Anthrax clinical guidelines for veterinarians
Veterinarians investigating a suspected anthrax case must take strict precautions to avoid potential personal infection and infection of others.
Clinical signs
The first indication of anthrax in grazing animals is often the report of sudden deaths by the livestock owner.
If animals survive long enough, clinical signs may include:
- weakness
- staggering
- laboured breathing.
Post-mortem signs include:
- blood-stained discharges from external orifices (not always present)
- rapid carcase decomposition
- unclotted blood oozing from orifices and predator wounds (for example, eyes and skin).
Cattle and sheep
Per-acute cases
- Sudden death within 1–2 hours of illness
- Muscle tremors
- Respiratory distress
- Terminal convulsions
- Possible dark, sticky blood discharges
Acute cases
- Disease course is approximately 48 hours
- High temperature (up to 42°C)
- Rapid, deep respirations
- Severe depression
- Congested, haemorrhagic mucous membranes
- Tachycardia
- Anorexia and rumen stasis
- Sudden drop in milk yield (milk may be yellow and blood-stained)
- Abortions
- Diarrhoea or dysentery
- Local oedema (tongue, throat, perineum)
Pigs
- Death within 12–36 hours (acute cases)
- High fever
- Dullness
- Anorexia
- Non-painful oedema (face, throat)
- Impaired swallowing and respiration
- Petechial haemorrhages
- Dysentery without oedema
Horses
Ingestion route
- Death in 2–3 days
- Septicaemia
- Enteritis
- Severe depression
- Colic
- High fever
Wounds or insect bites
- Death in 2–3 days
- Hot, painful oedematous swellings (throat, neck, ventral abdomen)
- Severe depression
- High fever
Dogs and cats
Generally resistant, but susceptible via scavenging.
Pathological signs
If the carcase is opened, pathological signs of anthrax may include:
- oedema
- petechial or ecchymotic haemorrhages on serosal surfaces
- unclotted blood in large veins
- enlarged haemorrhagic spleen (characteristic of anthrax).
Differential diagnosis
When investigating sudden deaths, consider other possible causes, including:
- clostridial diseases (for example, pulpy kidney, black disease, blackleg, malignant oedema)
- Hendra virus infection in horses
- acute leptospirosis
- tick fevers
- salmonellosis
- acute bloat
- hypomagnesaemic tetany
- per-acute chemical poisoning (for example, lead, arsenic)
- toxic plants (for example, bracken fern, Myoporum species)
- snake bites
- lightning strikes.
Necropsy
Do not start or continue a necropsy if anthrax is suspected.
- In unopened carcases, Bacillus anthracis does not sporulate and is destroyed by putrefaction.
- If the carcase is opened, bacteria are exposed to air, form spores, and can contaminate the environment for decades.
Signs of anthrax during necropsy
If the animal died from anthrax, the following may be observed:
- Carcase meat appears fevered and oozes fluid
- Blood fails to clot
- Ecchymotic haemorrhages throughout the body tissues
- Body cavities contain blood-stained serous fluid
- Severe enteritis
- Spleen is grossly enlarged, soft and liquefied
- Subcutaneous swelling is jelly-like, with enlarged local lymph nodes (especially in horses and pigs)
If anthrax is suspected during necropsy
- Stop the necropsy immediately.
- Prevent further contamination of the area.
- Confine all materials for decontamination and destruction.
- If your personal protective equipment (PPE) is inadequate for anthrax:
- Follow the personal disinfection process
- Put on appropriate PPE.
- Collect samples to confirm or exclude anthrax.
Conducting a necropsy
If anthrax is less likely (based on the animal's history or movements) but still a possibility due to sudden death and clinical signs:
- Wear PPE before proceeding.
- Position the carcase so the left side faces up and is accessible to you.
- Make an incision behind the last rib through the body wall.
- Use a wire hook or similar tool to lift the rib and expose the spleen, viscera and abdominal fluid.
Take care if the carcase is bloated to avoid infected material blowing back onto you.