Aujeszky's disease is caused by suid herpes virus 1 (SuHV-1), syn. pseudorabies virus from the subfamily Alphaherpesvirinae, genus Varicellovirus. Virus strains vary in virulence, but behave in a serologically uniform manner. Weakly virulent virus strains are strictly neurotropic and, in contrast to the highly virulent strains, do not cause further organ damage. Strongly virulent strains can be detected in lungs (infestation of alveolar macrophages) and genital tract, as well as in the semen of infected boars.
The virus multiplies primarily in the epithelia of the nasal and pharyngeal mucous membranes and the tonsils, or in the genital mucous membranes, and subsequently spreads in the nervous system. From the primary site of infection the virus migrates via afferent nerve tracts into the CNS. Nervous symptoms of disease occur 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 accumulation, mating season, birth) can reactivate the virus and cause it to 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 disinfectants based on chlorine, ammonium or formalin. However, alcohol and phenols are ineffective.
Mode of transmission
In domestic pig stocks, the virus is usually transmitted to healthy pigs through direct contact with infected pigs. In highly infected stocks, transmission may also occur during animal care via hand contact, feed, inanimate objects and/or, in close proximity, even via air movement ("aerogenic"). In areas with intensive pig farming the infection spreads rapidly.
Other sources of infection are meat, organs, milk and sperm. Pregnant sows spread the virus via aborted foetuses, the placenta and vaginal discharge.
Not only susceptible pigs but also vaccinated pigs can become carriers of the virus. Vaccination is therefore prohibited in Austria. After surviving the disease, the virus withdraws into the trigeminal ganglia and possibly tonsils, or into 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 shedding of the virus. The transmission of viruses is not linked to a season. For carnivores, the most important source of infection is the ingestion of meat and offal from infected (wild) pigs.
Piglets: Initial fever, vomiting, movement disorders, circular movements, paralysis in swallowing, strong salivation; then central nervous disorders: muscle trembling, cramps, paddling of the limbs and partial paralysis; in piglets up to 2 weeks old the mortality rate is 100%; in piglets 3-4 weeks old still 50%. Young animals at the age of 1-3 months show low appetite, rhinitis (nasal discharge), slight fever and shortness of breath. Death usually occurs only in case 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 a less pronounced symptomatology than domestic pigs - often without signs of disease.
Dog/cat/cow/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, diseased miscarriers have thirst, carnivores do not show symptoms of aggressiveness and ruminants do not show hydrophobia as well as pronounced symptoms of the respiratory tract, e.g. increased panting or shortness of breath.
In Austria the use of protective vaccination is prohibited. 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 boars, it is recommended to check the appropriate biosecurity measures on the own holding and to take appropriate measures to prevent contact between domestic pigs and wild boars (e.g. double fencing for wild boars).
Symptoms of dogs and cats
Diagnosis is based on clinical symptoms and rapid progressive course. Conspicuous symptoms are inability to eat, pathological sensitivity, severe itching followed by self-mutilation, extreme sensitivity to touch, numbness, salivation, reddened eyelid and oral mucosa, increased respiratory rate (60/min.) and frequent pulse (160/min.). In contrast to rabies, the diseased animals show thirst but no aggressiveness. The disease progresses so rapidly that no antibodies were formed until the time of death. A reliable diagnosis is only made after death by appropriate laboratory tests.