FREE SEMINER ON MICROBIAL BIOHAZARD

FREE SEMINER ON MICROBIAL BIOHAZARD

1.0 INTRODUCTION

Biological hazards, also known as biohazards, are organic substances that pose a threat to the health of humans and other living organisms. Generally speaking, biological hazards include pathogenic micro-organisms, viruses, toxins (from biological sources), spores, fungi and bioactive substances. Biological hazards can also be considered to include biological vectors or transmitters of disease. Outside the health area, biological hazards include substances that cause social and economic disruption, property damage and environmental degradation, such as insect plagues or infestations. Worldwide, it is estimated that around 320 000 workers die each year from communicable diseases caused by work-related exposures to biological hazards (Driscoll et al., 2005). 

Humans are exposed to biological hazards in the work environment in a variety of ways. For example, workers in health care professions are exposed via contact with human bodily matter, such as blood, tissues, saliva, mucous, urine and faeces, because these substances have a high risk of containing viral or bacterial diseases. Likewise, people who work with live animals or animal products (blood, tissue, milk, eggs) are exposed to animal diseases and infections, some of which (zoonoses) have the potential to infect humans (e.g. Q-fever, avian flu or Hendra virus) or cause serious allergy via sensitisation. For instance, it is estimated that up to one third of people exposed to laboratory animals develop allergies (Harrison, 2001) that can sometimes result in anaphylactic shock and death. Similarly, in a study of zoo veterinarians, 32% reported an allergy to the animals they treated and many report allergies to cats, pigs and poultry (Jeyaretnam et al., 2000). Exposure to biological hazards in the work environment can also occur when people are in contact with laboratory cell cultures, soil, clay and plant materials, organic dusts, food, and rubbish, wastewater and sewerage (OSHA, 2003). Exposure to moulds and yeasts is common in some industrial processes involving metal and wood, in museums and libraries, in workplaces with air conditioning systems and high humidity, and in the Construction industry. Exposure to biological hazards is therefore widespread and the risk of exposure is not always obvious (OSHA, 2003).

Although Safe Work Australia (or its predecessors) has published a specific Code of Practice for the management of exposure to the blood borne viruses hepatitis and HIV (NOHSC, 2003) and an information guide about diseases acquired from animals (NOHSC, 1989), currently Australia has no official regulations or Codes of Practice relating to work-related exposures to biological hazards generally. Australian Standards has developed a standard for Safety in Laboratories (AS2243.3) microbiological aspects and containment facilities. There are also numerous other relevant standards for work undertaken in the health care industry e.g. AS/NZS 3816 (1998) Management of Clinical and Related Wastes. The Australian Department of Health and Aging has published Infection Control Guidelines .The document outlines the principle involved in and the procedures necessary for the prevention of the transmission of infectious diseases in the health care setting (OSHA, 2005). 

The European Union (EU) has a directive on ‘biological agents’ (EEC, 1990), which are defined as ‘microorganisms, including those that have been genetically modified, cell cultures and human endoparasites, which may be able to provoke any infection, allergy or toxicity’. These biological agents are classified into four risk groups according to their level of risk of infection. Group One agents are unlikely to cause human disease. A Group Two agent can cause human disease and might be a hazard to workers, but is unlikely to spread to the community and usually has effective prophylaxis or treatment available. Group Three agents can cause severe human disease and present a serious hazard to workers. They may present a risk of spreading to the community but there is usually effective prophylaxis or treatment available. Group four biological agents cause severe human disease and are a serious hazard to workers. They may present a high risk of spreading to the community and there is usually no effective prophylaxis or treatment available. These risk group classifications have been adopted in a reworded but essentially unchanged format in the Australian Standards (AS2243.3) Safety in Laboratories: microbiological aspects and containment facilities. Both the EU and Australian and New Zealand risk groups are modified from the World Health Organisation (WHO) risk groups (Driscoll et al., 2005).

2.0 MICROBIAL BIOHAZARD 

Microbial biohazards, also known as biohazards, are organic substances that pose a threat to the health of humans and other living organisms. Generally speaking, biological hazards include pathogenic micro-organisms, viruses, toxins (from biological sources), spores, fungi and bioactive substances. Biological hazards can also be considered to include biological vectors or transmitters of disease. Outside the health arena, biological hazards include substances that cause social and economic disruption, property damage and environmental degradation, such as insect plagues or infestations. Worldwide, it is estimated that around 320 000 workers die each year from communicable diseases caused by work-related exposures to biological hazards (Driscoll et al., 2005).

2.1 TYPES OF  MICROBIAL BIOHAZARD

Biological hazard can be put in to three (3) different categories:

Bacteria.

Viruses.

Fungi.

Bacteria: Are unicellular microscopic organism that can easily be seen with light microscope. They occur in cluster or colonies. A bacterium has slimy capsule, cell wall, a cell membrane, and dense cytoplasmic granules with no nucleus but has a nuclear material called DNA (Deoxyribose Nucleic Acid) which spread through the cell. Bacteria are prokaryote whose size are measured in mm [um] and it has four shape which are; Cocci(round shape),Bacilli(rod shape),Spiral(Helical) and Vibrio(bend rod) (Micheal, 2008)

2.1.1 Bacterial diseases and Hazard they Cause

Pathogenic bacteria cause human death and cause infections such as tetanus( Clostidium tetani), typhoid fever(Salmonella typhi), anthrax (Bacillus anthracis), plague (Yersinia pestis), tularemia (Francisella tularensis) Legionnaires disease (Legionella pneumophila) and tuberculosis (Mycobacterium tuberculosis). Diphtheria (Corynebacterium dephtheriae), syphilis (Treponemma pallidum), cholera(Vibrio cholarae), foodborne illness, leprosy. Each species of pathogen has a characteristic spectrum of interactions with its human hosts. Some organisms, such as Staphylococcus or Streptococcus, can cause skin infections, pneumonia, meningitis and even overwhelming sepsis, a systemic inflammatory response producing shock, massive vasodilation and death (Fish, 2002).. Other organisms invariably cause disease in humans, such as the Rickettsia, which are obligate intracellular parasites able to grow and reproduce only within the cells of other organisms. One species of Rickettsia causes typhus, while another causes Rocky Mountain spotted fever. Chlamydia, another phylum of obligate intracellular parasites, contains species that can cause pneumonia, or urinary tract infection and may be involved in coronary heart disease (Belland et al., 2004). Finally, some species, such as Pseudomonas aeruginosa, Burkholderiacenocepacia, and Mycobacterium avium, are opportunistic pathogens and cause disease mainly in people suffering from immunosuppression or cystic fibrosis (Heise, 1982 and Saiman, 2004).

Table 1: Examples of some Bacterial Diseases that pose health hazard

     Disease

Causative agent

Prevention and cure

Typhoid

Salmonella typhi

- Avoid taking exposed food & drinks.

- Proper sanitation & disposal of excreta.

- Antibiotics should be administered

Tetanus

Clostridium tetani

-Tetanus vaccine

- Antibiotics

Diphtheria

Cholera

Tuberculosis 

Salmonellosis

Corynebacterium diphtheria

Vibro cholera

Mycobacterium tuberculosis

Salmonella typhi

- Diphtheria vaccine

- Antibiotics, tracheostomy

- Proper sanitation, dinking clean water, cholera vaccine

- Antibiotics

- Screening those at high risk

- Treatment of those infected

- Vaccination with bacillus Calmette-Guerin (BCG)

- Antibiotics

-Proper preparation and cooking of food

- Proper sanitation, dinking clean water

- Antibiotics

Plague

Yersinia pestis

-Plague vaccine

- Antibiotics and supportive care

Anthrax

Bacillus anthracis

- Anthrax vaccination

- Antibiotics

Gonorrhea

Niesseria gonorrhoeae

- Protected sexual contact (using condom)

-Antibiotics

Botulism  (food-poisoning)

ClostridIum botulinum

- Proper food preparation

- Antitoxin, Antibiotics

Viruses:These are very small sized etiological agents of disease  that are capable of passing through a filters that retain even bacteria,increase(multiply) only in the presence of living cell because they are obligate intracellular parasites and can give rise to new strain by mutation and can only be seen with electron microscope(Lecture note  2016). 

2.1.2 Viral Diseases and Hazard they Cause

Viruses play a vital role in causing various infection, it can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea (Koonin et al., 2006).Examples of common human viral diseases include the common cold, influenza, chickenpox, cold sores, equine encephalitides(Venezuelan equine encephalitis(VEE), eastern equine encephalitis(EEE), and western equine encephalitis(WEE) viruses),hemorrhagic fevers (are naviruses, filoviruses,floviruses, and  bunyaviruses),and smallpox (variolavirus), measles, a , Hantavirus and  rabies(Koonin et al., 2006).

Many serious diseases such as Ebola virus disease, AIDS, avian influenza, and SARS are caused by viruses. The relative ability of viruses to cause disease is described in terms of virulence. Other diseases are under investigation to discover if they have a virus as the causative agent, such as the possible connection between human herpesvirus 6 (HHV6) and neurological diseases such as multiple sclerosis and chronic fatigue syndrome (Komaroff, 2006). There is controversy over whether the bornavirus, previously thought to cause neurological diseases in horses, could be responsible for psychiatric illnesses in humans (Chen et al., 1999). Viruses have different mechanisms by which they produce disease in an organism, which depends largely on the viral species. Although viruses cause disruption of healthy homeostasis, resulting in disease, they may exist relatively harmlessly within an organism. An example would include the ability of the herpes simplex virus, which causes cold sores, to remain in a dormant state within the human body. This is called latency (Margoliset al., 2007) and is a characteristic of the herpes viruses, including Epstein–Barr virus, which causes glandular fever, and varicella zoster virus, which causes chickenpox and shingles. Most people have been infected with at least one of these types of herpes virus (Whitley and Roizman, 2001).

Table 2: Some Examples of Viral Diseases that pose health hazard

Disease

Causative agent

Prevention and control

Influenza (Flu)

Orthomyxo virus

-Influenza vaccine

Small pox (variola)

Variola virus

-Administration of vaccine

Chicken pox (Varicella)

Poliomylitis (Polio)

Genital Herpe

Varicella zoster virus

Polio virus

Herpis simplex virus

-Varicella vaccine

-Polio vaccine drop ( Oral polio vaccine, OPV) are given to children at certain intervals

Yellow Fever

SARS- Severe Acute Respiratory Syndrome

HIV

Flavi virus

SARS- Coronavirus

Human immunodeficiency virus

Vaccine available

SARS is mostly diagnosed by PCR (polymerase chain reaction) test

- Using of condom during sexual intercourse

-Antiretroviral drugs

Fungi:These are eukaryotic spore bearing,saprophytic or parasitic organism that generally  reproduce asexually and sexually.They are usually filamentous,branched structure and typically surrounded by cellwall containing chitin or cellulose or both,together with many othercomplex complex molecules. Fungi cell membrane is composed of steroid (Lecture note 2016).

2.1.3 Fungal Disease and Hazard they Cause

 Fungi can cause two broad classes of disease: superficial and deep. The superficial diseases are either cutaneous, growing on the skin, or subcutaneous, growing just below the skin. The deep diseases are either systemic, they colonize most of the body, or opportunistic (fungi that normally live in the body but become pathogenic only when the immune system is suppressed).

Some fungi can cause serious diseases in humans, several of which may be fatal if untreated. These include aspergillosis, candidiasis, coccidioidomycosis, cryptococcosis, histoplasmosis ,mycetomas, and paracoccidioidomycosis. Furthermore, persons with immuno-deficiencies are particularly susceptible to disease by genera such as Aspergillus, Candida, Cryptoccocus (Hube, 2004; Nielsen and Heitman, 2007 and Brakhage, 2005), Histoplasma (Kauffman, 2007), and Pneumocystis (Cushion et al., 2007). Other fungi can attack eyes, nails, hair, and especially skin, the so-called dermatophytic and keratinophilic fungi, and cause local infections such as ringworm and athlete's foot (Cook and Zumla, 2008). Fungal spores are also a cause of allergies, and fungi from different taxonomic groups can evoke allergic reactions (Simon et al., 2008).

Table 3: Examples of some Fungal Diseases that pose health hazard

Disease

Causative agent

Prevention and control

Dermatophytosis (Ring worm)

Vaginal Candidiasis (vaginal yeast infection)

Mycetoma

Sporotrichosis

Trichophyton, Microsporum, and Epidermophyton

 Candida albican

Eumycetoma

Sporothrx schenckii

-The skin dry

- avoid walking barefoot at public places

- not sharing personal items

- Antifungal creams such as clotrimazole or miconazole.

-Wearing of cotton underwear might help to reduce  the chances of getting yeast infection

- Proper usage of antibiotics

-Antifungal medicine

- Avoid walking barefoot

-Antifungal drugs

-Wearing long sleeve and gloves while working with the soil, hay bales, rose bushes, pine seedlings and sphagnum moss.

-Keeping cats indoors

- Antifungal drugs (Itraconazole and fluconazole)

Onychomycosis (Fungal nail infection)

Dermatophytes and Fusarium

-Avoid going barefoot in damp public places such as swimming pools, gyms etc.

- Avoid wearing of socks or shoes that hinder ventilation and do not absorb perspiration

- Antifungal medication (Terbinafine, ciclopirox)

3.0 BIOLOGICAL WEAPON

Bioweapons is a planned and deliberate use of pathogenic strains of microorganisms such as bacteria, viruses or their toxins to spread life-threatening diseases on a mass scale in order to devastate the population of an area. Biological agents listed for use in weaponization and war are many .Those commonly identified for prohibition by monitoring authorities are the causative agent of bacterial diseases which include those causing anthrax(Bacillus anthracis), plague (Yersinia pestis) ,tularemia (Francisella tularemia).Viruses causing equine encephalitides(Venezuelan equine encephalitis(VEE), eastern equine encephalitis(EEE), and western equine encephalitis(WEE) viruses),hemorrhagic fevers (are naviruses, filoviruses,floviruses, and  bunyaviruses),and smallpox (variolavirus) .Toxins include botulinum toxin from Clostridium botulinum; ricin toxin from the castor bean Ricinus communis;While fungi include trichothecene mycotoxins from Fusarium. Myrotecium, Tricboderma, Stachybotrys, and other filamentous fungi; staphylococcal enterotoxins from Staphylococcus aureus; and toxins from marine organisms such as dinoflagellates, shellfish, and blue-green algae (Cunidiff et al., 1999). If these agents are delivered successfully to a susceptible host, a lethal or   incapacitating outcome will occur, depending upon the agent. For instance, the most likely result from the agents causing anthrax and plague is death of the target host. Coxiella burnetii(the agent of Q-fever),staphylococcal enterotoxin B, and Venezuelan equine encephalitis virus are considered incapacitating agents. 

In a military context, incapacitating agents may be, in a certain sense, more effective because the affected unit will not be able to perform its mission and casualties will consume scarce medical and evacuation assets. In a biological terrorism scenario, both lethal and incapacitating agents could have an adverse impact on the civilian healthcare delivery system. Potential manifestations include terror in the affected population and in medical care personnel; an overwhelming number of casualties placing demands for ICU care or special medications; a need for personal protection in medical care settings, clinical laboratories, and autopsy suites; and problems with handling remains. Employing standard precautions or barrier nursing techniques (Miller et al., 1999), depending on the agent, can provide appropriate (or adequate) protection against biological agents to healthcare providers. However, additional precautions such as aerosol, droplet, or contact protection are recommended in instances where smallpox, Y. pestis (plague), the hemorrhagic fever viruses, or T-2 mycotoxin are suspected. There may be a hazard of person-to-person transmission, transmission by direct contact with blood or body fluids, or dermal activity (Department of the Army, the Navy, and the Air Force, February 1996; Franz, 1997; Franz, jahrling,Friedlander, et al., 1997;Gamer&Hosp. Infect. Control Pract, Advis, Comm., 1996; Gamer and Hosp. Infect.ControlPract.Advis,Comm., 1996; Rosen, 1999;Wannemacher and Wiener, 1997).

3.1 CHARACTERISTICS OF BIOLOGICAL WEAPONS

Biological weapons are organisms or toxins that are:

Easy to produce and deliver.

Safe for use by the offensive soldiers.

Able to incapacitate or kill individual attack in a reproducible and consistent manner (Christopher, et al., 1

3.2 PROPERTIES OF BIOLOGICAL AGENTS

Biological agents may be used, perhaps as an ultimate weapon, because of several characteristics valued by the perpetrator. These properties include;

1. Natural odouless occurance.

2. Invisible particles normally dispersed through aerosol spray without detection.

3. Entry through inhalation or ingestion. 

4. Pre-exposure treatment confers or enhances immunity through use of toxoids, vaccines, antibacterial protective clothing, biosensors and smoke detectors.

5. Effect of biological agents and toxins are diverse resulting incapatation or death occurring after contraction of disease resulting from infection by a specific biological agent eg anthrax caused by B. anthracis and faugue caused by Y. pistis

6. Production methods are simple and cheap relying on non-sophisticated technology and easily obtainable knowledge in biology, genetics engineering, medicine and agriculture

7. Not easily detected in export control and searches by routine detection system, eg X-ray.

Table 4. Major Categories of biological agents with probability to be used as bio-weapons 

Groups

  Disease

 Agents

A

Anthrax

Bacillus anthracis

Botulinum

Clostridium botulinum toxin

Plaugue

Yersinia pestis

Small pox

Variola major

Tularemia

Francisella tularensis

Viral haemorrhagic fevers

Filoviruses and Arenaviruses

B

Brucllosis

Brucella spp.

Epsilon toxin

Clostridium perfringens

Food safety threat

Salmonella spp.,shigella

Glanders

Burkholderia mallei

Melioidosis

Burkholderia pseudomallei

Psittacosis

Clamydia psittaci

Q  fever

Coxiella burnetiid

Ricin toxin

Ricinus communis

Staphylococcal enterotoxin B

Staphylococcus spp.

Typhus fever

Rickettsia prowezekii

Viral encephalitis

Alphaviruses

Water safety threat

Vibrio cholera, C. parvum

C

Emerging infectious disease

Nipahvirus and Hantavirus

(CDC, 2013)  

3.3 ROUTES OF EXPOSURE OF MICROBIAL BIOHAZARD

Biological agents can be transmitted through one or more ways. The transmission modes are:  parenteral; agents that are transmitted through body fluids or blood, airway (by droplets); agents that are emitted by infected individuals, which can then be inhaled by surrounding people. Contact; through which the agents present on the surface of the infected organism can infect another organism. Oral-fecal route: through objects, foods or other items contaminated with the feces of infected patients, or through sexual contact (Placa 2010).

3.3.1 Respiratory System

Inhalation most dangerous, inhaled, resembles flu symptoms but progresses to fluid in lungs and respiratory failure. The body is most vulnerable to this route of exposure because of  the large surface area and gas exchanging function of the lungs; because of the susceptibility of mucous membranes to infection; and because of the presence of phagocyte cells that, if unsuccessful in destroying a pathogenic microorganism, may instead carry it to the lymph system where it may proliferate and Cause most biological  agents affect the 30  American Journal of Biomedical Research lungs, Unlike vapors, aerosol particles of a certain size are accumulated over time in the respiratory system (Steffen 1997).

3.3.2 Skin and Mucous Membranes

Cutaneous, skin, least harmful, enters through abrasion or cuts, causes lesion with black scab. The presence of injuries, sores or skin rashes might change this significantly and allow even biological agents to enter the body by this route. As a rule, the thinner, more vascular, and moister the skin, the more prone it is to penetration. High relative humidity promotes skin penetration. Liquid spills and aerosols cause a hazard for skin penetration that can be several deliveries. In case of makeshift devices, a larger fraction of agent will be in the spills and a smaller part will usually order of magnitude higher than from vapors. Spills will occur mainly around the point of be aerosolized (Polhujis et al.,(1997). 

3.3.3 Digestive System

Gastrointestinal, ingesting infected meat or water, nausea, abdominal pain and bleeding, fever, vomiting, can be treated with antibiotics early on. Microbial agents can enter the digestive system in contaminated food or drinking water, by hand-mouth  contact after touching contaminated surfaces, or by swallowing of respiratory mucus after an accumulation of larger aerosol particles in the nose/throat and upper airways. Of all exposure routes this is the easiest to control, provided that the contaminated sources are known (Langenberge et al., 1997).

4.0 GENERAL MEASURES FOR PREVENTION AND CONTROL AGAINST MICROBIAL BIHAZARD.

The general population should be educated and made aware of the threat and risk associated with microbiological hazard.

Vaccination has advantage in protecting laboratory workers or individual working where the target diseases are endemic. Example, in preventing anthrax infection.

For those biohazard agents for whom a specific immunization is not available, the use of protective equipment combined with chemoprophylaxis may be employed to provide protection.

If an attack is felt to be imminent, or is known to have occurred, command-directed chemoprophylaxis would be appropriate for all personnel in that area.

Network of specialized laboratories should be established for a confirmatory laboratory diagnosis.

Existing disease surveillance system as well as vector control measures and mass immunization program in the suspected area should be pursued more rigorously.

Enhancing the knowledge of skills of clinician plays a vital role in controlling the adverse impact of the attack.

Immunizations, pre-exposure and post exposure prophylaxis, therapeutic and protective clothing are available to provide protection (Center for disease control and prevention, 2013) .

CONCLUSION. 

Microbial biohazard  have not been frequently used throughout human history, and their efficacy to be used as a war weapon has not been completely confirmed. Because natural infections pose a great risk for human health, as in case of infection with Influenza virus, where there is an involvement of  large population, mostly owing to easy spread, a threat of its use as a BW cannot be underestimated. There has been a continual fascination with biological weapons by nations in the last century, an addiction that continues even today. Particularly where regional hegemony (or resisting it) may require unconventional weapons, Microbial biohazard  remain a major threat. With zoonoses as the most likely infectious diseases to be used by bioterrorists to develop BW’s, human and veterinary medicine can benefit from cross-collaboration. Therefore measures should be taken in order to prevent the effect of biological hazard. 

 

REFERENCES

Alibek, K. and Handelman, S. (1999). Biohazard: The Chilling True Story of the Largest Covert Biological Weapons Program in the World — Told From Inside by the Man Who Ran It. New York, NY: Random House; 1999.

Arnon, S.S., Schechter, R., Inglesby, T.V., Henderson, D.A., Bartlett, J.G., Ascher, M.S., Eitzen, E., Fine, A.D., Hauer, J., Layton, M., Lillibridge, S., Osterholm, M.T., O'Toole, T., Parker, G., Perl, T.M., Russell, P.K., Swerdlow, D.L. and Tonat, K. American Journal of Biomedical Research  33 (2001).  Botulinum toxin as a biologicalweapon: medical and public health management. JAMA, 285:1059-1070..

, T.-C., & Harrison, J. (1998). Exposure-based Hazards: Biological. In J. A. Herzstein, L. E. Fleming and W. B. Bunn (Eds.), International occupational and environmental medicine. St Louis, MI: Mosby.

Baca, O.G. and Paretsky, D. (1983). Q fever and C.burnetiid: a model for host-parasite interactions. Microbiol. Rev., 47: 127-149.

Barton ES, White D.W, Cathelyn J,S, (2007): Herpesvirus latency confers symbiotic protection from bacterial infection. Nature. 2007; 447(7142):326–29.   doi:10.1038/nature05762 .  PMID 17507983.

Belland RJ, Ouellette SP, Gieffers J, Byrne GI (February 2004). "Chlamydia pneumoniae and atherosclerosis". Cellular Microbiology. 6 (2): 117–27. doi:10.1046/j.1462-5822.2003.00352.x. PMID 14706098..

Bhalla, D.K. and Warheit, D.B. (2004). Biological agents with potential for misuse: a historical perspective and defensive measures. Toxicol.Appl.Pharmacol. 199: 71-84.

Biological and chemical terrorism: strategic plan for preparedness and response (2000). recommendations of the CDC Strategic Planning Workgroup. MMWR Morb.Mortal.Wkly.Rep., 49: 1-14.

Brakhage A.A (December 2005). "Systemic fungal infections caused by Aspergillus species: epidemiology, infection process and virulence determinants". Current Drug Targets. 6 (8): 875–86. doi:10.2174/138945005774912717 .

Control Disease Center and Prevention (2001). Center for Law and the Public's Health at Georgetown and Johns Hopkins Universities. The Model State Emerg. Health Powers Act., 12: 25-28.\

Control Disease Center and Prevention (1999). Bioterrorism Alleging Use of Anthrax and Interim Guidelines for Management United States. Morb. Mortal. Wkly  Rep., 48: 69-74.

Control Disease Center and Prevention (2000).  Laboratory-acquired human glanders  Marlyland. MMWR, 49: 532-535.

Control Disease Center and Prevention (2013). Bioterrorism agents /diseases, CDC website. Available at: http://emergency.cdc.gov /agent/agentlist-category.asp.

Center for Disease Control and Prevention. (2009). Biosafety in microbiological and  biomedical laboratories (BMBL) (5th ed.). Retrieved from http://www.cdc.gov/biosafety/publications/bmbl5/

Centers for Disease Control and Prevention,( 2003), Multistate outbreak of monkeypox—Illinois, Indiana, and Wisconsin, 2003: Morb. Mortal.Wkly Rep., 52: 537-540.

Chen C, Chiu Y, Wei F, Koong F, Liu H, Shaw C, Hwu H, Hsiao K (1999):  High seroprevalence of Borna virus infection in schizophrenic patients, family members and mental health workers in Taiwan. Molecular Psychiatry. 1999; 4(1):33–38.  doi:10.1038/sj.mp.4000484. PMID 10089006.

Driscoll T, Takala J, Steenland K, Corvalen C and Fingerhut M. (2005). Review of estimates of the global burden of injury and illness due to occupational exposures. American Journal of Industrial Medicine, 48: 491-502.

European Commision (1990). Council Directive 90/679/EEC of 26 November 1990 on the protection of workers from risks related to exposure to biological agents at work (seventh individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC. The Council of the European Communities: 31990L0679.

Harrison D.J (2001). Controlling exposure to laboratory animal allergens. Institute for Laboratory Animal Research (ILAR) Journal, 42: 17-36.

Henderson, D.A. (1999). The looming threat of bioterrorism: Sci., 283: 1279-1282.

http://www.wildlifehealth.org.au/AWHN_Admin/ManageWebsite%5CFactSheets%5CU ploadedFiles/119/Hendra%20Virus%209%20Sept%202011%20(1.5).pdf

Jeyaretnam J, and Jones H. (2000). Physical, chemical and biological hazards in veterinary practice. Australian Veterinary Journal, 78: 751-758.