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Understand  –  Bacteria

Bacteria and infections

Throughout history, bacterial infections have played a central role in the lives and deaths of humans.

Bacteria cause many common infections such as pneumonia, wound infections, bloodstream infections (sepsis) and sexually transmitted diseases like gonorrhea, and have also been responsible for several major disease epidemics. One example from the 1340’s is the plague, also known as the “Black death”, that spread across Asia and Europe along the trading routes, killing millions of people. The disease is now known to be caused by the bacterium Yersinia pestis and is treatable by antibiotics.

When do bacteria cause disease?

Bacteria can be strictly pathogenic, which means that they will cause disease if they manage to overwhelm the human immune system. Other bacteria only cause disease given the right circumstances, these are so-called opportunistic pathogens. Opportunistic pathogens normally do not cause infections in healthy humans but when the immune system is compromised or suppressed by for example cancer chemotherapy, other diseases (like HIV/AIDS) or malnutrition, the risk of infection increases. These infections often originate from the individual’s own bacterial flora such as that on the skin or in the gut. Many bacterial pathogens can spread and infect via water and food, including Salmonella, Campylobacter and E. coli. Sometimes bacteria are transmitted directly or indirectly from animals to humans and cause disease. Such infections are called zoonotic infections. Other bacteria like Neisseria gonorrhea and Chlamydia trachomatis spread via sexual contacts.

Managing bacterial infections

The introduction of antibiotics to treat bacterial infections in combination with improved hygiene and sanitation, use of preventive vaccinations as well as increased knowledge about bacteria have greatly reduced deaths from bacterial diseases. However, antibiotic resistance among bacteria is now threatening to again leave us without effective treatments for many common bacterial infections. Resistant bacteria are now widespread in most parts of the world and more and more people die from bacterial infections because the antibiotics have stopped working. For information about antibiotic resistance, see Antibiotic resistance, and the sub-sections that follows.

Below are a set of resources about bacterial diseases and their spread.

Selected Resources

Resource Description
What are infectious diseases? Infectious disease: Facts about what it is and an introduction to the different groups of microorganisms that cause it (bacteria, viruses, fungi and parasites).
Understanding Microbes in Sickness and in Health Learn about microbes and their role in health and disease in this book written for the general public.
10 facts about zoonotic neglected tropical diseases Information about the impact and spread of neglected tropical diseases like rabies and porcine tapeworm infection.
Zoonotic Diseases This fact sheet explains more about common zoonotic infections – infections shared between animals and humans – and how they can spread (focus on the US). developed by the CDC.
The Black Death: The Greatest Catastrophe Ever Popular science article about “The Black Death”, the plague epidemic in the 1300s.

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