Emerging infectious diseases can be defined as infections that have newly appeared in a population or have existed but are rapidly increasing in incidence or geographic range.
Infectious disease mortality in the United States decreased markedly during most of the 20th century. The sharp increase in 1918 and 1919 was caused by the influenza pandemic, which killed more than 20 million people worldwide, including over 500,000 people in the U.S. Following World War II, it was widely believed that humans were winning the war against infectious microbes. Life threatening diseases such as tuberculosis and typhoid fever could be treated with antibiotics, and dreaded childhood diseases (polio, whooping cough, diphtheria) could be conquered with vaccination. Coupled with improvements in urban sanitation and water quality, vaccines and antibiotics dramatically reduced the incidence of infectious disease. But, in 1950, penicillin began to lose its power to cure infections caused by Staphylococcus aureus. In 1957 and 1958, new strains of influenza emerged in China and spread around the world. In the 1970’s, there was a resurgence of sexually transmitted diseases and new diseases identified in the U.S. and elsewhere (Legionnaire’s Disease, toxic shock syndrome, Lyme’s disease). During the 1980’s, HIV emerged as a new infection and tuberculosis re-emerged in an antibiotic resistant form. Between 1980 and 1992, the death rate from infectious diseases increased 58%. The increase in drug resistance in strains of bacteria forced the U.S. to return to the pre-antibiotic era in the battle against many common organisms, at the same time that new bacterial and viral pathogens were appearing.
The early history of ID was characterized by sudden, unpredictable outbreaks Scientific advances (vaccines, antibiotics) and improved sanitation in the late 19th and early 20th centuries resulted in prevention and control of many IDs. Despite these improvements in health, outbreaks of ID continue to occur, and new infections emerge
Multiple factors are involved with the initiation or potentiation of emerging infections Societal, technological, and environmental factors continue to have a dramatic effect on infectious diseases worldwide, facilitating the emergence of new diseases and the reemergence of old ones, sometimes in drug-resistant forms. Modern demographic and ecologic conditions that favor the spread of infectious diseases include rapid population growth; increasing poverty and urban migration; more frequent movement across international boundaries by tourists, workers, immigrants, and refugees; alterations in the habitats of animals and arthropods that transmit disease; increasing numbers of persons with impaired host defenses; and changes in the way that food is processed and distributed. Several recent health events underscore the need for a public health system ready to address whatever disease problems that might arise. An excellent discussion can be found in “Factors in the Emergence of Infectious Diseases” by Stephen S. Morse, Ph.D. in Emerging Infectious Diseases, Vol.1, No. 1, pgs 1-13.
The potential economic and societal impact of known emerging infections is enormous. HIV / AIDSConsidering a single “new infection” - HIV/AIDS, we can see the many effects just in South Carolina: hundreds of millions of dollars in direct medical care costs and indirect costs to society, the loss of thousands of valuable years of lives and major social disruption. The financial burden to society is great. The lifetime, discounted, direct medical costs of treating HIV is estimated to be $96,000 for adults and $161,000 for children infected since birth. Neither of these estimates include the financial impact of multi-drug therapy (HAART) costing more than $10,000/year. Annual HIV/AIDS related expenditures in SC were estimated to be about $69 million in 1997. Personal service expenditures for treatment and social support were by far the largest component of total expenditures. The medical treatment costs of HIV/AIDS exceeded $60 million. Hospital inpatient care consumed the major share, representing over $30 million. The average charge per hospital stay was $14,260. Hospital outpatient charges totaled $1.7 million. Nosocomial Infection When a patient on a medical ward acquires an infection in the hospital, treatment costs average $2,100. Septicemia causes patients to stay in the hospital longer and results in over $3,500 in additional hospital charges. USDHHS (1998), Preventing Emerging Infectious Diseases: A Strategy for the 21st Century. Atlanta: Centers for Disease Control and Prevention. SCDHEC (1999). HIV/AIDS and STD’S in South Carolina. Columbia:SCDHEC, June, 1999.
The routes of entry for the natural spread of disease are: Inhalation results in the deposition of infectious or toxic particles within lung and provides a direct pathway to the systemic circulation. The natural process of breathing causes a continuous influx of the agent to exposed individuals. Ingestion of contaminated food or water Percutaneous inoculation via breaks in the skin, including insect bites. Mucous membrane penetration Contact with infected blood and body fluids, consider sexually transmitted diseases and transfusion Person-to person spread is the simplest method of transmission. That microorganisms emerge and re-emerge is not new. This has been occurring since the beginning of time. New bacterial and viral pathogens emerge either from an unrecognized ecological environment to thrust itself upon man (e.g. AIDS, Ebola) or following scientific discovery of a new strain of a previously defined pathogen (e.g. Hepatitis C). Common bacterial path ogens (e.g. gonorrhea, malaria, enterococcus, pneumococcus, tuberculosis, staphylococcus, and streptococcus) have become resistant to many of the antibiotics used over the past 20 years and leave the medical community with no effective treatment for a growing list of infectious diseases. As pathogens strengthen their bold, broaden their reach, and pierce our defenses, our vulnerability is extending to the most mundane activities. Questions arise such as – Is my tap water safe to drink? Is the food I ordered in a restaurant safe to eat? Are my children likely to be bitten by disease-carrying insects or ticks while playing in the yard? Does my sex partner have an infection that might be passed on to me? Is it safe to vacation in a tropical country? Is the coughing person next to me on the subway or airplane spreading a deadly strain of influenza or tuberculosis? Whatever the cause, the resurgence of diseases attributed to newly emerging or re-emerging microbes poses a formidable challenge for the nation’s public health and health-care systems. The CDC is responsible for health policy and national leadership to meet these challenges posed by emerging diseases. These are target areas that the CDC has planned to work in to meet the challenge and lessen the threat posed by these organisms.
To accomplish these goals, objectives, and activities, CDC’s “Preventing Emerging Infectious Diseases: A Strategy for the 21st Century” targets nine categories of problems that cause human suffering and place a burden on society: Antimicrobial resistance. The emergence of drug resistance in bacteria, parasites, viruses, and fungi is reversing advances of the previous 50 years. As the 21st century approaches, many important drug choices for the treatment of common infections are becoming increasingly limited, expensive, and, in some cases, nonexistent. Foodborne and waterborne diseases. Changes in the ways that food is processed and distributed are causing more multistate outbreaks of foodborne infections. In addition, a new group of waterborne pathogens has emerged that is unaffected by routine disinfection methods. Vectorborne and zoonotic diseases. Many emerging or reemerging diseases are acquired from animals or are transmitted by arthropods. Environmental changes can affect the incidence of these diseases by altering the habitats of disease vectors. Diseases transmitted through blood transfusions or blood products. Improvements in blood donor screening, serologic testing, and transfusion practices have made the U.S. blood supply one of the safest in the world, despite its size and complexity. However, because blood is a human tissue, it is a natural vehicle for transmitting infectious agents. Therefore, continued vigilance is needed to ensure the safety of the U.S. blood supply. Chronic diseases caused by infectious agents. Several chronic diseases once attributed to lifestyle or environmental factors (e.g., some forms of cancer, heart disease, and ulcers) might be caused or intensified by infectious agents. This new knowledge raises the possibility that certain chronic diseases might someday be treated with antimicrobial drugs or prevented by vaccines.
Vaccine development and use. Certain childhood diseases (e.g., diphtheria, tetanus, polio, measles, mumps, rubella, and Haemophilus influenzae type b disease) have been virtually eliminated in the United States through universal vaccination. However, additional vaccines are needed to prevent diseases that are a societal burden in the United States or internationally (e.g., HIV/AIDS, dengue fever, hepatitis C, and malaria). Diseases of persons with impaired host defenses. Persons whose normal host defenses against infection have been impaired by illness, by medical treatment, or as a result of age are more likely to become ill with various infectious diseases. Infections that occur with increased frequency or severity in such persons are called opportunistic infections. Health-care providers and scientists must be ready to identify and investigate each new opportunistic infection as it appears, and to learn how to diagnose, treat, control, and prevent it. Diseases of pregnant women and newborns. Certain asymptomatic infections in a pregnant woman can increase her infant’s risk of prematurity, low birth weight, long-term disability, or death. In addition, infections can be transmitted from mother to child during pregnancy, delivery, or breast-feeding. Effective and accessible prenatal care is essential to the prevention of infection in pregnant women and newborn babies. Diseases of travelers, immigrants, and refugees. Persons who cross international boundaries (e.g., tourists, workers, immigrants, and refugees) are at increased risk for contracting infectious diseases and can also disseminate diseases to new places. International air travel has increased substantially in recent years, and more travelers are visiting remote locations where they can be exposed to infectious agents that are uncommon in their native countries. USDHHS, 1998. Preventing Emerging Infectious Diseases: A Strategy for the 21st Century, Atlanta: Centers for Disease Control and Prevention
Some of the functions listed above need further ellaboration. The role of public health includes Surveillance is the ongoing, systematic collection, analysis, and interpretation of health data. It is key to detecting, investigating, and monitoring emerging pathogens, diseases they cause, factors influencing emergence, and response to problems as they are identified. Our nationwide surveillance system requires involvement and resources at all levels. Medical providers (clinics, emergency rooms, labs) are required to report any disease conditions to the local health department; some require urgent action. These disease reports are monitored at the local level and sent to Columbia for statewide surveillance. Columbia in turn sends data to the CDC as part of national surveillance. The use of epidemiology provides early diagnosis and response to outbreaks and changing disease patterns, and allows for the detection of causes of disease or spread of disease even before specific laboratory diagnosis is made. Methods include risk assessment, investigation, interviewing individuals, fact finding, consultation with state epidemiologists/CDC, analysis of laboratory data, diagnosis verification, cause determination, and mobilization of the epidemiology teams. Early response includes rapid notification and immediate action to monitor changing disease patterns and medical management. Medical management includes medical interventions and treatment, safety measures, infection control, and isolation. Laboratory identification is required for rapid and accurate diagnosis of an outbreak or unusual disease. Sometimes a definitive diagnosis may not be possible immediately. Clinical signs and symptoms of the illness may be the only information available from which to develop a differential diagnosis.
Rapid communication links must be established with private medical providers and hospitals to alert them to outbreaks and disease changes as well as to facilitate collaboration, communication, and coordination. Communication with media is essential to inform the public and provide accurate information for action and prevention. Education of health care providers and the community about prevention or early identification and detection. Information should include a list of signs and symptoms, and guidelines for prophylactic treatment, protective clothing, or other personal protection. For example, during/following a hurricane, information about food spoilage and unclean water is widely disseminated along with tips on what to do with food in freezers that were without power – all in an effort to prevent secondary food and water-borne diseases in the midst of a disaster. Similarly, tetanus vaccinations are provided in flood areas where risk of a dirty injury is greater.
Some additional examples of emerging infectious diseases include: HIV/AIDS: First recognized in 1981, AIDS is caused by the HIV virus found in blood, semen, and vaginal secretions of infected persons. A strain of the virus has been circulating since at least 1959, and may have evolved from a virus carried by a nonhuman primate. Lyme disease: First recognized in the 1970’s, it has emerged as the most frequently reported tick borne disease in the US with an average of over 12,000 cases reported annually since 1993. It is the most common vector-borne disease in the US, with the number of cases steadily increasing since 1990 with slightly higher rates among the elderly. Legionnaire’s disease: First identified in Philadelphia in 1976, it is caused by the bacterium Legionella pneumophila. Transmitted through inhalation of aerosols of contaminated water, it is thought to account for 7% of all non-nosocomial pneumonias.
While previous influenza pandemics were naturally occurring events, an influenza pandemic could be started with an intentional release of a deliberately altered influenza strain. Even if a deliberately altered strain is not released, an influenza pandemic originating from natural origins will inevitably occur and will likely cause substantial illness, death, social disruption, and widespread panic. Globally, the 1918 pandemic killed at least 20 million people. This figure is approximately double the number killed on the battlefields of Europe during World War I. In the United States alone, the next pandemic could cause an estimated 89,000-207,000 deaths, 314,000-734,000 hospitalizations, 18-42 million outpatient visits, and 20-47 million additional illnesses. These predictions equal or surpass many published casualty estimates for a bioterrorism event. In addition to the potential for a large number of casualties, a bioterrorism incident and an influenza pandemic have similarities that allow public health planners to simultaneously plan and prepare for both types of emergencies. Preparing for both the next influenza pandemic and the next bioterrorist attack requires support and collaboration from multiple partners at the state, local, and federal level. Potential partners include the medical community, law enforcement, emergency management, and public health agencies.
Each year, influenza develops in up to 20% of all Americans. &gt;200,000 are hospitalized with the disease. Although influenza is commonplace and generally self-limited, an estimated 36,000 die each year from complications of the disease. Worldwide influenza infections develop in 3-5 million people annually, and 500,000 deaths occur. Outbreaks of avian influenza recently have drawn attention worldwide particularly in Southeast Asia, where at least 55 persons have become infected and 42 have died since January 2004. The current strain of avian influenza is highly pathogenic; it has killed millions of chickens and other birds. Although the virus can cross species to infect humans, suspected cases of human-to-human transmission have been rare. However, the virus could acquire characteristics that allow it to be transmitted among humans, which could cause a worldwide influenza pandemic, with the potential for killing millions of people. In the past, a pandemic of the “Spanish Flu” killed 20-50 million people worldwide.
These epidemics were caused by a virus, influenza A, with surface protein antigens which were not recognized by a susceptible host population. Surface protein antigens mutate so that the host does not recognize them and can not build up immunity. These surface protein antigens are called glycoproteins and attach themselves to the host lung tissue to initiate an infection
There are two glycoproteins which protrude from the surface of the influenza virus: hemagglutinin (H) and neuraminidase (N). Both of these antigenic surface proteins play key roles in the infection and dissemination.
There are 15 H antigens and 9 N antigens. Humans have been affected by H1,H2, and H3 thus far. The H antigens combined with their N counterparts have been responsible for the great pandemics of the past. The other H and N antigens affect other animals.
The Influenza A (H5N1) avian influenza virus has infected humans. Soon additional subtle mutations may allow the virus to transmit the infection which is then passed “efficiently” from person to person
The 2003 outbreak of severe acute respiratory syndrome (SARS) was contained largely through traditional public health interventions, such as finding and isolating case-patients, quarantining close contacts, and enhanced infection control. The independent effectiveness of measures to “increase social distance” and wearing masks in public places requires further evaluation. Limited data exist on the effectiveness of providing health information to travelers. Entry screening of travelers through health declarations or thermal scanning at international borders had little documented effect on detecting SARS cases; exit screening appeared slightly more effective. The value of border screening in deterring travel by ill persons and in building public confidence remains unquantified. Interventions to control global epidemics should be based on expert advice from the World Health Organization and national authorities. In the case of SARS, interventions at a country’s borders should not detract from efforts to identify and isolate infected persons within the country, monitor or quarantine their contacts, and strengthen infection control in health care settings.
Epi clue: unexplained bird (ie, crows) or horse deaths Notify public health department in mosquito season
It only took six years for WNV to spread from coast to coast
Ebola hemorrhagic fever (Ebola HF) is a severe, often-fatal disease in humans and nonhuman primates (monkeys, gorillas, and chimpanzees) that has appeared sporadically since its initial recognition in 1976. The disease is caused by infection with Ebola virus, named after a river in the Democratic Republic of the Congo (formerly Zaire) in Africa, where it was first recognized. The virus is one of two members of a family of RNA viruses called the Filoviridae. There are four identified subtypes of Ebola virus. Three of the four have caused disease in humans: Ebola-Zaire, Ebola-Sudan, and Ebola-Ivory Coast. The fourth, Ebola-Reston, has caused disease in nonhuman primates, but not in humans. The exact origin, locations, and natural habitat (known s the “natural reservoir”) of Ebola virus remain unknown. However, on the basis of available evidence and the nature of similar viruses, researchers believe that the virus is zoonotic (animal-borne) and is normally maintained in an animal host that is native to the African continent. A similar host is probably associated with Ebola-Reston which was isolated from infected cynomolgous monkeys that were imported to the United States and Italy from the Phillippines. The virus is not known to be native to other continents, such as North America. Ebola HF typically appears in sporadic outbreaks, usually spread within a health-care setting (a situation known as amplification). It is likely that sporadic, isolated cases occur as well, but go unrecognized.
Reservoir – The deer mouse (Peromyscus maniculatus) is the primary reservoir of the hantavirus that causes hantavirus pulmonary syndrome (HPS) in the United States. Transmission – Infected rodents shed the virus through urine, droppings, and saliva. HPS is transmitted to humans through a process called aerosolization. Aerosolization occurs when dried materials contaminated by rodent excreta or saliva are disturbed. Humans become infected by breathing in these infectious aerosols. HPS in the United States cannot be transmitted from one person to another. HPS in the United States is not known to be transmitted by farm animals, dogs, or cats or from rodents purchased from a pet store. Risk – Anything that puts you in contact with fresh rodent urine, droppings, saliva or nesting materials can place you at risk for infection. Virus – Hantaviruses have been shown to be viable in the environment for 2 to 3 days at normal room temperature. The ultraviolet rays in sunlight kill hantaviruses. Prevention – Rodent control in and around the home remains the primary strategy for preventing hantavirus infection. Cleaning – Use a bleach solution or household disinfectant to effectively deactivate hantaviruses when cleaning rodent infestations.
Challenges for the Future Scientists – government and academic, together with their investigative partners and international collaborators – have made great strides in the past 10 years in understanding many of the pathogenic mechanisms used by emerging and reemerging infectious diseases. Many of these have been translated into novel diagnostics, antiviral and antibacterial compounds, and vaccines, often with extraordinary speed. However many challenges remain. Paramount among these is finding a safe and effective HIV vaccine. The evolution of pathogens with resistance to antibacterial and antiviral agents continues to challenge better understanding of the mechanisms of drug resistance and to delay finding ways to circumvent the problem. These efforts will pave the way to developing countermeasures against deliberately engineered ____________. If history is our guide, we can assume that the battle between the will of the human species to find cures and the extraordinary adaptability of microbes will be never-ending. To successfully fight our microscopic invaders, we must continue to vigorously pursue research on the basic fundamentals that underlie microbial pathogenesis and develop novel strategies against these ingenious opponents.