this project began as part of a larger study concerned with a suspected nipah virus outbreak in the region . active surveillance of bats was performed in 3 districts of bangladesh : meherpur and naogaon during march 2003 and rajbari during february and march 2004 ( figure 1 ) . bats were anesthetized by a 0.05- to 0.1-mg intramuscular injection of ketamine hydrochloride . injured bats and those that had clinical signs and symptoms were euthanized under sedation by exsanguination . brains of all euthanized bats were removed at necropsy and placed into individual sterile containers . all specimens were held in temporary storage at 18c ( after collection ) and later placed at 80c . bat brains collected in 2003 ( n = 212 , table ) were tested by the direct fluorescent - antibody test ( dfat ) ( 10 ) , by using both monoclonal ( centocor inc . , malvern , pa , usa ) and polyclonal ( chemicon international , temecula , ca , usa ) fluorescein isothiocyanate  labeled anti  rabies virus antibodies , and were subsequently processed for isolation by the mouse inoculation test ( mit ) ( 11 ) . if death occurred during the mit , mouse brains were subjected to the dfat , and a second intracerebral passage was conducted with 5% brain suspensions , using 0.22-m filters ( millipore corp . , bedford , ma , usa ) . bat brains collected in 2004 ( n = 151 , table ) were subjected to the dfat only . * the presence of virus - neutralizing antibodies was determined by an adaptation of the rapid fluorescent focus inhibition test ( rffit ) , as described ( 7 ) . because of volume limitations and the cytotoxicity of some specimens , 207 serum samples were available for testing at a starting dilution of 1:20 , and 81 samples at a starting dilution of 1:50 ( table ) . four different lyssaviruses were used in an initial in vitro screening : aravan , khujand , irkut , and ablv . when a positive result was obtained , testing on the sample was repeated , and comparative assays undertaken for additional lyssaviruses : eblv-1 , eblv-2 , duvv , and rabv ( e.g. , routine rabies challenge virus standard , cvs-11 ) . the dose of each virus used for the rffit was 50 infectious units per 100 l . the duration of the test was 20 hours for ablv and cvs-11 and 40 hours for other challenge viruses . no evidence of lyssavirus antigen was detected in any bat brain by dfat , and no neurotropic viruses were isolated by mouse inoculation . if a limited number of deaths occurred during the initial mit ( 1 or 2 mice of 5 infected ) , those effects were not reproduced during the subpassage by filtration , which suggests that bacterial contamination of the field samples caused the death of mice during the initial mit . one serum sample repeatedly demonstrated neutralizing activity against khujand virus , at a titer of 54 . this sample was obtained from a young female giant indian flying fox ( pteropus giganteus ) ( figure 2 ) captured in the meherpur district in 2003 . two other serum samples obtained from the same species ( 1 male and 1 female ) in rajbari district in 2004 , neutralized aravan and khujand viruses at titers of 1416 . for these latter samples , neutralization was detected at dilutions of 1:20 and 1:25 but not detected at a dilution of 1:50 . the titers of all serum specimens were < 10 ( i.e. , no neutralization occurred in the dilution of 1:20 ) against other lyssaviruses . antigenic cross - reactivity has been reported among aravan , khujand , and other members of the lyssavirus genus ( 12 ) . therefore , detectable antibody may cross - react with other related lyssaviruses , as well as with viruses yet to be discovered . based upon this preliminary survey , thus , it is not surprising that all brain samples collected were negative for detection of lyssavirus antigen . because different lyssaviruses and bat species are found in asia , and therefore different virus - host interactions would be expected in the region , extrapolating antibody - positive / virus - positive ratios , as have been estimated from american ( 13,14 ) or european ( 15 ) bat populations , would be difficult . further surveillance for asian bat lyssaviruses should be conducted . public health authorities need to be aware of the potential for bats to transmit lyssaviruses , and public education of this potential should be enhanced . frugivorous bats forage in fruit plantations in many regions of the old world tropics , including bangladesh . absence of current information on human rabies after bat exposure may be a result of inadequate education , incomplete surveillance , and lack of characterization of viruses from rabies cases ( 6 ) .
lyssavirus surveillance in bats was performed in bangladesh during 2003 and 2004 . 
 no virus isolates were obtained . 
 three serum samples ( all from pteropus giganteus , n = 127 ) of 288 total serum samples , obtained from bats in 9 different taxa , neutralized lyssaviruses aravan and khujand . 
 the infection occurs in bats in bangladesh , but virus prevalence appears low .