Epidemiology and Public Health

Descriptive Epidemiology

Descriptive epidemiology focuses on describing disease distribution by characteristics relating to time, place, and people.

Learning Objectives

Describe the role of a descriptive epidemiology

Key Takeaways

Key Points

  • Epidemiology is the science concerned with the study of the factors that influence and determine the frequency and distribution of disease, injury, and other health -related events and their causes in a defined human population.
  • The more fully a descriptive epidemiologist can describe people, places and times, and any correlations between the three, the more likely it is that patterns will emerge which can be considered as risk factors for certain kinds of health issues.
  • Epidemiologists use data as an information source for communicating information to people and to influence public policy.

Key Terms

  • socioeconomic: Of or pertaining to social and economic factors.
  • epidemiology: The branch of a science dealing with the spread and control of diseases, computer viruses, concepts, etc., throughout populations or systems.
  • risk factor: A variable associated with an increased risk of disease or infection.

The goal of epidemiology is to establish causal factors for health issues in order to improve the health and safety of entire populations. A population can refer to a town, country, age group, or race. Health issues refer to anything that might impact health in the present or future. For epidemiologists, data on who is most likely to be injured in car crashes can be just as valuable as a topic of inquiry as data on what part of the population is most at risk for developing complications from the flu. In order to accomplish this, epidemiology has two main branches: descriptive and analytical.

Descriptive epidemiology evaluates and catalogs all the circumstances surrounding a person affected by a health event of interest. Analytical epidemiologists use data gathered by descriptive epidemiology experts to look for patterns suggesting causation. The end goal of both branches is to reduce the incidence of health events or diseases by understanding the risk factors for the health events or diseases. Both descriptive and analytical epidemiology often serve public health organizations by providing information that may reduce disease or reduce other kinds of events that impact people’s health.

The primary considerations for descriptive epidemiology are frequency and pattern. Frequency evaluates the rate of occurrence, and pattern helps analytical epidemiologists suggest risk factors. Descriptive epidemiology evaluates frequency and pattern by examining the person, place, and time in relationship to health events.

Descriptive epidemiology examines factors like age, education, socioeconomic status, availability of health services, race, and gender. Evaluations of specific individuals may also include gathering information on behaviors like drug abuse, shift work, eating, and exercise patterns.

Analytical Epidemiology

Epidemiology draws statistical inferences, mostly about causes of disease in populations based on available samples of it.

Learning Objectives

Describe the role of an analytical epidemiologist

Key Takeaways

Key Points

  • Epidemiologists employ a range of study designs from the observational to experimental and they are generally categorized as descriptive, analytic, and experimental.
  • Analytic epidemiology aims to further examine known associations or hypothesized relationships.
  • Analytical observations deal more with the ‘how’ of a health -related event.

Key Terms

  • analytical: pertaining to or emanating from analysis.
  • epidemiology: Epidemiology is the study (or the science of the study) of the patterns, causes, and effects of health and disease conditions in defined populations.

Epidemiology is the study (or the science of the study) of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and informs policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive medicine. Epidemiologists help with study design, collection and statistical analysis of data, and interpretation and dissemination of results (including peer review and occasional systematic review). Epidemiology has helped develop methodology used in clinical research, public health studies and, to some extent, basic research in the biological sciences.

Epidemiologists employ a range of study designs from observational to experimental and generally categorized as descriptive, analytic (aiming to further examine known associations or hypothesized relationships), and experimental (a term often equated with clinical or community trials of treatments and other interventions).

Where descriptive epidemiology describes occurrence of disease (or of its determinants) within a population, the analytical epidemiology aims to gain knowledge on the quality and the amount of influence that determinants have on the occurrence of disease. The usual way to gain this knowledge is by group comparisons. Such a comparison starts from one or more hypotheses about how the determinant may influence occurrence of disease. Analytical epidemiology attempts to determine the cause of an outbreak. Using the case control method, the epidemiologist can look for factors that might have preceded the disease. Often, this entails comparing a group of people who have the disease with a group that is similar in age, sex, socioeconomic status, and other variables, but does not have the disease. In this way, other possible factors, e.g., genetic or environmental, might be identified as factors related to the outbreak.

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Cholera Outbreak: The outdated public health advice demonstrates the lack of understanding of the disease and its actual causative factors in the absence of epidemiological analysis.

Experimental Epidemiology

Experimental epidemiology uses an experimental model to confirm a causal relationship suggested by observational studies.

Learning Objectives

Summarize the purpose of experimental epidemiology and the three case types: randomized control, field and community trial

Key Takeaways

Key Points

  • Experimental epidemiology is the study of the relationships of various factors determining the frequency and distribution of diseases in a community.
  • Experimental epidemiology contains three case types: randomized control trial (often used for new medicine or drug testing), field trial (conducted on those at a high risk of conducting a disease), and community trial (research on social originating diseases).
  • The method employs prospective population experiments designed to test epidemiological hypotheses, and usually attempt to relate the postulated cause to the observed effect. Trials of new anthelmintics are an example.

Key Terms

  • epidemiology: Epidemiology is the study (or the science of the study) of the patterns, causes, and effects of health and disease conditions in defined populations.
  • Experimental: An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis.
  • statistical: of or pertaining to statistics

Epidemiology is the study (or the science of the study) of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and informs policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive medicine. Epidemiologists help with study design, collection and statistical analysis of data, and interpretation and dissemination of results (including peer review and occasional systematic review). Epidemiology has helped develop methodology used in clinical research, public health studies and, to a lesser extent, basic research in the biological sciences.

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Early epidemiology: Original map by John Snow showing the clusters of cholera cases in the London epidemic of 1854. John Snow’s investigative work was one of the first examples of epidemiology. He discovered that families that drew their water from the Broad St well became infected with cholera.

Epidemiologists employ a range of study designs from the observational to experimental and they are generally categorized as descriptive, analytic (aiming to further examine known associations or hypothesized relationships), and experimental (a term often equated with clinical or community trials of treatments and other interventions). In observational studies, nature is allowed to “take its course”, as epidemiologists observe from the sidelines. Controversially, in experimental studies, the epidemiologist is the one in control of all of the factors entering a certain case study. Epidemiological studies are aimed, where possible, at revealing unbiased relationships between exposures such as alcohol or smoking, biological agents, stress, or chemicals to mortality or morbidity. The identification of causal relationships between these exposures and outcomes is an important aspect of epidemiology. Modern epidemiologists use informatics as a tool.

Experimental epidemiology contains three case types: randomized control trial (often used for new medicine or drug testing), field trial (conducted on those at a high risk of conducting a disease), and community trial (research on social originating diseases). Experimental epidemiology tests a hypothesis about a disease or disease treatment in a group of people. This strategy might be used to test whether or not a particular antibiotic is effective against a particular disease-causing organism. One group of infected individuals is divided randomly so that some receive the antibiotic and others receive a placebo—a “false” drug that is not known to have any medical effect. In this case, the antibiotic is the variable, i.e., the experimental factor being tested to see if it makes a difference between the two otherwise similar groups. If people in the group receiving the antibiotic recover more rapidly than those in the other group, it may logically be concluded that the variable—antibiotic treatment—made the difference. Thus, the antibiotic is said to be effective.

Although epidemiology is sometimes viewed as a collection of statistical tools used to elucidate the associations of exposures to health outcomes, a deeper understanding of this science is that of discovering causal relationships.

Public Health Measures for Disease Control

Promotion of hand washing, breastfeeding, delivery of vaccinations, and distribution of condoms are examples of public health measures.

Learning Objectives

Give examples of common public health measures that are recommended to control the spread of disease

Key Takeaways

Key Points

  • Hand washing for hand hygiene is the act of cleaning the hands with or without the use of water or another liquid, or with the use of soap, for the purpose of removing soil, dirt, and/or microorganisms.
  • Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts (i.e., via lactation) rather than from a baby bottle or other container.
  • Vaccination is the administration of antigenic material (a vaccine ) to stimulate an individual’s immune system to develop adaptive immunity to a pathogen.

Key Terms

  • hygiene: Those conditions and practices that promote and preserve health.
  • immunity: the state of being insusceptible to a specific thing.
  • vaccination: inoculation with a vaccine in order to protect a particular disease or strain of disease.

Public Health Measures

The focus of public health intervention is to improve health and quality of life through the prevention and treatment of disease and other physical and mental health conditions. This can be done through surveillance of cases, and the promotion of healthy behaviors. Promotion of hand washing and breastfeeding, delivery of vaccinations, and distribution of condoms to control the spread of sexually transmitted diseases, are examples of common public health measures.

HAND WASHING

Hand washing for hand hygiene is the act of cleaning the hands with or without the use of water or another liquid, or with the use of soap, for the purpose of removing soil, dirt, and/or microorganisms. Medical hand hygiene pertains to the hygiene practices related to the administration of medicine and medical care that prevents or minimizes disease and the spreading of disease. The main medical purpose of washing hands is to cleanse the hands of pathogens (including bacteria or viruses) and chemicals, which can cause personal harm or disease. This is especially important for people who handle food or work in the medical field, but it is also an important practice for the general public. People can become infected with respiratory illnesses, such as influenza or the common cold; for example, if they don’t wash their hands before touching their eyes, nose, or mouth. Indeed, the Centers for Disease Control and Prevention (CDC) has stated: “It is well documented that one of the most important measures for preventing the spread of pathogens is effective hand washing. ”

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Hand Cleaning Station: A hand cleaning station at the entrance of the Toronto General Hospital

As a general rule, however, handwashing protects people poorly or not at all from droplet- and airborne diseases, such as measles, chickenpox, influenza, and tuberculosis. It protects best against diseases transmitted through fecal-oral routes (such as many forms of stomach flu) and direct physical contact (such as impetigo). In addition to hand washing with soap and water, the use of alcohol gels is another form of killing some kinds of pathogens and healthful bacteria, but their effectiveness is disputed, and may lead to antibiotica-resistant bacterial strains.

BREASTFEEDING

Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts (i.e., via lactation) rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or more, without the addition of infant formula or solid food. After the addition of solid food, mothers are advised to continue breastfeeding for at least a year, and can continue for two years or more. Human breast milk is the healthiest form of milk for babies. There are few exceptions, such as when the mother is taking certain drugs or is infected with human T-lymphotropic virus, or has active untreated tuberculosis. Maternal HIV infection is always an absolute contraindication to breastfeeding in developed countries with access to infant formula and clean drinking water (regardless of maternal HIV viral load or antiretroviral treatment) due to the risk for mother to child HIV transmission. Breastfeeding promotes health and helps to prevent disease. Artificial feeding is associated with more deaths from diarrhea in infants in both developing and developed countries. Experts agree that breastfeeding is beneficial, and have concerns about artificial formulas but there are conflicting views about how long exclusive breastfeeding remains beneficial.

VACCINATION

Vaccination is the administration of antigenic material (a vaccine) to stimulate an individual’s immune system to develop adaptive immunity to a pathogen. Vaccines can prevent or ameliorate morbidity from infection. The effectiveness of vaccination has been widely studied and verified; for example, the influenza vaccine, the HPV vaccine, and the chicken pox vaccine. Vaccination is the most effective method of preventing infectious diseases; widespread immunity due to vaccination is largely responsible for the worldwide eradication of smallpox and the restriction of diseases such as polio, measles, and tetanus from much of the world.

CONDOMS

A condom is a barrier device commonly used during sexual intercourse to reduce the probability of pregnancy and spreading sexually transmitted diseases. It is put on a man’s erect penis and physically blocks ejaculated semen from entering the body of a sexual partner. Condoms are also used for collection of semen for use in infertility treatment. In the modern age, condoms are most often made from latex, but some are made from other materials such as polyurethane, polyisoprene, or lamb intestine. A female condom is also available, often made of nitrile.

Global Health

Global health is the health of populations in a global context and transcends the perspectives and concerns of individual nations.

Learning Objectives

Outline the various perspectives that provide the framework for global health initiatives: epidemiological, medical, economic and political approaches

Key Takeaways

Key Points

  • Health problems that transcend national borders or have a global political and economic impact are often emphasized.
  • The major international agency for health is the World Health Organization (WHO). Other important agencies with impact on global health activities include UNICEF, World Food Programme (WFP), United Nations University – International Institute for Global Health, and the World Bank.
  • Global health is a research field at the intersection of medical and social science disciplines, such as demography, economics, epidemiology, political economy and sociology.

Key Terms

  • health: The state of being free from physical or psychological disease, illness, or malfunction; wellness.
  • populations: A population is all the organisms that both belong to the same group or species and live in the same geographical area.
  • nations: A nation may refer to a community of people who share a common language, culture, ethnicity, descent, or history. In this definition, a nation has no physical borders.

Global Health

Global health is the health of populations in a global context and transcends the perspectives and concerns of individual nations. Health problems that transcend national borders or have a global political and economic impact are often emphasized. It has been defined as “the area of study, research and practice that places a priority on improving health and achieving equity in health for all people worldwide. ” Thus, global health is about worldwide improvement of health, reduction of disparities, and protection against global threats that disregard national borders. The application of these principles to the domain of mental health is called global mental health.

The major international agency for health is the World Health Organization (WHO). Other important agencies with impact on global health activities include UNICEF, World Food Programme (WFP), United Nations University – International Institute for Global Health, and the World Bank. A major initiative for improved global health is the United Nations Millennium Declaration and the globally endorsed Millennium Development Goals.

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Flag of the World Health Organization: This is the flag of the World Health Organization.

Global health is a research field at the intersection of medical and social science disciplines, such as demography, economics, epidemiology, political economy, and sociology. Through these different disciplinary perspectives, it focuses on determinants and the distribution of health in international contexts.

Global Health Perspectives

An epidemiological perspective identifies major global health problems. A medical perspective describes the pathology of major diseases, and promotes prevention, diagnosis, and treatment of these diseases.

An economic perspective emphasizes the cost-effectiveness and cost-benefit approaches for both individual and population health allocation. Aggregate analysis focuses on analysis for the health sector. For instance, governments and non-governmental organizations (NGOs) may engage in aggregate analysis.

Cost-effectiveness analysis compares the costs and health effects of an intervention to assess whether health investments are worthwhile from an economic perspective. It is necessary to distinguish between independent interventions and mutually exclusive interventions. For independent interventions, average cost-effectiveness ratios suffice. However, when mutually exclusive interventions are compared, it is essential to use incremental cost-effectiveness ratios. The latter comparisons suggest how to achieve maximal health care effects with the available resources.

Another ethical approach emphasizes distributional considerations. The Rule of Rescue, coined by A.R. Jonsen (1986), is one way to address distributional issues. This rule specifies that it is “a perceived duty to save endangered life where possible. ” John Rawls ideas on impartial justice is a contractual perspective on distribution. These ideas have been applied by Amartya Sen to address key aspects of health equity. Bioethics research also examines international obligations of justice, in three broadly clustered areas: When are international inequalities in health unjust? Where do international health inequalities come from? How do we meet health needs justly if we can’t meet them all?

A political approach emphasizes political economy considerations applied to global health. Political economy originally was the term for studying production, buying and selling, and their relations with law, custom, and government. Originating in moral philosophy (e.g., Adam Smith was professor of Moral Philosophy at the University of Glasgow), political economy of health is the study of how economies of states influence aggregate population health outcomes.

There are many perspectives and approaches to take when it comes to issues of global health, hence why the global health system is still struggling. Some perceive the immunization and prevention of disease to be a form of public democracy, others view it as a moral duty or an investment in self-protection. The journalist, Laurie Garrett explores the various perspectives shaping global health and suggests that it is due to perspective divergence that is hindering monetary funding and philanthropic efforts of organizations to properly control disease.

There are dangers to having divergent perspectives especially if it is a biased one; such as exemplified by Andrew Natsios of USAID, when he proclaimed that antiretrovirals should not be distributed to HIV-stricken Africa due to the occupants lacking a concept of time and clocks to properly facilitate the proper sequence of drug consumption. In addition, divergent perspectives can lead to “stove-piping”, which localizes funding to only specific causes while neglecting the larger and more important issues. The most important aspect in achieving global health is to take on a research approach and act accordingly to data and proven research because global health needs to be focused on as a whole, rather than specific causes.

Emerging and Reemerging Infectious Diseases

An emerging infectious disease is a disease with a rate of incidence that has increased in the past 20 years, and could increase in the near future.

Learning Objectives

Give examples of emerging and remerging infectious diseases

Key Takeaways

Key Points

  • Emerging infections account for at least 12% of all human pathogens.
  • Emerging infections deseases are caused by newly identified species or strains that may have evolved from a known infection or spread to a new population or area undergoing ecologic transformation, or be reemerging infections, such as drug resistant tuberculosis.
  • Adverse synergistic interactions between emerging diseases and other infectious and non-infectious conditions leading to the development of novel syndemics are of growing concern.

Key Terms

  • emerging infectious disease: An emerging infectious disease (EID) is an infectious disease with an incidence rate that has increased in the past 20 years and could increase in the near future. Emerging infections account for at least 12% of all human pathogens.
  • pathogens: A pathogen or infectious agent (colloquially known as a germ) is a microorganism (in the widest sense, such as a virus, bacterium, prion, or fungus) that causes disease in its host. The host may be an animal (including humans), a plant, or even another microorganism.
  • species: In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring.

An emerging infectious disease (EID) is an infectious disease whose incidence has increased in the past 20 years, and could increase in the near future. Emerging infections account for at least 12% of all human pathogens. EIDs are caused by newly identified species or strains (e.g., SARS, AIDS) that may have evolved from a known infection (e.g., influenza), or spread to a new population (e.g., West Nile virus ), or to an area undergoing ecologic transformation (e.g., Lyme disease). They could also be reemerging infections, such as drug resistant tuberculosis. Of growing concern are adverse synergistic interactions between emerging diseases and other infectious and non-infectious conditions leading to the development of novel syndemics.

SARS

Severe acute respiratory syndrome (SARS) is a viral respiratory disease in humans which is caused by the SARS coronavirus (SARS-CoV). Between November 2002 and July 2003, an outbreak of SARS in Hong Kong nearly became a pandemic, with 8,422 cases and 916 deaths worldwide (10.9% fatality), according to the World Health Organization (WHO). Within weeks, SARS spread from Hong Kong to infect individuals in 37 countries. The last infected human case of the outbreak occurred in June 2003, and there was a laboratory-induced infection case in 2004. SARS is not claimed to have been eradicated (unlike smallpox), as it may still be present in its natural host reservoirs (animal populations) and may return to the human population. During the outbreak, the fatality of SARS was less than 1% for people aged 24 or younger, 6% for those 25 to 44, 15% for those 45 to 64, and more than 50% for those over 65. For comparison, the fatality of influenza is usually under 0.03% (primarily among the elderly), but rose to 2% during the most severe pandemic to date.

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Coronaviruses: Coronaviruses are a group of viruses that have a halo, or crown-like (corona) appearance when viewed under an electron microscope. If you have a cold 10-15% of the time it is caused by a virus like this.

HIV

Human immunodeficiency virus infection/acquired immunodeficiency syndrome (HIV/AIDS) is a disease of the human immune system caused by the human immunodeficiency virus (HIV). During the initial infection a person may experience a brief period of influenza-like illness. This is typically followed by a prolonged period without symptoms. As the illness progresses it interferes more and more with the immune system, making people much more likely to get infections, including opportunistic infections, and tumors that do not usually affect people with working immune systems.

Influenza

Influenza, commonly known as the flu, is an infectious disease of birds and mammals caused by RNA viruses of the family Orthomyxoviridae, the influenza viruses. The most common symptoms are chills, fever, sore throat, muscle pains, headache (often severe), coughing, weakness/fatigue and general discomfort. Although it is often confused with other influenza-like illnesses, especially the common cold, influenza is a more severe disease caused by a different type of virus. Influenza may produce nausea and vomiting, particularly in children, but these symptoms are more common in the unrelated gastroenteritis, which is sometimes inaccurately referred to as “stomach flu” or “24-hour flu. ”

West Nile Virus

West Nile virus (WNV) is a mosquito-borne zoonotic arbovirus belonging to the genus flavivirus in the family flaviviridae. This flavivirus is found in temperate and tropical regions of the world. It was first identified in the West Nile subregion in the East African nation of Uganda in 1937. Prior to the mid 1990s, WNV disease occurred only sporadically and was considered a minor risk for humans. However, there was an outbreak in Algeria in 1994, with cases of WNV-caused encephalitis, and the first large outbreak in Romania in 1996, with a high number of cases with neuroinvasive disease. WNV has now spread globally, with the first case in the Western Hemisphere being identified in New York City in 1999; over the next 5 years, the virus spread across the continental United States, north into Canada, and southward into the Caribbean Islands and Latin America. WNV also spread to Europe, beyond the Mediterranean Basin. A new strain of the virus was recently (2012) identified in Italy. WNV is now considered to be an endemic pathogen in Africa, Asia, Australia, the Middle East, Europe and in the United States, which in 2012 has experienced one of its worst epidemics.

Tuberculosis

Tuberculosis, MTB, or TB (short for tubercle bacillus) is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis typically attacks the lungs, but can also affect other parts of the body. It is spread through the air when people who have an active TB infection cough, sneeze, or otherwise transmit their saliva through the air. Most infections are asymptomatic and latent, but about one in ten latent infections eventually progresses to active disease which, if left untreated, kills more than 50% of those so infected.

Biological Weapons

Biological warfare (BW) is the use of biological toxins or infectious agents with the intent to kill or incapacitate.

Learning Objectives

Recognize the characteristics of biological weapons

Key Takeaways

Key Points

  • Biological weapons (often termed “bio-weapons”, “biological threat agents”, or “bio-agents”) are living organisms or replicating entities (viruses) that reproduce or replicate within their host victims.
  • Biological weapons may be employed in various ways to gain a strategic or tactical advantage over an adversary, either by threats or by actual deployments.
  • As a tactical weapon for military use, a significant problem with a BW attack is that it would take days to be effective, and therefore might not immediately stop an opposing force.

Key Terms

  • Biological warfare: Biological warfare (BW) — also known as germ warfare — is the use of biological toxins or infectious agents such as bacteria, viruses, and fungi with the intent to kill or incapacitate humans, animals, or plants as an act of war.
  • psychochemical weapon: Agents used within the context of military aggression.

Biological warfare (BW) — also known as germ warfare — is the use of biological toxins or infectious agents such as bacteria, viruses, and fungi with the intent to kill or incapacitate humans, animals, or plants as an act of war. Biological weapons (often termed “bio-weapons”, “biological threat agents”, or “bio-agents”) are living organisms or replicating entities (viruses) that reproduce or replicate within their host victims. Entomological (insect) warfare is also considered a type of BW.

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Biological Bomblet: The E120 biological bomblet was one of a number of spherical biological bomblets that were developed before the United States discontinued its offensive program in the 1970s. The vaned outer shell of this spherical bomblet was designed to provide rotation during flight. On impact, the outer shell would shatter; the bomblet was asymmetrically weighted so that agent would then be sprayed from the top of the bomblet. The E120 bomblet was developed in the early 1960s. Its 11.4 cm diameter carried 0.1 kg of liquid biological agent.

Biological weapons may be employed in various ways to gain a strategic or tactical advantage over an adversary, either by threats or by actual deployments. Like some chemical weapons, biological weapons may also be useful as area denial weapons. These agents may be lethal or non-lethal, and may be targeted against a single individual, a group of people, or even an entire population. They may be developed, acquired, stockpiled, or deployed by nation states or by non-national groups. In the latter case, or if a nation-state uses it clandestinely, it may also be considered bioterrorism.

There is an overlap between BW and chemical warfare, as the use of toxins produced by living organisms is considered under the provisions of both the Biological Weapons Convention and the Chemical Weapons Convention. Toxins and psychochemical weapons are often referred to as midspectrum agents. Unlike bioweapons, these midspectrum agents do not reproduce in their host and are typically characterized by shorter incubation periods.

Offensive biological warfare, including the mass production, stockpiling, and use of biological weapons, was outlawed by the 1972 Biological Weapons Convention (BWC). The rationale behind this treaty, which has been ratified or acceded to by 165 countries as of 2011, is to prevent a biological attack which could conceivably result in large numbers of civilian fatalities and cause severe disruption to economic and societal infrastructure. Many countries, including signatories of the BWC, currently pursue research into the defense or protection against BW, which is not prohibited by the BWC.

A nation or group that can pose a credible threat of mass casualty has the ability to alter the terms on which other nations or groups interact with it. Biological weapons allow for the potential to create a level of destruction and loss of life far in excess of nuclear, chemical, or conventional weapons, relative to their mass and cost of development and storage. Therefore, biological agents may be useful as strategic deterrents in addition to their utility as offensive weapons on the battlefield.

As a tactical weapon for military use, a significant problem with a BW attack is that it would take days to be effective, and therefore might not immediately stop an opposing force. Some biological agents (especially smallpox, plague, and tularemia) have the capability of person-to-person transmission via aerosolized respiratory droplets. This feature can be undesirable, as the agent or agents may be transmitted by this mechanism to unintended populations, including neutral or even friendly forces. While containment of BW is less of a concern for certain criminal or terrorist organizations, it remains a significant concern for the military and civilian populations of virtually all nations.

Technology and New Infectious Agents

Technology aids in the identification of new infectious agents, but it also contributes to the emergence of new diseases.

Learning Objectives

Give examples demonstrating the positive and negative impacts technology has had on new infectious agents

Key Takeaways

Key Points

  • Advanced technology enables rapid identification of pathogens causing disease outbreaks and helps accelerate treatment strategies.
  • The effect of new technology on the environment is related to the emergence of many new infectious diseases.
  • Infectious diseases are sometimes called ” contagious ” when they are easily transmitted by contact with an ill person or their secretions (e.g., influenza).

Key Terms

  • infectious: Infectious diseases, also known as transmissible diseases or communicable diseases, comprise clinically evident illness (i.e., characteristic medical signs and/or symptoms of disease) resulting from the infection, presence, and growth of pathogenic biological agents in an individual host organism.
  • pathogens: A pathogen or infectious agent (colloquially known as a germ) is a microorganism (in the widest sense, such as a virus, bacterium, prion, or fungus) that causes disease in its host. The host may be an animal (including humans), a plant, or even another microorganism.

Technology: The Good

The use of advanced technology and molecular methods for detection, identification, and characterization of infectious agents is gaining importance in clinical microbiology laboratories. Emerging and re-emerging pathogens pose several challenges to diagnosis, treatment, and public health surveillance. Identification of an emerging pathogen by conventional methods is difficult and time-consuming due to the ‘novel’ nature of the agent. Identification requires a large array of techniques including cell cultures, inoculation of animals, cultivation using artificial media, histopathological evaluation of tissues (if available), and serological techniques using surrogate antigens.

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Influenza: TEM of negatively stained influenza virions, magnified approximately 100,000 times. Modern transport contributes in spreading diseases faster.

Looking back at past epidemics or outbreaks caused by previously unknown infectious agents, we realize that identification and characterization of a new infectious agent can take years, decades, or even centuries. Such time frames have been decreased to weeks or months by the use of powerful molecular techniques, as seen with the identification of severe acute respiratory syndrome coronavirus (SARS-CoV) within weeks of the first cases reported, the discovery of a new hantavirus in North America in 1993, and the detection of bacteria as etiological pathogens of human infections such as Ehrlichia chaffeensis and Anaplasma phagocytophilum in human monocytotropic ehrlichiosis and human granulocytotropic anaplasmosis, respectively.

Molecular techniques offer several advantages over conventional methods, including high sensitivity and specificity, speed, ease of standardization, and automation. Other advantages include identification of novel, non-cultivable or very slowly growing organisms, strain typing in epidemiological studies, antimicrobial susceptibility determination, and monitoring treatment by measuring bacterial or viral loads.

Technology: The Bad

The effects of new technology on the environment are related to the emergence of many infectious diseases. For example, Lyme disease, hantavirus pulmonary syndrome (HPS), and Lassa fever all emerged when humans began encountering the insect vector (for Lyme disease) or rodent host (for HPS and Lassa fever) of the causative agents in greater numbers than ever before. Factors related to the emergence of infectious diseases such as Legionnaire disease and hemolytic uremic syndrome include changing technologies: air conditioning systems and mass food production, respectively.

Technology: The Ugly

Several human activities have led to the emergence and spread of new diseases:

ENCROACHMENT ON WILDLIFE HABITATS

The construction of new villages and housing developments in rural areas forces animals to live in dense populations, creating opportunities for microbes to mutate and emerge.

CHANGES IN AGRICULTURE

The introduction of new crops attracts new crop pests and the microbes they carry to farming communities, exposing people to unfamiliar diseases.

DESTRUCTION OF RAIN FORESTS

As countries make use of their rain forests by building roads and clearing areas for settlement or commercial ventures, people encounter insects and other animals harboring previously unknown microorganisms.

UNCONTROLLED URBANIZATION

The rapid growth of cities in many developing countries tends to concentrate large numbers of people into crowded areas with poor sanitation. These conditions foster transmission of contagious diseases.

MODERN TRANSPORT

Ships and other cargo carriers often harbor unintended ‘passengers’ that can spread diseases to faraway destinations. With international air travel, people infected with a disease can carry it to distant lands, or home to their families, before their first symptoms appear.

Current Epidemics

An epidemic occurs when new cases of a disease, in a given human population, and during a given period, substantially exceed expectations.

Learning Objectives

Give examples of current epidemics

Key Takeaways

Key Points

  • Epidemiologists often consider the term outbreak to be synonymous to epidemic, but the general public typically perceives outbreaks to be more local and less serious than epidemics.
  • Epidemics of infectious disease are generally caused by a change in the ecology of the host population (e.g. increased stress or increase in the density of a vector species ), a genetic change in the parasite population or the introduction of a new parasite to a host population.
  • In the 20th century three influenza pandemics occurred, each caused by the appearance of a new strain of the virus in humans, and killed tens of millions of people.

Key Terms

  • epidemic: A widespread disease that affects many individuals in a population.
  • population: A collection of organisms of a particular species, sharing a particular characteristic of interest, most often that of living in a given area.
  • infectious: Infectious diseases, also known as transmissible diseases or communicable diseases, comprise clinically evident illness (i.e., characteristic medical signs and/or symptoms of disease) resulting from the infection, presence, and growth of pathogenic biological agents in an individual host organism.

Epidemics

In epidemiology, an epidemic occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience. Epidemiologists often consider the term outbreak to be synonymous to epidemic, but the general public typically perceives outbreaks to be more local and less serious than epidemics.

CAUSES

Epidemics of infectious disease are generally caused by a change in the ecology of the host population (e.g. increased stress or increase in the density of a vector species), a genetic change in the parasite population or the introduction of a new parasite to a host population (by movement of parasites or hosts). Generally, an epidemic occurs when host immunity to a parasite population is suddenly reduced below that found in the endemic equilibrium and the transmission threshold is exceeded.

EPIDEMIC VS. PANDEMIC

An epidemic may be restricted to one location; however, if it spreads to other countries or continents and affects a substantial number of people, it may be termed a pandemic. The declaration of an epidemic usually requires a good understanding of a baseline rate of incidence; epidemics for certain diseases, such as influenza, are defined as reaching some defined increase in incidence above this baseline. A few cases of a very rare disease may be classified as an epidemic, while many cases of a common disease (such as the common cold) would not.

INFLUENZA EPIDEMICS

Influenza is an infectious disease of birds and mammals caused by RNA viruses of the family Orthomyxoviridae, the influenza viruses. The most common symptoms are chills, fever, sore throat, muscle pains, headache (often severe), coughing, weakness/fatigue and general discomfort. Although it is often confused with other influenza-like illnesses, especially the common cold, influenza is a more severe disease caused by a different type of virus. Influenza may produce nausea and vomiting, particularly in children, but these symptoms are more common in the unrelated gastroenteritis, which is sometimes inaccurately referred to as “stomach flu” or “24-hour flu”.

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Influenza: TEM of negatively stained influenza virions, magnified approximately 100,000 times. Modern transport contributes in spreading diseases faster.

Typically, influenza is transmitted through the air by coughs or sneezes, creating aerosols containing the virus. Influenza can also be transmitted by direct contact with bird droppings or nasal secretions, or through contact with contaminated surfaces. Airborne aerosols have been thought to cause most infections, although which means of transmission is most important is not absolutely clear. Influenza viruses can be inactivated by sunlight, disinfectants and detergents. As the virus can be inactivated by soap, frequent hand washing reduces the risk of infection.

Influenza spreads around the world in seasonal epidemics, resulting in about three to five million yearly cases of severe illness and about 250,000 to 500,000 yearly deaths, rising to millions in some pandemic years.

In the 20th century three influenza pandemics occurred, each caused by the appearance of a new strain of the virus in humans, and killed tens of millions of people. Often, new influenza strains appear when an existing flu virus spreads to humans from another animal species, or when an existing human strain picks up new genes from a virus that usually infects birds or pigs. An avian strain named H5N1 raised the concern of a new influenza pandemic after it emerged in Asia in the 1990s, but it has not evolved to a form that spreads easily between people.

In April 2009 a novel flu strain evolved that combined genes from human, pig, and bird flu. Initially dubbed “swine flu” and also known as influenza A/H1N1, it emerged in Mexico, the United States, and several other nations. The World Health Organization officially declared the outbreak to be a pandemic level 6 on 11 June 2009. However, the WHO’s declaration of a pandemic level 6 was an indication of spread, not severity; the strain actually having a lower mortality rate than common flu outbreaks.

VACCINATIONS

Vaccinations against influenza are usually made available to people in developed countries. Farmed poultry is often vaccinated to avoid decimation of the flocks. The most common human vaccine is the trivalent influenza vaccine (TIV) that contains purified and inactivated antigens against three viral strains. Typically, this vaccine includes material from two influenza A virus subtypes and one influenza B virus strain. The TIV carries no risk of transmitting the disease, and it has very low reactivity. A vaccine formulated for one year may be ineffective in the following year, since the influenza virus evolves rapidly, and new strains quickly replace the older ones.

Antiviral drugs such as the neuraminidase inhibitor oseltamivir (Tamiflu) have been used to treat influenza; however, their effectiveness is difficult to determine due to much of the data remaining unpublished.