Infections: How Bacterial and Viral Infections Differ

An infection is a disease that develops after disease-causing microorganisms, viruses, or prions enter the body. Pathogens differ in their structure, reproduction, and response to treatment. Below is how bacterial and viral infections are recognized.

What an infectious disease is

Infectious diseases are a group of diseases caused by the entry of pathogenic microorganisms, viruses, and prions. To cause disease, an agent must be virulent: it must overcome the body's resistance and exert a toxic effect. Some pathogens poison the body with exotoxins that they release during their life (tetanus, diphtheria), while others release endotoxins when their cells break down (cholera, typhoid fever).

An infection has an incubation period — the time from infection to the first signs. Its duration depends on the route of infection and the type of pathogen and ranges from several hours to several years (the latter is rare). The site of entry is called the portal of entry: the cholera vibrio enters through the mouth and does not penetrate through the skin.

Bacterial infections: examples and features

Bacteria are single-celled organisms: under a microscope they look like spheres, rods, or spirals. There are about 10 times more bacterial cells in the human body than human cells, but most species do not cause disease, and some are beneficial: "good" bacteria in the digestive system help digest food and absorb vitamins and minerals.

Infectious bacteria multiply quickly, many release toxins that damage cells, and others invade tissues. Examples include streptococcus, staphylococcus, and the bacterium E. coli. They are transmitted in droplets during breathing, through hands and surfaces, through contact with cuts, from a pregnant woman to her child, through food and water, through insect and animal bites, and through sexual contact. The immune system sometimes copes on its own; when help is needed, doctors prescribe antibiotics, and each use carries a risk of bacterial resistance.

Viral infections: types and features

A virus is a very small pathogen: genetic material (DNA or RNA) in a protein coat. There are many viruses on Earth, but only a small proportion infect humans. Among the diseases they cause are the common cold, influenza, COVID-19, and HIV.

A virus enters living cells and uses them to reproduce — replicate; the process can kill, damage, or alter cells. Symptoms range from mild to very severe, and sometimes the immune system copes without them. Each virus usually infects one type of cell: hepatitis viruses infect liver cells, HIV infects a specific type of immune system cell. For most viral infections, treatment only relieves symptoms while the immune system fights; antiviral drugs exist for some. Antibiotics do not work on viruses.

Infections transmitted through insects

In Gromashevsky's classification of infectious diseases, malaria is classified as a "blood" infection. Some infections are transmitted through insect bites: mosquitoes and lice are considered potential carriers. General infection prevention measures include disinsection, that is, the destruction of insect vectors.

How bacterial and viral diseases differ

The first difference is the structure of the pathogen: a bacterium is an independent cell, while a virus is genetic material in a protein coat that reproduces only inside another cell. The second is the response to treatment: antibiotics act on bacteria but not on viruses. The third is prevention: vaccines exist against both bacterial and viral diseases.

How infections are diagnosed and when a doctor is needed

The diagnosis is confirmed in the laboratory, and the set of tests depends on the suspected pathogen.

• culture and Gram staining;
• PCR and rapid tests;
• blood immunoglobulins.

People consult a doctor when an infection is suspected: the doctor assesses the symptoms, the likely incubation period, and the portal of entry and decides which tests are needed. Whether antibiotics are needed is also decided by the doctor.

An infection by itself is not a reason to call an ambulance. 103/112 — for a life-threatening condition, for example signs of stroke or heart attack.

This material is for reference: it explains general principles and does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer