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Infectious Diseases
Infectious Diseases. Source: Merck

Emerging Infectious Diseases

Emerging Infectious Diseases

These recent outbreaks point to the fact that infectious diseases are not disappearing, but rather seem to be reemerging and increasing. In addition, a number of new diseases—emerging infectious diseases (EIDs)—have cropped up in recent years. These are diseases that are new or changing and are increasing or have the potential to increase in incidence in the near future. Some of the factors that have contributed to the development of EIDs are evolutionary changes in existing organisms (e.g., Vibrio cholerae; VIB-re¯-o¯ KOL-er-¯) and the spread of I known diseases to new geographic regions or populations by modern transportation. Some EIDs are the result of increased human exposure to new, unusual infectious agents in areas that are undergoing ecologic changes such as deforestation and construction (e.g., Venezuelan hemorrhagic virus). Some EIDs are due to changes in the pathogen’s ecology. For example, Powassan virus (POWV) was transmitted by ticks that don’t usually bite humans. However, the virus recently became established in the same deer ticks that transmit Lyme disease. An increasing number of incidents in recent years highlights the extent of the problem.

Zika Virus Disease

In 2015, the world became aware of Zika virus disease. Zika virus is spread by the bite of an infected Aedes mosquito; sexual transmission has also occurred. Zika is a mild disease usually presenting with fever, rash, and joint pain. However, Zika infection during pregnancy can cause severe birth defects in a fetus. The virus was discovered in 1947 in the Zika Forest of Uganda, but until 2007, only 14 cases of Zika virus disease were known. The first Zika epidemic occurred on the island of Yap in Micronesia in 2007, when 73% of the people became infected. Between 2013 and 2015, Zika epidemics occurred in French Polynesia and Brazil. Over 1600 cases of Zika have occurred in the United States. Until mid-2016, they were all acquired during travel to endemic areas (except one laboratory acquired infection). However, the first U.S. cases of transmission by mosquitoes occurred in Florida during the summer of 2016.

Middle East Respiratory Syndrome (MERS)

Since 2014, there have been 1800 confirmed human cases and 630 deaths caused by a new virus called Middle East respiratory syndrome coronavirus (MERS-CoV). The virus belongs to the same family that causes illnesses from the common cold to severe acute respiratory syndrome (SARS). Because the first reported cases were linked to the Middle East, this latest emerging infectious disease is called Middle East respiratory syndrome (MERS). MERS has spread to Europe and Asia, and two travel-associated cases occurred in the United States in 2014.


H1N1 influenza (flu), also known as swine flu, is a type of influenza caused by a new virus called influenza H1N1. H1N1 was first detected in the United States in 2009, and that same year WHO declared H1N1 flu to be a pandemic disease (a disease that affects large numbers of individuals in a short period of time and occurs worldwide).

Avian influenza A (H5N1), or bird flu, caught the attention of the public in 2003, when it killed millions of poultry and 24 people in southeast Asia. Avian influenza viruses occur in birds worldwide. In 2013, a different avian influenza, H7N9, sickened 131 people in China. In 2015, two cases of H7N9 were reported in Canada.

Influenza A viruses are found in many different animals, including ducks, chickens, pigs, whales, horses, and seals. Normally, each subtype of influenza A virus is specific to certain species. However, influenza A viruses normally seen in one species sometimes can cross over and cause illness in another species, and all subtypes of influenza A virus can infect pigs. Although it is unusual for people to get influenza infections directly from animals, sporadic human infections and outbreaks caused by certain avian influenza A viruses and pig influenza viruses have been reported. Fortunately, the virus has not yet evolved to be transmitted successfully among humans.

Human infections with avian influenza viruses detected since 1997 have not resulted in sustained human-to-human transmission. However, because influenza viruses have the potential to change and gain the ability to spread easily between people, monitoring for human infection and person to-person transmission is important.

Antibiotic-Resistant Infections

Antibiotics are critical in treating bacterial infections. However, years of overuse and misuse of these drugs have created environments in which antibiotic-resistant bacteria thrive. Random mutations in bacterial genes can make a bacterium resistant to an antibiotic. In the presence of that antibiotic, this bacterium has an advantage over other, susceptible bacteria and is able to proliferate. Antibiotic-resistant bacteria have become a global health crisis.

Staphylococcus aureus causes a wide range of human infections from pimples and boils to pneumonia, food poisoning, and surgical wound infections, and it is a significant cause of hospital-associated infections. After penicillin’s initial success in treating S. aureus infection, penicillin-resistant S. aureus became a major threat in hospitals in the 1950s, requiring the use of methicillin. In the 1980s, methicillin-resistant S. aureus, called MRSA, emerged and became endemic in many hospitals, leading to increasing use of vancomycin. In the late 1990s, S. aureus infections that were less sensitive to vancomycin (vancomycin-intermediate S. aureus, or VISA) were reported.

 In 2002, the first infection caused by vancomycin resistant S. aureus (VRSA) in a patient in the United States was reported. In 2010, the World Health Organization (WHO) reported that in Asia and eastern Europe, about 35% of all individuals with tuberculosis (TB) had the multidrug-resistant form of the disease (MDR-TB). Multidrug-resistant TB is caused by bacteria that are resistant to at least the antibiotics isoniazid and rifampicin, the most effective drugs against tuberculosis.

The antibacterial substances added to various household cleaning products inhibit bacterial growth when used correctly. However, wiping every household surface with these antibacterial agents creates an environment in which the resistant bacteria survive. Unfortunately, when you really need to disinfect your homes and hands—for example, when a family member comes home from a hospital and is still vulnerable to infection—you may encounter mainly resistant bacteria.

Routine housecleaning and handwashing are necessary, but standard soaps and detergents (without added antibacterials) are fine for these tasks. In addition, quickly evaporating chemicals, such as chlorine bleach, alcohol, ammonia, and hydrogen peroxide, remove potentially pathogenic bacteria but do not leave residues that encourage the growth of resistant bacteria.

In 2004, emergence of a new epidemic strain of Clostridium difficile (klo-STRID-e¯-um DIF-fi-se¯-il) was reported. The epidemic strain produces more toxins than others and is more resistant to antibiotics. In the United States, C. difficile infections kill nearly 29,000 people a year. Nearly all of the C. difficile infections occur in health care settings, where the infection is frequently transmitted between patients via health care personnel whose hands are contaminated after contact with infected patients or their surrounding environment.

Ebola Virus Disease

First detected in 1995, Ebola virus disease causes fever, hemorrhaging, and blood clotting in vessels. In the first outbreak, 315 people in the Democratic Republic of Congo contracted the disease, and over 75% of them died. The epidemic was controlled through use of protective equipment and educational measures in the community. Close personal contact with infectious blood or other body fluids or tissue leads to human-to-human transmission.

In 2014, a new outbreak in West Africa occurred. The countries Sierra Leone, Guinea, and Liberia experienced the worst impacts, with over 28,000 people infected over the next two years. Over one-third of those infected died. This time, a small number of health care workers from the United States and Europe who had been working with Ebola patients in Africa brought the disease back with them to their home countries, sparking fears that the disease would gain a foothold elsewhere in the world.

Marburg Virus

Recorded cases of Marburg virus, another hemorrhagic fever virus, are rare. The first cases were laboratory workers in Europe who handled African green monkeys from Uganda. Thirteen outbreaks were identified in Africa between 1975 and 2016, involving 1 to 252 people, with 57% mortality. African fruit bats are the natural reservoir for the Marburg virus, and microbiologists suspect that bats are also the reservoir for Ebola.

Just as microbiological techniques helped researchers in the fight against syphilis and smallpox, they will help scientists discover the causes of new emerging infectious diseases in the twenty-first century. Undoubtedly there will be new diseases. Ebola virus and Influenza virus are examples of viruses that may be changing their abilities to infect different host species.

Infectious diseases may reemerge because of antibiotic resistance and through the use of microorganisms as weapons. The breakdown of public health measures for previously controlled infections has resulted in unexpected cases of tuberculosis, whooping cough, and measles.

The diseases we have mentioned are caused by viruses, bacteria, and protozoa—types of microorganisms. This book introduces you to the enormous variety of microscopic organisms. It shows you how microbiologists use specific techniques and procedures to study the microbes that cause such diseases as AIDS and diarrhea—and diseases that have yet to be discovered. You will also learn how the body responds to microbial infection and how certain drugs combat microbial diseases. Finally, you will learn about the many beneficial roles that microbes play in the world around us.

About Fahmida Akter Bristi

I am currently doing my Bachelor degree. I love to write by exploring knowledge that is new to me. Hope this effort of mine benefits you all. Right now, I am the head of Project R. Franklin & Project Waksman in Society & Science Foundation. Knock me anytime. Email:

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