Introduction

• Cause: anthrax is caused by the gram positive bacilli, bacillus anthracis. 
• Signs: see below. 
• Diagnosis: polychrome methylene blue stained blood smears demonstrating the presence of gram positive bacilli.
• Treatment:
  • Severely ill animals are unlikely to recover.
  • Treatment with Procaine penicillin has been reported. 
• Prognosis: the disease is invariably fatal.

Pathogenesis

Etiology

• Anthrax is caused by the gram positive bacilli, Bacillus anthracis Bacillus anthracis.
• This bacteria has three virulence factors which aid in disease pathogenesis, a poly-D-glutamic capsule which confers resistance to phagocytosis and lethal and edema toxins.  
• The bacteria forms highly resistant spores which can survive decades in the environment. 

Predisposing factors

• Grazing specific “anthrax zones”, with high concentrations of anthrax spores in the soil.
• Drought following heavy rainfall and excavations which may unearth infected carcasses.
• Scavenging animals may spread spores.
• Insect bites have been shown to transmit anthrax through mechanical transmission. 

Pathophysiology

• Exposure of animals primarily occurs from grazing contaminated pastures and ingestion of spores.
• Forage grown on contaminated pastures, animal by-products, pica behaviour and scavenging carcasses in Phosphorus Phosphorus deficient cattle are also potential sources of infection.
• Following ingestion spores infection may occur across intact mucus membranes, through defects from erupting teeth or via scratches inflicted from tough, fibrous food.
• The organism resists phagocytosis, proliferates in regional lymph nodes and via the lymphatic vessels into the bloodstream inducing massive septicemia, tissue damage and in the majority of cases, death.

Timecourse

• The incubation period is not easy to determine but is probably 1-2 weeks.

Epidemiology

• Infection commences with the introduction of an infected animal or animal products into an area.
• When the animal dies putrefaction will destroy the bacteria providing the carcass is not opened.
• However, secondary cases can be spread extensively if the animal is still mobile before death, allowing infection to become established within a specific area. 
• One well established risk factor is the movement of hides and skins which are contaminated with Anthrax spores in ships holds which are then used to carry animal food. This can result in multiple deaths in animals on different farms ingesting the spores.

Diagnosis

Treatment

Prevention

Outcomes