Difference Between Viral and Bacterial Infection

Key Difference – Viral vs Bacterial Infection

Bacteria and viruses enter the human body and multiply to cause diseases. Though, both bacterial and viral infections present differently according to the affected organ, the key difference between viral and bacterial infection is that the bacterial infections increase neutrophil and eosinophil counts while viruses increase lymphocyte count.  Meningitis features fever, headache, photophobia, neck stiffness, and confusion. Sinusitis presents with face pain, fever, runny nose, blocked nose, post nasal drip and phlegm. Pneumonia features cough, sputum production, chest pain and fever. Urinary tract infections present with fever, lower abdominal pain, blood stained urine and painful urination.

When a bacterium or a virus enters the body, it encounters the protective mechanisms of the body. It meets white blood cells, macrophages, and dendritic cells, which engulf it and digest it. These bacteria and viruses contain molecules that are identified as foreign substances by the complex receptor system in the body. This triggers a complex series of reactions designed to destroy the foreign substances. Once the first few bacteria are digested, their foreign proteins get presented attach to the cell membrane of the cells which digested them. These proteins trigger B and T lymphocytes. B lymphocytes form antibodies and T lymphocytes form toxic substances designed to destroy the invaders. Complement system gets activated, and it also forms a membrane, which binds to the bacterial cell membrane leading to its destruction. When cells are damaged due to the toxic substances released by the protective cells, acute inflammation starts up. If the organism is virulent, there will be a major reaction. If the organism is persistent, abscess formation and chronic inflammation may occur. If the reaction removes the organism or drug treatment interferes with the natural progression of the disease, healing with resolution or scarring will follow.

What are Bacterial Infections?

Bacteria are single cell organisms. They have a cell membrane, organelles, and a nucleus. They consume substrates and oxygen and produce energy. They multiply to procreate. They can be commensals, which live in harmony without causing any symptoms, and pathogens that cause diseases. Among commensals, there are organisms that cause diseases if the opportunity arises. These are called opportunistic pathogens.

Bacterial infections present according to the severity of the infection. Bacterial infection results in the release of specific inflammatory mediators. Extracellular bacteria trigger migration of neutrophils. Thus, full blood count shows high numbers of neutrophils. Intra cellular bacteria trigger eosinophils, as well as neutrophils, and therefore, the full blood count shows elevated numbers of those cells. Red blood cell count may be relatively low. Some bacterial illnesses cause an anemia. Platelet count remains normal in most cases.

What are Viral Infections?

Viruses are microscopic life forms with a nucleic acid strand, protein core, and a capsule. They are simple organisms that need a cell to thrive and multiply. There are RNA viruses and DNA viruses. DNA viruses incorporate its DNA directly into the cellular replication system and makes copies of itself. RNA viruses produce a compatible DNA strand from its RNA with reverse transcription and incorporate it into the cellular mechanisms to produce copies of it. (Read the Difference Between DNA Replication and Transcription)

When viruses enter the cells, some of it is digested and the foreign proteins get presented attach to the cell membrane of the host cells. This triggers the body reactions against the viruses. Lymphocytes predominate in the reaction against viruses. Some viruses inhibit bone marrow function and limit cell formation. Therefore, white blood cell count, platelet count, and red blood cell count may drop in viral infections. Some viruses increase vascular permeability and cause fluid leakage.

What is the difference between Viral and Bacterial Infection?


Bacteria are single cell organisms while viruses are more primitive.


Bacterial infections increase neutrophil and eosinophil counts while viruses increase lymphocyte count. 

  • Guru

    PLease note there are other organism which causes infection( Which are not bacteria or virus) Common example is FUNGUS. Rickets, spirochaetes are other examples. Same time the bacteria are almost help to the human ( In the skin, Large intestine) Most of the bacteria are helpful. some are pathogens.