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BVD/MD is a recurrent generalized viral infection affecting a broad range of hosts and occurring in cervids, the major symptoms being haemorrhagic mucosal inflammation and general physical impairment. Seroepizootiological investigations in free ranging wild ruminants of several continents have revealed that a great number of species are seropositive to the BVD/MD virus. In some cases virus isolation was successful. In 1978 in Southern Germany (Rheinland-Pfalz) 6.6 % of the red deer samples (Cervus elaphus hippelophus) and 5.9 % of the roe deer samples (Capreolus capreolus) were seropositive, while only 0.6 % of the cervid sera contained antibodies against BVD/MD- virus in the former German Democratic Republic in 1988. The infection pathways for wild ruminants are not clear yet. This investigation among other issues is an attempt to clarify with regard to BVD/MD, whether cattle are a potential hazard for cervids and whether cervids represent a virus reservoir for domestic animals.A total of 382 sera and 203 spleen samples from different cervid species, chiefly from red deer, roe deer and fallow deer was tested. The samples were collected from 19901992 and on the one hand the samples originate from shot animals of three different biotops in the wild, on he other hand from immobilised or shot individuals of several wildlife parks and the two Berlin Zoos.There was no significant difference in seroprevalence between regions with high, intermediate and low cattle density. Thus, there appears o be no need for epizootiological contact with cattle suggesting an independent process of infection among the populations of cervids.Moreover there is no significant difference in the proportion of seropositive individuals among the three cervid species in investigations from 1972-78 in comparison to the present data from 1990-92. These findings indicate that there has been no increase in seroprevalence in cervids in the former Western part of FRG over the last 15 years, while BVD/MD infections in cattle increased during the last decades. These findings again suggest that there is no epizootiological need for contact with cattle, since otherwise the seroprevalence in cervids probably should have increased in ecent years.There were significantly more seropositive individuals in roe deer in comparison to fallow deer, suggesting that roe deer is more susceptible to the BVD/MD virus than fallow deer. Roe deer in general are very susceptible to diseases, while specific factors causing this situation are unknown.Significantly more seropositive individuals were found among juvenile animals than among adults. Also in cattle, BVD/MD primarily occurs among animals from 6 - 24 months of age.Seroprevalence in populations on free range was significantly higher compared with populations in enclosures. This suggests that MD in cervids in enclosures show fewer infections than those on free range, although the game density and thus possibility of transmission for game in enclosures ought to be higher. These data indicate that there was a natural source of infection for the cervids populations on free range. Seroprevalence in summer was significantly higher than in winter. Probably the foraging behaviour is responsible. Indigenous cervids forage much more frequently on meadows and pastures in summer. This provides better opportunities for them to infect each other than in winter, when they are not grazing much from the ground Cytopathogenic pestiviruses were isolated from two Schleswig-Holstein samples. All the other spleen samples reacted negatively. Both samples were obtained from seronegative roe deer.Pestiviruses were detected by four criteria:1. Both samples were reacting positively when applying direct immunofluorescence.2. Electronmicroscopic images showing virus particles which are characteristic for pestiviruses were produced.3. BVD/MD positive serum from cattle neutralised the respective isolates.4. The morphology of the cytopathic effect of the isolates resembles that of pestiviruses.Moreover the two isolates were identified without doubt by means of RT-PCR as reacting positively to pestiviruses when applying Pesti primers (Pesti 2 / BVD 3) in the PCR. However, they were negative, when specific BVD (LOPEZ primers) - or swine pest primers (HCV 1/2) were used. This suggests that the two isolates have other genome sections than those of classical BVD/MD or HCV stains. Probably the two seronegative cytopathogenic carriers of viruses were individuals infected with MD or acute transients of BVD. Up to now, noncytopathogenic BVD/MD virus from the spleen of roe deer was isolated only in Hungary, cytopathogenic BVD/MD in wild ruminants was isolated in a giraffe in Kenya only.The serum neutralisations test titres ranged from 1:5 to 1: 125. The titres of the strain Grub 313/83 were significantly higher in comparison with the strain NADL. This suggests an infection process with a BVD/MD virus in the wild ruminants testedwhich is closer to the antigene structure of the strain Grub 313/83 than to the strain NADL.Only one individual was found reacting with Border Disease virus. In case of the four other positive sera there appeared to be a cross reactivity between the BVD/MD and the Border Disease virus. The seropositive adult buck originated from a place in East Berlin. The Border Disease virus does not seem to play a role in the investigated areas, rather a pestivirus which is closer to the BVD/MD strain Grub 313/83 regarding its antigene structure and possibly represents a separate virus strain of wild ruminants" pesti or is a strain similar to BVD/MD.