Diagnostic Approaches for Anthrax

Animals infected with anthrax usually die suddenly so it is very important to examine clinical signs before it’s too late. Usually, it is difficult to diagnose anthrax from simply clinical symptoms thus laboratory confirmation tests are necessary. Blood is usually preferred to diagnose anthrax. It can be drawn from the animal’s peripheral veins, mammary, ear, limb, or the blood collected in the nasal cavity, ideally without opening the infected animal. These blood samples are then tested for the presence of bacillus anthracis by:

  1. 1. Optical microscopy

For the animals that have died for <24 hours, the bacillus’s capsule is intact and can be observed. A thin smear of blood or tissue fluid, fixed with heat or absolute methanol, stained with polychrome methylene blue will be positive for anthrax if appear as short chains of blue-squared rods, enveloped by pinkish red capsule under the light microscope. If the animal is dead for more than 24 hours or bacillus is grown in the presence of oxygen which induces sporulation, the capsule might not be detected by staining, and a PCR or culturing is required for confirmation.

  1. 2. Culturing and identification of Bacillus anthracis

Bacillus anthracis can be cultured on nutrient or blood agar. After 24 hours of incubation, the colonies have the following characteristics that allow bacillus anthracis to distinguish from other bacillus species:

  •          – 3-5 mm in diameter
  •          – Flat or slightly convex
  •          – Comma-shaped projections from the colony head
  •          – Have tenacity
  •          – Non-hemolytic
  •          – Sensitive to penicillin and gamma phage

It is required to induce the production of a capsule if bacillus is cultured aerobically on nutrient agar. This can be done by allowing the bacteria to grow in a few ml of blood for a minimum of 5 hours. Alternatively, nutrient agar supplied with 0.7% sodium carbonate incubated in the presence of CO2, at 37°C also induce the production of the capsule. These encapsulated colonies appear mucoid and can be observed under an optical microscope.

  1. 3. PCR assay

PCR assays are done to confirm the presence of bacillus anthracis by amplifying its characteristic virulence and chromosomal marker-specific genes.

  1. 4. Rapid immunochromatographic test

It is a rapid, onsite diagnostic test for the detection of protective antigen constituent of anthrax toxins.

Treatment of Anthrax

Anthrax has a mortality rate of 90% and most cases are accompanied by the sudden death of the animal without the occurrence of observable signs. If the symptoms are observed at an early stage of infection animal should be immediately quarantined to prevent the spread of infection. Due to the shortage of time, the prognosis is not favorable, and early supportive and antimicrobial therapy is preferred. Ciprofloxacin and doxycycline are considered to be the most effective antibiotics against bacillus anthracis. Anthrax spores can take up to 60 days to become activated inside the body, so individuals who have been exposed to anthrax must take antibiotics for that duration. Veterinary Research Institute (VRI), Lahore prepared the anthrax vaccine in 2011. It was a live attenuated spore suspension vaccine from the F2 Sterne strain of bacillus anthracis, which was non-pathogenic, non-capsulated. The vaccine provided immunity for 1 year.

Control Strategies for Anthrax

If anthrax infection appears in any animal of a herd following are immediate steps:

  •     – Notify relevant district health authorities
  •     – Quarantine the animals (after vaccination, 2 weeks before movement off the farm, 6 weeks if going to slaughter).
  •     – Vaccinate other animals or humans in the surroundings
  •     – If the animal died of anthrax, the carcass should be properly sent for burial or incineration.
  •     – If the disposal of the carcass cannot be done at the death site, the carcass can be transported by placing it onto a formalin sprayed double thick         plastic on a low-loading trailer, packing all in plastic.
  •     – Surrounding spore contamination can be reduced by spraying with 5% of formaldehyde.
  •     – It is advised to remove the soil at the site of the anthrax carcass at the depth of 20cm and disinfect it with heat treatment or 12.5% of formalin           solution.
  •     – Materials or equipment at the site can either be incinerated with the carcass or decontaminated with formaldehyde with a minimum of 30                   minutes of contact time.

If formalin solution isn’t available for disinfection, 6% household bleach or 3% peracetic acid solution or autoclaving can also be used

References;

Canada, G. o. (2013). Cleaning and Disinfection of Anthrax-Contaminated Sites and Materials. Retrieved from Goveronment of Canada: https://inspection.canada.ca/animal-health/terrestrial-animals/diseases/reportable/anthrax/cleaning-and-disinfection/eng/1363954818609/1363954874392

WHO. (2008). Disinfection, decontamination, fumigation, incineration. Retrieved from NCBI: https://www.ncbi.nlm.nih.gov/books/NBK310477/

DGHS, P. a. (2015). Guidelines for Prevention and Control of Anthrax. Lahore: Communicable Disease Control Wing.

Weiss, S. (2011). Antibiotics Cure Anthrax in Animal Models. NCBI.