Aujeszky’s disease virus (ADV), also called Pseudorabies virus (PRV) is a herpes virus, causing life-long latent infection, reproductive failure, potentially very high piglet mortality, immunosuppression, and reduced appetite leading to reduced growth, and lactation of tremendous impact to infected herds.
The reproductive failure is clinically characterised as SMEDI, like PPV and PCV2, but faster in the inter-foetal spread following transplacental or seminal transmission: higher fractions of litters will be affected and at a much more similar gestational stage. Hence infertility, embryonic death (return to service), mummified, and stillborn.
The infected mother will have produced appetite for 6-10 days, hardly noticed if not during lactation.
Late intra-uterine and neonatally infected piglets aged 0-7 days will have a 100% mortality usually presented as sudden death. At 2-3 weeks of age (woa) the still 100% mortality will follow severe CNS signs. From then on mortality will slowly regress from 50% at 4 woa to <5% at 22 woa. From 3-6 woa neurological signs are still possible, 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.
Commonly, losses due to ADV/PRV other than reproductive failure and increased piglet mortality following characteristic CNS signs, are not appreciated in endemic farms at all. The reasons for that can be either poor monitoring quality, signs attributed erroneously to other infections, or poor managemental standards, usually a combination of all three. The general poorly performance and high rate of secondary infections are usually attributed other infections, high swine density and sought covered for by substantial 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 relatively resistant to all imaginable 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 please in the upper respiratory mucosa and transported to all tissues by lymph and/or blood. This includes neural tissues, where it will locate persistently and act as a life long laten infection. Latent to full activation by any kind of sufficient stress from transport, handling, adverse climatic conditions, “other disease” and the like. Other reactivating factors are hormonal changes during heat/gestation and around farrowing.
Logically all ADV/PRV control builds on avoiding build of 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.
The only way of ADV/PRV control is to use a sufficiently attenuated, non-shedding, non-reverting MLV-marker vaccine 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 can not be cleared of virus by any vaccination, only have reduced shedding from the best capable vaccine in an optimal vaccination schedule. The MLV-marker vaccine 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 control progresses the glycoprotein E (gE) deleted marker vaccine will make it possible to serum sample and stamp out successively, gE positive breeders present and infected before initiation of the optimal vaccination program. This way speeding up control with a potential of eradication, and facilitation successive success monitoring.
Whether from a farm to stay fully controlled: ADV/PRV gB positive, gE negative (virus negative), or to eradicate will depend on risk of reinfection: neighbourhood contamination, external biosecurity etc.