The role of spatial factors in the success of an Aujeszky's disease eradication programme in a high pig density area (Northeast Spain, 2003-2007).

We tested the role of several spatial variables on the risk of a sow herd being Aujeszky's disease virus (ADV) seropositive in certain areas of North Eastern Spain and during different periods of the eradication programme. Distance to the nearest slaughterhouse, distance to the nearest conventional road and number of ADV serologically positive sows and ADV serologically positive fattening pigs within different distances (1000, 1500 and 2000 m) of each sow herd, were included in a hierarchical Bayesian binomial model. A variable without spatial characteristics, type of herd (farrow to weaning and farrow to finish), was also included. Presence of positive fattening pigs or positive sows up to a distance of 1500 m of a sow herd increased its risk of being seropositive, although this variable had no effect on the risk when located at distances up to 1000 or 2000 m. The number of seropositive sows increased the risk of a sow herd being ADV seropositive only in the first period of study, when the proportion of serologically positive sow herds was nearly 60%. The spatial pattern of the residuals of the hierarchical Bayesian binomial model (observed versus predicted) was very similar to the observed infection in sow herds in all of the eradication periods, showing that spatial factors might not be the main factors related to the eradication of Aujeszky's disease from sow herds. Other herd-specific risk factors might be much more strongly related to the risk of a sow herd being ADV seropositive.

Cytokine GM-CSF genetic adjuvant facilitates prophylactic DNA vaccine against pseudorabies virus through enhanced immune responses.

Granulocyte/macrophage colony-stimulatory factor (GM-CSF) is an attractive adjuvant for a DNA vaccine on account of its ability to recruit antigen-presenting cells (APCs) to the site of antigen synthesis as well as its ability to stimulate the maturation of dendritic cells (DCs). This study evaluated the utility of GM-CSF cDNA as a DNA vaccine adjuvant for glycoprotein B (gB) of pseudorabies virus (PrV) in a murine model. The co-injection of GM-CSF DNA enhanced the levels of serum PrV-specific IgG with a 1.5-to 2-fold increase. Moreover, GM-CSF co-injection inhibited the production of IgG2a isotype. However, it enhanced production of an IgG1 isotype resulting in humoral responses biased to the Th2-type against PrV antigen. In contrast, the co-administration of GM-CSF DNA enhanced the T cell-mediated immunity biased to the Th1-type, as judged by the significantly higher level of cytokine IL-2 and IFN-gamma production but not IL-4. When challenged with a lethal dose of PrV, the GM-CSF co-injection enhanced the resistance against a PrV infection. This suggests that co-inoculation with a vector expressing GM-CSF enhanced the protective immunity against a PrV infection. This immunity was caused by the induction of increased humoral and cellular immunity in response to PrV antigen.

Determination of the effectiveness of Pseudorabies marker vaccines in experiments and field trials.

The aim of vaccination in an eradication campaign is not only to induce clinical protection, but primarily to stop transmission of infections within and between herds by inducing herd immunity. Consequently, vaccines should be evaluated for their capacity to reduce virus transmission in the population. Glycoprotein E (gE) negative marker vaccines against Pseudorabies virus (PRV) infections in pigs have been evaluated this way in experiments and field studies. PRV infection in groups of (vaccinated) pigs was determined by measuring antibodies against gE of PRV from regularly taken serum samples. For the statistical analysis of the experiments a stochastic susceptible-infectious-removed (SIR) model was used. A measure for the transmission of virus is the reproduction ratio R, which is defined as the average number of secondary cases caused by one typical infectious individual. This implies that an infection will always fade out in a population when R < 1, but the infection can spread massively when R > 1. From several experiments it was shown that R < 1. Field studies showed that the R within herds was still > 1, but by reducing further contacts the R could be reduced to a value below one. This would imply that PRV could be eradicated by means of vaccination. In The Netherlands, an eradication campaign was launched in 1993, and in 2002 the virus was eradicated, as shown by a negligible number of gE-positive pigs. Farmers' organizations have to decide whether or not to stop vaccination.

Vaccination of pigs with a recombinant porcine adenovirus expressing the gD gene from pseudorabies virus.

Five week old, commercially available large white pigs were vaccinated with either a single dose or two doses of a recombinant porcine adenovirus expressing the glycoprotein D gene from pseudorabies virus (PRV). Pigs were monitored for the development of serum neutralizing antibodies to PRV and challenged 3 weeks after final vaccination. Prior to challenge, pigs given 2 doses of the vaccine demonstrated boosted levels of antibody compared with those given a single dose, and all surviving pigs had increased neutralization titres over pre-challenge levels. Following challenge, pigs were monitored for clinical signs of disease, with blood and nasal swabs collected for virus isolation. All control animals became sick with elevated temperatures for 6 days post challenge, whereas; vaccinated animals displayed an increase in body temperature for only 2-3 days. Control pigs and those given a single dose all lost condition, but the group given 2 doses remained healthy. At postmortem, gross lesions of pneumonia only occurred in control animals and those given a single dose of vaccine. Histology carried out on the brains of all animals demonstrated a difference in severity of infection and frequency of immunohistochemical antigen detection between test animals, with control and single dose groups being most severely affected and pigs given 2 doses the least. Virus isolation studies demonstrated that no viraemia could be detected, but virus was found in nasal swabs from some animals in both groups of vaccinates following challenge.