Anthrax menurut WOAH

 

 

Anthrax (Chapter 2.1.2 OIE Terrestrial Manual 2018)

SUMMARY 

Description and importance of the disease: Anthrax is primarily a disease of herbivorous animals, although all mammals, including humans, and some avian species can contract it. Mortality can be very high, especially in herbivores. 

The aetiological agent is the spore-forming, Gram-positive rod-shaped bacterium, Bacillus anthracis. The disease has world-wide distribution and is a zoonosis. The disease is mediated mainly by exotoxins. Peracute, acute, subacute and, rarely, chronic forms of the disease are reported. Ante-mortem clinical signs may be virtually absent in peracute and acute forms of the disease. 

Subacute disease may be accompanied by progressive fever, depression, inappetence, weakness, prostration and death. Acute, subacute, and chronic disease may show localised swelling and fever. In chronic disease, the only sign may be enlarged lymph glands. Identification of the agent: Bacillus anthracis is readily isolated in relatively high numbers from blood or tissues of a recently dead animal that died of anthrax, and colony morphology of B. anthracis is quite characteristic after overnight incubation on blood agar. The colony is relatively large, measuring approximately 0.3–0.5 cm in diameter. It is grey-white to white, non-haemolytic with a rough, ground-glass appearance and has a very tacky, butyrous consistency. The vegetative cells of B. anthracis are large, measuring 3–5 µm in length and approximately 1 µm in width. Ellipsoidal central spores, which do not swell the sporangium, are formed at the end of the exponential cell growth phase. The cells stain strongly Gram positive, and long chains are often seen in vitro, while paired or short chains are seen in vivo. Visualization of the encapsulated bacilli, usually in large numbers, in a blood smear stained with polychrome methylene blue (M’Fadyean reaction) is fully diagnostic. Serological tests: Antibody detection in serum from infected animals is rarely used for diagnostic purposes and is essentially a research tool. 

The predominant procedure used is the enzyme-linked immunosorbent assay. Requirements for vaccines: The most widely used livestock anthrax vaccine developed by Max Sterne in 1937 is a live, non-encapsulated, spore former held in suspension. In Russia and Eastern Bloc countries, an equivalent type of vaccine is used (strain 55). A list of producers is given in the World Health Organization anthrax guidelines. 

A. INTRODUCTION 

Anthrax, an acute bacterial disease primarily of herbivores, is transmissible to humans. The aetiological agent, Bacillus anthracis, is a Gram-positive spore-forming rod-shaped bacterium. Anthrax is known by many names around the world including charbon, woolsorters’ disease, ragpickers’ disease, malignant carbuncle, malignant pustule and Siberian ulcer. Animals become infected by ingesting spores, or possibly by being bitten by flies that have fed on an infected animal or carcass. Infected animals are usually found dead as death can occur within 24 hours. A careful postmortem examination of recently dead animals may show any number of lesions, none of which is pathognomonic or entirely consistent. To avoid environmental contamination, post-mortem examinations of carcasses of animals suspected to have died of anthrax are discouraged. Lesions most commonly seen are those of a generalised septicaemia often accompanied by an enlarged spleen having a ‘blackberry jam’ consistency and poorly clotted blood. Haemorrhage from the nose, mouth, vagina and/or anus at death may be found. Gram-positive rod-shaped B. anthracis is an obligate pathogen. Most of the other species of Bacillus are common ubiquitous environmental saprophytes, although a number, notably B. cereus, B. licheniformis and B. subtilis, are occasionally associated with food poisoning in humans and with other clinical manifestations in both humans and animals. 1. Zoonotic Risk and biosafety Requirements More than 95% of human anthrax cases take the cutaneous form and result from handling infected carcasses or hides, hair, meat or bones from such carcasses. Bacillus anthracis is not invasive and requires a lesion to infect. Protection for veterinarians and other animal handlers involves wearing gloves and other protective clothing when handling specimens from suspected anthrax carcasses and never rubbing the face or eyes. The risk of gastrointestinal anthrax may arise if individuals eat meat from animals infected with anthrax. The risk of inhaling infectious doses becomes significant in occupations involving the processing of animal byproducts for manufacturing goods (industrial anthrax). These include the tanning, woollen, animal hair, carpet, bone processing, and other such industries, where the potential for aerosolisation of substantial numbers of spores increases the risk of exposure to infectious doses. It is important that industrial workers use appropriate personal protective clothing and equipment and follow standard operating procedures that minimise the risk of transmission. Efficient air extraction equipment should be positioned over picking, combing, carding and spinning machines. Air blowing machinery should never be used for cleaning equipment due to the risk of spore dispersal. Clinical specimens and cultures of B. anthracis should be handled with appropriate biosafety and containment procedures as determined by biorisk analysis (see Chapter 1.1.4 Biosafety and biosecurity: Standard for managing biological risk in the veterinary laboratory and animal facilities). Vaccination of laboratory personnel is recommended. 

B. DIAGNOSTIC TECHNIC 

Test Method available for diagnosis of Anthrax and their purpose Method Purpose Population freedom from infection Individual animal freedom from infection prior to movement Contribute to eradication policies Confirmation of clinical cases Prevalence of infection – surveillance Immune status in individual animals or populations postvaccination.

1. IDENTIFICATION OF AGENT 

Demonstration of encapsulated B. anthracis in smears of blood or tissues from fresh anthrax-infected carcasses and growth of the organism on blood agar plates is relatively uncomplicated and within the capability of most bacteriology laboratories. Difficulty may be encountered in the case of pigs and carnivores in which the terminal bacteraemia is frequently not marked, or in animals that received antibiotics before death. Recovery of B. anthracis from old decomposed carcasses, processed specimens (bone meal, hides), or environmental samples (contaminated soil) is often difficult, requiring demanding and labour-intensive procedures. However live spores may be recovered from the turbinate bones of dead livestock and wildlife for an extended period after death (M. Hugh-Jones, personal communication). 

1.1. Culture and Identification of Bacillus Anthracis 

1.1.1. Fresh Speciment 

Bacillus anthracis grows readily on most types of nutrient agar, however, 5–7% horse or sheep blood agar is the diagnostic medium of choice. Blood is the primary clinical material to examine. Swabs of blood, other body fluids or swabs taken from incisions in tissues or organs can be spread over blood agar plates. 

After overnight incubation at 37°C, B. anthracis colonies are grey-white to white, 0.3–0.5 cm in diameter, non-haemolytic, with a ground-glass surface, and very tacky when teased with an inoculating loop. Tailing and prominent wisps of growth trailing back toward the parent colony, all in the same direction, are sometimes seen. This characteristic has been described as a ‘medusa head’ or ‘curled hair’ appearance. Confirmation of B. anthracis should be accomplished by the demonstration of a capsulated, spore-forming, Gram-positive rod in blood culture. Absence of motility is an additional test that can be done. Anthrax-specific phages were first isolated in the 1950s, and the specifically named gamma phage was first reported in 1955 (Brown & Cherry, 1955) and quickly became the standard diagnostic phage for anthrax. Gamma phage belongs to a family of closely related anthrax phages (World Health Organization [WHO], 2008). 

Two tests for confirming the identity of B. anthracis are gamma phage lysis and penicillin susceptibility. The typical procedure for these tests is to plate a lawn of suspect B. anthracis on a blood or nutrient agar plate and place a 10–15 µl drop of the phage suspension on one side of the lawn and a 10-unit penicillin disk to the other side. Allow the drop of phage suspension to soak into the agar before incubating the plate at 37°C. 

A control culture, e.g. the Sterne vaccine or the NCTC strain 10340, should be tested at the same time as the suspect culture to demonstrate the expected reaction for gamma phage lysis and penicillin susceptibility. If the suspect culture is B. anthracis, the area under the phage will be devoid of bacterial growth, because of lysis, and a clear zone will be seen around the penicillin disk indicating antibiotic susceptibility. Note that some field isolates of B. anthracis may be phage resistant or penicillin resistant. As the performance of the gamma phage lysis assay may be affected by the density of bacterial inoculum, Abshire et al. (2005) recommend streaking the suspect culture on the agar plate over several quadrants instead of using a lawn format and inoculating a drop of gamma phage on the first and second quadrants on the plate. If antibiotic or phage resistant B. anthracis is suspected then polymerase chain reaction (PCR) diagnostic methods may be applied. Phage suspensions may be obtained from central veterinary laboratories or central public health laboratories. The phage can be propagated and concentrated by the following protocol. Store phage at 2– 4°C and do not freeze phage as it will quickly become non-viable. 

1.1.1.1. Stage one 

i) Spread a blood agar (BA) plate of the Sterne vaccine strain of B. anthracis. Incubate overnight at 37°C. 

ii) Inoculate approximately 10 ml of nutrient broth (NB) with growth from the BA plate and incubate at 37°C for approximately 4 hours or until just cloudy, then refrigerate. 

iii) Spread 100 µl of the culture from step ii on three pre-dried BA plates and incubate at 37°C for 30–60 minutes. 

iv) Spread 100 µl of the phage suspension to be amplified over the same plates. Incubate at 37°C overnight. 

v) Harvest the phage-lysed growth on the BA plate in 5 ml of NB followed by a second ‘wash’ of 5 ml NB. Incubate at 37°C overnight. 

vi) Filter (0.45 µm) and count by dropping 20 µl drops (three drops per dilution) of tenfold dilutions of the filtrate in saline onto lawns of the B. anthracis culture prepared as in step iii. 

1.1.1.2. Stage Two 

This is essentially the same procedure as Stage one, only uses the filtrate from step vi to harvest the phage from the plates. 

vii) Prepare three Sterne strain lawns on BA, as in step iii. Incubate at 37°C for 30– 60 minutes. 

viii) Spread 100 µl phage from step vi. Incubate at 37°C overnight. 

ix) To 9 ml of filtrate from step vi, add 1 ml of 10× concentrated NB. 

x) Harvest the phage from step viii with 5 ml of the solution from step ix, followed by a second 5 ml wash with the rest of the solution from step vi. 

 xi) Add 10 ml of 1× NB. 

 xii) Incubate at 37°C overnight, filter and count. 

1.1.1.3. Stage Three 

xiii) Inoculate 100 ml of brain–heart infusion broth with approximately 2.5 ml of the culture from step ii. Incubate on a rotary shaker at 37°C until just turbid. xiv) Add the 20 ml of filtrate from step xii and continue incubation overnight. xv) The resultant filtrate is checked for sterility and titrated in tenfold dilutions on lawns of the vaccine strain as in step vi to determine the concentration of the phage. This should be of the order of 108–109 plaque forming units per ml. 

1.1.2. Capsule Visualization 

Virulent encapsulated B. anthracis is present in tissues and blood and other body fluids from animals that have died from anthrax. Thin smears may be prepared from blood from ear veins or other peripheral veins, exudate from orifices and, for horses and pigs, from oedematous fluid or superficial lymph nodes in the neck region. However if the animal has been dead more than 24 hours, the capsule may be difficult to detect. The bacteria should be looked for in smears of these specimens that have been dried, fixed either using heat or by dipping the smear in 95– 100% alcohol for about 1 minute and air dried and then stained with polychrome methylene blue (MacFadyean’s reaction). The capsule stains pink, whereas the bacillus cells stain dark blue. The cells are found in pairs or short chains and are often square-ended (the chains are sometimes likened to a set of railway carriages – so-called ‘box-car’ or ‘jointed bamboo-rod’ appearance). Gram and Giemsa stains do not reveal the capsule. The capsule is not present on B. anthracis grown aerobically on nutrient agar or in nutrient broths, but can be seen when the virulent bacterium is cultured for a few hours in a few millilitres of blood (defribrinated horse or sheep blood seems to work best). Alternatively, the capsule is produced when the virulent B. anthracis is cultured on nutrient agar containing 0.7% sodium bicarbonate and incubated in the presence of CO2 (20% is optimal, but a candle jar works well). The agar is prepared by weighing nutrient agar base powder required for a final volume of 100 ml but reconstituting the measured agar in only 90 ml of water. Autoclave and cool to 50°C in a water bath. Add 10 ml of a filter-sterilized (0.22–0.45 µm filter) 7% solution of sodium bicarbonate. Mix and pour into Petri dishes. The encapsulated B. anthracis will form mucoid colonies and the capsule can be visualised by making thin smears on microscope slides, fixing, and staining with polychrome methylene blue (MacFadyean’s stain). 

Polychrome methylene blue can be prepared as follows: 0.3 g of methylene blue is dissolved in 30 ml of 95% ethanol; 100 ml of 0.01% potassium hydroxide (KOH) is mixed with the methylene blue solution. Ideally, this should be allowed to stand exposed to the air, with occasional shaking, for at least 1 year to oxidize and mature. Addition of K2CO3 (to a final concentration of 1%) hastens the ‘ripening’ of the stain, but before it is regarded as diagnostically reliable, its efficacy should be established by testing it in parallel with an earlier, functional batch of stain on bona fide samples. It has been found that stains that give positive reactions with cultures of B. anthracis cultured artificially in horse blood sometimes do not give positive results in the field. In making smears for staining, only small drops of blood or tissue fluid are needed and a thin, small smear is best. After fixing (either using heat or by dipping the smear in 95–100% alcohol for about 1 minute) and drying, a small (approximately 20 µl) drop of stain is placed on the smear and spread over it with an inoculating loop. After 1 minute, the stain is washed with water, blotted, air-dried and observed initially using the ×10 objective lens under which the short chains appear like short hairs; once found, these can be observed under oil immersion (×1000) for the presence of the pink capsule surrounding the blue/black-staining bacilli. To avoid laboratory contamination, the slide and blotting paper should be autoclaved or left for some hours in a 10% sodium hypochlorite solution. 

1.1.3. Other specimens 

Identification of B. anthracis from old, decomposed specimens, processed materials, and environmental samples, including soil, is possible but these samples often have saprophytic contaminants that outgrow and obscure B. anthracis on non-selective agars. The following procedure is suggested: 

i) The sample is blended in two volumes of sterile distilled or deionised water and placed in a water bath at 62.5 ± 0.5°C for 15–30 minutes. Turnbull et al. (2007) have demonstrated that heat activation of spores can be conducted at a temperature range of 60–70°C with holding times not exceeding 15–30 minutes for best recovery. 

ii) Tenfold dilutions to 10–2 or 10–3 are then prepared. From each dilution, 10–100 µl are plated on to blood agar and optionally 250–300 µl on to PLET agar (polymyxin, lysozyme, EDTA [ethylene diamine tetra-acetic acid], thallous acetate) (Knisely, 1966; WHO, 2008). All plates are incubated at 37°C. 

iii) Blood agar plates are examined for typical colonies as previously described after overnight incubation, and the PLET plates are examined after 40–48 hours. Confirmation of the identity of suspect colonies as B. anthracis is done as described above. measured agar in only 90 ml of water. Autoclave and cool to 50°C in a water bath. Add 10 ml of a filter-sterilized (0.22–0.45 µm filter) 7% solution of sodium bicarbonate. Mix and pour into Petri dishes. The encapsulated B. anthracis will form mucoid colonies and the capsule can be visualized by making thin smears on microscope slides, fixing, and staining with polychrome methylene blue (MacFadyean’s stain). 

Polychrome methylene blue can be prepared as follows: 0.3 g of methylene blue is dissolved in 30 ml of 95% ethanol; 100 ml of 0.01% potassium hydroxide (KOH) is mixed with the methylene blue solution. Ideally, this should be allowed to stand exposed to the air, with occasional shaking, for at least 1 year to oxidize and mature. Addition of K2CO3 (to a final concentration of 1%) hastens the ‘ripening’ of the stain, but before it is regarded as diagnostically reliable, its efficacy should be established by testing it in parallel with an earlier, functional batch of stain on bona fide samples. It has been found that stains that give positive reactions with cultures of B. anthracis cultured artificially in horse blood sometimes do not give positive results in the field. In making smears for staining, only small drops of blood or tissue fluid are needed and a thin, small smear is best. After fixing (either using heat or by dipping the smear in 95–100% alcohol for about 1 minute) and drying, a small (approximately 20 µl) drop of stain is placed on the smear and spread over it with an inoculating loop. After 1 minute, the stain is washed with water, blotted, air-dried and observed initially using the ×10 objective lens under which the short chains appear like short hairs; once found, these can be observed under oil immersion (×1000) for the presence of the pink capsule surrounding the blue/black-staining bacilli. To avoid laboratory contamination, the slide and blotting paper should be autoclaved or left for some hours in a 10% sodium hypochlorite solution. PLET medium (Knisely, 1966; WHO, 2008) is prepared by using heart-infusion agar base (DIFCO) made up to the manufacturer’s instructions with the addition of 0.25–0.3 g/litre EDTA and 0.04 g/litre thallous acetate. The mixture is autoclaved and uniformly cooled to 50°C before adding the polymyxin at 30,000 units/litre and lysozyme at 300,000 units/litre. After mixing thoroughly, the agar is dispensed into Petri dishes. Reports of procedures for direct detection of B. anthracis in soils and other environmental specimens using the PCR are emerging. None of these has become routinely applicable at the present time. Animal inoculation may be considered for recovery of B. anthracis if all other methods fail. Examples of when this might occur are specimens from animals that received antibiotic therapy before death or environmental samples containing sporostatic chemicals. Due to the increasing concern to eliminate the use of animals for biological testing, this approach should be used as a last resort and only if justified. Adult mice or guinea-pigs are the animals of choice. If the samples involved are soils, the animals should be pretreated, the day before testing, with both tetanus and gas gangrene antiserum. The samples are prepared as described for culturing, including heat-shocking at 62.5°C for 15 minutes. Mice are injected subcutaneously with 0.05– 0.1 ml; guinea-pigs are inoculated intramuscularly with up to 0.4 ml (0.2 ml in each thigh muscle). Any B. anthracis present will result in death in 48–72 hours and the organism can be cultured from the blood as described above. 

1.2. Immunological detection and diagnosis 

It needs to be borne in mind that B. anthracis is antigenically very closely related to B. cereus, which is considered a ubiquitous component of the environmental microflora. The only unshared antigens that lend themselves to differentiating these two species by immunological approaches are the anthrax toxin antigens, produced during the exponential phase of growth, and the capsule of B. anthracis. This places considerable constraints on the extent to which immunological methods can be used in routine detection methodology. 

1.2.1 Ascoli Test on methodology. 

Ascoli (1911) published a procedure for the detection of thermostable anthrax antigen in animal tissue being used for by-products. This uses antiserum raised in rabbits to produce a precipitin reaction. The test lacks high specificity, in that the thermostable antigens of B. anthracis are shared by other Bacillus spp., and is dependent on the probability that only B. anthracis would proliferate throughout the animal and deposit sufficient antigen to give a positive reaction. This test appears to be used only in Eastern Europe. To perform the Ascoli test, put approximately 2 g of sample in 5 ml of saline containing 1/100 final concentration of acetic acid and boil for 5 minutes. The resultant solution is cooled and filtered through filter paper. A few drops of rabbit antiserum (see preparation below) are placed in a small test tube. The filtrate from the previous step is gently layered over the top of the antiserum. A positive test is the formation of a visible precipitin band in under 15 minutes. Positive and negative control specimen suspensions should be included. Antiserum is prepared in rabbits by the subcutaneous inoculation of Sterne anthrax vaccine on days 1 and 14. On days 28 and 35, the rabbits receive 0.5 ml of a mixture of several strains of virulent B. anthracis not exceeding 105 colony-forming units (CFU)/ml suspended in saline. Alternatively, the live virulent bacteria can be inactivated by prolonged suspension in 0.2% formalised saline, but the antigen mass needs to be increased to 108–109 CFU/ml. The suspension should be checked for inactivation of the B. anthracis before animal inoculation by culture of 0.1 ml into 100 ml of nutrient broth containing 0.1% histidine and, after incubation at 37°C for 7 days, subculture on to blood or nutrient agar. The dose regimen for the formalised suspension after initial vaccination on days 1 and 14 is increasing doses of 0.1, 0.5, 1, and 2 ml given intravenously at intervals of 4–5 days. Following either procedure, a test bleed at 10 days after the last injection should determine whether additional 2 ml doses should be administered to boost the precipitin titre. 

1.2.2. Immunofluorescence 

While some success has been achieved with immunofluorescence for capsule observation in the research situation (Ezzell & Abshire, 1996), it does not lend itself to routine diagnosis. 

1.3. Confirmation of virulence with polymerase chain reaction 

Confirmation of virulence can be carried out using the PCR. The following instructions are taken from the WHO (2008). Template DNA for PCR can be prepared from a fresh colony of B. anthracis on nutrient agar by suspension of a loop of growth in 25 µl sterile deionised (or distilled) water and heating to 95°C for 20 minutes. Following cooling to approximately 4°C, and brief centrifugation, the supernatant can be used for the PCR reaction. Examples of suitable primers (Beyer et al., 1996; Hutson et al., 1993) for confirming the presence of the pXO1 and pXO2 plasmids are given in the table below. 

Target Primer ID Sequence 5’–3’ Product size Concentration Protective antigen (PA) PA 5 3048–3029 TCC-TAA-CAC-TAA-CGA-AGT-CG 596 bp 1 mM PA 8 2452–2471 GAG-GTA-GAA-GGA-TAT-ACG-GT Capsule 1234 1411–1430 CTG-AGC-CAT-TAA-TCG-ATA-TG 846 bp 0.2 mM 1301 2257–2238 TCC-CAC-TTA-CGT-AAT-CTG-AG PCR can be carried out in 50 µl volumes using the above primers, 200 µM each of dATP, dCTP, dTTP and dGTP, 1.5 mM MgCl2 and 2.5 units of DNA polymerase, all in NH4 buffer, followed by the addition of 5 µl of template DNA. 

A 2% agarose gel has been found to work best with these small fragments. Alternatively, premixed, predispensed, dried beads available commercially can be used. These are stable at room temperature, containing all the necessary reagents, except primer and template, for performing 25 µl PCR reactions. The template can be added in a 2.5 µl volume. 

The following PCR cycle can be used: 1 × 95°C for 5 minutes; 30 × 95°C for 0.5 minute followed by 55°C for 0.5 minute followed by 72°C for 0.5 minute; 1 × 72°C for 5 minutes; cool to 4°C. It should be noted that the primers given in the table above have proved successful for confirming the presence or absence of pXO1 and/or pXO2 in pure cultures of isolates from animal (including human) specimens or environmental samples. They may be unsuitable, however, for direct detection of B. anthracis in such specimens or samples. A choice of alternatives can be found in Jackson et al. (1998) and Ramisse et al. (1996). For the rare possibility that an isolate may lack both pXO1 and pXO2, a chromosomal marker should also be run; primers for these are also described in Jackson et al. (1998) and Ramisse et al. (1996). Real-time PCR assays have been developed for enhanced speed, sensitivity and specificity of detection of pXO1, pXO2 and chromosomal genes of Bacillus anthracis and other closely related Bacillus spp. (e.g. Hadjinicolaou et al., 2009; Hoffmaster et al., 2002; Irenge et al., 2010; Qi et al., 2001; Rao et al., 2010). Selection of a particular assay will be dependent on the fitness for purpose and source of starting material (e.g. isolates, clinical specimen, environmental sample), requirement to differentiate from other Bacillus spp. or vaccine strains, demonstration of genetic diversity or confirmation of isolate identity. It is important that the laboratory conducting real-time PCR evaluate the performance of the test for their purpose and complete a validation analysis to ensure that it has been optimised and standardised for its intended use (see Chapter 1.1.6 Principles and methods of validation of diagnostic assays for infectious diseases). 

C. REQUIREMENT OF VACCINE 

1. Background 

1.1. Rationale and intended use of the product 

The most widely used vaccine for prevention of anthrax in animals was developed by Sterne (1937). He derived a rough variant of virulent B. anthracis from culture on serum agar in an elevated CO2 atmosphere. This variant, named 34F2, was incapable of forming a capsule and was subsequently found to have lost the pXO2 plasmid, which codes for capsule formation. It has become the most widely used strain world-wide for animal anthrax vaccine production. In Central and Eastern Europe, an equivalent pXO2– derivative, Strain 55, is the active ingredient of the current livestock vaccine. A list of manufacturers of anthrax vaccine for use in animals is given in Annex 5 of WHO (2008). The following information concerning preparation of the anthrax vaccine for use in animals is based on Misra (1991) and the WHO (1967). Generalised procedures are given; national regulatory authorities should be consulted in relation to Standard Operating Procedures that may pertain locally. 2. Outline of production and minimum requirements for conventiomal vaccine.

2.1. Characteristic of the seed 

2.1.1. Biological characteristic 

Anthrax vaccine production is based on the seed-lot system. A seed lot is a quantity of spores of uniform composition processed at one time and maintained for the purpose of vaccine preparation. Each seed lot is no more than three passages from the parent culture and must produce a vaccine that is efficacious and safe for use in animals. It is recommended that a large seed lot be prepared from the parent strain and preserved by lyophilisation for future production lots. The parent culture can be purchased2. 2.1.2. Quality criteria The seed lot is acceptable for anthrax vaccine if a vaccine prepared from the seed lot or a suspension harvested from a culture derived from a seed lot meets the requirements for control of final bulk with respect to freedom from bacterial contamination, safety and efficacy (immunogenicity). 

2.2. Method of Manufacture

 

2.2.1. Procedure 

i) Preparation of the master seed Seed lots are cultured on solid media formulated to promote sporulation of the organism. The solid medium formula for casein digest agar (sporulation agar)given in Misra (1991) is: 50 g tryptic digest of casein; 10 g yeast extract; 0.1 g CaCl2 .6H2O; 0.01 g FeSO4 .7H2O; 0.05 g MgSO4 .7H2O; 0.03 g MnSO4 .4H2O; 5.0 g K2HPO4 ; 1.0 g KH2PO4 ; 22 g agar; 1000 ml deionized or distilled water. The ingredients are dissolved in the water with the appropriate amount of heating; the solution is adjusted to pH 7.4, distributed into Roux bottles (120 ml per bottle) or other appropriate container, sterilized by autoclaving and cooled in the horizontal position. After the agar has solidified, excess liquid should be removed aseptically and the bottles left in an incubator (37°C) for at least 2 days to dry and to check the sterility. Volumes of 2 ml of vaccine seed should be spread across the agar in Roux bottles, which should be incubated at 37°C until at least 80% sporulation is apparent by microscopic examination of aseptically extracted loopfuls (at least 72 hours). The growth is harvested with 10 ml per bottle of sterile deionized or distilled water and checked for purity. After washing three times in sterile deionized or distilled water with final suspension, also in sterile deionized or distilled water, sterilized lyophilization stabilizer is added and the suspension is dispensed into lyophilization vials and freeze-dried. Attenuated vaccine strains can gradually lose their antigenicity over repeated subculturing conditions. Therefore, it is recommended that master seed lots be made in bulk and kept within three passages from the original seed culture. A large number of master seed stocks should be prepared. 

ii) Preparation and testing of the working seed Reconstitute a vial of seed stock and inoculate several slants (approximately 10 ml) of sporulation (casein digest) agar. Incubate at 37°C for 72 hours and store in a refrigerator. Test the slants for purity by culture on to nutrient agar plates and in nutrient broth (0.1 ml in 100 ml of nutrient broth). The latter should be subcultured on to nutrient agar after incubation at 37°C for 7 days and should be a pure culture of B. anthracis. A sample of the broth culture should also be checked for lack of motility. Volumes of seed needed for a production run should be calculated on the basis of harvesting the spores from each slant with 10 ml of sterile deionized or distilled water and using this to inoculate five Roux bottles. 

iii) Preparation of vaccine concentrate Roux bottles with casein digest agar are prepared as for the master seed in Section C.2.2.1.i above. One Roux bottle can be expected to yield about 2000 doses of vaccine. Each Roux bottle is inoculated with 2 ml of working seed suspension and incubated at 37°C with porous plugs for several days until small loopfuls of culture from randomly selected bottles show at least 90% of the organisms to be in sporulated forms when examined in wet mounts by phase contrast (phase bright spores) or following staining for spores. The growth from each bottle is then harvested with 20 ml of physiological saline. Tests for contaminants should be carried out by subculture to nutrient agar plates and inoculation of 100 ml nutrient broth with 0.1 ml of harvested spores followed by subculture to nutrient agar after 7 days at 37°C and by tests for motility. Acceptable harvests (i.e. those showing no evidence of contaminants) are pooled. 

iv. Glycerination 

Twice the volume of sterile, pure, neutral glycerol should be added to the bulk pool of vaccine concentrate. Saponin (0.1% final concentration) may also be added at this point if it is to be included as an adjuvant. Mix thoroughly (the inclusion of sterilised glass beads may be helpful). Carry out a purity test and hold for 3 weeks at ambient temperature to allow lysis of any vegetative bacteria, determine the viable spore count and store under refrigeration thereafter. 

v. Determining and dilution for use 

The number of culturable spores in the product is then calculated by spreading tenfold dilutions on nutrient agar plates. The suspension is diluted so that the final bulk contains the number of culturable spores desired. The diluent should contain the same proportions of saline, glycerol and (if being included) saponin as present in the vaccine concentrate. The vaccine should contain a minimum of 2–10 × 106 culturable spores per dose for cattle, buffaloes and horses, and not less than 1–5 × 106 culturable spores per dose for sheep, goats and pigs. VI. Filling the container Distribution of aliquots of vaccine into single and multidose containers is performed as outlined in WHO (1965). Basically, the final bulk is distributed to containers in an aseptic manner in an area not used for production, and any contamination or alteration of the product must be avoided. The vaccine may be lyophilized after distribution into appropriate dosage containers. Containers are sealed as soon as possible with a material that is not detrimental to the product and that is capable of maintaining a hermetic seal for the life of the vaccine. 

REFERECIES 

ABSHIRE T.G., BROWN J.E. & EZZELL J.W. (2005). Production and validation of the use of gamma phage for identification of Bacillus anthracis. J. Clin. Microbiol., 43, 4780–4788. 

ASCOLI A. (1911). Die Präzipitindiagnose bei Milzbrand. Centralbl. Bakt. Parasit. Infeckt., 58, 63–70. BEYER W., GLOCKNER P., OTTO J. & BOHM R. (1996). A nested PCR and DNA-amplification-fingerprinting method for detection and identification of Bacillus anthracis in soil samples from former tanneries. Salisbury Med. Bull., No. 87, Special Suppl., 47–49. 

BROWN E.R. & CHERRY W.B. (1955). Specific identification of Bacillus anthracis by means of a variant bacteriophage. J. Infect. Dis., 96, 34–39. 

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Chapter 2.1.2 OIE Terrestrial Manual 2018)