Biowarfare: Epidemiology, Detection, Control, Prevention, and Global Public Health Implications

Biological and chemical weapons, while unlikely to be used in conventional warfare, represent an ongoing threat to public health, particularly when they fall into the hands of non-state actors. The epidemiology of these agents is complex, requiring specialized laboratory detection, robust surveillance, and rapid response capabilities. Prevention and control strategies must integrate ethical oversight, regulatory enforcement, public health preparedness, and international collaboration.

The ethical responsibility of scientists is central to this effort. Knowledge and technology can either protect or endanger humanity, and the global scientific community must ensure that education, oversight, and moral guidance prevent the misuse of biological research. Ultimately, safeguarding populations from biowarfare is not solely a matter of defense or policy, it is a multidimensional challenge requiring coordination across science, public health, governance, and society. By addressing the epidemiology, detection, control, prevention, and ethical dimensions of biowarfare, nations can reduce the risk of deliberate biological attacks, enhance preparedness for emerging pathogens, and strengthen the resilience of public health systems worldwide.

Chemical and biological agents represent a distinct class of weapons of mass destruction (WMD) that differ fundamentally from conventional warfare tools such as firearms, artillery, or even nuclear weapons. Unlike conventional weapons, chemical and biological weapons are often invisible, odorless, and capable of producing delayed and insidious effects in affected populations. Exposure to these agents may not produce immediate symptoms, and the clinical manifestations can range from mild illness to fatal systemic disease depending on the agent, route of exposure, and dose. This latent nature, combined with the potential for high morbidity and mortality, makes these agents uniquely frightening and challenging from a public health perspective.

Historically, the use of biological and chemical weapons has been limited in formal warfare due to international treaties and global norms. The 1925 Geneva Protocol, followed by the 1972 Biological Weapons Convention (BWC), explicitly prohibited the development, production, and stockpiling of biological weapons, while the Chemical Weapons Convention (CWC) of 1993 extended similar restrictions to chemical agents. Despite these treaties, the risk of non-state actors particularly terrorist groups acquiring and deploying these agents remains real. Unlike nation-states, extremist organizations may not adhere to international norms or legal constraints, making their potential use of biological or chemical weapons a serious public safety concern.

Epidemiology of Biological and Chemical Warfare Agents

The epidemiology of biowarfare agents is complex, as it intersects with microbiology, environmental science, and social behavior. Biological agents, including bacteria, viruses, and toxins, have natural reservoirs in animals, humans, or the environment. For instance, Bacillus anthracis, the causative agent of anthrax, exists naturally in soil, while viruses such as smallpox (Variola virus) have historically been eradicated from natural populations but may persist in laboratory collections. When deliberately released, these agents can spread rapidly depending on their mode of transmission airborne, vector-borne, or via contaminated food and water.

Unlike naturally occurring outbreaks, the deliberate use of a bioweapon introduces a strategic element to epidemiology. Attackers may aim to maximize disruption, fear, and mortality, rather than allow the pathogen to behave according to its natural transmission dynamics. This creates unusual outbreak patterns that can be detected epidemiologically by public health authorities, such as sudden clustering of cases, atypical geographic distribution, or the appearance of rare pathogens in urban populations.

Chemical agents, while non-infectious, also pose significant public health risks. Agents such as sarin, VX, and chlorine gas act rapidly on biological systems, causing respiratory, neurological, or dermatological effects. Unlike biological agents, chemical exposure is typically limited by the dispersal method and environmental stability, yet the acute toxicity of these substances requires immediate medical and environmental intervention.

Role of Clinical Microbiology and Biosafety in Detection

A cornerstone in responding to a biological attack is the clinical microbiology laboratory. These laboratories, particularly those designated as Biological Safety Level-4 (BSL-4), are equipped to safely handle high-risk pathogens with pandemic potential. Laboratory scientists are tasked with the critical responsibility of detecting and identifying the exact biological agent used in a bioterrorism event. Accurate and rapid identification informs public health interventions, including quarantine, treatment, vaccination, and environmental decontamination.

Safety in these laboratories is paramount. Personnel must adhere to strict biosafety protocols, including the use of full-body protective suits, high-efficiency particulate air (HEPA) filtration systems, and specialized containment units. Even minor lapses in safety can result in laboratory-acquired infections, which in the context of a highly virulent agent, may seed new outbreaks. Moreover, laboratories serve a critical communication role, providing verified information to government agencies and the public regarding the pathogen’s pathogenicity, mode of transmission, and containment measures.

Drivers of Bioweapon Development

Understanding why biological weapons are developed is crucial for prevention. Rogue nations and extremist organizations pursue biological weapon programs for several reasons. Ideological motivations may drive groups to employ terror as a tool to disrupt societies and advance political goals. Financial incentives also exist; a potent biological agent can serve as a “cheap” strategic weapon compared to the costs associated with conventional military campaigns. Additionally, the quest for military superiority may motivate certain states or actors to develop novel bioweapons as deterrence or offensive tools.

From a scientific ethics standpoint, the participation of educated scientists in the development of these weapons represents a profound moral dilemma. Scientists are traditionally trained to improve human health and welfare. Diverting their expertise to intentionally harm populations violates fundamental ethical principles, such as the Hippocratic tenet to “do no harm,” and erodes public trust in the scientific community. The global scientific community must therefore actively cultivate ethical standards, oversight mechanisms, and whistleblower protections to prevent misuse of knowledge.

Detection and Surveillance Systems

Early detection of biowarfare agents is essential for mitigating the public health impact. Surveillance systems operate at multiple levels: environmental, clinical, and epidemiological. Environmental surveillance involves monitoring air, water, and soil for pathogenic organisms or toxins, often using molecular detection techniques such as polymerase chain reaction (PCR) or next-generation sequencing (NGS). Clinical surveillance requires healthcare providers to recognize unusual symptom clusters and report them promptly to public health authorities. Epidemiological surveillance integrates these data streams, using computational modeling to predict the spread and identify sources of infection.

Advances in rapid diagnostic technologies have improved response capabilities. For example, portable PCR-based devices can detect high-priority pathogens in field conditions within hours. Coupled with geospatial mapping and real-time reporting, these tools allow for targeted interventions, including vaccination campaigns, prophylactic treatment, and localized containment measures.

Control and Prevention Strategies for Bioterrorism 

Preventing bioterrorism requires an integrated approach that combines legal, scientific, and public health measures. Key strategies include:

1. Regulation and Oversight: Strengthening international and national regulatory frameworks to prevent the proliferation of biological and chemical weapons. This includes rigorous control of pathogenic strains in research laboratories and monitoring of dual-use technologies that could be misapplied.

2. Public Health Preparedness: Developing national and regional preparedness plans that include stockpiling vaccines, antibiotics, and medical countermeasures. Training healthcare professionals to recognize and respond to unusual disease presentations is essential.

3. Community Education: Educating the public about potential threats, hygiene practices, and emergency response procedures enhances resilience and reduces panic during a bioterrorism event.

4. Rapid Response Infrastructure: Establishing specialized response teams, such as Rapid Response Teams (RRTs), equipped to contain outbreaks through isolation, decontamination, and treatment. Collaboration between military, public health, and scientific communities is critical in such efforts.

5. International Collaboration: Sharing intelligence, research, and resources across borders is vital. Agencies such as the World Health Organization (WHO) play a central role in coordinating global preparedness and response.

Ethical and Societal Considerations

The development and potential use of bioweapons raise profound ethical and societal questions. Beyond the immediate health risks, bioterrorism can induce widespread fear, economic disruption, and erosion of social trust. Ethical considerations extend to scientists, policymakers, and healthcare workers, each of whom faces dilemmas regarding confidentiality, duty of care, and moral responsibility in high-stakes scenarios.

The scientific community must engage proactively in education, policy advocacy, and research ethics training. Programs such as dual-use research oversight ensure that studies with potential bioweapon applications are rigorously reviewed and monitored. International treaties must also evolve to address emerging technologies, including synthetic biology and gene editing, which could facilitate the creation of novel pathogens with unpredictable impacts.

Public Health Concerns

The public health implications of biowarfare are extensive. Deliberate outbreaks can overwhelm healthcare infrastructure, cause significant morbidity and mortality, and disrupt essential services. Effective containment requires coordinated efforts across epidemiology, clinical care, laboratory science, and emergency management. Psychological impacts, such as fear, anxiety, and social unrest, are also significant, necessitating mental health interventions as part of the response.

Importantly, the threat of biowarfare is dynamic. Advances in biotechnology, the accessibility of laboratory equipment, and the rise of extremist networks have increased the potential for novel biological threats. Public health systems must therefore adopt adaptive, evidence-based approaches, leveraging technology, data analytics, and international collaboration to anticipate and mitigate these risks.

BL4 Laboratories, Global Oversight, and Strategic Preparedness Against Bioterrorism

BL4 laboratories serve as a critical first line of defense against high-risk pathogens, enabling safe study while preventing accidental release. Global conventions such as the BWC, along with disarmament initiatives and OPCW operations, provide essential frameworks to prevent the development and use of biological and chemical weapons. Ethical oversight, scientific responsibility, and transparent research governance are crucial in ensuring that technological advances are applied for human benefit rather than destruction.

Preparedness and rapid response infrastructures ranging from stockpiling countermeasures to deploying specialized rapid response teams enhance resilience against potential bioterrorism events. International collaboration, strict enforcement of biosecurity laws, and proactive public health strategies reduce the likelihood and impact of attacks.

Preventing the misuse of biological and chemical agents requires a multidimensional strategy that integrates high-containment laboratory research, ethical scientific conduct, robust international treaties, and coordinated public health action. Sustained vigilance, global cooperation, and responsible technological advancement remain indispensable to safeguarding humanity from the evolving threats of bioterrorism and weapons of mass destruction 

Biological Safety Level-4 (BL4) laboratories represent the pinnacle of containment for hazardous microbial pathogens. These facilities provide the highest level of protection against microbial contamination, ensuring that the microorganisms being studied are fully contained and cannot escape into the surrounding environment. Personnel working in BL4 laboratories are encased in full-body positive-pressure suits supplied with filtered air, effectively creating a barrier between the worker and highly dangerous pathogens (Figure 1). The biological agents handled within these laboratories are typically those that cause severe or lethal human diseases for which immediate preventive or therapeutic interventions are unavailable. Examples include Ebola virus, Marburg virus, and Variola virus (smallpox). The combination of advanced engineering controls, rigorous protocols, and highly trained personnel makes BL4 laboratories essential nodes in the global defense against bioterrorism.

The establishment of BL4 facilities is not merely a scientific advancement; it reflects a strategic public health imperative. Proper containment ensures that high-risk pathogens do not inadvertently cause outbreaks and that research intended to improve health and safety does not become a source of harm. Researchers in these laboratories must adhere to stringent operational standards, including multiple layers of containment, decontamination procedures, and continuous training in biosafety protocols. Failure to comply with these procedures can lead to catastrophic consequences, underscoring the importance of both technical and ethical rigor in high-containment research.

Strengthening International Conventions and Oversight

The global community has long recognized the threat posed by biological and chemical weapons. The 1972 Biological Weapons Convention (BWC) provided the first comprehensive framework to prohibit the development, production, and stockpiling of biological agents for warfare. In 2002, the BWC was rationalized to reinforce international surveillance, urging member states to strengthen monitoring mechanisms and cooperation to prevent the illicit development of biological weapons. This framework emphasizes the dual need for scientific advancement and public safety, balancing research innovation with security considerations.

In parallel, efforts by the United Nations and associated disarmament teams have sought to eliminate existing stockpiles of chemical weapons. The international mission to remove Syria’s chemical arsenal, including sarin and mustard gas, represents a significant achievement in enforcing global norms against weapons of mass destruction (WMD). These operations not only prevent further civilian casualties but also send a clear signal that the use of chemical and biological weapons is unacceptable under international law.

Furthermore, preparedness through biomedical innovation is essential. The development and distribution of potent vaccines and therapeutics against high-priority pathogens represent a proactive strategy to mitigate the impact of potential bioterrorism events. Vaccination campaigns targeting anthrax, smallpox, or other potential bioterrorism agents exemplify this preventive approach, highlighting the critical interplay between laboratory research, clinical medicine, and public health policy.

Enhancing Global Biosecurity

Global norms against the use of biological and chemical agents must be strengthened to deter rogue actors. When the international community unites against bioterrorism, it becomes increasingly difficult for terrorist organizations and rogue nations to pursue WMD development. Enforcement mechanisms, including sanctions, inspections, and legal accountability, must be applied rigorously to ensure compliance with international treaties. Biosecurity laws should be harmonized across nations, with clear reporting requirements for research involving dual-use pathogens—those that could be used for legitimate scientific purposes but also adapted for malicious intent.

The BWC should expand its oversight functions to include more proactive monitoring of research laboratories, industrial biotechnology firms, and national defense programs. Countries with ongoing high-risk research should submit to regular inspections and transparent reporting. Similarly, research organizations and scientists must adhere to ethical guidelines that prioritize public safety over strategic or financial interests. The misuse of scientific knowledge for the creation of biological weapons represents a profound ethical violation and threatens the global scientific enterprise itself.

Responsible Scientific Advancement

Advancements in biomedical research and biotechnology offer unprecedented opportunities to improve human health. However, these same technologies can be misapplied in the development of biological weapons. Gene editing, synthetic biology, and pathogen engineering can create highly virulent or drug-resistant microorganisms if misused. Therefore, international monitoring must accompany technological progress, ensuring that innovation serves public good rather than destructive purposes.

Nations and private organizations suspected of using scientific capabilities for WMD development should be closely monitored and, if necessary, disarmed through coordinated international action. Compliance should be verified through inspections, reporting requirements, and sanctions for violations. By maintaining strict oversight, the global community can dissuade other states, research organizations, and extremist groups from pursuing bioterrorism.

The Role of Ethical Oversight and Scientific Responsibility

Scientific advancement comes with responsibility. Researchers working with high-risk pathogens must recognize the potential consequences of their work. Ethical oversight committees, dual-use research governance, and whistleblower protections are necessary to prevent misuse of knowledge. Scientists must ensure that their research prioritizes human health, environmental safety, and societal welfare. The deliberate diversion of scientific expertise toward WMD development not only endangers civilians but also undermines public trust in science as a force for good.

Scientific advancement is a cornerstone of human progress, but it must be accompanied by a strong commitment to ethical responsibility. Researchers working with high-risk pathogens, emerging infectious agents, and other sensitive biological materials have a duty to carefully consider the potential implications of their work. While scientific discoveries can contribute significantly to public health, disease prevention, and medical innovation, the same knowledge and technologies may also be vulnerable to misuse if adequate safeguards are not in place.

Robust ethical oversight mechanisms are therefore essential. Institutional review boards, biosafety and biosecurity committees, dual-use research governance frameworks, and transparent regulatory systems play a critical role in ensuring that scientific activities are conducted responsibly. Equally important are protections for whistleblowers and mechanisms that encourage accountability, allowing concerns about unsafe practices or potential misuse to be raised without fear of retaliation.

Scientists must uphold the highest standards of integrity by ensuring that their research prioritizes human health, environmental protection, and societal well-being. Responsible conduct includes assessing risks, promoting transparency where appropriate, and adhering to national and international biosafety guidelines. The deliberate diversion of scientific expertise or biological research toward the development of weapons of mass destruction poses severe risks to global security, threatens civilian populations, and erodes public confidence in science. Maintaining ethical vigilance is therefore essential to preserving science as a force for innovation, safety, and the common good.

Emerging Threats and the Evolving Terrorism Landscape

While the likelihood of a pandemic-scale chemical or biological attack remains low, the growing sophistication of terrorist networks increases the risk. Technological advancements, including synthetic biology, create opportunities for actors with malicious intent to develop novel pathogens. The global spread of terrorism demands vigilant monitoring, rapid intelligence sharing, and coordinated counterterrorism efforts. World leaders, public health professionals, and security agencies must remain united, proactive, and well-prepared to detect, contain, and respond to potential threats.

Preparedness also extends to social and psychological support. Bioterrorism events can induce widespread fear, panic, and social disruption. Mental health interventions, clear communication, and community engagement are integral to mitigating these secondary effects. A comprehensive preparedness framework integrates epidemiology, laboratory science, ethical oversight, public health infrastructure, and international diplomacy.

Biohazard Awareness, Personal Protection, and Public Preparedness in Bioterrorism Scenarios

The proper identification and management of high-risk biological agents are central to preventing laboratory-acquired infections and mitigating the effects of bioterrorism. One of the primary tools for raising awareness in high-containment laboratories is the biohazard symbol, which should always be prominently displayed at the entrances of Biological Safety Level-4 (BL4) laboratories and other reference laboratories handling highly infectious organisms (Figure 2). These signs serve as a visual warning to non-laboratory personnel, signaling the need for heightened caution and restricted access. By clearly marking areas where dangerous pathogens are manipulated, the biohazard symbol plays a critical role in protecting both laboratory personnel and the broader public from inadvertent exposure.

BL4 laboratories represent the highest level of biological containment, designed to safely manage pathogens that pose severe or lethal risks to humans. Such facilities employ multiple layers of containment, including specialized ventilation systems, airlocks, sealed workspaces, and mandatory use of full-body protective suits with filtered air. The biohazard symbol complements these physical safety measures by communicating risk and ensuring that individuals approaching the laboratory understand the danger posed by the organisms within. It is a fundamental element of laboratory safety culture, reinforcing procedural adherence and fostering awareness of the potential consequences of mishandling high-risk pathogens.

The Role of Biohazard Symbols

The biohazard symbol (Figure 2) serves as a universal indicator of risk. Its presence signals that high-level laboratory work or experimentation is underway, often involving pathogens that can cause severe human disease. Passersby, including non-scientific personnel, are thereby alerted to exercise caution and avoid exposure. Beyond laboratory doors, biohazard signs can also be deployed in temporary containment areas, research facilities, or emergency response zones during outbreaks. Their consistent use reinforces a culture of safety, helping to prevent accidental contact with dangerous microorganisms or contaminated materials.

In addition to marking hazardous areas, the biohazard symbol communicates broader information about the nature of ongoing work. It indicates the presence of biologically or chemically harmful samples, the requirement for strict hygiene protocols, and the need for specialized protective equipment. By integrating visual cues with operational procedures, laboratories and emergency responders create a safer environment for both staff and the public.

Protective Equipment for First Responders and Medical Personnel

In the event of a biological or chemical attack, medical personnel and first responders face heightened risks of exposure. Proper protective equipment is essential to prevent contamination and ensure their ability to provide timely care. Protective masks, such as the M-40/M-42 gas mask, are designed to shield the wearer from a wide range of chemical and biological agents (Figure 3). These masks provide comprehensive respiratory protection, preventing inhalation of aerosolized microbial spores, viral particles, and toxic chemicals. They also incorporate eye protection and face shields, offering additional defense against airborne contaminants that could enter mucous membranes or damaged skin.

The use of such protective equipment is critical not only within laboratory settings but also in field environments where a chemical or biological incident may occur. First responders must continue to wear these masks when entering contaminated zones until proper decontamination has been completed. In addition to masks, other personal protective equipment (PPE) including gloves, full-body suits, boots, and face shields is necessary to prevent contact transmission and minimize secondary contamination. The consistent and correct use of PPE is a core principle in reducing the spread of infectious agents during bioterrorism events.

M-40/M-42 Protective Masks and Advanced Respiratory Defense

The M-40/M-42 protective mask (Figure 3) is specifically designed for extreme conditions, including chemical, biological, radiological, and nuclear (CBRN) threats. It provides comprehensive protection against inhalation of hazardous particles, chemical vapors, and microbial spores. The mask’s filtration systems remove toxic substances from inhaled air while maintaining airflow for safe respiration. Additionally, integrated eye protection prevents exposure to aerosols and splashes, completing a full suite of defenses against environmental contaminants.

In practice, first responders, military personnel, and healthcare workers must wear these masks continuously in contaminated zones. Proper training in donning, fitting, and maintaining the masks is essential to ensure optimal protection. Masks must be used in conjunction with other PPE, including protective suits, gloves, and boots, to prevent secondary contamination. Such rigorous protection allows personnel to perform critical tasks, including patient care, environmental decontamination, and evidence collection, without compromising their own safety.

Early Detection and Intelligence Sharing

Minimizing casualties in a bioterrorism event relies heavily on early detection, timely intelligence, and rapid response. Surveillance systems should be capable of detecting unusual disease clusters or environmental contamination before widespread transmission occurs. Clinical laboratories play a pivotal role in this process by identifying pathogens, determining their virulence, and providing critical data to public health authorities. Environmental monitoring—such as air, water, and soil sampling can also reveal the presence of chemical or biological agents before human cases emerge.

Intelligence gathering is equally important. Preventing terrorist groups from accessing or deploying WMDs requires active monitoring of suspicious activities, scientific research with dual-use potential, and the distribution of high-risk materials. Close coordination between public health authorities, security agencies, and international organizations ensures that threats can be mitigated before they escalate into mass-casualty events. The combination of laboratory detection and field intelligence forms the backbone of an effective early-warning system that can save countless lives.

Public Education and Community Preparedness

Public awareness is a critical component of bioterrorism preparedness. Communities must understand what bioterrorism entails, the risks associated with exposure, and the steps to take in the event of an outbreak. Public education campaigns can teach citizens how to recognize biohazard warnings, avoid contaminated areas, and follow official instructions for evacuation, decontamination, or medical treatment. Such initiatives foster societal resilience, reducing panic and improving compliance with containment measures during an emergency.

Public health specialists and microbiologists working in the field should adhere to strict protective protocols, wearing appropriate PPE when interacting with potentially contaminated environments or clinical samples. The combination of professional vigilance and informed communities creates a layered defense that limits the impact of a bioterrorism event. By promoting awareness and preparedness, society as a whole contributes to the containment of high-risk pathogens and the protection of vulnerable populations.

Integration of Laboratory, Field, and Public Health Measures

Effectively responding to chemical or biological threats requires integration across multiple domains: laboratory research, field response, and public health coordination. BL4 laboratories provide the technical foundation for pathogen identification, while field teams equipped with PPE and respiratory protection translate this knowledge into actionable interventions. Public health authorities, in turn, deploy vaccination, treatment, and containment strategies to affected populations. This multi-tiered approach ensures that high-risk pathogens are identified rapidly, exposure is minimized, and casualties are reduced.

Early treatment and vaccination play a central role in reducing morbidity and mortality during bioterrorism events. For pathogens with known vaccines, rapid immunization campaigns can prevent disease spread and protect at-risk populations. Where vaccines are unavailable, prompt medical intervention supported by accurate pathogen identification and appropriate PPE can mitigate disease severity. Together with surveillance and intelligence sharing, these measures form a comprehensive strategy for bioterrorism preparedness and response.

Ethical and Operational Considerations

The deployment of PPE, biohazard signage, and laboratory containment measures also raises ethical and operational considerations. Personnel must balance personal safety with the imperative to provide care or conduct research. Ethical guidelines dictate that protective measures should never be compromised, even in high-pressure scenarios, to prevent unnecessary exposure or loss of life. In addition, laboratories and response teams must maintain transparency with public health authorities and the community, ensuring that risk communication is accurate, timely, and comprehensible.

Operationally, maintaining high levels of preparedness requires ongoing investment in training, equipment, and infrastructure. BL4 laboratories must remain up-to-date with containment technologies, PPE standards, and decontamination protocols. First responders must engage in regular drills to practice rapid deployment, mask usage, and coordination with health authorities. Public education campaigns should be periodically refreshed to account for evolving threats, emerging pathogens, and advances in protective technology.

The biohazard symbol and protective measures such as the M-40/M-42 mask are critical components of global bioterrorism preparedness. BL4 laboratories provide the highest level of containment, enabling safe study of lethal pathogens while minimizing the risk of accidental release. First responders and medical personnel rely on advanced PPE to protect themselves during interventions, while public awareness ensures that communities understand the risks and appropriate protective behaviors.

Integration across laboratory research, field operations, and public health coordination is essential to detect, respond to, and contain chemical or biological threats. Early detection, timely intelligence, vaccination, and treatment are key strategies for reducing casualties in bioterrorism events. Moreover, ethical adherence, operational discipline, and ongoing investment in training and infrastructure ensure that preparedness measures remain effective over time.

The combination of visual risk communication, respiratory and protective equipment, and community education forms a layered defense against bioterrorism. Through consistent application of these measures, society can protect laboratory personnel, first responders, and the general public from the potentially devastating effects of chemical and biological attacks.

References

Aschengrau A and Seage G.R (2013). Essentials of Epidemiology in Public Health. Third edition. Jones and Bartleh Learning,

Aschengrau, A., & G. R. Seage III. (2009). Essentials of Epidemiology in Public Health.  Boston:  Jones and Bartlett Publishers.

Castillo-Salgado C (2010). Trends and directions of global public health surveillance. Epidemiol Rev, 32:93–109.

Centers for Disease Control and National Institutes of Health (1999). Biosafety in Microbiological and Biomedical Laboratories, 4th edn, Washington DC: CDC.

Guillemin J (2006). Scientists and the history of biological weapons. European Molecular Biology Organization (EMBO) Reports, Vol 7, Special Issue: S45-S49.

Halliday JE, Meredith AL, Knobel DL, Shaw DJ, Bronsvoort BMC, Cleaveland S (2007). A framework for evaluating animals as sentinels for infectious disease surveillance. J R Soc Interface, 4:973–984.

Nelson K.E and Williams C (2013). Infectious Disease Epidemiology: Theory and Practice. Third edition. Jones and Bartleh Learning. 

Porta M (2008). A dictionary of epidemiology. 5^th edition. New York: Oxford University Press.

Rothman K.J and Greenland S (1998). Modern epidemiology, 2^nd edition. Philadelphia: Lippincott-Raven. 

Rothman K.J, Greenland S and Lash T.L (2011). Modern Epidemiology. Third edition. Lippincott Williams and Wilkins, Philadelphia, PA, USA.