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 causative agent of 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 have a uniform serological behaviour. Weakly virulent virus strains are strictly neurotropic and, in contrast to the strongly virulent strains, cause no further organ damage. Strongly virulent strains are detectable in the lungs (infestation of alveolar macrophages) and in the genital tract, as well as in the semen of infected boars.

The virus multiplies primarily in the epithelia of the nasal and pharyngeal mucosa and the tonsils or in the genital mucosa and subsequently spreads in the nervous system. From the primary site, the virus migrates into the CNS via afferent nerve pathways. Nervous symptoms develop when damage to the neurones 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 lead to reactivation of the virus and consequently to further spread.

The virus can survive in the environment at 25 °C for up to 40 days. The virus is inactivated by heating 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 during animal care via hand contact, feed, inanimate objects and/or even via air movement ("aerogenic") in close neighbourhoods. The infection spreads rapidly in areas with dense pig farming.

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

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

Symptoms

Piglets: Initially fever, vomiting, movement disorders, circular movements, swallowing paralysis, heavy salivation; then central nervous disorders: Muscle tremors, cramps, paddling movement of the limbs and partial paralysis; in piglets up to 2 weeks old, mortality is 100%; in 3-4 week old piglets still 50%. Young animals aged 1-3 months show a poor appetite, rhinitis (nasal discharge), slight fever and shortness of breath. Death usually only occurs in the case of central nervous disorders.

Runner/fattening pigs: Diseases of the respiratory tract, 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 boar: Usually do not show as pronounced symptoms as domestic pigs - often without signs of disease.

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

In contrast to rabies, infected false hosts are thirsty, carnivores have no symptoms of aggression and ruminants have no water shyness and pronounced symptoms of the respiratory tract, e.g. increased panting or shortness of breath.

The use of protective vaccination is prohibited in Austria. The live vaccines developed for pigs are pathogenic for cattle, dogs and cats; inactivated vaccines are not effective enough. Due to the occurrence of Aujeszky's disease in wild boar, it is recommended that you review the relevant biosecurity measures on your own farm and ensure that contact between domestic and wild boar is prevented (e.g. by double fencing to keep wild boar out).

Symptoms in dogs and cats

The diagnosis is based on the clinical symptoms and the rapid progressive course. Conspicuous symptoms are reluctance to eat, abnormal sensitivity, severe itching followed by self-mutilation, extreme sensitivity to touch, numbness, salivation, reddened conjunctiva and oral mucosa, increased respiratory rate (60/min.) and frequent pulse (160/min.) In contrast to rabies, the affected animals show thirst, but not aggression. The disease progresses so rapidly that no antibodies have been produced by the time of death. A reliable diagnosis is only made after death by means of appropriate laboratory tests.

Information for hunters

Blood used for training hunting dogs can be tested for the absence of viruses (PCR test required).

Direct contact between wild boar and hunting dogs should be limited as much as possible during hunting operations. In any case, "socialising" with wild boar organs, intensive contact with wounds made by wild boar, the cutting of wild boar by the dog, direct contact with openings or wild boar tracks should be avoided. If the protective measures are observed, the 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 when, where and to what extent the virus is acutely present or whether it 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.