Validation of a commercial ELISA for the detection of bluetongue virus (BTV)-specific antibodies in individual milk samples of Dutch dairy cows.

A recently developed indirect ELISA for the detection of bluetongue virus (BTV)-specific antibodies in bovine milk samples was compared to that of the routinely used competitive ELISA on serum samples. During the bluetongue outbreak in the Netherlands in 2006, caused by BTV serotype 8, coupled serum and milk samples were obtained from 470 individual cows from 10 BTV-infected farms with an average seroprevalence of 57%. In addition, bulk milk samples of the same farms, and historically BT-negative samples were tested. Compared to the ELISA for sera, the relative specificity and sensitivity of the ELISA for milk samples is 96.5% and 98.9%, respectively when using a S/P% cut-off value of 50% as advised by the manufacturer. The optimal cut-off value was found at S/P% of 90% revealing an optimal specificity (99.0%) combined with an optimal sensitivity (98.1%). Titres in positive individual milk samples ranged from 1 to 2048 with a peak titre of 128. Bulk milk samples contained antibodies with titres ranging from 64 to 512. The ELISA for milk samples was found to be a reliable and robust test. This diagnostic tool is very useful, and may replace the ELISA for serum samples as first choice in order to get insight into the status of lactating individual animals and therewith of the entire herd with respect to BTV infection.

Public health awareness of emerging zoonotic viruses of bats: a European perspective.

Bats classified in the order Chiroptera are the most abundant and widely distributed non-human mammalian species in the world. Several bat species are reservoir hosts of zoonotic viruses and therefore can be a public health hazard. Lyssaviruses of different genotypes have emerged from bats in America (Genotype 1 rabies virus; RABV), Europe (European bat lyssavirus; EBLV), and Australia (Australian bat lyssavirus; ABLV), whereas Nipah virus is the most important recent zoonosis of bat origin in Asia. Furthermore, some insectivorous bat species may be important reservoirs of SARS coronavirus, whereas Ebola virus has been detected in some megachiropteran fruit bats. Thus far, European bat lyssavirus (EBLV) is the only zoonotic virus that has been detected in bats in Europe. New zoonotic viruses may emerge from bat reservoirs and known ones may spread to a wider geographical range. To assess future threats posed by zoonotic viruses of bats, there is a need for accurate knowledge of the factors underlying disease emergence, for an effective surveillance programme, and for a rapid response system. In Europe, primary efforts should be focussed on the implementation of effective passive and active surveillance systems for EBLVs in the Serotine bat, Eptesicus serotinus, and Myotis species (i.e., M. daubentonii and M. dasycneme). Apart from that, detection methods for zoonotic viruses that may emerge from bats should be implemented. Analyses of data from surveillance studies can shed more light on the dynamics of bat viruses, (i.e., population persistence of viruses in bats). Subsequently, studies will have to be performed to assess the public health hazards of such viruses (i.e., infectivity and risk of infection to people). With the knowledge generated from this kind of research, a rapid response system can be set up to enhance public health awareness of emerging zoonotic viruses of bats.

European bat lyssaviruses, The Netherlands.

To study European bat lyssavirus (EBLV) in bat reservoirs in the Netherlands, native bats have been tested for rabies since 1984. For all collected bats, data including species, age, sex, and date and location found were recorded. A total of 1,219 serotine bats, Eptesicus serotinus, were tested, and 251 (21%) were positive for lyssavirus antigen. Five (4%) of 129 specimens from the pond bat, Myotis dasycneme, were positive. Recently detected EBLV RNA segments encoding the nucleoprotein were sequenced and analyzed phylogenetically (45 specimens). All recent serotine bat specimens clustered with genotype 5 (EBLV1) sequences, and homologies within subgenotypes EBLV1a and EBLV1b were 99.0%-100% and 99.2%-100%, respectively. Our findings indicate that EBLVs of genotype 5 are endemic in the serotine bat in the Netherlands. Since EBLVs can cause fatal infections in humans, all serotine and pond bats involved in contact incidents should be tested to determine whether the victim was exposed to EBLVs.

Evaluation of tests for antibodies against bovine herpesvirus 1 performed in national reference laboratories in Europe.

Sets of serum and milk samples were collected from various countries and prepared, lyophilised and distributed by 1 laboratory to 12 reference laboratories in Europe. The serum sets contained the three European bovine herpesvirus 1 (BHV1) reference serum samples (EU1, EU2 and EU3), serum samples from naturally and experimentally BHV1-infected cattle, from vaccinated, and vaccinated-challenged cattle, from uninfected cattle, and a series of serum dilutions. In addition, sets of milk samples were distributed. The samples were tested for antibodies against BHV1 in virus neutralisation tests, in gB-specific ELISAs, in indirect ELISAs and in gE-specific ELISAs. It was found that the virus neutralisation test and the gB-specific ELISAs were most sensitive for the detection of antibodies in serum, whereas for assaying milk samples the indirect ELISAs were the tests of choice. The results show that the quality of most laboratories appeared to be adequate, but that one laboratory performed considerably below an acceptable level of quality. Four samples from the panel have been proposed that might be selected as reference sera in addition to the three European reference samples.