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Anthrax in Humans and Animals. 4th edition. Geneva: World Health Organization; 2008.

Annex 6Contingency plan for the prevention and control of anthrax

1. Action in the event of an outbreak of anthrax in livestock

The control programme, instituted by the Department of Natural Resources and Environment, Victoria, Australia, in response to an outbreak of anthrax in cattle affecting some 83 farms during the first half of 1997, was subsequently established as an Australian standard and serves well as a global model for anthrax control. The following summary, based on the report by Turner (unpublished, 1997), Chief Veterinary Officer, Victoria, is included here by kind permission.

On each affected farm, the following measures should be applied:

  1. Quarantine should be imposed on the flocks and herds in which anthrax has occurred. The quarantine should comprise limiting: (i) contact between infected and non-exposed herds/flocks; and (ii) the access of susceptible animals to infected sites until at least 14 days, and preferably 20 days (OIE incubation period), after they have been vaccinated.
  2. The carcasses of infected animals should (see section 8.3) either be burnt at the site of death and the ashes buried deeply, or wrapped in double-thickness plastic, to prevent spilling of body fluids, and removed to a more suitable site (e.g. a quarry) to be burnt and the ashes buried. (Consideration may be given to removing the carcasses to suitable commercial incinerators or rendering plants.)
  3. The site where the animal died should, where possible, be thoroughly scorched with a down-directed flame and/or disinfected with 10% formalin after disposal of the carcass. (Caution: formalin should be handled with the appropriate cautions as indicated in Annex 3 and more specifically in its section 1.1.)
  4. On moving the herd out of the contaminated area/field/pasture, Hugh-Jones (personal communication, 2002) recommends that all animals be treated with a suitable long-acting antibiotic to abort covert incubating infections. If they are to be returned to the contaminated area, they should be vaccinated after the antibiotic has cleared (see section 7.2.1.3).
  5. Affected properties should be quarantined for at least 20 days after the last case or the accepted period after vaccination (see Annex 5, section 2.3), whichever is later.
  6. Any movement of susceptible livestock, or of risk items (hides, skins, carcasses, etc.) that have left the property in the 20 days before the first anthrax case, should be traced and appropriate action taken where necessary.
  7. As far as possible, vehicles should remain on made roads in infected and vaccinated farms; where vehicles have to enter the pasture fields, the vehicle should be disinfected before exiting the property by washing down with water and detergent to remove mud, followed by a disinfectant wash. This should take place in a corner of the property where animals will not come in contact with the washings. Every attempt should be made to decontaminate the washings along the lines suggested in Annex 3, sections 6.2 & 6.4. Formalin 10% may be the best option. (Caution: formalin should be handled with the appropriate cautions as indicated in Annex 3 and more specifically in its section 1.1.)
  8. People entering infected properties should wear protective clothing and footwear which can be disinfected or bagged for incineration before leaving the property.
  9. All animals within a buffer zone, a few to several kilometres (1–3 properties) wide, around the infected property (-ies) should also be vaccinated and quarantined with the same post-vaccination holding conditions described under (5) above (see also section 8.7).
  10. Milk from herds may not need to be destroyed (see section 3 below).

2. Other actions in the event of a case, or cases, of anthrax in livestock

The appearance of anthrax in animals from a previously uninfected premise may be dealt with in the following ways:

  1. Identify, isolate and remove apparently healthy animals, and monitor these carefully for signs of illness (see (5) below and section 7.2.1).
  2. Decontaminate soil, bedding, unused feed, manure, etc., or disinfect premises that may have become contaminated by exudations from the dying or dead animals (see Annex 3, sections 3.1, 3.2 & 6.1).
  3. Avoid any unnecessary ante- and postmortem operation in animals on the premises (see section 3.5.2).
  4. Destroy carcasses and their parts by burning, removal for rendering or, as a last resort, deep burial after disinfection, preferably with 10% formalin (see section 8.3 and Annex 3, section 7). If carcass disposal has to be delayed, the carcass and surrounding ground should be disinfected with 10% formalin and the carcass covered with strong plastic to prevent access of scavengers. The apparent failure of formalin to seriously deter scavengers and flies has been referred to in section 8.3.2.1.
  5. As outlined in sections 8.6.2 & 8.7, and in Annex 5, section 2.2, vaccinate or monitor and treat other members of the herd or flock if there is reason to believe that they continue to be exposed to the source of the incident. It should be remembered that antibiotics and vaccine should not be administered simultaneously (see section 8.7 and Annex 5, section 2.2).
  6. Control scavengers and minimize possible vectors such as flies, rodents and birds.
  7. Carry out an epidemiological investigation to detect the source of infection (history of site, feed, disturbance of the environment, etc.) to identify the source of the incident (see section 9.3).
  8. Take proper measures to avoid the contamination of water and soil and to prevent the spread of the infection to other farms and environments. Disturbed soil thought to be related to the incident should be fenced off and, ideally, not used for grazing again, at least until it has become well overgrown with vegetation, preferably of the type that inhibits access by susceptible animals (see section 8.3.2.1).
  9. Alert public health authorities (see section 9.1.2).

3. Guidance on actions relating to milk from herds/flocks in which anthrax has occurred

Action to be taken on milk from a herd or flock experiencing cases of anthrax infection occasionally presents a dilemma for health authorities. Wasteful destruction of large quantities of milk, and consequent financial losses, may be avoided by considering the following points. OIE now recommends that, in the first place, only milk from healthy animals should be regarded as acceptable but, in the case of herds or flocks experiencing anthrax, milk should be pasteurized before being processed into products for human consumption.

It is accepted that milk from healthy animals in anthrax outbreaks does not pose a risk to humans for the following reasons:

  1. Animals with anthrax do not usually discharge the infecting organism in their milk before death, although there have been occasional exceptions (see (2) below; sections 3.3.8 & 3.5.2; Annex 5, section 2.7). Secretion of milk would normally be expected to cease with onset of bacteraemia and illness. The organism would normally only gain entry to the milk-secreting glands through breakdown of blood-vessel walls at terminal stages of the disease, long after secretion of milk had stopped (M’Fadyean, 1909). Milk from other healthy animals in the herd/flock poses no risk of carrying anthrax organisms.
  2. There are rare exceptions where the vegetative forms are excreted in milk (Weidlich, 1935). B. anthracis strain ASC 65 (from Baptista, Department of Agriculture, South Rio Grande State, Brazil) was chronically secreted in the milk from four cows and was isolated during routine mastitis-screening tests on milk samples in 1983. Two cows subsequently died. The two that survived had been vaccinated. In such an event it should be borne in mind that:
    • The organisms are in vegetative form.
    • The organisms are unable to sporulate (Bowen & Turnbull, 1992) as a result of having minimal aeration and, where commercial processing follows, of rapid cooling to refrigeration temperatures.
    • The pH rapidly falls on standing, increasing the killing effect on any vegetative cells present.
    • The vegetative forms die quite rapidly in the milk (Bowen & Turnbull, 1992) and will be killed immediately by pasteurization (72–73 °C for 16 seconds, or HTST (high temperature short time) at 80–82 °C for 19–20 seconds).
    • Any anthrax organisms reaching the bulked milk will have been considerably diluted; the infectivity of anthrax organisms for humans by the oral route is very low and vegetative forms will be killed by the gastric juices.
  3. There appear to be no instances on record of human anthrax cases resulting from handling or consumption of milk from herds/flocks experiencing anthrax and processed dairy products have never been associated with human anthrax. Action on the part of farmers/owners and public health authorities aimed at reducing the minimal risk to zero risk should consist of:
    • milking only healthy animals; animals showing signs of illness should be set aside for appropriate treatment and the milk from those animals, and utensils used in its collection, should be sterilized;
    • ensuring hygienic practices are in place that prevent the environment of the premises from becoming contaminated with anthrax spores and, further, prevent milk becoming contaminated from the environment;
    • ensuring that all milk is rapidly cooled to 4 °C or less within 4 hours of milking and is held at this temperature until processed at a licensed dairy plant;
    • pasteurizing of all milk before processing for human or animal consumption.

If the veterinary inspector is satisfied that these requirements have been met, milk from healthy animals in herds/flocks in which cases of anthrax have occurred need not be excluded from processing, and bulked milk containing such milk need not be condemned.

4. Deliberate release into animal populations

Bioaggression scenarios involving the use of anthrax and targeted at animal populations are conceivable, and could take the form of airborne infection or deliberate infection of animal feeds or water with virulent spores. Reference is readily found on the Internet to declassified Second World War records of British retaliatory preparedness to respond to an anticipated biological attack from Germany, and in which several million cattle-cakes injected with anthrax spores were made ready for aerial drops over grazing areas in Germany. The cakes were never used and were destroyed by incineration after the war.

The response required to such an event would still involve the control principles outlined in sections 1 & 2 above. Infected and exposed animals would be defined by determining the source of infection and the nature of the release, and thereby the likely exposed population. Priorities could then be assigned to ensure that vaccination is carried out first in those herds and flocks believed to have highest exposure.

It is essential that all the other control procedures described in section 1 above are applied, along with vaccination, if further occurrence of disease is to be minimized in animals and humans. It will be important to safely dispose of carcasses to reduce environmental contamination as a further source of infection. It would be an essential extra task to develop appropriate press releases and to establish an education programme for the public about the disease and the control measures being applied, to prevent local panic.

5. Outbreaks in wildlife

5.1. Proaction plans and control actions

When it comes to wildlife, circumstances are likely to be very varied, and it is difficult to cover all eventualities within this section. Sporadic cases in large game-management areas (GMA) are likely to be seen as being of consequence only if livestock are at risk. Even with bigger outbreaks, in those large wildlife national parks from which livestock are excluded and which have “hands off” management policies for all but emergency situations, control actions may be regarded as interference with natural processes. This is discussed in sections 8.9 and 8.10. Each GMA that encounters anthrax, or knows it is at risk of encountering anthrax, should have an action plan in place in line with its management policies and particular needs (Clegg et al. 2006a). For smaller commercial or sustainable GMAs, a proaction plan is advisable with prevention as the primary aim. The essence of this is to:

  • ensure that risk factors and warning signs are recognized, for example, awareness of cases of anthrax in livestock in areas around the GMA;
  • have surveillance in place which ensures that unexpected deaths are observed and diagnosed promptly and correctly;
  • have good links with veterinary and public health services and good relations with surrounding communities;
  • have an action plan in place;
  • undertake relevant training of rangers and scouts on the nature of the disease, and prepare action plans and possibly educational material for surrounding communities;
  • prevent the development of overdense populations of susceptible species in any part of the GMA;
  • keep strategic stocks of vaccine and other items needed to implement the action plan as soon as an outbreak occurs;
  • prepare information sheets for staff and tourists in case of an outbreak;
  • make appropriate budgetary provision for the eventuality of an outbreak and the actions to be taken, e.g. for the extra personnel, vehicles, machinery, fuel, insecticides, disinfectants, protective clothing, veterinary and medical services, vaccine, information sheets, etc., that will be involved.

Where action is seen to be necessary, the following suggestions are offered:

  • Identify if possible the source of the outbreak and isolate it, for example, by veld burning, or vulture decoys with uncontaminated meat.
  • Liaise with veterinary and public health services and inform local communities, tourists, etc., by issuing information sheets.
  • Take measures to prevent the infection being transmitted from the dead animals to live ones, e.g. covering carcasses to prevent access by scavengers, fly control, ring vaccination, etc. The problem is likely to be that it will not be possible to dispose of carcasses promptly or easily while the outbreak is active. In this event, the aim should be to keep carcasses unopened and intact for as long as possible to minimize the development of contamination; the quickest and most effective way may be to cover carcasses with tarpaulins or thick plastic, possibly wetting the carcass (and surrounding soil) with 10% formalin first. (Caution: formalin should be handled with the appropriate cautions as indicated in Annex 3 and more specifically in its section 1.1.) As mentioned in section 8.3.2.1 and section 1 above, this will help keep the skin intact and kill anthrax organisms. The apparent failure of formalin per se to seriously deter scavengers and flies has been referred to in section 8.3.2.1. Opened carcasses may also be treated with 10% formalin and covered until proper disposal actions can be implemented.
  • If possible, capture and vaccinate at least a core of endangered or otherwise precious species, possibly restricting them to a fenced-off enclosure or other confined area. For maximum protection, it may be advisable to revaccinate after about 4 weeks.
  • Take actions to encourage animals to move away from the area, e.g. close off or empty artificial waterholes.
  • Set up monitoring to detect cases that might occur in the animals that have moved away but which might have been already infected.
  • Before access to the affected area is reopened, all carcasses are best burnt but, if this is impractical, they should be buried, preferably disinfecting them first with 10% formalin (section 8.3 and section 2 above). (Caution: formalin should be handled with the appropriate cautions as indicated in Annex 3 and more specifically in its section 1.1.)
  • Consider the possibility of disinfecting artificial water holes where this is feasible. Heavy chlorination (final concentration at least 5000 ppm) is probably the only practical approach available, at least for small holes, but its limitations should be appreciated (Annex 3, section 1.2.1). Whether it is necessary or feasible to treat large bodies of water, especially when extensive amounts of organic matter are present, and how to do so if it is deemed necessary, are topics needing research. Control may depend more on the water holes not playing a major role in maintenance of the outbreak than on the effectiveness of disinfection attempts.

It is difficult to advise on the value and cost-effectiveness of these suggested actions. History shows that an explosive outbreak in a particular location is generally not followed by another one at the same location for several to many years. However, logic suggests that future outbreaks, even many years later, are less likely if measures are taken to minimize the residual environmental contamination resulting from an outbreak occurring today.

5.2. Models for answering frequently asked questions

Question. In an outbreak situation, should we put staff involved in burning or burying carcasses onto long-term antibiotic prophylaxis?

Answer. No. Prolonged antibiotic prophylaxis has only been a recommendation for persons known to have been, or strongly suspected of having been, exposed to very substantial doses of aerosolized spores in a deliberate release scenario. Antibiotics should not be administered in that way for other situations; they cause side-effects and there is the risk of producing resistant strains of other (unrelated) organisms which then do not respond if a person subsequently suffers another infection. Antibiotics should only be used for treatment, not prophylaxis, unless there is a real danger (see also section 7.3.2.3). There have been many epizootics of anthrax in African wildlife, but reports of cases in the humans dealing with these are exceedingly few in number (section 4.2.1.2), giving plenty of circumstantial evidence that the category of danger for staff is not very high. The appropriate approach is:

  • Educate staff about the disease, including about not butchering and eating meat from the carcasses, and leaving the disposal of these to veterinary or other trained personnel.
  • When disposing of carcasses, sensible protective equipment should be worn (coveralls, boots, gloves). If a lot of dust is created at a site where the dust is likely to be contaminated, a good-quality properly-fitted dust mask should be used that ensures breathing through it and not around it (see also Annex 1, section 7.1.2).
  • Make sure that if any person develops a spot/pimple/boil-like lesion, especially on exposed areas, or flulike illness, he/she reports to the doctor, who can then give them penicillin or other chosen antibiotic(s) for 3–7 days (spots, etc.) or 10–14 days (flulike illness) (see section 4.4).

To avoid creating dust, objects should be dampened down, preferably with 10% formalin if they are likely to be contaminated. Clothing should be sterilized or, if disposable, burned after use. Everyone involved should be advised to be careful with formalin: it is effective for killing spores, and for the same reason it can damage human tissues.

Question. What are the environmental impact considerations when it comes to using formalin?

Answer. As first applied in a 10% solution, it will kill any living thing – microbe, plant, animal. However, it degrades readily through natural processes (see Annex 3, section 6.1).

Question. Can we expect naturally acquired immunity resulting from the outbreak, or vaccine-induced immunity to prevent a repeat outbreak?

Answer. The immunity from first-time vaccination may not be very long-lasting, It is better after anamnestic (the immune system’s memory) responses following subsequent boosters. The pattern of history is that another large outbreak in the near future is unlikely, but whether it is the result of acquired immunity or not is not known. Tests have not confirmed or refuted it. Seasonal sporadic cases may be expected every year.

Question. Should the chlorine level be raised in the local water supply?

Answer. No. Filters and other water purification systems may be usefully checked, but chlorine needs to be at a very high concentration (approximately 5000 to 10 000 ppm) to be effectively sporicidal. If there is serious reason to fear the water, boiling for 20–30 minutes is probably the only option available (Annex 3, section 6.3).

Question. Can fish be carriers of anthrax? A number of animals dying from anthrax have done so in the dam. People catch fish from this for consumption. Is there a possibility that they could be infected through eating these fish? Some of the fish will have fed on the carcasses.

Answer. The following is a working model to build on:

  1. If the fish was caught within a few hours of eating anthrax meat, and was opened up and filleted before eating, and was eaten uncooked, the risk would be a little less than for a person handling and eating the meat itself. There is a chance, probably in the order of 1:20 to 1:50, of contracting cutaneous anthrax from handling the opened fish, and probably around a 1:100 to 1:1000 chance of ingestion anthrax.
  2. As in (1) above, but the fish is cooked before eating. There would still be the 1:20 to 1:50 chance of cutaneous anthrax from handling the fish before cooking, but a greatly reduced risk of ingestion anthrax, e.g. 1:1000 to 1:10 000 chance, or lower, depending on how the fish was cooked. The hotter the temperature and the longer the cooking period, the lower the risk.
  3. As in (2) above, but the fish was not opened up before cooking. The chance of cutaneous anthrax is reduced to almost nil and the chance of ingestion anthrax to 1:1000 to 1:10 000, or lower, depending on the extent of the cooking.
  4. As in (1) above, but the fish was caught 24 hours after eating the meat. Risks of cutaneous and ingestion anthrax would be greatly reduced to, for example, 1:100 to 1:500 (cutaneous) and 1:1000 to 10 000 (ingestion). The risks would decline fairly rapidly with time after that as the ingested anthrax spores are expelled from the fish.
  5. As in (2) above, but the fish was caught 24 hours or more after eating the meat. The risks are getting very small to non-existent.

In summary, it depends on: (i) the precise habits (how the persons handle, treat and cook the fish before eating); (ii) the period of time between the fish eating the anthrax-infected meat and being caught; and (iii) the particular fish – some species will and some will not eat animal meat.

Anecdotal evidence indicates that humans are moderately resistant to infection. However, there can be no guarantee that one or two persons may not be unlucky and contract infection. The message is for them to know that they must report any sickness or developing spots or pimples to a medical practitioner for administration of penicillin or another chosen antibiotic in that event.

6. Precautions for exposed personnel

Persons who must handle animals known to be, or suspected of being, infected with anthrax or carcasses from such animals, or parts of such carcasses, should take the following precautions:

  • avoid all blood-spilling operations (slaughtering included) on infected or suspect animals/carcasses;
  • use protective clothing such as strong gloves, boots, coveralls, etc., as appropriate, to avoid direct contact with infected/contaminated materials. Cuts, abrasions or other lesions should be properly dressed before putting on the protective clothing. The equipment used must be adequately disinfected or appropriately destroyed (see Annex 1, sections 7.8 & 7.9);
  • avoid any contact with other persons (family included) or animals, without first changing clothing, washing hands, and taking appropriate disinfection measures (see Annex 1, section 7);
  • report to a physician any suspect symptoms appearing after contact with infected animals or materials;
  • where there is a risk of aerosolization of spores, consider further precautions, such as damping down the material, possibly with 10% formalin. (Caution: formalin should be handled with the appropriate cautions as indicated in Annex 3 and more specifically in its section 1.1.)

As noted in section 8.6.3 and Annex 5, section 3, anthrax vaccines for humans are mostly unavailable outside certain countries and circumstances. If available, they should be considered for persons likely to have repeated exposure to animals infected with anthrax or animal products from such animals, or to B. anthracis itself. However, even when available, such vaccines require several doses over an extended time period to be effective, and the best approach is to use proper personal protection methods (Annex 1, section 7.1.2). Antibiotic prophylaxis is generally not to be recommended (section 7.3.2.3).

Copyright © World Health Organization 2008.

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