Bacteria vs. virus: what is the difference?

Nov ,22 2016

Almost every person has suffered from fever, coughing, headaches, aching muscles and runny noses. It is more the hassle of dealing with these symptoms than the illness itself, as most colds and other respiratory infections are not serious for adults in good health. But, are they caused by a bacteria, or instead by a virus? This difference is important, as it determines the way the illness should be treated.

Which is which?
For sure everybody will have heard the word “germ”. It refers to any microscopic particle that can cause illness in humans. Indeed, it includes not only viruses and bacteria, but also certain types of fungi, protists and prions. The word comes from germen that means seed, as early scientists thought of them as seeds that spread between organisms.

Bacteria are single-celled organisms that live pretty much everywhere. They are in water, soil, the air and inside our body. Nobody knows how many types of bacteria exist, but the estimates range between tens of thousands and hundreds of millions. Fortunately, most bacteria are harmless for us, and even many of them are beneficial for our metabolism and other aspects of human health. In fact, there are 10 times more bacteria in our body than human cells.

On the other hand, we find the viruses. There are different opinions about them being living organisms or not. Actually, they could be defined as forms of organic structures that interact with living organisms. Most respiratory infections are caused by viruses rather than by bacteria. Viruses are some of the tiniest entities known, and unlike bacteria, they do not divide and do not reproduce on their own. Instead, they are forced to invade a cell to they take over its machinery and force the cell to reproduce the virus in massive numbers. Viruses infect animals, plants, and bacteria, and cannot be wiped out by antibiotics.

Then, do we deal with them differently?

It is all about the biological differences between such organisms. Bacteria are considered living organisms, and are characterized by a cell wall and a cell membrane. They are typically a few micrometres in length, and have a number of shapes, ranging from spheres to rods and spirals. They are unicellular organisms and do not possess a nucleus. The DNA or RNA is free in the cytoplasm, and they reproduce by simple division. Many of them are beneficial for the host, and when infection occurs, it is normally localized. They are linked to many respiratory infections such as otitis media (ear), tonsillitis (tonsils), pneumonia (lungs), bronchitis (airways), sinusitis (sinuses), pharyngitis (throat), and whooping cough (airways). However, and as pointed out previously, most respiratory infections are caused by viruses.

Viruses do not possess cell wall. Instead, they present a protein coat. Some of them have a membrane, but this is acquired from the infected cell when the virus is released, so actually the viruses do not generate it. Viruses are not beneficial for the host. They are always infectious agents that replicate only inside the host, that is, a living cell of other organism. They invade host cells and use their machinery to make copies of the viral DNA/RNA. Once new viral particles are formed, they are released from the host cell, destroying it. Size is normally small (approximately 20 nm) as opposed to bacteria, whose size generally reaches 1000 nm. They do not possess a nucleus. Instead, the viral DNA or RNA is enclosed inside a coat protein. In general, it is very difficult to treat viral diseases, and vaccines normally prevent only the spread. Antiviral medications can slow replication however they cannot stop it completely. Instead of being localized, a viral infection is frequently systemic, attacking several parts of the organism. Viruses cause respiratory infections such as the common cold, the flu, some pneumonias and bronchiolitis. Viruses are not beneficial, however they can be useful in genetic engineering as, for example, in destroying brain tumours.

A bacteriophague is a type of virus that infects bacteria. The picture gives an idea of the different size between these two organisms. Picture taken from

How to know if my illness is viral or bacterial?

It can be very difficult to determine whether you have a viral or bacterial infection because the symptoms are often similar, and the doctor will probably have to conduct specific tests to determine the origin.

A cold or a cough is usually viral. Viral infections may temporarily decrease your resistance and are frequently followed by a secondary bacterial infection. If a fever recurs after the first few days, we can be thinking of a secondary infection caused by bacteria. This is why it is important for immunocompromised people (people suffering from diabetes or another chronic illness that weakens the immune system) to go to the doctor as soon as they suspect they have got a respiratory infection.

A persistent earache may mean a bacteria-based ear infection. With a sore throat, it takes a throat culture to determine if it is bacterial. The only common bacterial throat pathogen is streptococcus. The majority of sore throats, especially in adolescents and adults, are viral.

Most viruses remain alive for a period of time in airborne particles that people breathe, sneeze, and cough, as well as on surfaces for about an hour after they are touched by an infected person. That is why it is important to wash hands regularly and immediately after handling potentially viral-contaminated objects such as doorknobs, shopping carts, telephones, toys, and other commonly shared items.

Many viral infections do not produce symptoms immediately. So, you or someone you're in contact with may be contagious for several days before you know it. This makes prevention difficult.
And finally, here is a tip useful for any kind of infection, no matter if it is viral or bacterial: don't smoke, as it weakens the immune system and makes the respiratory system more vulnerable to infection.