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Bacterial and Viral Infections
Bacterial and viral infections have many similarities. Both types of infections are caused by microbes -- bacteria and viruses, respectively -- and spread by routes such as:
- Coughing and sneezing.
- Contact with contaminated people, especially through activities such as kissing and sexual intercourse.
- Contact with contaminated surfaces, food, and water.
- Contact with contaminated creatures, including household pets, livestock, and insects such as fleas and ticks.
Microbes can also cause:
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- Acute infections,which are short-lived.
- Chronic infections,which can last for weeks, months, or a lifetime.
- Latent infections, which may not initially cause symptoms but which can reactivate over a period of months and years.
Most importantly, bacterial and viral infections -- which are defined as an invasion of microbes able to reproduce in the body -- can cause mild, moderate, and severe disease.
Throughout history, millions of people have succumbed to diseases such as bubonic plague or the Black Death, which is caused by the Yersinia pestis bacterium, and smallpox, which is caused by the variola virus. In recent times, viral infections have been responsible for two major pandemics: the 1918-1919 “Spanish flu” epidemic that killed 20-40 million people, and the ongoing HIV/AIDS epidemic that killed an estimated 2 million people worldwide in 2008 alone.
Bacterial and viral infections can cause similar symptoms such as coughing and sneezing, fever, inflammation, vomiting, diarrhea, fatigue, and cramping -- all of which are ways the immune system tries to rid the body of infectious organisms. But bacterial and viral infections are dissimilar in many other important respects, most of them due to the organisms' structural differences and the way they respond to currently available antimicrobial medications.
The Differences Between Bacteria and Viruses
Although bacteria and viruses are both too small to be seen without a microscope, they're structurally as different as giraffes and goldfish.
Bacteria are relatively complex, single-celled creatures with a rigid wall and a thin, rubbery membrane surrounding the fluid or cytoplasm inside the cell. Shaped like balls, rods, or spirals, they contain all of the genetic information needed to make copies of themselves. Fossilized records show that bacteria have existed for about 3.5 billion years, and it's known that bacteria can survive in a variety of environments, including extreme heat and cold, radioactive waste, and the human body.
Most bacteria are harmless, and some -- such as the Lactobacilli acidophilus bacteria that can live in the human intestine -- actually help digest food, destroy disease-causing microbes, fight cancer cells, and provide essential nutrients. Fewer than 1% of bacteria cause disease in people.
In contrast, viruses are tiny: the largest of them are smaller than the smallest bacteria. Viruses come in varied shapes, and have a limited genetic blueprint. All they have is a protein coat and a core of genetic material: either RNA or DNA. Unlike bacteria, viruses can't survive without a host. They can only reproduce by attaching themselves to cells and hijacking the cells' cellular machinery. In most cases, they reprogram the cells to make new viruses until the cells burst and die. In other cases, they turn normal cells into malignant or cancerous cells.
Also unlike bacteria, most viruses do cause disease, and they're quite specific about the cells they attack. For example, certain viruses are programmed to attacks cells in the liver, respiratory system, or blood. In some cases, viruses called bacteriophages target bacteria.
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