Bacteria vs Virus - from composition, to transmission


Whilst both can cause disease, a key difference between the two is that bacteria are living organisms, whereas viruses are not.

Bacteria can live in almost every environment, including in or on the human body. Less than 1% of bacteria cause disease, and most are beneficial for our health and the health of Earth’s ecosystems. Bacteria that do cause infections in humans are referred to as pathogenic bacteria.

Viruses are parasitic, which means they require living cells or tissue to grow in. Viruses can invade the cells of your body, using the components of your cells to grow and multiply. Some viruses kill host cells as part of their life cycle. Most viruses do cause disease.




Bacteria are living organisms that consist of a single cell that can generate energy, make its own food, move, and reproduce, allowing bacteria to live in many places and serve many purposes. Bacteria have been in existence for at least 3.5 billion years, making them one of the oldest living things on earth. The smallest bacteria are about 0.4 micron (one millionth of a meter) in diameter.



Viruses consist of a piece of genetic material, such as DNA or RNA (not both) surrounded by a protein shell. Viruses only grow and reproduce inside of the host cells they infect. When found outside of these living cells, viruses are dormant. Their “life” therefore requires the hijacking of the biochemical activities of a living cell. As well as humans and animals, viruses can also infect plants, although virtually all plant viruses are transmitted by insects or other organisms that feed on plant walls. Viruses range in size from 0.02 to 0.25 micron



Pathogenic bacteria have a more varied operation and will often infect when the right opportunity arises, leading to opportunistic infection. The infection caused by pathogenic bacteria is usually confined to a part of the body, described as a localized infection. These infections may be caused by the bacteria themselves or by endotoxins they produce.


Viruses infect a host cell and then multiply by the thousands, leaving the host cell and infecting other cells of the body. A viral infection is therefore systemic, spreading throughout the systems of the body.




Bacterial infections are usually treated with antibiotics. They either kill bacteria or stop them multiplying.


Treatment for viral infections varies depending on the virus, and can include managing symptoms (e.g. consuming fluids), taking paracetamol to manage fever, and stopping viral reproduction using antiviral medicines, such as medicines for HIV/AIDS and cold sores. Preventing infection in the first place is done via vaccines.


Several coronaviruses cause respiratory infections that range from the common cold to more serious illnesses, including the Middle East Respiratory Syndrome (MERS), identified in 2012, and Severe Acute Respiratory Syndrome (SARS), which appeared for the first and only time in 2002.

The current virus is known as Coronavirus SARS-CoV-2 and the disease that it causes is COVID-19.

A SARS-CoV-2 particle enters a person's nose or mouth and floats in the airway until it comes into contact with a lung cell that has an ACE2 receptor on the surface. The virus then binds to that cell, gets inside and uses the cell to help make copies of itself. The virus breaks out, leaving the cell dead, and moves on to penetrates other cells. Once they have been infected, the cells send out signals to the immune system to try to neutralize or destroy the pathogens, but the viruses can prevent or intercept the signals, buying time to replicate before a person shows any symptoms.