SWINE Aujeszky Disease/ Pseudorabies virus
Aujeszky’s disease virus (ADV), also called Pseudorabies virus (PRV,) is a herpes virus causing life-long latent infection, reproductive failure, high piglet mortality, immunosuppression, and reduced appetite leading to reduced growth and lactation, negatively impacting infected herds tremendously.
Reproductive failure associated with this pathogen is clinically characterized by SMEDI—stillbirth, mummification, embryonic death, and infertility— syndrome similar to infections caused by PPV and PCV2. However, it progresses more rapidly due to efficient inter-fetal spread following transplacental or seminal transmission. As a result, a higher proportion of litter is affected, often at a similar gestational stage. This leads to outcomes such as infertility, embryonic death (manifested as return to service), mummified fetuses, and stillbirths.
The infected mother will have a reduced appetite for around 6-10 days, which often goes unnoticed unless it is during lactation.
Late intra-uterine and neonatally infected piglets aged 0-7 days will have 100% mortality, presented as sudden death. At 2-3 weeks of age (WOA) the 100% mortality will follow severe central nervous system (CNS) signs. From then on, mortality rates will slowly regress from 50% at 4 WOA to <5% at 22 WOA. From 3-6 WOA, neurological signs are still possible but not as frequent. Later the only ADV/PRV induced clinical signs will be reduced appetite for 6-10 days, and the usual overriding of secondary infections due to the clinically inconspicuous immunosuppression.
Often losses due to ADV/PRV, other than reproductive failure and increased piglet mortality following characteristic CNS signs, are not seriously noted in endemic farms at all. The reasons for this can be poor monitoring quality, symptoms mistakenly attributed to other infections, or poor managemental standards, but it is usually a combination of all three. The general poor performance and high rate of secondary infections are usually attributed to other infections and high swine density. These issues are frequently masked by extensive routine antimicrobial programs.
Infected and life-long latently infected, reactivated animals shed high viral concentrations for 18-25 days in ALL imaginable excretions and secretions. The virus is relatively resistant to all environmental conditions apart from clean, dry and arid conditions plus UV-light, Routes of transmission are oro-nasal, inhalation of aerosols (from long distances), venereal (seminal), and conjunctival.
The initial multiplication takes place in the upper respiratory mucosa and is transported to all tissues by lymph and/or blood. This includes neural tissues, where they will be located persistently and act as a lifelong latent infection. The virus remains latent until full activation by any kind of sufficient stress from transport, handling, adverse climatic conditions, “other disease” and more. Other reactivating factors are hormonal changes during heat/gestation and around farrowing.
Logically all ADV/PRV control starts with avoiding building life-long latent infections, starting with and maintaining maximal focus on the breeding stock, but also ensuring protection and control in growing pigs. Antimicrobial routine programs will have no effect on the causal virus but may alleviate secondary bacterial infections to reduce associated clinical signs
The only way of ADV/PRV control is to use a sufficiently attenuated, non-shedding, non-reverting modified live vaccine (MLV) marker in a whole herd program protecting piglets from cease of colostral protection and vaccine-response blocking, through young-gilt stage, into repeated breeder booster vaccination.
Animals already persistently infected cannot be cleared of virus by any vaccination, only have reduced shedding from the best capable vaccine in an optimal vaccination schedule. The MLV-marker needs to inhabit the neural loci before the field strain and maintain that position by booster vaccination. For that reason, inactivated vaccines are of little, if any, use in ADV/PRV control.
As ADV/PRV control progresses, the use of glycoprotein E (gE)-deleted marker vaccines enables targeted serological monitoring. By identifying and removing gE-positive breeders—those infected prior to the initiation of an optimal vaccination program—control efforts can be accelerated, with the potential for eradication. This approach also facilitates ongoing monitoring of success through serological surveillance.
Whether a farm aims to remain under control (ADV/PRV gB-positive, gE-negative—indicating virus-free status) or pursue full eradication depends largely on the risk of reinfection, which is influenced by factors such as neighboring herd status and the strength of external biosecurity measures.