Anthrax

Description

Anthrax is found in most areas of the world and reported throughout recorded history. It is an acute, naturally occurring disease caused by a spore-forming bacterium called Bacillus anthracis. When exposed to air, these bacteria form inactive spores that can survive in the soil for years.

Anthrax in animals is almost always fatal and causes death very rapidly. Death loss can vary from a single animal to a scenario where large numbers of animals die in a very short period of time. Economic losses to producers can be significant.

While most animals are susceptible to anthrax, it primarily affects and is fatal in herbivores. In Alberta, most anthrax outbreaks in recent history have been recorded in beef cattle and bison. However, anthrax can also occur in dairy cattle, sheep, goats and horses.

Omnivores such as pigs and humans are somewhat less susceptible, while carnivores such as dogs, cats, wolves and bears are relatively resistant. Birds are least susceptible.

How to report

Anthrax is a provincially notifiable disease under Alberta's Animal Health Act, and must be monitored. It is also a reportable disease under the federal Health of Animals Act.

This means veterinarians must notify the province, and practitioners and laboratories must report suspected positive anthrax test results to the Canadian Food Inspection Agency (CFIA).

All suspected or confirmed cases must be reported to the Office of the Chief Provincial Veterinarian (OCPV) within 24 hours:

Hours: 8:15 am to 4:30 pm (open Monday to Friday, closed statutory holidays)
Phone: 780-427-3448
Toll free: 310-0000 before the phone number (in Alberta)
Fax: 780-415-0810

Clinical signs

In ruminants

• most commonly found dead with no premonitory signs
• staggering, trembling and difficulty breathing may be observed a few hours before collapse, terminal convulsions and death
• occasionally see an acute form with signs for up to 2 days before death, including fever and excitement progressing to depression, stupor, disorientation, tremors, difficulty breathing, abortion, congested mucous membranes and bloody discharge from orifices
• a chronic form with subcutaneous swellings of the neck, thorax and shoulders is uncommon
• in carcasses, leaking of blood and blood-tinged fluids from carcass orifices, blood is not clotting, and there are bruises (ecchymotic hemorrhages) in tissues, gross enlargement of the spleen and an absence of stiffness (rigor mortis)

In horses

• sudden, rapid death is less common in horses than in ruminants
• can see fever, chills, loss of appetite, depression and severe colic with bloody diarrhea for up to a week before death
• subcutaneous swellings in the neck, sternum, lower abdomen and groin (inguinal region) are common

In pigs

• inflammatory swelling of the face and throat is quite characteristic
• may also be found dead or with signs similar to ruminants and horses

Where it is found

Anthrax is a sporadic disease that may not occur for many years, then suddenly reappear in areas where it has been reported in past years. It may also appear in areas where there is no recorded occurrence.

Anthrax has been reported in most Canadian provinces, including Alberta. A few sporadic cases of anthrax are reported in western Canada nearly every year, with repeated outbreaks in the Mackenzie Bison Range in the Northwest Territories and in Wood Buffalo National Park in northern Alberta.

Typically in Canada, cases are reported between the months of July to September and usually following periods of hot and dry, or hot and wet weather. But it has been reported in every season, including winter.

How it spreads

The anthrax bacterium forms very hardy spores, which means the potential for infection can persist for many years after soil has become contaminated. Spores in soil are the source for outbreaks that are often separated by several years. Control protocols are designed to deal with an immediate outbreak, minimize soil contamination and reduce the chance the disease will persist and reoccur in the future.

Animals can be infected with anthrax when they ingest spore-contaminated soil, feed, or water. The inactive spores germinate into active bacteria inside the animal and then cause disease and often rapid death within hours, with livestock typically found dead on pasture.

Environmental factors increase the risk of occurrence. These include any disruption of soil from tillage or excavation, flooding or drought, especially after flooding. Once anthrax has been seen in any area, the risk in subsequent years is higher because of increased environmental contamination with spores.

Humans can become infected by direct or indirect contact with infected animals or carcasses, or exposure to infected or contaminated animal products. The disease does not spread from person to person.

Risk to humans

While people can get sick from anthrax through contact, anthrax is not contagious. Which means you cannot catch it like a cold or flu.

Humans can become infected with one of 3 forms of the disease:

Cutaneous

Skin infections are most common and are contracted.

People can contract cutaneous anthrax by handling infected animal tissues or equipment without protective barriers to prevent the organism from entering broken skin. These infections are rarely fatal if properly treated with antibiotics.

Symptoms generally appear within 7 days of exposure. A raised itchy bump like an insect bite appears and develops into a painless ulcer (1 to 3 cm in diameter). A black spot appears in the center within 2 days.

Gastrointestinal

Consumption of contaminated meat can cause gastrointestinal infections. Modern meat inspection and food safety processes have made this type of anthrax very uncommon, but there are reports of infections arising from carcasses slaughtered for personal use.

Pulmonary

Inhalation of large quantities of anthrax spores can cause severe, often fatal respiratory infections. Handling of infected animal carcasses generally does not pose a risk of pulmonary anthrax because there are insufficient airborne spores around the carcass to cause infection. Pulmonary anthrax is seen in situations where there are large numbers of air-borne spores, for example in tanneries where spores from multiple infected carcasses may be concentrated and thrown into the air by hide drying and tanning processes.

Contact your doctor if you see these symptoms. While there is about a 20% mortality rate if untreated, mortality is rare in humans if treated with antibiotics.

Prevention and control

Vaccination and treatment

Vaccination will protect susceptible animals within 7 to 10 days. Talk with your veterinarian about vaccination. They will help you decide whether vaccination in your herd is appropriate based on the risk of disease in your area.

Preventive antimicrobial treatment of exposed animals can be effective.

Do not treat animals with antibiotics if they have been vaccinated less than 2 weeks previously, and do not treat with antibiotics if you plan to vaccinate them within the next 2 weeks.

Biosecurity

Biosecurity refers to practices designed to prevent, reduce or eliminate the introduction and spread of disease. Concerns over the spread of animal diseases, particularly those of foreign origin, are high within the livestock industry. Livestock diseases can affect any type of operation regardless of size. Biosecurity practices tailored to each operation minimize the introduction and transmission of disease.

Find out more about Biosecurity and livestock – Overview

Response plans

Response plan for producers

• Remove surviving animals from pasture and monitor them for signs of illness.
• Cover infected carcasses to protect them from scavenging.
• Do not move dead animals.
• Do not call for dead stock pick-up.

If there is any suspicion of anthrax, your local veterinarian will draw a blood sample from a dead animal rather than doing a post-mortem exam, since this could cause more soil contamination. The veterinarian will then send the samples for testing.

After sample(s) are collected, you must obtain and follow the veterinarian's instructions regarding dead stock disposal. Proper disposal is very important to limit the spread and recurrence of anthrax. Natural disposal, scavenging and dead stock pick-up both increase the risk of future anthrax outbreaks by spreading the spores over a wider area.

Response plan for veterinarians

Detection

The OCPV will help veterinarians and producers with cases of anthrax. They will:

• provide assistance in diagnosing the disease
• work veterinarians to provide advice on how to protect your herd and prevent spread of the disease to other herds and animals

Veterinarians must also report suspected positive anthrax test results to the CIFA. The CIFA does not respond to cases of anthrax. Instead, provincial animal health authorities will assist producers and veterinarians in case of outbreaks of this disease.

Response

If a case of anthrax is suspected, a veterinarian will:

• Follow all instructions from the OCPV for sample submission and testing.
• Wear gloves, long sleeves and protective clothing when handling carcasses.
• Obtain samples as soon as possible after the death of the animal:
  • take a blood sample from the tail vein of the freshest carcass (within 36 hours of death)
  • if it is not possible to obtain a blood sample, then a swab of excreted blood and blood-tinged fluids will suffice
• Cover all suspect carcasses with heavy-duty plastic or tarp and stake down for 72 hours.
• Remove surviving animals from the pasture and monitor them for signs of illness.
• Prevent scavenging of carcasses.
• Wash and disinfect footwear and all exposed clothing before leaving the farm, and destroy disposables by incineration.
• Wash hands and arms afterward.
• NOT move dead animals, especially by dragging.
• NOT open the carcass, do a post mortem, or submit any tissues for testing.
• NOT call for dead stock pick-up.

Carcass disposal

When Bacillus anthracis bacteria are exposed to air, they form spores that are very hardy and survive in the soil for years. If the carcass is opened through post mortem, scavenging or moving, more spores will be formed. If the carcass is not opened, the high temperatures achieved in the decaying carcass will destroy the vegetative form of the bacteria and reduce the risk of spore formation.

The OCPV will provide instructions on carcass disposal. Follow all instructions from the OCPV. Do not move the carcasses unless absolutely necessary.

Incineration is the preferred disposal method as this destroys the spores. The goal is to completely reduce the carcass to ash to avoid attracting scavengers and flies.

Burial of positive carcasses should only be considered as a last resort if burning is not possible. There is always a risk that the carcass may be accidentally opened during burial or uncovered at a later date, allowing for spore formation and soil contamination.

Related

• Canadian Food Inspection Agency – Anthrax
• World Organization for Animal Health – Anthrax
• Alberta notifiable human disease guidelines