Anthrax
Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | Additional sources of information
Victorian statutory requirement
Anthrax infection (Group A disease) must be notified immediately by telephone or fax followed by written notification within five days.
School exclusion is not required.
Infectious agent
Bacillus anthracis is a gram-positive, aerobic rod-shaped bacterium that is encapsulated, spore-forming and non-motile.
Identification
Clinical features
Anthrax is an acute bacterial disease that usually affects the skin. It may rarely involve the lungs after inhalation or the intestinal tract after ingestion.
Cutaneous anthrax
This form accounts for over 95% of anthrax cases. Lesions usually occur on exposed skin and often commence with itchiness. They pass through several stages:
- papular stage
- vesicular stage with a blister that often becomes haemorrhagic
- eschar stage that appears two to six days after the haemorrhagic vesicle dries to become a depressed black scab (malignant pustule) which may have surrounding redness and extensive oedema (swelling).
Anthrax lesions are usually painless but pain may result due to surrounding oedema. Untreated lesions can progress to involve regional lymph nodes. An overwhelming septicaemia can occur in severe cases.
Untreated cutaneous anthrax has a case fatality rate of 5–20% but death is rare with early appropriate treatment.
Pulmonary (inhalational) anthraxThis is very rare and often presents with mild and non-specific symptoms including fever, malaise and mild cough or chest pain (upper respiratory tract symptoms are rare). Early symptoms may be confused with a flu-like illness.
This is followed within three to six days by rapid onset of hypoxia, dyspnoea and high temperature, with radiological evidence of mediastinal widening. Meningitis frequently occurs.
The mortality rate approaches 100% with delayed or no treatment. Commencement of appropriate antibiotics during the prodrome significantly decreases the mortality rate.
Intestinal/oropharyngeal anthrax
These are very rare forms of anthrax in developed countries but may occur in large outbreaks in developing countries following ingestion of meat from infected animals.
In intestinal anthrax, gastro-intestinal symptoms may be followed by fever, septicaemia and death. Case fatality rates of 25–75% have been reported.
In oropharyngeal anthrax, fever, neck swelling due to lymphadenopathy, throat pain, oral ulcers and dysphagia may be followed by severe local ulcers and swelling, septicaemia and death. Case fatality rates are similar to the intestinal form.
Method of diagnosis
Laboratory confirmation of anthrax is by demonstrating the presence of
B. anthracis in blood, lesions or discharges by direct staining of smears using Gram or other special stains, or by isolation of the organism by culture or animal inoculation. Serological and nucleic acid testing are likely to be available in the near future from reference laboratories.
Incubation period
The incubation period is typically one day for cutaneous anthrax and one to seven days for pulmonary anthrax. Evidence from mass exposures indicates incubation periods up to 60 days are possible for pulmonary anthrax, related to delayed activation of inhaled spores. The incubation is typically three to seven days for the gastrointestinal form.
Public health significance & occurrence
Anthrax is primarily a disease of herbivores. Humans usually become infected when they come into contact with infected animals or their products.
Anthrax is primarily an occupational hazard for handlers of processed hides, goat hair, bone products, wool and infected wildlife. It can also be contracted by contact with infected meat, for example in abattoir workers.
New areas of infection in livestock may develop through introducing animal feed containing bone meal. Cutaneous outbreaks sometimes occur in knackery workers and those handling pet meat. Anthrax spores can persist in the soil of certain tracts of land for years such as areas where carcasses of animals dying of anthrax are buried.
Anthrax can also be used as a bio-warfare or bio-terrorism agent, most likely spread as an aerosol. Any new case should be assessed with this possibility in mind, particularly but not exclusively in cases of pulmonary anthrax.
Reservoir
Spores may remain viable in contaminated soil for many years. Dried or processed skins and hides of infected animals may also harbour spores for years.
Mode of transmission
Cutaneous anthrax is usually introduced through a skin injury. It can occur:
- by contact with tissues of animals such as cattle, horses, pigs and others dying of the disease, or in processing after death
- by contact with contaminated hair, wool, hides or products made from them (Hide-porter’s disease)
- by contact with soil associated with infected animals and contaminated bone meal used in some gardening products
- possibly by biting flies that have fed on infected animals in some parts of the world but not seen in Australia.
Pulmonary anthrax (‘woolsorter’s disease’) can occur:
- by inhalation of aerosolised spores in industries that inadvertently may deal with contaminated tissues or products such as tanning hides, processing wool or bone products, or by accident in laboratory workers
- by intentional release of spores using a variety of aerosol devices including mail-items.
Intestinal or oropharyngeal anthrax is caused by ingestion of anthrax contaminated undercooked meat. There is no evidence of transmission through the milk of an infected animal.
The deliberate release of anthrax spores through contaminated letters in the USA in October 2001 resulted in 22 cases of anthrax, of which half were cutaneous and half were pulmonary anthrax.
Period of communicability
There is no evidence of direct spread from person to person. Articles and soil contaminated with spores may remain infective for years.
Susceptibility & resistance
Recovery is usually followed by prolonged immunity.
Control measures
Preventive measures
- Immunise high risk persons, usually laboratory workers who are liable to handle B. anthracis, with the cell-free vaccine giving annual boosters as recommended. Protection is likely to be greater against cutaneous exposures than pulmonary exposures. The vaccine is not currently licensed for use in the general community.
- Educate employees who are handlers of potentially infected articles in the proper care of skin abrasions.
- Ensure proper ventilation in hazardous industries and the use of protective clothing.
- Sterilise hair, wool or hides, bone meal or other feed of animal origin prior to processing.
Control of case
The following treatment advice is to be used as a guide only. Always consult the current version of Therapeutic guidelines: antibiotic (Therapeutic Guidelines Limited) and seek expert advice from an infectious diseases physician.
Cutaneous/gastrointestinal anthrax
- Ciprofloxacin, penicillin or doxycycline are the drugs of choice, usually given for 7–10 days in cutaneous anthrax. The duration of therapy for gastrointestinal anthrax is not well defined.
- If the case is associated with a bio-terrorist attack involving aerosolised anthrax where the risk is high, ciprofloxacin or doxycycline are recommended and should be given for at least 60 days.
- For patients with signs of systemic involvement, extensive oedema, or lesions on the head or neck, antibiotics should be administered intravenously, as for patients with pulmonary disease.
Pulmonary anthrax
The following recommendations were developed in the USA following experience during the deliberate release of anthrax through the postal system in 2001.
- Recommended initial treatment of pulmonary anthrax is an intravenous multi-drug regimen of either ciprofloxacin or doxycycline along with one or more agents to which the organism is typically sensitive.
- Ciprofloxacin has been recommended on the basis of in vivo (animal) findings. It should be used in preference to doxycycline in cases where meningitis is suspected because of the lack of adequate central nervous system penetration by the latter.
- Bacteremic patients are often initially treated with an empiric multi-drug regimen which provides adequate therapy for B. anthracis and other possible pathogens.
- After susceptibility testing and clinical improvement, the empiric regimen may be altered. A penicillin-based antibiotic, such as amoxycillin or amoxycillin/
clavulanic acid may then be used to complete the course. - Treatment should be continued for 60 days in all cases of pulmonary anthrax.
Keys to successful management appear to be early institution of antibiotics and aggressive supportive care. Chest tube drainage of the recurrent pleural effusions, which are typically hemorrhagic, often leads to dramatic clinical improvement.
Control of contacts
Although there is no person to person transmission, the Department of Human Services will trace and follow-up anyone who may have been exposed to the same source as the case, and it may be recommended that they take prophylactic antibiotics.
Control of environment
If an animal anthrax case is suspected, it should be reported to the Department of Primary Industries (DPI). Movement of animals and animal products from the farm is suspended. Appropriate samples are collected and tested at a laboratory. This can take 12–24 hours. If the case occurs on a dairy farm, the dairy factory is advised to suspend collection of milk until the case is investigated and Dairy Food Safety Victoria is advised.
If an animal anthrax case is confirmed, the affected property is quarantined, potentially exposed stock vaccinated, dead animals buried and contaminated sites disinfected. The quarantine is not released until occurrences of anthrax cases have ceased and at least six weeks have elapsed since the last round of vaccinations on the property. DPI staff will liaise with knackeries, local veterinary practitioners, the dairy industry, health authorities, local government and regional emergency services staff.
Decontamination of environments contaminated after a deliberate release of anthrax spores requires full HAZMAT decontamination by appropriately protected trained personnel using strong chlorine-based disinfectants. The risk of secondary aerosolisation is generally thought to be very low, although spores produced for bioterrorism may be deliberately prepared to increase this risk. Although the risk of anthrax can be significantly reduced by environmental decontamination measures, evidence from deliberate release of anthrax spores in other countries suggests that complete environmental decontamination of anthrax spores is extremely difficult.
Outbreak measures
A single case of anthrax should be considered an outbreak and should be managed with great urgency. If one or more patients seem to have been infected in an unusual way, such as no evidence of exposure to infected animals or their products, a deliberate release of anthrax organisms must be considered.
If a focus of infection was identified or a deliberate release of organisms is suspected, outbreak control measures would include:
- coordination with appropriate emergency services including the police force if required
- active case finding
- alerts for medical practitioners and hospitals
- release of appropriate public information
- control of contacts including field workers involved in environmental control measures
- environmental control measures.
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