Extensive rearing hinders Maedi-Visna Virus (MVV) infection in sheep

Abstract

-Maedi-Visna Virus (MVV) seroprevalence and its relationship with housing and mode of rearing of replacement ewe-lambs was investigated in 38 non-randomly selected sheep-flocks in Spain. They included extensive lamb-producing Manchega cross-bred flocks raised almost permanently at pasture, semi-intensive Latxa dairy flocks housed 2-8 months/year and intensively raised Assaf dairy flocks housed most time and at higher stocking density in less ventilated buildings than other flocks. Most flocks raised replacement lambs naturally with their dams until weaning and as a separate flock thereafter until lambing at one year of age. Seroprevalence (95% confidence intervals) was 77%, 25% and 5% (4-6) in intensive, semi-intensive and extensive flocks, respectively and the median (interquartile range) flock-seroprevalence was 82% (66-94) in intensive flocks, 31% (14-31) in semi-intensive flocks and 4% (0-7) in extensive flocks. Seroprevalence was lowest in one year-old sheep and increased to flock levels during the year after introduction into the adult flock in most intensive flocks and more gradually in other flocks. Adult flock seroprevalence was associated with housing time but this relationship was not evident within a particular rearing system, indicating that other unknown factors are critical in horizontal MVV-transmission. Low seroprevalence in extensive flocks further supports previous indications that lactogenic MVV-infection is relatively inefficient and horizontal transmission is necessary to ensure long-term maintenance of MVV and this could explain that MVV has not been reported from countries with mainly extensively reared sheep such as Australia and New Zealand. Moreover, it indicates that MVV-control in extensive and semi-intensive flocks can be simple and inexpensive.Maedi-Visna Virus / sheep / seroprevalence / intensive and extensive rearing / Spain

Ovine Progressive Pneumonia Virus Is Transmitted More Effectively via Aerosol Nebulization than Oral Administration

“…The finding that a mammary derived virus passaged through GSM cells can transmit experimentally using aerosol Nb, and the fact that horizontal transmission comprises accounts for the majority of natural infection amongst ewes [7][8][9] suggests that mammary derived viruses may transmit horizontally by aerosols to naïve ewes in a natural lambing situation. Further experimental OPPV infections using aerosol Nb of colostrum and milk needs to be conducted on naïve post-partum ewes.…”

“…The few lambs that became infected in these scenarios were either thought to have suckled briefly or acquired infection in utero [6]. More recently, field studies in Spanish flocks have shown increased VMV seroprevalence in intensive versus exten-sive operations suggesting horizontal transmission plays a large role in transmission [7,8]. Furthermore, a molecular epidemiology study in dam and daughter sets of a naturally infected Idaho, USA ewe flock showed that maternal transmission of OPPV contributed only 10% -14% of transmission events; whereas, non-maternal transmission, which includes horizontal transmission and possible paternal transmission during conception, accounted for the remaining 86% -90% of transmission [9].…”

Risk factors associated with small-ruminant lentiviruses in sheepfold buildings

“…The virus can also spread through a flock via an aerogenic mechanism. As claimed by Leginagoikoa et al (2006), minimizing crowding and improving the ventilation in animal housing facilities can decrease the risk of SRLV infection in sheep. Unfortunately, to-date, factors directly associated with animal welfare have gained little attention.…”

“…Unfortunately, to-date, factors directly associated with animal welfare have gained little attention. The significance of these factors, however, is demonstrated by the higher frequency of SRLV infection in flocks of sheep bred in closed sheepfolds, compared with flocks bred under semi-intensive conditions involving the use of pastures [15].…”

Ocorrência de anticorpos contra o vírus Maedi-Visna em ovinos Santa Inês, no Estado de Sergipe, Brasil

“…Animais infectados podem eliminar o vírus principalmente a partir de secreções pulmonares e por meio do leite contendo macrófagos infectados, transmitindo-o, desta forma, a animais suscetíveis, especialmente sob condições de estreito contato, como aquelas observadas em sistemas de criação intensiva (Simard;Morley, 1991;Carey;Dalziel, 1993;Pinheiro et al, 2004;Leginagoikoa et al, 2006;Shuljak, 2006).…”