Monograph

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definition: 

Other name: pseudorabies

Contagious disease caused by a herpesvirus mainly affecting pigs, but also carnivores, ruminants and horses.

Situation in America: 

Worldwide geographical distribution, especially in those countries where pig farming is significant. Declaration to the OIE by the following countries (in 2004): Brazil, Columbia, Costa Rica, Cuba, Mexico, Panama, USA. Few outbreaks and low level of infection, difficult to calculate.

Susceptible species: 

Pigs, wild boars, dogs, cats, bovines, ovines, horses.

Humans are not susceptible to the disease.

Etiological agent: 

A DNA enveloped virus from the Herpesviridae family, a sub-family of Alpha-herpesviridae: type 1 porcine Herpes virus.

A neurotropic virus that also causes respiratory and genital tropism in pigs. Lytic infection cycle < 24h. Ability to establish latent infection in the nervous system.

Stable between 4 and 25°C and at a pH of 6-8. Sensitive to classical disinfectants. May remain virulent in the outside environment for several weeks.

Methods of transmission
Source: 

Only pigs and wild boars already infected or healthy carriers are reservoirs for the disease. In these species the infection is perennial and is often not apparent. Vaccinated animals may also act as reservoirs by carrying the virus. Other species are "epidemiological dead ends".

Virulent matter: Oronasal (possible aerosols) and genital secretions, semen, milk, carcasses, offal and meat (risk for domestic carnivores).

 

Receptivity and susceptibility factors

• Species: pigs are very receptive but less susceptible than other species, in which death occurs rapidly.

• Age: affects mainly the young (applies to pigs only).

• Stress: end of the latency phase, viral excretion favored.

Transmission: 

Direct: "from snout to snout", through covering, suckling.

Indirect:

• On the farm through equipment, feed, coughing, etc.

• Over a long distance through contaminated equipment, aerosols/wind (1-2km), swill, etc.

Method of contamination: 

• Pig: mainly oronasal or genital

• Carnivores: ingestion of raw pork meat or offal.

• Ruminants: air-borne during cohabitation with pigs affected by the respiratory form of the disease.

Symptoms: 

Short incubation period: 2-5 days.

Pig:

In its clinical form, the disease progresses differently according to age and sex. In young pigs under 3 months old, the nervous system is affected. Animals for fattening suffer from the respiratory form and reproductive disorders occur in sows.

Piglets less than 2 weeks old: fever (>41°C), meningoencephalitis (trembling, convulsions, paddling) death occurs in only a few hours.

Piglets from 2 weeks to 3 months old: fever, inappetence, meningoencephalitis (hyperesthesia, convulsions, pharyngeal paralysis). Convalescence with retarded growth or death.

Fattening pigs: flu-like respiratory symptoms (cough, dyspnea, sneezing), general state of health affected (exhaustion, inappetence, fever). Significant retarded growth, rarely death.

Sows: inappetence, casting, stillbirth in the whole or part of the litter.

Wild boars: asymptomatic form the most often.

Other species:

Clinical presentation of encephalomyelitis (pseudorabies) with pharyngeal paralysis.

In carnivores and ruminants: intense pruritis, at the virus inoculation point. Rapidly evolves towards death (48h).

Cats: frequently infected. Inconstant pruritis, encephalomyelitis, lethargy, non-aggressive anxiety, paralysis of the pharynx, ptyalism, anisoscoria, rapid death (6-48h).

Dogs: ditto + self-mutilation of the mouth.

Ruminants: ditto + mastication.

Horses: absence of pruritis, as in pigs.

Lesions
Macroscopic lesions: 

Absence of characteristic lesions. In piglets under 10 days old, small patches of whitish necrosis in the spleen and liver.

Microscopic lesions: 

Viral encephalomyelitis lesions with neuronal necrosis, accumulation of glial cells, intranuclear inclusion.

Diagnostics
Clinical diagnosis: 

Suspicion on casting, on high death rates in piglets showing signs of meningoencephalomyelitis, on respiratory difficulties in fattening pigs and on observation of cases in carnivores (dogs, cats) and farm ruminants (indicative).

Differential diagnosis: 

In pigs, Aujeszky's disease must not be confused with:

Reproductive disorders: classical swine fever (chronic form), erypsela, reproductive and respiratory syndrome, parvovirus infection, leptospirosis, brucellosis, SMEDI virus infection

Nervous disorders: classical swine fever (slower progression, all ages are affected), pig contagious paralysis, sodium chloride intoxication, rabies.

Respiratory disorders: enzootic pneumonia, porcine influenza, reproductive and respiratory syndrome.

In other species, possible causes such as infectious encephalomyelitis should be considered, and especially rabies (rapid progression, aggressively), intoxication, etc.

Laboratory diagnosis: 

Virological diagnosis: by isolation of the virus in cell cultures and determination of the cytopathic effect and identification by seroneutralisation or immunofluorescence. Possibility of PCR testing.

Samples to be taken from pigs: brain, tonsils, whole pig, stillborn foetuses, nasal swabs.

In other species, brain and tonsils. In ruminants, the spinal cord can be taken from the region affected by pruritis, where the symptoms are not situated in the head region.

NB: process samples as for a suspected case of rabies.

Serological diagnosis using an ELISA test. Antibodies can be detected one week after infection. This test cannot therefore be carried out in pigs. Differential ELISA tests can be carried out to distinguish vaccinated animals (deleted vaccines) from infected animals.

Blood tests: either 2 blood tests 10 days’ apart (kinetic study) or once only 10 days after the appearance of symptoms.

Treatment: 

Absence of any specific treatment.

Prophylaxis: 

Sanitary prophylaxis

In a disease-free or low-contaminated zone: basic hygiene + introduction of serologically controlled animals from disease-free farms. Vaccination proscribed.

Medical-sanitary prophylaxis

In contaminated zones, combination of vaccination + sanitary precautions

Pure-bred pigs:

- If the level of infection is low (<20%): regular serological detection and rapid slaughter of positive cases. Interruption as soon as 2 negative tests at 2-3 months interval are obtained for all pure-breds

- If the level of infection is high (>20%): total slaughter or medical-sanitary prophylaxis (vaccination).

Fattening pigs: Cleaning/disinfection after fattening.

Other species: avoid all contact with pigs, do not feed domestic animals raw pork meat or offal.

Vaccines: 

Vaccination does not stop any latent or asymptomatic infection occurring. It offers clinical protection and significantly reduces virus excretion in case of infection.

Two types of vaccine are available: Inactive or attenuated live virus vaccines. Both can be produced from deleterious viruses. They enable vaccinated animals to be distinguished from infected animals.

In sows, the vaccination aims to protect piglets via the colostrums. Only use inactive vaccines.

For fattening pigs, both types of vaccine can be used.

In general, only pigs are vaccinated, but only under certain circumstances. Ruminants and carnivores can be vaccinated with inactive vaccines (use outside MAA).


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