Special Veterinary Pathology

TETANUS

Synonym : Lock jaw

Definition

• Acute fatal infectious disease of man and animals characterized by involuntary contraction of voluntary muscles caused by toxins of Clostridium tetani

Aetiology

• Clostridium tetani
• Exotoxin - CI. Tetani - Gram positive sporulating rod shaped anaerobe, Spores – “Drum Stick”

Incidence

• Tetanus occurs in all parts of the world

Susceptibility

• Hores and mules are susceptible

Transmission

• Wound infection

Pathogenesis

• Incubation period : 1 to 3 Wk
• The organisms enter the body through the nail prick, castration, docking, shearing, umbilical wound (tetanus neonatorum) or during parturition
• Anaerobic condition allows germination of spores and release exotoxin

Three toxins

• Haemolysin – Tetanolysin – Not important
• Neurotoxin -tetanospasmin- responsible for the nervous symptoms
• Fibrinolysin- not very potent
• Toxin gets fixed to a substance called "protagon” which act on the inhibitory synapses interferes with action of transmitter thus producing spastic action -spasmodic contraction
• The toxins causes hyperirritability responsible for the tetanic spasms
• The toxin causing spasmodic contraction of muscles, stiffness and immobilization.

Clinical signs

• Involuntary, persistent, intense painful contraction of one or more group of muscles.
• Horse- Stiffness and moves like 'wooden horse'.
• Raised Tail, third eyelid Protrusion, and Stiffness of Jaw muscle -‘ Lock Jaw’
• Ruminants – Symptoms are less severe

Gross lesion

• No characteristic lesion
• Death due to Toxaemia

Microscopic lesions

• No specific microscopic lesions. Degeneration of the neurones in the brain and spinal cord (due to anoxaemia)

Diagnosis

• Characteristic clinical signs.
• Organisms are local but not septicaemic
• Demonstration of toxin in the serum