 70% ethanol , respectively , for an additional 20 min of contact time .
b ) survival in animal groups tested with samples inactivated by fixative or detergent buffers . for all test groups ,
* dpbs , dulbecco s phosphate - buffered saline ; na , non - applicable ; nd , not done ; sds , sodium dodecyl sulfate ; tcid50 , tissue culture infectious dose 50 . 
initial sample virus titers were as follows : liquid virus stock ( 1  10 tcid50/ml ) , infected cells ( 1  10 tcid50/ml , 1  10 cells / ml ) , blood ( 10 tcid50/ml ) , tissue ( 10 tcid50/mg ) .
infected cells ( 5  10 cells ) were pelleted by centrifugation and lysed in test reagent ( buffer rlt ; qiagen , valencia , ca , usa ) , pelleted and resuspended in 250 l dpbs before addition of test reagent ( trizol ; life technologies , grand island , ny , usa ) , or used directly in solution at the concentration and volume described in the table ( fixative , heat , and sds testing ) .
infected blood and liver tissue were collected from balb / c mice infected with mouse - adapted ebola virus at the height of infection , or from mock infected mice at a corresponding day . 
addition of ethanol : after contact time with buffer avl ( qiagen , valencia , ca , usa ) or buffer rlt , samples were transferred to a clean tube with 560 l 100% ethanol ( for avl inactivation ) or 600 l 70% ethanol ( for rlt inactivation ) and allowed an additional 20 minutes contact time at 20c .  
although spectra / por float - a - lyzer g2 dialysis tubes ( spectrum laboratories , lawrenceville , ga , usa ) were used for all other reagent removal by dialysis , slide - a - lyzer cassettes ( fisher scientific , pittsburgh , pa , usa ) were used with trizol because the cassettes are more resistant to direct degradation by the reagent . 
tissue samples < 1 cm were treated with a 7-day contact time , whereas samples > 1 cm were treated with a 30-day contact time . 
# samples were boiled in an accublock digital dry bath ( sigma - aldrich , st .
all other heat treatments were carried out in a nonshaking water bath .  * * 4 sds loading buffer contains 200 mmol / l tris ( ph 6.8 ) , 4% sds , 35% glycerol , 0.05% bromophenol blue and 20% 2-me ( added at the time of use ) .
a combination of 250 l 4 buffer , sample , and dpbs for a combined volume of 1 ml was tested ; an appropriate volume of dpbs was substituted for 2-me as necessary for testing of sds as the single inactivating reagent .
negative control samples included dpbs and noninfected vero e6 cells and tissue homogenates ( mouse ) ; positive control samples included untreated virus stocks and infected vero e6 cells and mouse tissues .
for in vitro testing , all samples were increased in volume to 3 ml and equally divided to infect vero e6 cells ( 80% confluency ) in triplicates .
cells were incubated at 37c for 14 days and monitored regularly for cpe or fluorescence . for in vivo testing , samples were increased in volume to 1 ml and equally divided to infect 5 mice intraperitoneally .
balb / c mice ( female , 68 weeks old ; charles river laboratories , wilmington , ma , usa ) were housed in microisolator cages and were monitored daily for 28 days . because in vitro and in vivo safety testing correlated well , we discontinued mouse infections for ethical reasons .
we used buffer avl and buffer rlt ( qiagen , valencia , ca , usa ) and trizol ( life technologies , grand island , ny , usa ) according to manufacturers recommendations .
avl was mixed with stock virus at different ratios , and infected cells were resuspended in rlt ( table ) .
samples were either immediately dialyzed or treated with ethanol ( avl , 100% ethanol , 560 l ; rlt , 70% ethanol , 600 l ) .
infected liver tissue was homogenized in rlt with a stainless steel bead ( 10 min at 30 hz ) . a soluble aliquot ( 30 mg )
was transferred to a new tube , and fresh rlt was added , followed by 70% ethanol ( 600 l ) .
similar to a results in a previous study ( 10 ) , avl and rlt treatment alone for 10 minutes at either ratio did not fully inactivate ebov ; however , the addition of ethanol ( the next step of the manufacturer s protocol ) rendered all samples completely noninfectious .
avl alone resulted in complete inactivation with longer contact times ( i.e. , refrigerated overnight or frozen for 7 days ) ( table ; figure ) .
infected cells were resuspended and treated with trizol ( 1:4 vol / vol ) . infected liver samples were homogenized in 1 ml trizol as described in the previous paragraph .
after centrifugation , an aliquot of tissue homogenate ( 50 mg ) was transferred to a new tube , and fresh trizol was added .
additionally , blood from infected animals was mixed ( 1:4 vol / vol ) with trizol .
after dialysis , vero e6 cells were inoculated and monitored for cpe or fluorescence . in all cases ,
formalin , paraformaldehyde , and glutaraldehyde can be used to fix cells or tissues for histologic or microscopic studies .
infected cells were diluted 1:4 in 10% neutral - buffered formalin ( 7.5% fixative ) or 1:5 in either 2.5% glutaraldehyde or 2.5% paraformaldehyde ( 2% fixative ) .
monitoring of cell culture and animals resulted in the absence of cpe or fluorescence and clinical signs , respectively , indicating complete inactivation of ebov ( table ; figure ) .
infected liver segments were incubated in 10% neutral - buffered formalin , 2% glutaraldehyde , or 2% paraformaldehyde ( 10 ml ) for a period of 7 days ( < 1-cm piece ) or 30 days ( > 1-cm piece ) at 4c .
subsequently , a small section of tissue ( 150 mg ) was dissected , homogenized in dpbs with a stainless steel bead ( 10 min at 30 hz ) , and then dialyzed .
we tested the parameters of 60c for 30 min , 65c for 15 or 30 min , and 70c for 15 min in conjunction with a buffer containing 0.5% triton x-100 and 0.5% tween-20 ( both from sigma - aldrich , st .
stock virus was diluted 1:25 in this buffer and heated for the appropriate times before samples were clarified of detergent and used to infect vero e6 cells or mice .
all samples were completely inactivated as indicated by lack of cpe or fluorescence in cells and clinical signs in mice ( table ; figure ) . boiling ( at 100c for 10 min or 120c for 5 min ) might be sufficient to inactivate ebov ( table ) ( 11 ) but is often used in conjunction with sodium dodecyl sulfate ( sds)containing buffers for protein analysis .
aliquots of infected cells were diluted in dpbs and 4 loading buffer ( 1% sds final ) .
infected liver tissue ( 150 mg ) were placed in dpbs and 4 loading buffer ( 1% sds final ) .
the samples were then homogenized with a stainless steel bead ( 10 min at 30 hz ) .
after detergent removal , samples were used to infect vero e6 cells ; all treated cells and tissue homogenates were negative for infectious ebov ( table ) .
our study establishes inactivation procedures for ebov that can be safely applied to distinct specimen types and research purposes and might also apply to other enveloped , single - strand , negative - sense rna viruses .
our findings should help to improve and approve sops for inactivation without the need for safety testing each individual sample , an unfeasible and unwarranted task in current diagnostic and research operations in high - level biocontainment settings .
safety testing for inactivation , at least for ebov , can rely on cell culture only because this seems to be as sensitive as in vivo testing .
technical appendix . materials and methods used to establish effective chemical inactivation of ebola virus .
reliable inactivation of specimens before removal from high - level biocontainment is crucial for safe operation . to evaluate efficacy of methods of chemical inactivation , we compared in vitro and in vivo approaches using ebola virus as a surrogate pathogen 
 . consequently , we have established parameters and protocols leading to reliable and effective inactivation .