Aujeszky's disease is primarily a viral disease of pigs. However, dogs, cats and virtually all other domestic mammals can also contract it. For all susceptible species except pigs, the disease is fatal. The symptoms are similar to those of rabies, which is why the disease is also called pseudo-rabies. According to current knowledge, humans are not susceptible to the infection.

Aujeszky's disease is widespread worldwide. In Austria, the disease does not occur in the domestic pig herd. However, as in other European countries, Aujeszky's disease is present in the wild boar population.

Pigs (domestic and wild) are the natural reservoir. Dogs, cats, other carnivores (minks, ferrets) and ruminants (cattle, sheep, goats), as well as equids, on the other hand, are false hosts that hardly play a role in the spread of the disease. The disease is fatal in all abortive hosts, only pigs survive the disease - also depending on their age.

Transmission occurs from pig to pig via the respiratory or digestive tract, in wild boar also via mating. Other animals become infected through direct contact with pigs. For carnivores, the main source of infection is ingestion of meat and offal of infected (wild) pigs. In the current epidemiological situation in Austria, hunting dogs are particularly at risk.

2 to 6 days

In pigs, symptoms range from subclinical disease (often in feral pigs) to abortions, respiratory disease, neurological symptoms and death in very young piglets. False hosts always react to the infection with a fatal disease of the central nervous system, often accompanied by restlessness, itching, self-mutilation and seizures.

There is no therapy against the virus. The disease leads to death in all susceptible animals except pigs.

In Austria, the disease does not occur in domestic pigs. Aujeszky's disease is notifiable in domestic pig herds. Vaccination is prohibited. In order to maintain this status, serological surveillance programmes are carried out every year. In addition, abortions of domestic pigs sent to AGES are also examined for Aujeszky's disease. The examination of wild boar is carried out exclusively by private order or within the framework of research projects.

Due to the permanent surveillance program, Austria has been officially recognized free of Aujeszky's disease in domestic pigs since 1997. In 2022, a total of 15,157 pigs were serologically tested for antibodies against Aujeszky's disease virus. The majority of these samples (13,690) came from the official sampling program. In addition, 64 abortions were tested for Aujeszky's disease virus. In none of these cases was either the virus itself or antibodies to Aujeszky's disease virus detected.

The pathogen responsible for Aujeszky's disease is Suid Herpesvirus 1 (SuHV-1), syn. Pseudorabies virus from the subfamily Alphaherpesvirinae, genus Varicellovirus. The virus strains vary in their virulence, but behave serologically uniformly. Weakly virulent virus strains are strictly neurotropic and, unlike the highly virulent strains, do not cause further organ damage. Highly virulent strains can be detected in the lungs (infection of alveolar macrophages) and in the genital tract, as well as in the semen of infected boars.

The virus primarily replicates in the epithelium of the nasal and throat mucosa and the tonsils, or in the genital mucosa, and subsequently spreads to the nervous system. From the primary site, the virus migrates to the CNS via afferent nerve pathways. Nervous symptoms develop when damage to the neurons has occurred. If the primary infection is survived (only in pigs), the animals remain latently infected. At this stage, they are not infectious, but stressors (transport, mass gatherings, mating season, birth) can cause the virus to reactivate and spread.

The virus can survive in the environment for up to 40 days at 25 °C. The virus is inactivated by heating to above 55 °C or by chlorine-, ammonium- or formalin-based disinfectants. However, alcohol and phenols are ineffective.

Transmission

In domestic pig herds, the pathogen is usually transmitted to healthy pigs through direct contact with infected pigs. In heavily infected herds, transmission can also occur via care personnel, feed, inanimate objects and/or, in close proximity, even through the air ("aerogenic").

Other sources of infection include meat, organs, milk and semen. Pregnant sows spread the virus via aborted foetuses, the placenta and vaginal discharge.

Not only susceptible pigs, but also vaccinated pigs can become virus carriers. Vaccination is therefore prohibited in Austria. After the disease has been overcome, the virus retreats to the trigeminal ganglia and, if necessary, the tonsils, or to the sacral ganglia (especially in wild boars), depending on the point of entry (latent infection). Stress factors such as transport etc. can lead to reactivation and excretion of the virus. The transmission of the virus is not linked to a particular season. For carnivores, the most important source of infection is the consumption of meat and offal from infected (wild) pigs.

Symptoms

Piglets: Initially fever, vomiting, movement disorders, circular movements, swallowing paralysis, excessive salivation; followed by central nervous disorders: muscle tremors, convulsions, paddling movements of the limbs and partial paralysis; mortality is 100% in piglets up to 2 weeks old and still 50% in piglets 3-4 weeks old. Young animals aged 1-3 months show poor appetite, rhinitis (nasal discharge), mild fever and respiratory distress. Death usually only occurs in cases of central nervous disorders.

Runners/fattening pigs: Respiratory tract diseases, high fever, depression, poor weight gain, rarely central nervous disorders. The incubation period is 3-5 days with a disease rate of 100% and a mortality rate of 5%.

Sows/boars: Fertility problems, including abortions

Wild boars: Usually show less pronounced symptoms than domestic pigs – often with no signs of disease.

Dogs/cats/cattle/small ruminants: Inflammation of the brain and spinal cord with central nervous system symptoms, salivation and severe itching. The disease is always fatal in these animals, usually after 1-3 days.

Unlike rabies, infected accidental hosts are thirsty. Carnivores show no symptoms of aggression and ruminants show no fear of water or pronounced respiratory symptoms, e.g. increased panting or shortness of breath. Symptoms in dogs and cats include loss of appetite, pathological sensitivity, severe itching followed by self-mutilation, extreme sensitivity to touch, numbness, salivation, reddened conjunctiva and oral mucosa, increased respiratory rate (60/min) and a rapid pulse (160/min). The disease progresses so rapidly that no antibodies are formed before death. A definitive diagnosis can only be made after death by means of appropriate laboratory tests.

The use of protective vaccination is prohibited in Austria. The live vaccines developed for pigs would cause disease in cattle, dogs and cats. Due to the occurrence of Aujeszky's disease in wild boars, it is recommended that the relevant biosecurity measures be reviewed on your own farm and that appropriate measures be taken to prevent contact between domestic and wild boars (e.g. by means of double wild boar-proof fencing).

Information for hunters

Blood used to train hunting dogs can be tested for viruses (PCR test required).

Direct contact between wild boar and hunting dogs should be limited as much as possible during hunting. In any case, the following should be avoided: coming into contact with wild boar organs, intensive contact with entry and exit wounds, the dog cutting into wild boar, and direct contact with carcasses or wild boar kills. If the protective measures are observed, infection of hunting dogs can be prevented with a high degree of certainty.

Laboratory diagnostics in (wild) pigs

• Examination for antibodies from blood (serum) by ELISA or serum neutralisation test: The result allows a statement as to whether the animal has had contact with the virus; however, the result of the test does not indicate whether the virus is excreted. The detection of antibodies also does not imply immunity. In international trade, the differentiation of vaccinated animals may be important, which is possible with the help of special ELISA tests due to the use of so-called marker vaccines.
• Examination by PCR from organs (tonsils, brain, spinal cord, lungs, spleen, kidney, liver, lymph nodes), including aborted material, as well as from naso- and oropharyngeal swabs: PCR directly detects the virus or virus components. Even latent infection can be detected by PCR if the corresponding target tissues (trigeminal or sacral ganglia) are sampled.
• Virus isolation: in contrast to PCR, this allows a statement to be made as to whether the virus is capable of infection, as well as further typing. Virus isolation is rarely used in routine diagnostics.

Laboratory diagnostics in case of dogs

• As no antibodies are formed due to the rapid course of the disease, only direct pathogen detection by PCR (if necessary also by virus isolation) is useful. In this case, CNS (brain and/or spinal cord, in the latter case especially the region of the spinal cord which was responsible for the supply of the skin sites where the itching was observed) should be brought for examination.

In all cases, the shipment of samples to the laboratory should ideally be carried out with the addition of refrigerants and consideration of the appropriate transport regulations (UN3373) by an authorized logistics company.