Infectious Diseases - All you need to know

Infectious diseases are caused by organisms, usually microscopic in sizes, such as bacteria, viruses, fungi, or parasites that are passed, directly or indirectly, from one person to another. Humans can also become infected following exposure to an infected animal that harbors a pathogenic organism that is capable of infecting humans.

Infectious diseases are a leading cause of death worldwide, particularly in low-income countries, especially in young children. Three infectious diseases were ranked in the top ten causes of death worldwide in 2016 by the World Health Organization. They are lower respiratory infections (3.0 million deaths), diarrheal diseases (1.4 million deaths), and tuberculosis (1.3 million deaths). HIV/AIDS, which was previously on the list, has dropped from the global list of the top ten causes of death (1.0 million deaths in 2016 compared with 1.5 million in 2000), but it is still a leading cause of death in low-income countries. Another infectious disease, malaria, accounts for a top cause of death in low-income countries. 

Lower respiratory infections (including pneumonia) and diarrheal diseases are caused by a variety of infectious agents. The other infectious diseases on the list - HIV/AIDS, tuberculosis, and malaria - are due to a single infectious agent. 

Agents that Cause Infectious Diseases

Infectious diseases can be caused by several different classes of pathogenic

organisms. These are viruses, bacteria, protozoa, and fungi. Almost all of these organisms are microscopic in size and are often referred to as microbes or microorganisms.

Although microbes can be agents of infection, most microbes do not cause disease in humans. In fact, humans are inhabited by a collection of microbes, known as the microbiome, that plays important and beneficial roles in our bodies.

The majority of agents that cause disease in humans are viruses or bacteria, although the parasite that causes malaria is a notable example of a protozoan.

Examples of diseases caused by viruses are HIV/AIDS, influenza, Ebola, MERS, smallpox, diarrheal diseases, hepatitis, and West Nile. Diseases caused by bacteria include anthrax, tuberculosis, salmonella, and respiratory and diarrheal diseases.

Transmission of Infectious Diseases

There are a number of different routes by which a person can become infected

with an infectious agent. For some agents, humans must come in direct contact with a source of infection, such as contaminated food, water, fecal material, body fluids or animal products. With other agents, the infection can be transmitted through the air.

The route of transmission of infectious agents is clearly an important factor in how quickly an infectious agent can spread through a population. An agent that can spread through the air has greater potential for infecting a larger number of individuals than an agent that is spread through direct contact.

Another important factor in the transmission is the survival time of the infectious agent in the environment. An agent that survives only a few seconds between hosts will not be able to infect as many people as an agent that can survive in the environment for hours, days, or even longer. These factors are important considerations when evaluating the risks of potential bioterrorism agents.

Impact of Infectious Diseases on Society

Infectious diseases have plagued humans throughout history, and in fact, have even shaped history on some occasions. The plagues of biblical times, the Black Death of the Middle Ages, and the “Spanish flu” pandemic of 1918 are but a few examples. The 1918 flu pandemic killed more than a half million people in the United States and up to 50 million people worldwide and is thought to have played a contributing role in ending World War I.

Epidemics and pandemics have always had major social and economic impacts on affected populations, but in our current interconnected world, the impacts are truly global.

HIV/AIDS

The HIV/AIDS epidemic, particularly in sub-Saharan Africa, illustrates the economic and social impacts of prolonged and widespread infection. The disproportionate loss of the most economically-productive individuals has reduced workforces and economic growth rates of affected countries, especially those with high infection rates. This impacts the health care, education, and political stability of these nations.

In southern Africa where the infection rate is highest, life expectancy has plummeted in a mere decade from 62 years in 1990 -1995 to 48 years in 2000 – 2005. The existence of approximately 18 million children worldwide under that age of 18 that have been orphaned by HIV/AIDS highlights the impact of infectious diseases on families and societies.

Influenza

Another recent example of an infectious disease outbreak is H1N1 influenza or “swine” flu pandemic that began in the spring of 2009. For the first time in the long history of flu pandemics, the beginnings of an outbreak were detected, and the spread of the disease was monitored on an almost daily basis as air travelers carried it around the globe.

The new H1N1 flu traveled around the world with unprecedented speed and in a few short months made its impact felt global. Even though the disease was relatively mild for most people, some schools closed – more than 700 across the United States at its peak - and a number of infected people were quarantined. Mexico suffered great economic loss and damage to its tourism industry in an attempt to contain the outbreak in its early stage.

After the H1N1 flu waned, yet another variant of the influenza virus emerged. The new H7N9 virus was first detected in birds and humans in China in the spring of 2013, but it currently does not appear to be spreading from person to person.

A severe pandemic potentially could cause major disruptions to national and global economies, close schools and businesses for weeks, restrict social interactions, and lead to disagreements between nations regarding the allocation of limited doses of antiviral drugs and vaccine.

Challenges in Infectious Disease Research

Despite significant advances in infectious disease research and treatment, the control and eradication of these diseases face major challenges.

A WHO report released in 2007 warns that infectious diseases are spreading more rapidly than ever before and that new infectious diseases are being discovered at a higher rate than at any time in history. In just the past five years, the WHO has identified over 1000 epidemics of infectious diseases including avian flu, swine flu, polio, and cholera.

With greatly increased human mobility, infectious diseases have the potential to swiftly become global epidemics and pandemics.

Some of the reasons for the difficulty in combating infectious diseases are:

• New infectious diseases continue to emerge
• Old infectious diseases increase in incidence or geographical distribution
• Old infectious diseases previously under control begin to re-emerge
• Potential for the intentional introduction of infectious agents by bioterrorists
• Increasing resistance of pathogens to current antimicrobial drugs
• Breakdowns in public health systems and communication between nations

According to WHO nearly 50,000 men, women, and children are dying every day from infectious diseases. Let's stand together and raise the awareness at 5th World Congress on Virology and Infectious Diseases

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