Anthrax occurs worldwide, notifiable in many countries. It affects pigs of all ages and there is also a human risk. The effects of the disease are illness, fever, bloody diarrhoea, swollen neck, breathing difficulty, death.
Causes of Anthrax
The organism usually causes disease at the point it actually enters the body of the pig (tonsil or intestine) but can invade the blood to causes septicaemia. Organisms resist attack by the white cells of the body by means of a capsule of polyglutamic acid which is present around the cell and cause disease by means of 3 powerful toxins.
The affected tissue become inflamed, filled with bloodstained fluid and swells. When septicaemia occurs, the infection often results in death. B. anthracis may be shed in urine and faeces and in discharges or in blood from dead animals and may remain for a period in lymph nodes of recovered pigs.
Recovery and solid immunity may occur but damage to the skin over affected areas of the neck may remain in some cases. Anthrax bacilli can infect man through scratches and cause local blackened abscesses or in dust by aerosol to give pneumonia or by eating infected meat. It can be fatal.
Effects of Anthrax
When the infection localises in the intestine (intestinal form), fever, digestive disturbance, loss of appetite and the passage of bloody faeces may be seen. Death is uncommon in this form. When the organisms cause septicaemia (septicaemic form), pigs may be found dead. Others in the group may have transient fever and recover completely or develop the intestinal form or have swollen necks.
Diagnosis of Anthrax
If anthrax is suspected, the carcass should not be opened and a blood sample should be taken from an ear or tissue fluid taken from the swollen neck for laboratory examination by a state veterinarian. Anthrax is often first suspected following post-mortem examination.
In the pharyngeal form there is massive enlargement and reddening of the cervical lymph nodes which are surrounded by gelatinous oedema fluid.
In the intestinal form, copious peritoneal fluid may be present and there may be blackened infarcted areas in the spleen, thickening of the intestinal wall, swollen mediastinal (intestinal) lymph nodes and adhesion between pieces of intestine. The intestinal lining may be covered with necrotic (dead) tissue.
In the septicaemic form, the carcass and its lymph nodes may be reddened, the spleen enlarged, and the kidneys petechiated (spotted with blood). Laboratory confirmation is by demonstration of the organism with its characteristic capsule in smears made safe by fixation and by culture of blood, oedema fluid or an affected organ.
Treatment & Control of Anthrax
The affected farm is usually isolated while the disease is controlled. Affected pigs are treated or killed. The bodies of dead affected pigs should be incinerated or buried unopened as exposure to the air allows the resistant spores to form. All areas in contact with the carcasses should be disinfected using an approved disinfectant which can kill the spores. Slurry from the affected pigs should be disinfected and disposed of safety.
In the longer term the Anthrax Spore Vaccine can protect pigs from the disease. Recent improvements in food safety mean that meat plants are unwilling to accept pigs from anthrax infected herds and the whole herd may have to be slaughtered, thus increasing the significance of the disease for the pig industry.
The disease usually enters in contaminated meat and bone meal, but the organisms are so rare in traded product, that measures to prevent disease are not worthwhile in most pig-rearing countries.
