Factors associated with the seroprevalence of Aujeszky's disease virus in seropositive breeding herds of Northern Germany during area-wide compulsory vaccination

Aujeszky's disease and the effects of infection on Japanese swine herd productivity: a cross-sectional study

Pseudorabies virus (PRV) is endemic in some regions of Japan. We investigated the effects of PRV infection status on herd productivity. Serum samples were obtained from 48 swine herds in Japan. Within each herd, three serum samples were obtained from growing pigs at four different ages, as well as from sows in low and high parity groups. Sera were tested for antibodies against wild-type PRV via competitive ELISA. Herds were classified into PRV positive and negative groups based on serological results. Herds infected with PRV exhibited postweaning mortalities (6.84%) that were significantly (P=0.0018) higher than those in unaffected herds (4.73%). Because of the reduced productivity in PRV positive herds, the current PRV eradication program must be strengthened.

Risk factors for Aujeszky's-disease seropositivity of swine herds of a region of northern Italy

Vaccination programs to control Aujeszky's-disease virus (ADV) using gE-deleted vaccines are being considered in several European countries. Knowledge of factors influencing ADV-seropositivity for vaccinated herds might contribute to the success of these programs. A multivariable analysis of ADV-seropositivity in 1248 swine herds (332 farrow-to-finish, 260 farrow-to-feeder and 656 finishing herds) in the Emilia-Romagna region of Italy revealed that (1) high pig density (number of pigs in a 6-km radius), (2) gilt purchasing, and (3) increased number of fattening pigs were risk factors for farrow-to-finish herds. In farrow-to-feeder herds, ADV-seropositivity was related to (1) increased number of breeders, (2) heavy-gilt purchasing, and (3) increased pig density. In finishing herds, (1) increased herd size was related to ADV-seropositivity, whereas (2) periodic rearing suspension was protective.

Empirical and theoretical evidence for herd size as a risk factor for swine diseases

Herd size is frequently studied as a risk factor for swine diseases, yet the biological rationale for a reported association with herd size (whether positive or negative) is rarely adequately discussed in published epidemiological studies. Biologically plausible reasons for a positive association between herd size and disease include a greater risk of introduction of pathogens from outside the herd, greater risk of transmission of pathogens within and among herds when the herd is large, and effects of management and environmental factors that are related to herd size. However, compared with owners of small herds, owners of large herds might more frequently adopt management and housing practices that mitigate this theoretically increased risk. We used studies of pleuritis, pneumonia and pseudorabies to describe the epidemiological issues involved in evaluations of the relationship between management factors, herd size and disease. In future studies, we recommend that (i) herd size be measured in a way that best characterizes the true population at risk; (ii) studies that evaluate management-related risk factors should account for herd size wherever possible; (iii) population-based studies of the interrelationships among management factors and between management factors, herd size, herd density and pig density be done; (iv) likely biological reasons for any herd-size effect be postulated; and (v) the distribution of herd sizes in the source population and the study sample be described.

Prevalence of herds with young sows seropositive to pseudorabies (Aujeszky's disease) in northern Belgium

In Belgium, pseudorabies in swine has been the subject of a mandatory eradication programme since 1993. From December 1995 to February 1996, a survey was conducted in the five provinces of northern Belgium to estimate the provincial pseudorabies virus (PRV) herd seroprevalence. Seven hundred and twenty randomly selected herds were included in this survey. To detect recently infected animals, only young sows were sampled. The results show that 44% of these herds had an important number of PRV-seropositive young sows. The highest herd seroprevalence was observed in West Flanders (68%), followed by Antwerp (60%), East Flanders (43%), Limburg (18%), and Flemish Brabant (8%). Assuming a diagnostic test sensitivity and specificity of 95% and 99%, respectively, and a true PRV within-herd prevalence of 43%, the overall true PRV herd prevalence was estimated to be 35%. A logistic multiple-regression revealed that the presence of finishing pigs was associated with a two-fold increase in odds of a herd being seropositive (odds ratio (OR)=2.07, 95% confidence interval (CI) = 1.31-3.26); a breeding herd size > or =70 sows was associated with a four-fold increase in odds of a herd being seropositive (OR = 4.09, 95% CI = 2.18-7.67); a pig density in the municipality of >455 pigs/km2 was associated with a 10-fold increase in odds of a herd being seropositive (OR = 9.68, 95% CI = 5.17-18.12). No association was detected between the PRV herd seroprevalence and purchase policy of breeding pigs (purchased gilts, or use of homebred gilts only).

Pseudorabies virus eradication by area-wide vaccination is feasible

This article reviews the rationale for using marker vaccines and companion diagnostic tests in the eradication of pseudorabies virus (PRV). Recent advances in vaccinology and epidemiology indicate that, despite the inability to induce complete immunity, vaccination is a useful tool in the battle against PRV. This review focuses on the effectiveness of vaccination under field conditions and on herd, management and regional factors that are associated with PRV introduction or transmission.