Neurological Conditions

Introduction

The importance of neurological conditions in pigs will relate to the purpose for which they are being kept. In commercial herds contagious and infectious neurological diseases are very important. In small pig herds management causes of neurological conditions, e.g. water deprivation leading to salt poisoning, will be important. Individual pet pigs kept until they are very old may suffer from brain tumours. Practitioners must have at the forefront of their minds that whatever type of pig is being examined may have neurological signs which are either primary or secondary to notifiable diseases.

The predominant signs

These are best observed before handling. They include: abnormalities of gait including high stepping, abnormal posture, aural discharge, circling, convulsions, facial paralysis, flaccid tail, head tilt, hyperaesthesia, lack of pedal withdrawal, loss of balance, mania, nystagmus, ocular discharge, opisthotonos, paddling, recumbency, stupor and tremor.

Diagnosis

This will rely on an accurate history and on accurate observation. Certain conditions will be age related. The condition of the skin and the rectal temperature will be useful.

Neurological Diseases Caused by Viruses

African swine fever

The virus enters the pig via the upper respiratory tract and after multiplying travels up the olfactory nerves to the CNS. There is venereal spread. Some strains will cause respiratory disease. Animals will start shedding virus within 2 days of infection. This may continue for 3 weeks.

Morbidity and mortality may reach 100% in suckling piglets. Mortality in fattening pigs may be as high as 15%. Often adults show only mild pyrexia but 50% may abort. Normally mortality in adults is under 2%. The virus causes infertility in boars.

Often there are no gross pathological findings. In piglets there may be small petechiae in the lymph nodes and the kidney. There may be congestion in the meninges and an excess of CSF. There may be a few white necrotic foci in the tonsils. In the respiratory form there will be lung involvement. Boars may have one testicle enlarged. Aborted piglets will have yellow necrotic foci in the liver. The placentae may appear normal but histology will reveal necrotic lesions and inclusion bodies. The main histological findings are in the CNS.

The disease will spread with the introduction of carrier animals. It will also spread by aerosol for a mile or so. Greater distances have been recorded. It may be spread in semen, fomites and rodents. Wild boar may be a reservoir of infection. It may cause death in other species e.g. cats, dogs, sheep and cattle. Pruritis is marked in other species.

Diagnosis may be confirmed by FAT on frozen tonsil tissue. Serology will indicate past infection. Meat juice may be used as a screening test.

There are various live and dead vaccines available. They are not now used in the UK or in the rest of the EU or the USA.

Bovine spongiform encephalopathy

Bovine spongiform encephalopathy (BSE) has been experimentally induced in pigs but it cannot be transmitted by feeding either infected bovine brain or scrapie material obtained from sheep.

Classical swine fever