Introduction
Infectious diseases have been a major threat to human progress and survival globally for over a millennium and are the leading causes of death and disability. Despite the advances in the development of diagnostics, therapeutics, vaccines, the ease of travel, and increased interdependence among countries, it has only made it more difficult to contain these infectious diseases. The world health organization (WHO), in its 2007 report, warned that infectious diseases are emerging at a more rapid rate than before. Studies of these emerging infectious diseases have revealed the evolutionary characteristics of the pathogenic microorganism and the relationships between microorganisms, their hosts, and the environment.
What Are Emerging Infectious Diseases?
Emerging infectious diseases are either new, newly identified, or unique in a geographic area with rapid prevalence.
The national institute of allergy and infectious diseases (NIAID) defines emerging infectious diseases as:
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Emerging of a previously unknown disease.
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A known disease is new to a geographic region or has a rapidly increasing incidence.
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Uncontrollable existing disease.
The most recent example of an emerging infectious disease is the case of coronavirus (SARS- CoV-2), causing COVID-19. It illustrates how viruses can move from animals to humans (from bats to humans), acquire the ability to spread among people in a confined space like a hospital, and then reach around the globe exponentially as a result of air travel. Another salient example of an emerging disease is HIV (human immunodeficiency virus) or AIDS (acquired immunodeficiency syndrome). It was believed that humans contracted HIV from close contact with chimpanzees. It then spread from rural areas to cities and then internationally through air travel, causing a spread globally. Later, human behavior and practices like sexual transmission, intravenous drug use, and transfer of blood products before the disease was recognized contributed to the rapid and extensive spread of HIV.
What Are Re-Emerging Infectious Diseases?
Re-emerging infectious diseases are infections that reappear after being on a significant decline for a while. Re-emergence of a disease may occur due to the evolution of an already under control disease-causing organism's strain. It may also be due to a decline in the public health safety measures for diseases under control. Another reason for re-emergence could be climatic conditions like the El Niño-southern oscillation (ENSO) phenomenon associated with the re-emergence of cholera and malaria.
What Are Deliberately Emerging Diseases?
Deliberately emerging infectious diseases are infections that are man-made, usually used as a bioweapon for bioterrorism. These are made using naturally present microorganisms but can be modified to increase their virulence or resistance to antibiotics. Terrorists may use these as an alternative to conventional weapons to cause widespread destruction with minimal cost and without being detected. Anthrax, smallpox, and tularemia are some of the past deliberately emerging diseases.
What Factors Contribute to the Emergence or Re-Emergence of a Disease?
Factors that contribute to the emergence of a new disease or re-emergence of an old disease include:
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Microbial Adaptation: Pathogens may evolve naturally over time as a result of mutation, new genetic variations, adaptation, and recombinations.
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Susceptibility of People to Infection: Immunocompromised people are more susceptible to an infection, for example, HIV patients.
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Environmental Factors: Environmental factors like climate change can lead to the emergence and re-emergence of viral and bacterial vector-borne diseases. For example, a warm climate may favor mosquitoes and the disease they carry to spread to regions they have not been to before.
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Farming Practices and Land Use: Pesticides in agriculture lead to the elimination of biological controls like amphibians and insectivorous birds that could control the disease-carrying vectors. And construction of dams, deforestation, and irrigation systems can cause a rise in malaria and other mosquito-borne diseases.
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Human Demographic Changes and Economic Development: Increased growth in population, overcrowding, poor sanitation, and housing, and increased mobility.
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Travel Facilities: International travel and population mix are determinants of disease spread. For example, COVID-19, which commenced in Wuhan in 2019, became a pandemic due to population movement and mass gatherings.
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Human Behavior: Human behavior and practices may also lead to changes within the bacteria to adapt to the new environment. For example, the overuse of antibiotics has led to resistant strains of microorganisms. And the recently decreased vaccination compliance has led to the re-emergence of diseases like measles and pertussis.
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The Decline in Public Safety Health Measures.
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Bioterrorism: Using potentially dangerous pathogens as a bioweapon and causing the deliberate emergence or re-emergence of the disease. For example, anthrax and smallpox.
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Advanced Technology: Although technological advances have eased the burden of infections globally, it has introduced many new ways for the spread and emergence of infection, like blood transfusion, hypodermic needles, and iatrogenic immunosuppression.
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Poverty: Diseases like tuberculosis are usually a problem in low-income areas.
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Wildlife Trade: Increased contact between humans and animals has led to zoonotic diseases like the Nipah virus, coronavirus, and influenza virus.
Which Are the Top Eight Emerging Diseases Identified by WHO?
In 2015, WHO identified eight diseases that are likely to cause severe outbreaks in the coming future:
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Crimean-Congo hemorrhagic fever.
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Lassa virus.
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Nipah virus infection.
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Rift valley fever.
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SARS - severe acute respiratory syndrome.
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MERS - Middle-East respiratory syndrome.
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Ebola virus disease.
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Marburg virus disease.
Can Emerging Infectious Diseases Be Controlled?
Over time, humans have successfully eradicated many diseases like smallpox and rinderpest and controlled many conditions like polio, measles, etc. However, pathogenic microorganisms like the Influenza virus undergo rapid genetic changes in response to changing host and environmental factors, making it difficult to control these diseases. Therefore, controlling these diseases is challenging and may take years or even decades.
Many approaches have been made in developing strategies to prevent and mitigate outbreaks. Once the causative agent of an infectious disease is isolated, measures to stop the spread can be easily established based on the knowledge of the transmission modes. However, these actions often fail due to the lack of basic sanitation and the lack of education of the population affected by a disease outbreak.
Thus, the prevention of emerging infectious diseases should be focused on strengthening basic social and environmental factors, such as access to health and education services for all and preserving the environment. “One health” is one such approach; it is a collective local, national and global effort to achieve the best health for humans, animals, and the environment. In addition to this, investing in new technological tools for diagnosing and detecting pathogens is also crucial.
How Can One Reduce the Risk of Infectious Diseases?
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Be up-to-date on all the immunization vaccinations that the country suggests.
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Be aware of the existing infectious diseases and take preventive medications and measures a healthcare provider suggests.
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If traveling, find out proper information about the place of destination, the available medical facilities, and any infectious diseases that are prevalent there.
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If a person experiences uncommon symptoms and suspects an infectious disease, contact a healthcare provider immediately, and quarantine oneself to prevent the spread of the disease.
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Medical practitioners must obtain a detailed travel history and report the case if they suspect an abnormal condition.
Conclusion
Infectious diseases remain a threat to humans and animals with their ever-evolving nature. They are difficult to predict and a challenge to manage. Each new disease has unique challenges, forcing us to adapt continuously to ever-changing threats. Recognizing drivers that contribute to an outbreak helps make strategies for health care providers to work together; one health strategy. The battle against emerging infectious diseases is an ongoing process; eliminating every last disease is never possible. But instead, it is better to get ahead of the next one.
