Seroprevalence of border disease virus and other pestiviruses in sheep in Algeria and associated risk factors.

BACKGROUND: Border disease virus (BDV) is a pestivirus responsible for significant economic losses in sheep industry. The present study was conducted between 2015 and 2016 to determine the flock seroprevalence of the disease in Algeria and to identify associated risk factors. 56 flocks from nine departments were visited and 689 blood samples were collected from adult sheep between 6 and 24 months of age (n = 576) and from lambs younger than 6 months (n = 113). All samples were tested by RT-PCR as well as by Ag-ELISA, to detect Persistently Infected (PI) animals. Serum samples from adults were tested by Ab-ELISA (Enzyme Linked Immuno-Sorbent Assay), to detect specific antibodies against pestivirus and 197 of them were further characterized by VNT (virus neutralization test) for the detection of neutralizing antibodies specific for BDV and for Bovine virus diarrhea virus (BVDV-1 and BVDV-2). RESULTS: No PI animals were found among the 689 sheep tested. 144/197 sera were positive in VNT for BDV, and 2 sera were strongly positive BVDV-2. Fifty-five flocks (98%) had at least one seropositive animal and the apparent within-flock seroprevalence was estimated to be 60.17% (95% C.I.: 52.96-66.96). The true seroprevalence based on estimated sensitivity and specificity of the Ab-ELISA was 68.20% (95% C.I.; 60.2-76.3). Several risk factors were identified as linked to BDV such as climate, landscape, flock management and presence of other ruminant species in the farm. CONCLUSION: These high seroprevalence rates suggest that BDV is widespread and is probably endemic all over the country. Further studies are needed to detect and isolate the virus strains circulating in the country and understand the distribution and impact of pestiviruses in the Algerian livestock.

Influence of communal alpine pasturing on the spread of pestiviruses among sheep and goats in Austria: first identification of border disease virus in Austria.

The purpose of this investigation was to determine the influence of communal Alpine pasturing on the spread of pestivirus infections among sheep and goats. The study included 481 sheep from 23 farms and 131 goats from 26 farms pastured on separated Alpine meadows in the western part of Austria. At the starting of pasturing on the sheep meadow, 325 (67.6%) animals were seropositive, on the goat meadows in 16 (12.2%) samples antibodies to pestiviruses were detected. At the end of pasturing, 74 seronegative sheep and two seronegative goats had seroconverted. Between the beginning and the end of pasturing the seroprevalence in sheep increased significantly from 67.6% to 83% (P<0.05). Moreover, in the peripheral blood mononuclear cells of four sheep, pestivirus-specific RNA was detected before as well as after pasturing; these animals remained serologically negative throughout the investigation. They were, therefore, identified as persistently infected. Sequence analysis in the N(pro) region revealed that the detected pestiviruses were the same at genetic level and they were grouped into the Border disease virus (BDV)-3 genotype. No pestivirus RNA was found in goat samples. The results of this survey indicate that communal Alpine pasturing does play a key role in the spread of BDV. Moreover, BDV has been identified and characterized for the first time in sheep in Austria, which until then had been regarded as being free from BD.

Border disease in sheep.

The current knowledge on border disease in sheep is reviewed. This is a congenital and teratogenic disorder induced by pestivirus. The history, etiology, epidemiology, clinical aspects, and pathologic lesions at postnatal and intrauterine infections (as well as in congenitally affected animals), pathogenesis, immunity, diagnosis, and control and prevention of the syndrome are discussed.

Comparative studies of border disease and closely related virus infections in experimental pigs and sheep.

A pestivirus originally isolated from weaner pigs was shown to be capable of infecting weaners experimentally, but without inducing significant signs of disease. When inoculated into pregnant sows and ewes in early gestation, both the porcine virus and an antigenically similar ovine border disease isolate could induce congenital infections in both species.

Pathogenesis and epidemiology of border disease.

The pathogenesis of BD virus infection of sheep is reviewed briefly. The most serious consequences occur when susceptible pregnant sheep are infected. The virus crosses the placenta readily and can cause foetal death with resorption, mummification or stillbirths. Other lambs survive, however, and are born with varying degrees of tremor and/or hairy fleeces. Many such "hairy-shaker" lambs die shortly after birth but survivors gradually recover. These survivors plus other apparently normal lambs can be persistently infected with virus and excrete it constantly often for the rest of their lives. It is these persistently infected sheep that are the key to the epidemiology of the virus and may be responsible for its introduction into a susceptible flock. In addition, cattle grazed with sheep are potentially an important source of pestiviruses capable of causing BD since in some herds the prevalence of cattle persistently infected with pestivirus is one to three per cent. Results are presented of studies on antigenic relation ships among Scottish isolates of cattle pestiviruses (BVD) and BD viruses, and the conclusion drawn that while a single strain of BVDV may be suitable for use as a cattle vaccine this would not be very efficacious in preventing BD since two antigenically distinguishable strains of BD virus have been identified. An effective vaccine against BD would have to protect sheep against both these strains and ideally a cattle vaccine should also contain both strains.