Anthrax: Guidelines for vets

This guide is for veterinarians who are asked to investigate suspect cases of anthrax in animals. Situations may also occur where anthrax is considered as a differential diagnosis during the course of a routine investigation into livestock deaths.

Anthrax is caused by a bacterium, Bacillus anthracis. When exposed to the air, the bacteria form resistant spores that can remain viable for at least 50 years when buried in the soil. Anthrax is a zoonosis and people can become ill and die from this disease (anthrax in humans is notifiable to Queensland Health). Therefore disease investigations require specific sampling procedures, carcass disposal, site decontamination and careful attention to the safety of all people involved.

If anthrax is confirmed as the cause of death of livestock, the control of the outbreak will be handled according to the AUSVETPLAN for anthrax.

Background

Anthrax was first introduced into Australia in 1847 near Sydney, and spread along stock routes throughout New South Wales and southern Queensland. Occasional outbreaks have occurred since then in South Australia, Victoria and Tasmania. Routine quarantine with vaccination on and around infected premises was adopted in the 1890s and has been very successful in controlling the disease.

In 1993, one infected animal was detected in Queensland on a farm north of Rockhampton. This was geographically distant from the areas of historical outbreaks and was apparently due to contaminated feed. In 2002, anthrax occurred on a property in southern Queensland near the New South Wales border and further cases occurred in cattle moved from the index property to another property some 400 km north.

Anthrax spores that have been long buried in the soil may be exposed after heavy rainfall or earthmoving such as that undertaken in road building or dam excavations.

Health and safety

Anthrax has occurred rarely in humans in Australia. In the 1920s and 1930s, cases were associated with infected shaving brush bristles. A number of people died from this source of infection since there were no antibiotics available at that time. In the early 1960s, a farm worker in New South Wales contracted cutaneous anthrax after conducting autopsies on dead sheep. The worker refused early medical treatment and died from the disease. Human cases have become less common over time, reflecting the reductions in animal cases.

A veterinarian investigating a disease situation where anthrax is a possible diagnosis must take precautions to avoid potential personal infection or infection of other people.

Livestock owners should be advised of the human health risks. All people on the property should be instructed to keep away from the carcase and any contamination from it, unless appropriate personal protective equipment (PPE) is worn and appropriate decontamination conducted afterwards.

Anyone who has been exposed to a suspect case of anthrax should seek urgent medical advice. They should contact a doctor or local Queensland Health population health unit.

Clinical and autopsy signs of anthrax in animals

The first indication that grazing animals may have anthrax is usually when sudden deaths are reported. If they survive long enough, clinical signs of weakness, staggering and laboured breathing may be observed. Blood may be seen in the urine and milk of affected animals.

Pigs affected by anthrax are usually seen to be ill as they tend to survive longer than grazing animals. Dogs and cats are generally resistant to anthrax.

After death, blood-stained discharges at external orifices are characteristic of the disease but not all anthrax cases show these signs. There is rapid putrefaction of the carcass and the blood may fail to clot, continuing to ooze from orifices and where predators have attacked the carcass e.g. eyes and skin.

If the carcass has been opened, the pathological signs of anthrax are oedema, petechial or ecchymotic haemorrhages on the serosal surfaces and unclotted blood in the large veins. An enlarged haemorrhagic spleen is characteristic of anthrax.

Field investigation

Anthrax is a notifiable disease and any person suspecting anthrax in an animal is required to notify Biosecurity Queensland immediately.

If a dairy farm producing milk for human consumption is involved, Safe Food Production Queensland should be informed immediately as the milk will have to be withheld while investigations proceed.

Wherever possible, a Biosecurity Queensland veterinary officer will investigate suspect cases of anthrax in animals. However, a private veterinarian may be requested to investigate. In some situations private veterinarians may be obliged to investigate animal deaths before it is possible to contact Biosecurity Queensland.

A full disease investigation must be conducted and a report submitted. The following must be recorded:

• property information including the property identification code (PIC) and, if applicable, the Safe Food Production Queensland accreditation number
• a full history of the property and animals concerned
• any cattle that have recently entered the food chain
• all clinical signs shown by any ill animals
• pathological changes shown by dead animals.

The danger with anthrax is that the bacteria can form spores that will stay in the environment for many decades as a source of infection. The following precautions are essential:

• do not drive your vehicle close to the carcass
• record the GPS coordinates of the carcass
• do not walk in discharges from the carcass
• do not contaminate your vehicle with carcass material
• do not open the carcass
• do not move the carcass.

Equipment

• overalls
• gloves
• face mask
• eye protection
• rubber boots
• disinfectant
• bucket, scrubbing brush etc. for decontamination.

Sampling and packaging materials required per animal are:

• glass slides
• scalpel blades
• syringes
• blood containers
• a sealable container for blood smears
• clip-seal bags
• 50 mL containers for soil samples
• marker pen
• Esky and ice brick for transporting samples.

Disinfectant

Personal disinfection

Prevention of skin contamination by using full PPE is the best option as there are no appropriate disinfectants registered for use on skin.

If skin contamination occurs, thorough washing with soap and water will remove anthrax organisms and significantly reduce the possibility of infection. Water used for washing should be contained to a small area and this area must be disinfected with gluteraldehyde or formaldehyde at a later time. A doctor or local Queensland Health population health unit should be consulted as a precaution.

Equipment and clothing disinfection

Virkon will kill the anthrax organism and is registered in the UK for use against spores. It should be used at 1:120 dilution and a 30-minute wet-contact time allowed. It is not registered for use on skin.

Gluteraldehyde at 4% (e.g. 200 mL 'Microcide' per 5 L of water) is a suitable disinfectant for clothes and equipment. Exposure should be for four hours. It is not for use on skin. Care needs to be taken in its use. The label directions or Safety Data Sheets (SDS) must be followed.

A 5%-formaldehyde solution is suitable for disinfecting equipment. Take care when using formaldehyde or formalin and follow the label's instructions or SDS.

Conducting or continuing an autopsy

If you suspect anthrax, DO NOT UNDERTAKE AN AUTOPSY. In the unopened carcass, anthrax bacilli do not sporulate and are destroyed by the putrefactive process. Collect samples to exclude anthrax.

When there is less likelihood of anthrax because of the animal's immediate history or movements, but a suspicion of anthrax still exists because of a history of sudden death and appropriate clinical signs, protective clothing must be worn before proceeding. The carcass should be placed with the near (left) side uppermost and an incision made behind the last rib through the body wall. Lift the rib with a wire hook or similar tool to expose the spleen, viscera and nature of any abdominal fluid. This must be done with care if the carcass is badly bloated to prevent infected material blowing back onto the operator.

If an autopsy is carried out in unawareness, and the animal has died from anthrax, the following signs will be seen:

• the carcass meat will look fevered and ooze fluid
• blood fails to clot
• ecchymotic haemorrhages are present through the body tissues
• body cavities contain bloodstained serous fluid
• there is severe enteritis
• the spleen is grossly enlarged, soft and the structure liquefied
• any subcutaneous swelling are jelly-like and local lymph nodes enlarged. This particularly applies to horses and pigs.

If the carcass is opened, the bacteria form spores on exposure to air and can contaminate the environment around the carcass for many years. If the carcass is already opened when anthrax is first suspected, the autopsy should be ceased immediately and further contamination of the surrounding area prevented. All materials should be confined to a small area for decontamination and destruction.

If the PPE being worn is inadequate for anthrax, personal disinfection should be immediately undertaken as set out above and more suitable PPE put on to complete sampling.

A doctor or local Queensland Health population health unit should be consulted as soon as possible if anthrax is suspected, particularly if a skin injury or needle stick injury has been sustained while conducting the examination and sampling.

Samples

A blood smear and a blood sample are preferred. A blood smear is usually best obtained from the ear or the tail. A small stab is made in the skin with a scalpel blade and a small volume of blood is collected using a syringe. The puncture site should be covered with a swab soaked in a suitable disinfectant. One drop of the blood is used to make a blood smear on a slide which is air-dried and packed securely in a closed container. The remainder of the blood should be place in a secure blood tube. All the samples should be placed in a plastic bag or container and sealed. The outside of the container should    be disinfected.

If it is not possible to collect from these sites, blood may be extracted from the jugular or brachial veins or as a last resort any other bloody exudates. Any puncture site should be treated with a suitable disinfectant e.g. a cottonwool swab soaked in formalin.

If other tissue samples are collected for differential diagnoses, these samples should also be collected and packaged as above.

If it is not possible to collect suitable blood samples, environmental (soil) samples should be collected from the ground at the nasal and anal areas of the carcass i.e. where the discharge has contaminated the soil. Around 50 g of soil from each site should be placed in sample containers. These are then placed into plastic bags, sealed and the outside disinfected.

Used sampling materials (syringe, tissues, pipettes etc.) should be placed in a container with disinfectant for later disposal. Disinfect the outside of this container and put aside for later removal.

All samples must be fully identified and double-bagged.

Transporting samples

The samples above should be placed in a transport box that will contain any fluids and materials from breakage of slides or bottles. Decontaminate the outside of the box.

Laboratory submission forms should be placed in an envelope and attached to the outside of the box.

Contact the laboratory to warn them that suspect anthrax samples are being submitted.

As anthrax is a human pathogen, particular care should be taken to ensure that all statutory requirements are met for transporting specimens. Specimens should be packed and labelled for transport in compliance with the carrier's conditions, government and postal regulations and International Air Transport  Association (IATA) regulations as appropriate.

Sharps must not be forwarded with the samples - they should be disposed of in a sharps container. This may be burnt with the carcase along with other equipment.

Site decontamination and carcase disposal

Animals that have died from anthrax should be disposed of under the control of Biosecurity Queensland officers. It is critical to minimise the contamination of the area and the persistence of spores in the soil. It is now known that anthrax spores on the surface of the soil are far more easily destroyed than spores buried below the soil surface.

Advice should be sought from the Department of Natural Resources, Mines and Energy regarding the contaminated site. The site should be permanently identified and a GPS reading recorded.

Burning is the preferred way to dispose of infected carcasses. This should occur where the carcass is situated and as soon as possible. Any people assisting with the operation must be made aware of the risks to human health and the precautions necessary while preparing for burning the carcass. As a    final measure, the area of contaminated soil should be decontaminated by the liberal use of a 5% formaldehyde solution at the rate of 5 L/m². It is necessary to wet the soil sufficiently to keep it moist for 12 hours. Care must be taken in using formaldehyde or formalin as per the label instructions or SDS sheets.

If burning is not possible:

• bury carcasses with a soil-coverage depth of at least 1 m, preferably 2 m
• liberally treat the carcass with quicklime (pH 11 - 13)
• permanently identify the burial site by recording a GPS reading
• decontaminate surface soil using a 5% formaldehyde solution as above.

Where burning or burial is delayed or not appropriate, an alternative approach is to leave carcasses where they are, intact, to undergo natural putrefaction. They must be protected from scavenging by wild animals by an appropriate fence or barrier. Both the carcass and the surrounding soil must be decontaminated with 5% solution of formaldehyde as above.

On no account should any animals suspected to have died from anthrax be transported to a knackery.

Personal decontamination procedure

The routine for personal decontamination should be as follows:

• At all stages of personal decontamination, it is important to avoid contamination of the skin.
• While standing on the contaminated site, gross contamination (mud and grass) should be removed from boots and placed with the carcass.
• Disposable overalls, masks and gloves should be removed and secured with the carcass for later disposal with the carcass.
• Re-usable overalls should be placed in a strong plastic bag or bucket and completely soaked in an appropriate disinfectant for at least 12 hours.
• Boots should be scrubbed with disinfectant; paying attention to remove all material, especially from the soles.
• It is now possible to move away from the contaminated site to clean ground.
• Boots should be placed in a plastic bag or bucket and kept damp for at least 12 hours.
• All reusable protective equipment should be double-bagged for removal.
• Hands and all exposed skin should be washed with liberal amounts of soap and water.
• The site where wash-down has occurred should be marked for later disinfection when the carcass is disposed of. It is essential not to walk back over the potentially contaminated ground in street shoes.
• It is recommended that as soon as possible anyone exposed to the animal or site, have a shower and launder their clothes.

Reporting

When anthrax is confirmed as the cause of death, further actions will be taken by the government to control spread of the disease and further losses.

A full report of the disease investigation must be submitted to the Chief Veterinary Officer as soon as possible.

Vaccination

Vaccination of animals is the key control measure in managing outbreaks of anthrax. Vaccine use requires the approval of the Chief Veterinary Officer. Approval will normally be given to vaccinate livestock on an infected property. Animals on neighbouring properties may also need to be vaccinated. New stock introduced onto the infected property and calves reaching two months of age will also be vaccinated. A vaccination program will be continued for three years after the outbreak. Vaccinating exposed animals for three years on infected premises following an incident provides time for the dispersal    and inactivation of spores on the soil surface to levels unlikely to support further disease incidence.

Vaccinated animals need to be permanently identified and must not be slaughtered for human consumption for a minimum withholding period of 42 days.

The anthrax vaccine contains living spores of the non-capsulated naturally avirulent (live) Stern 34F2 strain of Bacillus anthracis. A single vaccination is usually effective for 6-12 months, provided that animals receive the full dose and are not under antibiotic therapy within 10-14 days before or after vaccination. Animals that are vaccinated twice, at least six months apart, are probably immune for life.