Aujeszky’s Disease

Morbus Aujeszky; Pseudowut; Pseudorabies, infektiöse Bulbärparalyse, Juckseuche, mad itch

Changed on: 17.05.2021
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Animal disease categories: C D E

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

Occurrence

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

Reservoir

Pigs (domestic and wild boar) are the natural reservoir. Dogs, cats, other carnivores (minks, ferrets) and ruminants (cattle, sheep, goats), as well as equines, are end hosts that play hardly any role in the further spread of the disease. The disease ends fatally in all miscarriers, only pigs survive the disease - depending on age.

Mode of transmission

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

Incubation period

2 to 6 days

Symptoms

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

Treatment

There is no treatment for Aujeszky's disease. The virus causes death in all susceptible animals except pigs.

Preventive measures

In Austria the disease is not present in domestic pigs. Aujeszky's disease is notifiable in domestic pig stocks. Vaccination is prohibited. Serological surveillance programmes are carried out every year to maintain this status. In addition, cases of abortion in domestic swine sent to AGES are also examined for Aujeszky's disease. The examination of feral pigs is carried out exclusively by private commission or within the framework of research projects.

Situation in Austria

Austria has been officially recognised as being free from Aujeszky's disease in domestic pigs since 1997 as a result of a permanent surveillance programme. In 2019, 15,116 pigs from 3,320 holdings were examined within the framework of the surveillance programme. Within the scope of abortus examinations 124 pig fetuses were tested. A total of 17,381 pigs were serologically tested for antibodies against Aujeszky's disease (also within the framework of other investigations, e.g. insemination centres). All tests gave negative results.

Figure 1: Testing of pigs for Aujeszky's disease


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    Professional information

    Veterinary Medicine

    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.

    Symptoms

    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.

    Hunters

    Infection of hunting dogs in contact with infected blood cannot be excluded. However, infection can be avoided if blood or organ material from a dead wild boar tested for abscence of the virus is used for training. Infection by inhaling the scent of wild boar is unlikely. However, as no studies are known on this or on the survival of the virus in urine, it is not possible to make a clear statement.

    Direct contact between wild boar and hunting dogs should be restricted in hunting operations, if possible. In any case, "comrades making" with organs from wild boar, intensive contact with entry and exit wounds, cutting of wild boar, contact with outbreaks or wild boar tracks should be avoided. If the protective measures are met, the infection of hunting dogs with Aujeszky's disease can be reduced to a high degree of certainty.

    Diagnostics

    Laboratory diagnostics in (wild) pigs

    • Testing for antibodies from blood (serum) by ELISA or serum neutralisation test: The result gives information whether the animal has been in contact with the virus; however, the result of the test does not give any indication as to when, where and how far the virus is acutely present or whether it is shed. The detection of antibodies also does not imply immunity. In international trade, it may be important to distinguish vaccinated from not vaccinated animals, which is possible using special ELISA tests based on the use of so-called marker vaccines.
    • Examination by PCR from organs (tonsils, brain, spinal cord, lung, spleen, kidney, liver, lymph nodes), including abortion material, and from naso- and oropharyngeal swabs: PCR directly detects the virus or virus components. Even a latent infection can be detected by PCR if the corresponding target tissue (trigeminal or sacral ganglia) is sampled.
    • Virus isolation: in contrast to PCR, this method shows if the virus is capable of infection, as well as further virus characterisation. Virus isolation is rarely used in routine diagnostics.

    Laboratory diagnostics for accidental hosts

    • Since no antibodies are formed due to the rapid progression of the disease, only the direct detection of the pathogen by PCR (if necessary also by virus isolation) makes sense. Here, CNS (brain and/or spinal cord, in the latter case especially the region of the spinal cord responsible for the skin areas where itching was observed) should be brought for examination.

    In all cases, samples should be shipped to the laboratory (see contact), ideally with the addition of coolants and taking into account the relevant transport regulations (UN3373), by an authorised logistics company.

    Contact, forms

    Institute of Veterinary Medicine Mödling (national reference laboratory)

    Robert Koch-Gasse 17
    A-2340 Mödling

    Tel: +43 (0) 505 55-38112
    Fax: +43 (0) 505 55-38108

    E-mail: vetmed.moedlingno@Spam@agesno.Spam.at

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