Pseudorabies Disease

24/06/2022

Both domestic pigs and wild swine are the only natural reservoir hosts of Aujeszky’s disease virus (ADV) and able to survive a productive infection. It remains unexplained whether other members of the artiodactyl suborder Suina are susceptible to ADV. The virus can infect a wide range of other mammals, in particular animals in close contact with pigs such as sheep, cattle, goats cats and dogs. In those species the disease caused is nearly always fatal, but the virus is rarely shed and transmitted from such animals. Reports of horses contracting ADV are very rare

03/04/2022

https://fb.watch/c9qkhz2y3w/

18/11/2021

As a child, when the swine disease pseudorabies (Aujeszky’s disease) forced his father to sell all the family’s pigs and start over, Andrew Bents got the calling to become a swine veterinarian.

Today, he understands that weather conditions including fog, high winds and even thawing roads help contribute to the spread of swine disease, as he explains in a video produced as part of the Vets on Call series.

“It starts with biosecurity,” explains Bents, now a veterinarian with the Veterinary Medical Center in Worthington, Minn.

“Clean hands, clean hair and clean clothes help ensure that we’re not tracking disease from the outside into the barn,” he adds as he showers upon arrival at a nursery barn.

Checking the nursery pigs’ health status, Bents pauses to give a pig the “nose-to-tail assessment,” pointing out its nasal discharge, “hay fever”-looking eyes, drooping ears and rough hair coat. He recognizes an acute case of porcine epidemic diarrhea (PEDv) and administers the appropriate antibiotic treatment.

“In our quest to reduce antibiotics and take care of disease, we’re really being aggressive about diagnosing disease before it gets out of hand in the entire herd,” he explains.

After observing all the pigs in the barn, Bents stops to check the detailed treatment log kept on every animal receiving antibiotics. The log ensures that no animals are sold before the withdrawal time of the antibiotic is met.

“I know the care that producers take to make sure that if the animal is treated, it’s not going to market until we’re absolutely positive that the treatment has been metabolized and exhausted from the body,” he stressed.



Vets on Call is a video series presented by Zoetis to showcase the important roles veterinarians play in food-animal production.

25/07/2021

Treatment and prevention
There is no treatment although hyper-immune serum may protect piglets less than 4 weeks old in some countries. Control is by herd vaccination in countries where the disease is widespread and by prevention of re-infection where eradication has taken place. Vaccination is with live or killed vaccines made from virus lacking one of the glycoproteins or the thymidine kinase. These protect, and antibody to them can be distinguished in ELISA tests from that to wild type virus. Sow vaccination prevents abortion and disease in young pigs, but maternal antibody may prevent successful vaccination of piglets and 3 vaccinations, the last at 14 weeks of age may be needed to prevent disease in finishers. Serum antibody profiles determine the correct time to vaccinate a herd when antibody is absent. Aujeszky's disease has been eradicated by slaughtering herds containing infected animals or by vaccinating herds to reduce disease and then slaughtering pigs with antibody to wild type virus. Wind can spread virus for 2-17 km on land and 70 km over water, so eradication is best carried out on an area basis. Disease free stock, embryos and semen must be available and depopulated units must be disinfected or left empty for 10-12 weeks.

Special note
This disease is not transmissible to humans, but is notifiable in many countries, especially in the EU.

25/07/2021

Postmortem lesions
Post-mortem findings such as necrotic (dead) tonsils or nasal septum and turbinates (conchae) may indicate Aujeszky's disease. The characteristic intranuclear inclusions seen by microscopic examination are diagnostic, but occur in less than half the cases. Confirmation of disease is by laboratory tests for virus in tissues of infected pigs or for antibody in sera. Virus can be grown from the brain, spleen and lung of affected pigs, demonstrated in the tonsil or brain using a fluorescent antibody, immunoperoxidase, DNA probes, in situ DNA hybridisation and the Polymerase Chain Reaction, a DNA test which detects tiny amounts of virus especially in latent infections. The origin of virus can be determined and whether it belongs to wild or vaccine types. ELISA tests for serum antibody are used widely on recovered pigs and in herd diagnosis. They, too, can distinguish wild and vaccine type infections.

03/07/2021

03/07/2021

Postmortem lesions
Post-mortem findings such as necrotic (dead) tonsils or nasal septum and turbinates (conchae) may indicate Aujeszky's disease. The characteristic intranuclear inclusions seen by microscopic examination are diagnostic, but occur in less than half the cases. Confirmation of disease is by laboratory tests for virus in tissues of infected pigs or for antibody in sera. Virus can be grown from the brain, spleen and lung of affected pigs, demonstrated in the tonsil or brain using a fluorescent antibody, immunoperoxidase, DNA probes, in situ DNA hybridisation and the Polymerase Chain Reaction, a DNA test which detects tiny amounts of virus especially in latent infections. The origin of virus can be determined and whether it belongs to wild or vaccine types. ELISA tests for serum antibody are used widely on recovered pigs and in herd diagnosis. They, too, can distinguish wild and vaccine type infections.

Treatment and prevention
There is no treatment although hyper-immune serum may protect piglets less than 4 weeks old in some countries. Control is by herd vaccination in countries where the disease is widespread and by prevention of re-infection where eradication has taken place. Vaccination is with live or killed vaccines made from virus lacking one of the glycoproteins or the thymidine kinase. These protect, and antibody to them can be distinguished in ELISA tests from that to wild type virus. Sow vaccination prevents abortion and disease in young pigs, but maternal antibody may prevent successful vaccination of piglets and 3 vaccinations, the last at 14 weeks of age may be needed to prevent disease in finishers. Serum antibody profiles determine the correct time to vaccinate a herd when antibody is absent. Aujeszky's disease has been eradicated by slaughtering herds containing infected animals or by vaccinating herds to reduce disease and then slaughtering pigs with antibody to wild type virus. Wind can spread virus for 2-17 km on land and 70 km over water, so eradication is best carried out on an area basis. Disease free stock, embryos and semen must be available and depopulated units must be disinfected or left empty for 10-12 weeks.

03/07/2021

03/07/2021

03/07/2021

Clinical signs
Clinical signs in piglets under 4 weeks of age begin within 3-7 days of infection and they may vomit or show diarrhoea and become depressed, with fever (41.5˚C, 107˚F), trembling, in-coordination (including circling) the adoption of a dog-sitting position, spasms followed by prostration and death in 100% of newborn animals after 12 hours but only 40-60% die by 4 weeks of age. The disease lasts 4-8 days in animals aged 1-5 months. Anorexia (inappetence) with occasional vomiting occurs within 3 days of the onset of fever and from the 4th day, tremor and incoordination of the hind limbs progress to muscle spasms and to short convulsions followed by prostration and death in up to 15% of animals. Finishing periods may be extended by 10-14 days. Severe pneumonia has been recorded in weaned pigs in addition to the nervous signs described above. Infection in adults may be inapparent, result in transient inappetence or a rise in temperature accompanied by mild nervous and respiratory signs. Up to 50% of affected pregnant animals abort or give birth to mummified or macerated foetuses. Reproductive failure may follow. Semen quality may decline from 10-14 days post-infection for a period of 1-2 weeks.

Abortion, neonatal deaths, nervous signs in piglets and coughing and listlessness in finishing pigs spreading through a non-immune herd should suggest Aujeszky’s Disease. Clinical signs may be slight or undetectable in vaccinated, partially immune herds, breeding herds or those with finishers only. Pruritis and death in farm cats and dogs, cattle or sheep is a common early sign, as these species may also be affected. Confirmation of disease is by laboratory tests for virus in tissues of infected pigs, especially from tonsillar swabs, or for antibody in serum samples from whole or part of a herd.

03/07/2021

Measures to prevent infection of a herd in an area where the disease is endemic include isolation of domestic pigs from ADV infected feral pigs or wild boar, prevention of entry onto the premises of contaminated fomites, and potentially infected people and animals.

Modern eradication programmes involve measures such as use of vaccines, removal of latently infected animals, and quarantine. The use of blanket vaccination with inactivated (particularly in breeding animals) and modified live virus vaccines (in finishers) to control of disease, but not infection is no longer practised.

Today, a combination of modern genetically modified live deletion (gE, gC or gG) marker vaccines against AD and differential ELISAs to discriminate between vaccinated, ADV-uninfected animals from wild-type ADV-infected animals (DIVA strategy - test and removal) is the method of choice for eliminating ADV from domestic pigs

Depopulation of infected herds can be applied in the final phase of an eradication programme to facilitate achieving an AD-free status.

For measures to be taken to determine the AD status of a country or zone, and recommendations for importation of pigs for breeding, rearing and slaughter from countries and zones with different AD statuses see chapter Chapter 8.2., Infection with Aujeszky's disease virus of the OIE Terrestrial Animal Health Code

03/07/2021

Humans and apes are considered resistant against natural ADV infection (Jentzsch and Apostoloff, 1970). Although isolated reports describe putative infections of humans with ADV, this has never been substantiated by virus isolation (Kluge et al., 1999).

03/07/2021

In a cost-benefit study of the USA Aujeszky virus eradication programme, productivity and economic impacts were calculated for infected and non infected herds, including preweaning, nursing, grower and finisher pig mortality, breeding-herd mortality, feed conversion, layout and veterinary and biologic/pharmaceutical expenses. The study calculated that there was a US$ 6.00/hundredweight reduction of profitability due to Aujeszky virus herd infection (Anderson et al., 1989; Miller et al., 1996; cited in Kluge et al., 1999)

03/07/2021

Aujeszky’s disease virus (ADV) is shed via secretions (lachrymal fluid, preputial and vaginal secretions) and excretions (saliva, nasal discharge, urine, faeces). Hence, the disease can be transmitted by direct and indirect contact with infected animals. Oro-nasal, vertical (transplacental), and venereal (s*xual encounters) transmission are a result of direct contact. Within non-domestic swine ADV appears to be preferentially transmitted by the venereal route (Mettenleiter et al., 2012).

Indirect contact due to exposure with ADV aerosol created by exhalation of infected animals and contaminated urine, faeces, water run-off, fomites, slurry and feed/carcasses as well as artificial insemination (virus contaminated semen). Transmission between herds is mainly through the introduction of infected animals into an uninfected herd. The virus can rapidly spread through a naive herd. The manifestation of disease in a pig herd is affected by the herd's demographics, stage of farrowing, immunological status and husbandry conditions.

Depending on age and virulence of the prevailing ADV strain, incubation period in pigs can range between 1-8 days up to 3 weeks. There is a short incubation period of about 2-4 days in suckling pigs, whereas clinical signs in grower-finisher pigs occur after 3-6 days. The capacity of ADV to persist for the lifetime in their host in a latent state is characteristic with trigeminal ganglia, sacral ganglia and tonsils as the most common sites of latency. Hence, pigs may remain permanently infected without exhibiting clinical signs. However, clinical signs may be caused in latently infected animals as a result of immunosuppression, e.g. after episodes of stress, such as transport, and in over-crowded housing.

The virus is highly environmentally resistant depending on pH, humidity, and temperature (for details see Mettenleiter et al., 2012). Bedding and water can remain infected for several days after contamination with the virus. It can remain viable for up to seven hours as an aerosol in humidities over 55% and can travel up to 2 km (CFSPH, 2006).

ADV infections are widespread in populations of non-domestic swine across the world, in particular Europe and North America (for review see Müller et al., 2011).

03/07/2021

After oronasal infection of the natural host and primary replication in epithelial cells of the upper respiratory tract, the virus gains access to neurons innervating the facial and oropharyngeal area, in particular, the olfactory, trigeminal, and glossopharyngeal nerves. By fast axonal retrograde transport, it spreads centripetally and reaches the cell bodies of infected neurons, where either lytic or latent infection ensues. ADV is also able to cross synapses to infect neurons of higher order. Viremia disseminates it to many organs, where the virus replicates in epithelia, vascular endothelium, lymphocytes, and macrophages. Replication of ADV in the CNS is characterized by nonsuppurative meningoencephalitis causing severe central nervous disorders. Trigeminal ganglia, sacral ganglia, and tonsils are considered prime sites of latency in pigs. The demonstration of the sacral ganglia as the most common sites of ADV latency in feral swine supported the hypothesis that these viruses are primarily transmitted venereally and not by the respiratory route, as is common in domestic swine, in which the trigeminal ganglia are the predominant sites of virus latency. In nonporcine species, ADV is rather strictly neuroinvasive.

03/07/2021

Rapid detection of viral infection is essential for the effective control of AD. Clinical observations are only sufficient to lead to a suspicion of AD because the infection produces no pathognomonic clinical signs or gross post-mortem lesions in swine. Therefore, laboratory confirmation is required.

Viral antigen can be detected using immunoperoxidase and/or immunofluorescence staining with polyclonal or mAbs on impression smears and cryosections of tissues, for example, brain, lungs, and tonsils. Diagnosis is confirmed by virus isolation in conventional cell cultures requiring about 2-5 days. In the absence of any obvious CPE, blind passages should be performed. ADV can be isolated from secretions and excretions and from tissues, for example, brain, tonsils, lungs, and spleen, of infected animals. In latently infected pigs, the trigeminal ganglion and tonsils are the most consistent sites for virus isolation. As there is no CPE characteristic of ADV, and CPE may vary with the prevailing ADV strain and the cell line used, virus identity is confirmed by immunofluorescence, immunoperoxidase, or neutralization assays using specific antisera or mAbs.

Viral DNA can be detected by direct filter hybridization, DNA hybridization dotblot assay, ADV-specific PCR, nested and real-time quantitative PCR (qPCR) assays with the latter ones being the method of choice for detection of ADV in secretions or organ samples under routine conditions. Several conventional PCRs targeting genes encoding gB, gC, gD, or gE have been established, but there is as yet no internationally agreed upon standard.

According to OIE for routine testing, the virus neutralization (VN) test and ELISAs are standard reference serological test to detect ADV specific antibodies. Robust and sensitive indirect or competitive ELISAs detect antibodies against the complete ADV or against distinct viral antigens. The latex agglutination test (LAT) and immunoblotting are alternatives. VN and LAT are highly reliable but cannot differentiate between antibodies resulting from natural infection or vaccination. The development of ELISAs able to detect serum antibodies against gE (or gC or gG) allowed for the differentiation of infection from vaccination and led to the “marker” or differentiating infected from vaccinated animal (DIVA) concept. These ELISAs became a key part of AD eradication programs.

For more information on diagnostic tests for international trade purposes see the relevant chapter in the World Organisation for Animals Health’s (OIE) ‘Manual of Diagnostic Tests and Vaccines for Terrestrial Animals

03/07/2021

The presence and severity of clinical signs, as well as morbidity and mortality, depend on the age and immunological status of the pig. Furthermore, the route of infection and the virulence of the Aujeszky's disease virus (ADV) strain are important factors. In general, clinical signs manifest as neurological signs in young (sucking and weaned) and respiratory signs in older pigs. The disease is therefore more easily diagnosed in herds with both weaning or sucking and older pigs. Sow aborting is often one of the earlier signs of a herd being affected.

ADV infections in fully susceptible swine result in high morbidity and mortality, especially in juvenile animals in which meningoencephalitis and viremia-associated signs predominate. In neonatal pigs less than 7 days of age, the disease may be characterized by sudden death with few, if any, clinical signs. In 2- to 3-week-old piglets, severe signs of central nervous system (CNS) involvement, for example, trembling, incoordination, nystagmus, oposthotonos, epileptiform-like seizures, convulsion, tremor, ataxia, and paralysis, are seen with mortality up to 100%. Suckling pigs with neurological signs usually die within 24-36 h of onset of disease.

Older animals (3-6 weeks of age) may show neurological signs, but usually develop age-dependent resistance. Mortality may decrease to 50% by the fourth week of age and to less than 5% in 5-month-old pigs and even lower as the age of the infected pigs increases. Clinical signs can be present for 6-10 days. Animals may recover within a few days, but lose weight over the course of the disease. In finishing and fattening pigs, because of the population density, clinical signs can amplify and animals often die from secondary bacterial pneumonia. Signs in gilts and sows depend on the phase of gestation and include embryonic death, resorption of fetuses, mummified fetuses, abortion, or stillbirth, in addition to respiratory signs and fever. Pigs surviving a ADV infection become latently infected.

In the case of coinfections with other swine viruses, for example, porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2), and swine influenza virus (SIV), a severe and often fatal proliferative and necrotizing pneumonia (PNP) may develop in weaning and postweaning pigs.

03/07/2021

There are no AD-specific gross lesions in pigs, and changes are often absent or minimal. Gross lesions may occur in non-neural tissues, including lymphoid organs, and respiratory, digestive, and reproductive tracts. Particularly in young suckling pigs lacking passive immunity, multifocal necrosis is observed in these tissues, as well as in the liver, spleen, and adrenal glands. Typically, exudative keratoconjunctivitis, serous to fibrinonecrotic rhinitis, laryngitis, tracheitis, and necrotizing tonsillitis may be present. The CNS is free of gross lesions except for leptomeningeal hyperemia. Gross lesions in the upper respiratory tract are most common, including rhinitis with patchy epithelial necrosis and necrotizing laryngotracheitis, often in conjunction with multifocal tonsillar necrosis. Lesions in the lower respiratory tract may be pulmonary edema and scattered small foci of necrosis, hemorrhage, or bronchointerstitial pneumonia. However, the pulmonary lesions are less consistent and are composed of areas of reddening and consolidation scattered throughout the lungs, especially focused on the cranioventral lung lobes. Multiple, small foci (1-3 mm in diameter) of acute hemorrhagic necrosis characteristic of alphaherpesviral infections may be seen in the liver, spleen, lungs, intestines, adrenals, and placenta.

In sows, necrotizing placentitis and endometritis with thickened, edematous wall of the uterus are observed after abortion. Aborted fetuses may be macerated or, occasionally, mummified (stillbirth, mummified fetuses, embryonic death, infertility [SMEDI]). In fetuses or neonatal pigs, necrotic foci in the liver and spleen, lungs, and tonsils are common. ADV infection may also cause edema of the scrotal region.

03/07/2021

Aujeszky’s disease (also known as pseudorabies) is a viral disease of pigs that is endemic in most parts of the world. It is caused by Suid herpesvirus 1 (also known as Aujeszky's disease virus and pseudorabies virus), a member of the subfamily Alphaherpesvirinae and the family Herpesviridae. The virus infects the central nervous system and other organs, such as the respiratory tract, of a variety of mammals, but only pigs are able to survive a productive infection and are thus considered the natural host.

According to the World Organisation for Animal Health (OIE) Aujeszky’s disease is listed as a notifiable disease. Please see the AHPC library for further information on this disease from OIE, including the International Animal Health Code and the Manual of Standards for Diagnostic Tests and Vaccines

03/07/2021

Aujeszky’s disease (AD) is spread in domestic or wild swine and has an almost worldwide distribution, particularly in regions with high population densities of domestic swine. There are only a few regions where the disease has never been endemic in the domestic pig population, such as Norway, Australia, and most of the Southeast Asian islands. In recent years, strict implementation of national eradication programmes has resulted in virtual disappearance of the infection from domestic pigs in several parts of the world, e.g. Europe, North America and New Zealand.

The current dimension of the regional occurrence of AD in eastern and southeastern Europe, Latin America, Africa, and Asia is difficult to assess as information from those countries is often fragmentary, incomplete or even lacking. Recently, severe clinical outbreaks with high morbidity and lethality have been reported from China.

The distribution in the summary table is mainly based on information available from OIE or the European Union (EU). For current information on disease incidence, see OIE's WAHID database.

03/07/2021

Aujeszky’s Disease (AD) or Pseudorabies is a notifiable infectious disease of pigs. It is caused by a herpes virus and other species are also susceptible, for example, cattle, sheep, dogs and cats. It is not transmissible to humans.

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Covid-19
Please note, due to Covid-19, sampling for the Aujeszkys Disease Surveillance scheme outlined below was paused from April but sampling has now resumed. Private Veterinary Practitioners can begin AD blood sampling on-farm again while complying with the current Public Health Agency advice and the RCVS COVID-19 work place guidelines.

Surveillance scheme for Aujeszky’s disease
From 1st March 2013 a new surveillance scheme was phased in to ensure Northern Ireland maintains its status as an Aujeszky’s Disease free zone.
To maintain regional freedom from disease an annual surveillance of the national pig herd will be undertaken, which will require low level sampling of breeding herds up to a maximum of 14 pigs per separate epidemiological unit. This new sampling regime will commence on 1 March 2013. Those herd keepers who have completed a Monitoring Test in the past will have been notified when their next test is due.

Sampling of breeding pigs should be carried out by your nominated Private Veterinary Practitioner (PVP) on farm as before. Herd keepers of breeding units do not need to arrange additional sampling for their finishing pigs.

DAERA may, on the basis of a veterinary risk assessment, require additional samples to be taken e.g. samples from finished pigs at the point of slaughter. The relevant abattoirs will be notified in advance and these samples collected by their staff.

Samples must be tested at AFBI, Veterinary Sciences Division, Stoney Road, Belfast.

For further information contact:.0300 200 7840 – Epizootics Branch

Regional freedom
Following a presentation to SCoFCAH (Standing Committee on Food Chain and Animal Health) on 11th September 2012 , Member States voted unanimously on 2nd October to recognise Northern Ireland (NI) as a region free of Aujeszky’s Disease (AD). This follows a detailed submission to the European Commission in March 2012. The decision was formalised on 13 Nov 2012 (Decision 2012/701/EU(external link opens in a new window / tab)) when Ireland and Bolzano Province in Italy were also granted regional freedom at the same time. This will allow NI to trade on an equal basis with Great Britain and opens up new market opportunities further afield. All breeding and production pigs imported from regions which are not AD free will be required to meet additional health and certification requirements.

This is a very significant milestone for animal health in Northern Ireland and the culmination of a lot of work by Industry and various Divisions in DAERA, most notably Veterinary Service Audit and StanDAERAs Branch and Central Policy Group.

Current situation
The European Commission recognised Northern Ireland as free from Aujeszky’s Disease (Annex I status) at a vote on 2nd October 2012. This is the result of the dedication of a joint Industry / Government working group which has worked since 2004 to eradicate this disease from NI.

This decision was published in the European Commission’s Official Journal on 13 November 2012.

Annex I status allows for the export of pigs to GB and other Annex I listed regions without the previously required blood sampling regimes and provides further guarantees for pigs imported into NI.

Annex I status also opens up opportunities for trade in new markets.
Last reviewed 20 December 2012.

Clinical signs of Aujeszky's
Clinical signs and mortality depend on the age and immune status of the pigs affected and the strain on virus involved.

In summary the signs are:

Sows
coughing
fever
nervous signs
reproductive failure
abortions
mummified piglets
stillbirths
birth weak litters
Piglets
nervous signs
incoordination
sneezing
coughing
high mortality
low / poor viable piglets
Weaners & growers
fever
sneezing
coughing
pneumonia
nervous signs including incoordination and fits
some strains of the virus can cause severe respiratory disease and others severe rhinitis
usually low mortality
All other species – cattle, sheep, dogs and cats
nervous signs
death
Pig herd registration
Anyone who keeps pigs in NI is required to register with DAERA, including keepers of a pet pig(s). Applicants must register their holding with DAERA and make an application for a holding code.

A DAERA officer will then be in contact to progress the registration which includes an inspection of the proposed premises. An application form can be obtained by contacting your local DAERA office. Information on Pig Identification and Registration and Movement Recording can be accessed by clicking on the following link:

Animal identification, registration and movement
Pet pigs
Keepers of pet pigs are required to register with DAERA and obtain a holding code. An AD status will be applied to newly registered holdings and appropriate movement licences issued. Movement licences should accompany all pigs moving from registered pet holdings and a copy returned to the local DAERA office. Pet pigs which are being bred for sale will be subject to the same testing regime as commercial pig holdings. Pet pigs being moved will required to be identified as per the regulations.

Aujeszky’s Disease surveillance
The Aujeszky’s Disease Order (NI) 2012 and the Aujeszky’s Disease Scheme Order (NI) 2012 provide the legislative framework for Aujeszky’s Disease surveillance.

The Aujeszky’s Disease Order (NI) 2012(external link opens in a new window / tab)
Aujeszky’s Disease Scheme Order (NI) 2012 (external link opens in a new window / tab)
Aujeszky's disease eradication letter to herdkeepers

03/07/2021

This is an important disease of pigs caused by a herpes virus. The virus can remain hidden in nerves of the pig in a carrier state for long periods of time and then be reactivated. Once introduced into a herd the virus usually remains there and it can continually affect reproductive performance at varying levels. The virus can survive for up to three weeks outside the pig. Acute outbreaks of disease occur when virulent strains of the virus first infect an unvaccinated susceptible herd. The virus crosses the uterus and placenta and infects the foetuses.

The pig is the main host. Dogs and cattle may become infected, show nervous signs and die.

Similar diseases
When disease is first introduced into a susceptible breeding herd there are few other diseases except possibly swine fever that would be confused with AD. Once the disease has become chronic it could be confused with PRRS and chronic swine fever. Laboratory tests would be required to differentiate them.

Clinical signs
Sows
Coughing.
Fever
Nervous signs
Reproductive failure.
Abortions.
Mummified piglets.
Stillbirths.
Birth weak litters.
Piglets
Nervous signs.
Uncoordination.
Sneezing.
Coughing.
High mortality.
Low/ poor viable piglets.
Weaners and growers
Fever.
Sneezing.
Coughing.
Pneumonia.
Nervous signs including uncoordination, fits and meningitis.
Some strains of the virus can cause severe respiratory disease and others severe rhinitis.
Usually low mortality.
All other species
Nervous signs.
Death.
Acute disease
Acute outbreaks of disease occur when virulent strains of the virus first infect an un-vaccinated susceptible herd. The virus crosses the uterus and placenta and infects the foetuses. Often the first clinical signs are abortions, stillbirths and the birth of weak litters which soon die. Abortions may rise to 5 percent over about 6 weeks followed by reproductive failure at all stages of the cycle. Embryos are killed and absorbed and sows return to heat.

These reproductive problems may occur in up to 20 percent of dry sows. However these are not the only clinical signs seen in the herd. Dogs and cattle may become infected, show nervous signs and die.

Chronic disease
In an un-vaccinated herd, when the early acute phase of the disease is over and the herd has developed an immunity clinical signs are sporadic and milder. The signs may also be difficult to associate with an infertility problem because of their insidious nature. Depression of reproductive efficiency across all parameters is a feature of the chronic infection with increased levels of repeats, mummification, stillbirths and piglet mortality. Young carrier females that are stressed shed virus thus maintaining infection throughout the herd. Spread of infection in the breeding herd is low with immunity and infection waning and rising over one to two year cycles.

Carrier state
After the acute phase clinical signs of disease may die out altogether and this is often seen in small herds of less than 100 sows. Sometimes the virus itself may disappear. However it is more likely to persist in a few animals sporadically.

Diagnosis
When a susceptible breeding herd first breaks down with this disease the clinical signs described above strongly suggest Aujeszky's disease and are almost diagnostic. Laboratory tests are required to confirm the diagnosis. The common ones are as follows:

Fluorescent antibody tests on dead piglet tissues particularly tonsils. This is reliable and results are available in few hours.
Virus isolation from the lung and tonsils and its identification. This test is slow taking several days but may be done for added confirmation.
Blood tests (serology) to demonstrate rising antibodies take too long to be useful.
Causes
Movement of carrier pigs.
Airborne - at least 3km (2 miles).
Infection from feral (wild) pigs.
The role of mechanical spread by birds is questionable.
From contaminated carcasses.
Mechanically on people.
From contaminated vehicles.
Through infected semen via AI or a carrier boar.
From infected slurry.
Prevention
AD (PR) is a disease you cannot afford to live with.
Gilts and boars should only be purchased from known free herds and be vaccinated before arrival or in isolation.
Keep it out of the herd by isolating all purchased breeding stock and blood sampling them before they enter the herd.
Only buy from AD free herds.
If your herd is at risk, in other words within a 3km radius of large infected herds then vaccinate it to prevent disease.
Vaccination helps to prevent the establishment of the virus.
If you have AD, adopt strategies for eliminating disease as discussed in chapter 12.
Treatment
There is no treatment available but antibiotic medication to control secondary bacteria in a new outbreak could be considered such as:
600-800g of CTC or OTC in the breeding ration for 3-4 weeks as advised by the veterinarian.
Vaccination. This is the key action to take. As soon as disease is identified all breeding stock should be vaccinated with a gene deleted vaccine to mitigate the effects and reduce spread of the virus.