What type of viruses

For example, the herpes zoster virus can cause chickenpox. The person recovers, but the virus may stay in the body. Years later, it may cause shingles in the same individual. Coronaviruses are a large family of viruses and include viruses that cause the common cold. However, it has changed many times since scientists first identified it in China. By September , scientists had logged over 12, mutations, and the development continues. Some variants are more transmissible and more likely to cause severe illness than others.

The main concern with new variants is the unpredictability of their impact. The main symptoms of COVID are dry cough , fatigue , and fever, but there are many possible symptoms. Anyone who has symptoms should seek a test.

It is also important to self-isolate until 10 days after symptoms appear and when no fever has been present for 24 hours. If a person has difficulty breathing , they should seek emergency medical attention.

However, special T cells, known as cytotoxic T cells, can recognize cells that contain viruses, and release substances that kill those cells.

Some viruses can escape detection by cytotoxic T cells, but other immune cells — natural killer cells — can cause the cell containing the virus to die. In addition, body cells that contain a virus emit proteins called interferons, which warn other cells that a virus is present.

This gives healthy cells a chance to defend themselves by changing the molecular makeup of their surface. Antibodies can also help fight a virus before it enters a cell. They do this by neutralizing or damaging the virus or by changing its features so that it can no longer enter healthy cells. Antibiotics treat bacterial infections , but they cannot treat a viral infection. People will need either a vaccination to prevent infection, or antiviral drugs to treat any symptoms.

Sometimes, the only option is symptom relief. In recent decades, scientists have developed antiviral drugs, largely in response to the AIDS pandemic. These drugs do not destroy the virus, but they slow or prevent its development.

With antiviral treatment for HIV, for example, the level of virus in the body can become so low that tests cannot detect it. At this point, it becomes untransmittable, which means that a person cannot pass the virus on to another person. Antivirals are also available to treat infection with HSV, hepatitis B , hepatitis C , influenza, shingles, and chickenpox. Tamiflu is an example of an antiviral drug. People can use it to manage influenza.

Some vaccines have succeeded in eliminating diseases such as smallpox, which experts believe has been around for at least 3, years. In addition, flu vaccines will NOT protect against infection and illness caused by other viruses that also can cause influenza-like symptoms.

There are many other viruses besides influenza that can result in influenza-like illness ILI that spread during flu season. To receive weekly email updates about Seasonal Flu, enter your email address:. Skip directly to site content Skip directly to page options Skip directly to A-Z link. Influenza Flu. Section Navigation. Facebook Twitter LinkedIn Syndicate.

Types of Influenza Viruses. Minus Related Pages. Close This is a picture of an influenza flu A virus. What CDC Does. To receive weekly email updates about Seasonal Flu, enter your email address: Email Address. What's this? Links with this icon indicate that you are leaving the CDC website. Linking to a non-federal website does not constitute an endorsement by CDC or any of its employees of the sponsors or the information and products presented on the website.

There are vaccines for both hepatitis A and hepatitis B. Other ways to prevent viral hepatitis include not sharing needles or razors, practicing safe sex , and avoiding food or drinks that may be contaminated by feces.

Cutaneous viral diseases cause lesions or papules to form on the skin. In many cases, these lesions can stick around for a long time or come back after disappearing for a while. These viruses are contagious. Papules that form due to warts or molluscum contagiosum often go away on their own.

They can also be removed by simple in-office procedures, such as cryotherapy. Practicing good hygiene habits, avoiding the sharing of personal items, and avoiding close contact with people who have active lesions can reduce your risk of developing a cutaneous viral disease.

Some hemorrhagic viral diseases, such as dengue fever and yellow fever, are spread through the bite of an infected insect. Others, such as Ebola, are spread to other people through contact with the blood or other bodily fluid of someone with the virus. Lassa fever is spread through inhaling or consuming the dried feces or urine of a rodent with the virus. Some people may need intravenous IV fluids to maintain electrolyte balance. Supportive care to maintain hydration and electrolyte balance is essential.

In some cases, the antiviral drug ribavirin may be given. Researchers are in the process of developing vaccines for several hemorrhagic viruses. A yellow fever vaccine is currently available for people traveling to areas where yellow fever is common. If you live or work in an area where viral hemorrhagic diseases are common, you can do the following to reduce your risk:. Some viruses can infect the brain and surrounding tissues, causing neurologic viral diseases. This can result in a range of symptoms, including:.

Many neurologic viruses are spread through the bite of an infected animal or bug, such as a mosquito or tick. Other viruses, such poliovirus and other enteroviruses, are quite contagious and spread through close contact with someone with the virus.

Contaminated objects can also contribute to the spread of these viruses. Getting plenty of rest, staying hydrated, and taking OTC anti-inflammatories to ease pain or headaches can all help. In some cases, antiviral medication may be prescribed.

An extract obtained from TMD-infected tobacco plants was made to determine the cause of the disease. Initially, the source of the disease was thought to be bacterial. It was surprising to everyone when Ivanovski, using a Chamberland filter, found that the cause of TMD was not removed after passing the extract through the porcelain filter.

So if a bacterium was not the cause of TMD, what could be causing the disease? Ivanovski concluded the cause of TMD must be an extremely small bacterium or bacterial spore. It was Beijerinck, in , who eventually concluded the causative agent was not a bacterium but, instead, possibly a chemical, like a biological poison we would describe today as a toxin. Even though he was not able to see the virus that caused TMD, and did not realize the cause was not a bacterium, Ivanovski is credited as the original discoverer of viruses and a founder of the field of virology.

Today, we can see viruses using electron microscopes Figure 1 and we know much more about them. Viruses are distinct biological entities; however, their evolutionary origin is still a matter of speculation. In terms of taxonomy, they are not included in the tree of life because they are acellular not consisting of cells. In order to survive and reproduce, viruses must infect a cellular host, making them obligate intracellular parasites.

The genome of a virus enters a host cell and directs the production of the viral components, proteins and nucleic acids, needed to form new virus particles called virions. New virions are made in the host cell by assembly of viral components. The new virions transport the viral genome to another host cell to carry out another round of infection. Table 1 summarizes the properties of viruses. Figure 1. Viruses can infect every type of host cell, including those of plants, animals, fungi, protists, bacteria, and archaea.

Most viruses will only be able to infect the cells of one or a few species of organism. This is called the host range. However, having a wide host range is not common and viruses will typically only infect specific hosts and only specific cell types within those hosts.

The viruses that infect bacteria are called bacteriophages , or simply phages. The word phage comes from the Greek word for devour. Other viruses are just identified by their host group, such as animal or plant viruses. Once a cell is infected, the effects of the virus can vary depending on the type of virus. Viruses can be transmitted through direct contact, indirect contact with fomites , or through a vector : an animal that transmits a pathogen from one host to another.

Arthropods such as mosquitoes, ticks, and flies, are typical vectors for viral diseases, and they may act as mechanical vectors or biological vectors. Mechanical transmission occurs when the arthropod carries a viral pathogen on the outside of its body and transmits it to a new host by physical contact. Biological transmission occurs when the arthropod carries the viral pathogen inside its body and transmits it to the new host through biting.

In humans, a wide variety of viruses are capable of causing various infections and diseases. Some of the deadliest emerging pathogens in humans are viruses, yet we have few treatments or drugs to deal with viral infections, making them difficult to eradicate.

Viruses that can be transmitted from an animal host to a human host can cause zoonoses. For example, the avian influenza virus originates in birds, but can cause disease in humans. Reverse zoonoses are caused by infection of an animal by a virus that originated in a human. The emergence of superbugs, or multidrug resistant bacteria , has become a major challenge for pharmaceutical companies and a serious health-care problem. According to a report by the US Centers for Disease Control and Prevention CDC , more than 2 million people are infected with drug-resistant bacteria in the US annually, resulting in at least 23, deaths.

One potential solution is the use of phage therapy , a procedure that uses bacteria-killing viruses bacteriophages to treat bacterial infections. Phage therapy is not a new idea. The discovery of bacteriophages dates back to the early 20th century, and phage therapy was first used in Europe in by the English bacteriologist Frederick Twort. Interest in phage therapy outside of the countries of the former Soviet Union is only recently re-emerging because of the rise in antibiotic-resistant bacteria.

Phage therapy has some advantages over antibiotics in that phages kill only one specific bacterium, whereas antibiotics kill not only the pathogen but also beneficial bacteria of the normal microbiota.