Bacterial and Viral Infections

Bacterial and viral infections commonly make people sick. Both are caused by microbes, microscopic organisms that easily enter human bodies and begin reproducing in people's cells. Bacterial infections are caused by bacteria, while viral infections are caused by viruses. Each type of infection can cause a range of illnesses in a person. Some of these illnesses are relatively mild and usually resolve on their own, as in the case of common colds, which are caused by viruses. Other illnesses, such as strep throat and urinary tract infections (UTIs)—both caused by bacteria—can be more serious and may need to be treated with medication. Antibiotic drugs are taken for bacterial infections, while antiviral medications treat viral infections. Abuse of either type of drug can allow bacteria and viruses to become drug-resistant and more difficult to treat in the future. Many viral infections can be prevented altogether with vaccines.

Background

Both bacteria and viruses are microbes. Although both can cause infections in the bodies of humans and other animals, the two microbes are different in some fundamental ways. Bacteria are single-celled organisms that have existed for about 3.5 billion years. They can survive almost anywhere, including in extreme conditions. Many bacteria live inside the human body, where they execute useful functions, such as helping to digest food, killing infectious cells, and distributing healthy vitamins. Bacteria are also used to make yogurt and fermented milk. Most bacteria—about 99 percent—are either helpful or harmless to the human body.

Other types of bacteria are pathogenic, meaning they can cause infections in other organisms. Pathogenic bacteria reproduce rapidly once they have entered a body. They then emit toxic chemicals that harm cells and ultimately lead to illnesses such as sinusitis, ear infections, strep throat, and pneumonia. Bacterial infections are highly contagious and can be spread in the air through coughs and sneezes. Infected people can spread their bacterial germs on surfaces, food, and water. If uninfected people inadvertently touch these germs and transfer them to their mouth, eyes, or nose, they will likely become infected by the bacteria, too.

Viruses cause infections just as bacteria do but in a different way. Viruses are extremely small organisms, smaller than the largest bacteria. Unlike bacteria, they cannot survive on their own but rather need living hosts in which to replicate themselves. A virus, composed of a simple capsule containing genetic information, invades a healthy cell and reprograms it to create copies of itself. This is how viruses spread within a host organism. Reprogramed cells eventually die, causing sickness.

Viral infections are not as easy to treat as bacterial infections. Rounds of antibiotics may cure most bacterial infections, but they have no effect on viral infections because viruses essentially hide inside their host's cells. This makes them impervious to medications, which travel in the blood. The most effective way to avoid becoming infected with viruses is by receiving vaccines, which can prevent illnesses such as polio, measles, chickenpox, and influenza (the flu). Antiviral medications can treat some viral infections as they arise, but they cannot destroy the original virus.

Impact

A commonly known type of bacterial infection is streptococcal pharyngitis, or strep throat. This illness involves an inflamed and sore throat, white spots on the tonsils, fever, and swollen lymph nodes in the neck. Oral antibiotics may be used to treat strep throat. Patients should exercise great care when taking antibiotics for any kind of bacterial infection. Bacteria are adaptable organisms that can eventually become resistant to antibiotics. Over time, taking antibiotics unnecessarily can lead to antibiotic resistance. A person who later contracts a bacterial infection from antibiotic-resistant bacteria will be unable to treat the illness. This could lead to further health complications.

Another common bacterial infection is sinusitis, or a sinus infection. This type of infection inflames the tissues in the sinuses, causing a runny nose, cough, head congestion, and facial pain. Pneumonia is a bacterial infection that inflames the lungs while filling them with fluid. The bacterial infection tuberculosis causes a persistent, often blood-filled cough, while a urinary tract infection can damage the kidneys if left untreated.

In many cases, bacterial infections are secondary infections, meaning they occurred soon after a viral infection had a chance to weaken a host's immune system. Secondary infections can usually be identified if symptoms of the virus seem worse than they should or last longer than expected. Common secondary infections include sinusitis, pneumonia, and ear infections, which involve ear pain and fever.

As with bacterial infections, illnesses caused by viral infections range from mild to serious. The common cold—with its symptoms of a runny nose, cough, sneezing, sore throat, and head congestion—is caused by a virus. The influenza virus causes influenza, or the flu, which manifests all the symptoms of a cold but with the addition of a high fever and body aches. Annual vaccines can prevent people from contracting the flu during flu season; antiviral drugs can lessen the severity of the flu if they are taken within about two days of contracting the illness.

The viruses that cause less serious infections in the body, such as colds or flus, generally do not require any medical action to resolve, as the body's immune system will eventually kill them. Other viruses can be more serious and even deadly. Human papillomavirus (HPV) infections, measles, the liver disease hepatitis, and the crippling disease polio are all caused by viruses but can be easily prevented with vaccines.

Vaccines are effective only if they are administered before contraction of the illness. For certain other viral infections, antiviral medications may be taken as needed to lessen the infections' symptoms. Infections caused by flu, herpes simplex, and human immunodeficiency viruses (HIV) may all be treated with antiviral drugs. Like antibiotics, however, antiviral medications taken over an extended period can lead to the development of drug-resistant viruses that may be more difficult to treat.

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