What Is Viral Infection?


A virus is a type of germ that can be seen only under the microscope as it is too small to be seen with the naked eye. Viruses, like other infection-causing agents, can enter the body through the eyes, mouth, nose, a break in your skin, anus or genitals etc and they multiply locally at the site of entry and later can spread through other parts of the body through the blood vessels and lymphatic system to produce infection. Viruses do not have cells of their own, so if they want to replicate they use our cells (host). Viral infection occurs when the viruses start to replicate within the host, thereby making the host fall sick. Though viral infections can affect most parts of the body the most commonly seen are respiratory and digestive illnesses.

Causes of viral infection

There are many types of viruses that can cause infections by entering your body through different routes and affecting different parts of the body. Some common ways you can contract viral infections include:

  • Through other people (through coughing, sneezing or close contact)
  • By coming in contact with surfaces or objects that someone with a virus has touched (like countertops, doorknobs or phones)
  • From vaginal, oral or anal sex
  • When bit by an infected animal, mosquito or tick
  • By consuming contaminated food or water

Signs and symptoms of viral infection

It's important to differentiate between symptoms of viral infection and bacterial infection to know what treatment you need. Symptoms of viral infection depend on the type of viral infection you have. Some of the symptoms of common viral infections are listed below.

Influenza (Flu)  

The main symptoms are fever (38℃ or above), headache, tiredness and weakness, dry and chesty cough, and general aches and pain. You may also experience cold-like symptoms such as runny nose, sore throat, and sneezing but they tend to be less severe than other symptoms.

Respiratory tract infection 

The symptoms include cough, stuffy or runny nose, sneezing, headaches, sore throat, wheezing or tight chest, muscle aches, fever, and feeling generally unwell.

Viral skin infection

The symptoms include fever, headache, malaise and other common symptoms of viral infection with a rash that develops rapidly.

Viral gastroenteritis

The most common symptoms include nausea, vomiting, and watery diarrhoea. Other symptoms like fever, headache, stomachache, chills and signs of dehydration like dry skin, thirst, dizziness, dark-coloured urine, decreased urine output in adults and soft spots on the top of an infant's head (Sunken fontanel), drowsiness, lack of tears, dry mouth, and dry diapers from lack of urination in children are also seen.

Management and treatment for viral infection

The treatment options vary based on the viral infection. For viral infections that can cause chronic or life-threatening illnesses, healthcare providers might prescribe antiviral medications, convalescent plasma, and post-exposure prophylaxis to treat the infection.

  • Antiviral medications: used to stop viruses from replication. They are made to target only a specific virus. Antiviral medications are available for COVID-19, hepatitis B and C, flu, HIV, and pox
  • Convalescent plasma treatment: Done through blood transfusion. The plasma contains antibodies that help to fight the infection. Some cases of Ebola and COVID-19 are treated with convalescent plasma.
  • Post-exposure prophylaxis: Treatment of certain viral infections can prevent you from getting sick after being exposed. These include antiviral medication and immunoglobulin ( antibody) treatments given by the GP even before the symptoms appear. Post-exposure prophylaxis is available for rabies, HIV, Hepatitis B, and chickenpox.

For viral infections that rarely cause serious illnesses like the common cold, you don't need medication and you can treat the symptoms at home. You can manage the symptoms at home by drinking plenty of fluid, getting enough rest, and using over-the-counter over-the-counter (OTC) medications.

Antibiotics can't cure or treat infections caused by viruses but can be used to treat bacterial infections.


How is a viral infection diagnosed?

Your healthcare provider might send your body fluid or tissue samples to labs for analysis to confirm the diagnosis of viral infection:

  • Blood 
  • Cerebrospinal fluid (CSF)
  • Cervical or vaginal swab
  • Conjunctiva swab
  • Feces.
  • Nasal swab
  • Nasopharynx aspirate or swab
  • Oral swab
  • Sample from vesicular
  • Throat swab
  • Tissue
  • Urine
  • Urethral swab

Viruses don't grow in culture media like bacteria. The most important rapid virological tests are nucleic acid amplification tests that are useful for accurate diagnosis and monitoring of antiviral treatment. Examples of these tests include real-time or multiplex reverse transcription-polymerase chain reaction assays ( RT-PCR). Other tests for diagnosis include the detection of viral antigens by enzyme immunoassay and immunofluorescence.2

Can viral infection be prevented?

The best way to decrease the risk of viral infection is to get vaccinated. Vaccinations are available for: 

  • Hepatitis B
  • Hepatitis A
  • COVID-19
  • Chickenpox
  • Human papillomavirus (HPV)
  • Measles, mumps, and rubella
  • Flu (influenza)
  • Rotavirus
  • Polio
  • Rabies
  • Shingles

Other ways to prevent viral infections are:

  • Practicing safe food habits like heating meat and poultry to a safe temperature, storing food properly, and washing fruits and vegetables before eating
  • Washing your hands frequently
  • Protecting yourself from bug bites by wearing protective clothing, sleeping under a mosquito net, and using a bug spray
  • Use a dental dam or a condom during any kind of sex
  • Avoid being around other people when you are sick
  • Get post-exposure prophylaxis
  • Don't handle aggressive or wild animals.

What are the types of viral infections?

There are several types of viral infections: 

Respiratory infections 

They spread from person to person by contact with infected respiratory droplets. It is more severe in infants, the elderly, and patients with a lung or heart disorder  Respiratory viruses include influenza A and B, parainfluenza viruses, respiratory syncytial viruses  A and B, coronaviruses, rhinoviruses, avian influenza A viruses, and human metapneumovirus. 

Gastrointestinal infections 

They are transmitted through the oral-fecal route. Examples include rotavirus, norovirus, adenovirus 40 and 41, and COVID-19. The main symptoms are diarrhoea and vomiting.

Exanthematous infections

They are transmitted by mosquito vectors. Mostly causes only skin lesions.

Hepatic infections

Transmitted from person to person by coming in contact with infected blood or body secretions or by the faecal-oral route in case of hepatitis A and E. Examples include Epstein-Barr virus, yellow fever virus, and cytomegalovirus.

Neurologic infection

It causes encephalitis. Blood-sucking arthropods transmit many viruses, these viruses are called arboviruses.

Other infections 

Hemorrhagic fever causes, cutaneous or mucosal infection, multisystem disease, nonspecific febrile illness etc

Is viral infection contagious?

Yes, viral infection is contagious. You can spread the infection to other people before you start to feel sick or notice a rash.

Who is at risk of viral infection?

The risk for upper respiratory viral infection increases with: 

  • Poor hygiene
  • Going to overcrowded areas
  • People with certain health conditions like heart, lung, or kidney disease, weak immune systems, pregnant individuals, and those with asthma or allergies, tend to have a higher risk for colds or the flu
  • Children and older people are at a higher risk
  • Smoking

How common is viral infection?

Viral infections are very common infections, with the viral upper respiratory infection being the most common.

In a study, 14.5% of lower respiratory tract infections in hospitalized adults were found to be related to common respiratory viruses.3

When should I see a doctor?

You must see your doctor if: 

  • You have any symptoms of viral infections lasting longer than expected
  • You have symptoms of COVID-19 or the flu and if you are at risk of developing serious illnesses 
  • You've been exposed to rabies, HIV, hepatitis B, and chickenpox


Viral infections occur when the virus replicates within the host making use of the host’s cells. It can affect various parts of the body but most commonly causes respiratory and digestive illnesses. Viruses can gain entry into the host through their eyes, mouth, nose, a break in the skin, anus or genitals etc and start replicating locally or travel through the blood vessels and lymphatic system leading to the development of the infection. The most commonly experienced symptoms during a viral infection are headaches, fever, and malaise and they are treated usually with antiviral medications, post-exposure prophylaxis, and convalescent plasma. Mild viral infections can be managed at home with over-the-counter medications and home remedies. You can prevent it by vaccinating yourself against viruses. Viral infections are contagious. Elders and children have a higher risk of being infected. If you experience any symptoms or you are at risk of viral infection it is advisable to fix an appointment with your doctor.


  1. FENNER F, BACHMANN PA, GIBBS EPJ, MURPHY FA, STUDDERT MJ, WHITE DO. Pathogenesis: infection and the spread of viruses in the body. Veterinary Virology [Internet]. 1987 [cited 2023 Sep 15];133–52. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7173411/ 
  2. Chi-Chung Cheng, V., Fuk-Woo Chan, J., FN Hung, I., & Yuen, K.-Y. (2016). Viral infections, an overview with a focus on prevention of transmission. Reference Module in Biomedical Sciences, B978-0-12-801238-3.90174-0. https://doi.org/10.1016/B978-0-12-801238-3.90174-0.
  3. Wang, Y., Dong, T., Qi, G., Qu, L., Liang, W., Qi, B., Zhang, Z., Shang, L., Gao, H., Du, X., Lu, B., Guo, Y., Liu, Z., Yu, H., Cui, Q., Wang, X., Li, Y., Guo, W., & Qu, Z. (2018). Prevalence of common respiratory viral infections and identification of adenovirus in hospitalized adults in harbin, china 2014 to 2017. Frontiers in Microbiology, 9. https://www.frontiersin.org/articles/10.3389/fmicb.2018.02919.
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Malaz Ameer Ata Almanan

Medical Student - University of Bahri, Khartoum, Sudan

Malaz Ameer Ata Almanan Mohammed. 4th year medical student. Researcher enthusiast. Passionate about ophthalmic surgery. I would like to be ophthalmologist.

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