Last updated on October 20th, 2022 at 07:53 am
Viruses are everywhere, from the air we breathe to the food we eat. They’re also extremely contagious. Viruses are not just an inconvenience; they can be dangerous too. Learn about the viral infection symptoms and how to prevent them.
At its simplest, a viral infection is a disease caused by a virus. A virus is a small, infectious particle that can survive only in living cells. This means that the only way for viruses to reproduce is to infect healthy cells and replicate themselves.
The most common Viral Infection Symptoms are fever, headache, body aches and fatigue. Other symptoms may include a sore throat, swollen glands and nausea. A person with a viral infection cannot infect another person. Without treatment, the symptoms will usually last for up to two weeks.
What is Virus?
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A virus is composed of nucleic acid, either DNA or RNA, surrounded by a protein coat. It requires a living cell in which to multiply. A viral infection can lead to a spectrum of symptoms, from asymptomatic (no overt symptoms) to severe disease.
- People may get viruses by swallowing or inhaling them, by being bitten by insects, or through sexual contact.
- Most commonly, viral infections involve the nose, throat, and upper airways, or systems such as the nervous, gastrointestinal, and reproductive systems.
- Doctors may base the diagnosis on symptoms, blood tests and cultures, or examination of infected tissues.
- Antiviral drugs may interfere with the reproduction of viruses or strengthen the immune response to the viral infection.
A virus is a small infectious organism, much smaller than a fungus or bacterium that must invade a living cell to reproduce (replicate). The virus attaches to a cell (called the host cell), enters the cell, and releases its DNA or RNA inside the cell. The virus’s DNA or RNA is the genetic material containing the information needed to make copies of (replicate) the virus. The virus’s genetic material takes control of the cell and forces it to replicate the virus. The infected cell usually dies because the virus keeps it from performing its normal functions. When it dies, the cell releases new viruses, which infect other cells.
Types of Viruses
Viruses are classified as DNA viruses or RNA viruses, depending on whether they use DNA or RNA to replicate. RNA viruses include retroviruses, such as HIV (human immunodeficiency virus). RNA viruses, particularly retroviruses, are prone to mutate. Some viruses do not kill the cells they infect, but alter the cell’s functions. Sometimes the infected cell loses control over normal cell division and becomes cancerous.
Some viruses, such as hepatitis B virus and hepatitis C virus, can cause chronic infections. Chronic hepatitis can last for years, even decades. In many people, chronic hepatitis is quite mild and causes minor liver damage. However, in some people, it eventually results in cirrhosis (severe scarring of the liver), liver failure, and sometimes liver cancer.
Viruses usually infect one particular type of cell. For example, common cold viruses infect only cells of the upper respiratory tract. Most viruses infect only a few species of plants or animals. Some infect only people. Many viruses commonly cause infections in infants and children and older adults.
Types of Viral Infections
Probably the most common viral infections are:
- Respiratory infections: Infections of the nose, throat, upper airways, and lungs. The most common respiratory infections are upper respiratory infections, which include a sore throat, sinusitis, and the common cold. Other viral respiratory infections include influenza, pneumonia, and coronaviruses.
In small children, viruses also commonly cause croup (which is an inflammation of the upper and lower airways, called laryngotracheobronchitis) or lower airways (bronchiolitis). Respiratory infections are more likely to cause severe symptoms in infants, older people, and people with a lung or heart disorder.
- Gastrointestinal tract: Infections of the gastrointestinal tract, such as gastroenteritis, are commonly caused by viruses, such as noroviruses and rotaviruses.
- Liver: These infections result in hepatitis.
- Nervous system: Some viruses, such as the rabies virus and the West Nile virus, infect the brain, causing encephalitis. Others infect the layers of tissue that cover the brain and spinal cord (meninges), causing meningitis or polio.
- Skin: Viral infections that affect only the skin sometimes result in warts or other blemishes. Many viruses that affect other parts of the body, such as chickenpox, also cause a rash.
- Placenta and fetus: Some viruses, such as the Zika virus, the rubella virus, and cytomegalovirus, can infect the placenta and fetus in pregnant women.
Some viruses typically affect many-body systems. Such viruses include enteroviruses (such as coxsackieviruses and echoviruses) and cytomegaloviruses.
How Viruses Spread?
Viruses are spread (transmitted) in various ways. They may be.
- Spread by the bites of insects, such as mosquitoes, certain biting flies, or ticks
- Spread sexually (in sexually transmitted diseases)
- Spread during transfusion of contaminated blood
New human viruses sometimes develop from viruses that usually affect animals (for example, SARS-CoV and SARS-CoV-2). This happens when the infected animal host comes into close contact with susceptible humans.
Many viruses that were once present in only a few parts of the world are now spreading. These viruses include the chikungunya virus, Crimean-Congo hemorrhagic fever virus, Japanese encephalitis virus, Rift Valley Fever virus, West Nile virus, Ross River virus, Zika virus, and louping ill virus. These viruses are spreading partly because climate change has resulted in more areas where the mosquitoes that spread the viruses can live. Also, travellers may be infected, then return home and be bitten by a mosquito, which spreads the virus to other people.
How to Protect from Viral Infections?
The body has many defences against viruses:
- Physical barriers, such as the skin, discourage easy entry.
- The body’s immune defences, which attack the virus
When a virus enters the body, it triggers the body’s immune defences. These defences begin with white blood cells, such as lymphocytes and monocytes, which learn to attack and destroy the virus or the cells the virus has infected. If the body survives the virus attack, some of the white blood cells remember the invader and can respond more quickly and effectively to subsequent infection by the same virus. This response is called immunity. Immunity can also be produced by getting a vaccine.
What are Viral Infection Symptoms?
People can help prevent many viral infections by commonsense measures to protect themselves and others (personal protective measures). These measures vary depending on how the virus is spread. Measures include the following;
- Frequently and thoroughly washing the hands with soap
- Consuming only food and liquids that have been appropriately prepared or treated
- Avoiding contact with infected people and contaminated surfaces
- Sneezing and coughing into tissues (which should be thrown away) or into the upper arm, completely covering the mouth and nose
- Using safe-sex practices
- Preventing bites by ticks, mosquitoes, and other arthropods
How to Diagnose Viral Infections?
- A doctor’s consultation
- For infections that occur in epidemics, other similar cases
- For some infections, blood tests, and cultures,
- Common viral infections (such as measles, rubella, or chickenpox) may be diagnosed based on symptoms.
- For infections that occur in epidemics (such as influenza), other similar cases may help doctors identify a particular infection. Laboratory diagnosis is important for distinguishing between different viruses that cause similar symptoms, such as COVID-19 (SARS-CoV-2) and influenza.
- For other infections, blood tests and cultures (growing microorganisms in the laboratory from samples of blood, body fluid, or other material taken from an infected area) may be done. Polymerase chain reaction (PCR) techniques may make many copies of the viral genetic material. PCR techniques make it easier for doctors to rapidly and accurately identify the virus. Blood may also be tested for antigens, which are proteins on or in viruses that trigger the body’s defence. Blood may also be tested for antibodies to viruses. (Antibodies are proteins produced by the immune system to help defend the body against a particular attack.) Tests are usually done quickly, especially when the infection is a serious threat to public health or when symptoms are severe.
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A sample of blood or other tissues is sometimes examined with an electron microscope, which provides high magnification with clear resolution.
Viral Infection Symptoms and Treatment
There are no specific treatments for many viruses. However, many things can help relieve certain symptoms, such as:
- Dehydration: Plenty of fluids, sometimes given by vein (intravenously)
- Diarrhoea: Sometimes an antidiarrheal drug, such as loperamide
- Fever and aches: Acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs)
- Nausea and vomiting: A clear-liquid diet and sometimes an antiemetic (antinausea) drug, such as ondansetron
- Some rashes: Soothing or moisturizing creams and sometimes an antihistamine is taken by mouth for itching
- A runny nose: Sometimes nasal decongestants, such as phenylephrine or phenylpropanolamine
- A sore throat: Sometimes throat-numbing lozenges containing benzocaine or dyclonine
Not everyone who has these symptoms needs treatment. If symptoms are mild, it may be better to wait for them to go away on their own. Some treatments may not be appropriate for infants and young children.
Drugs that combat viral infections are called antiviral drugs. There are no effective antiviral drugs for many viral infections.
Many antiviral drugs work by interfering with the replication of viruses. Most drugs used to treat HIV infection work this way. Because viruses are tiny and replicate inside cells using the cells’ metabolic functions, there are only a few metabolic functions that antiviral drugs can target.
In contrast, bacteria are relatively large organisms, commonly reproduced by themselves outside of cells, and have many metabolic functions that antibacterial drugs (antibiotics) can target. Therefore, antiviral drugs are much more difficult to develop than antibiotics. Also, unlike antibiotics, which are usually effective against many species of bacteria, most antiviral drugs are usually effective against only one (or a very few) viruses.
Antiviral drugs can be toxic to human cells. Also, viruses can develop resistance to antiviral drugs. Most antiviral drugs can be given by mouth. Some can also be given by injection into a vein (intravenously) or muscle (intramuscularly). Some are applied as ointments, creams, or eye drops or are inhaled as a powder. Antibiotics are not effective against viral infections, but if a person has a bacterial infection besides a viral infection, an antibiotic is often necessary.
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Reference: MSD Manual
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