Three common types of viruses

Common examples of contagious viral diseases include the flu, the common cold, HIV, and herpes. Other types of viral diseases spread through other means, such as the bite of an infected insect.

Respiratory viral diseases are contagious and commonly affect the upper or lower parts of your respiratory tract. Respiratory viruses are spread by droplets generated through coughing or sneezing. If someone with a viral illness coughs or sneezes nearby and you inhale these droplets, you may develop the disease. These viruses can also be spread through contaminated objects, such as doorknobs, tabletops, and personal items.

If you touch one of these objects and then touch your nose or eyes, you could develop a disease. Respiratory viral diseases usually heal on their own. But over-the-counter OTC medications, including nasal decongestants, cough suppressants, and pain relievers, can help to reduce symptoms. In addition, Tamiflu, an antiviral drug, is sometimes prescribed if someone is in the very early stages of developing the flu.

The best way to avoid respiratory viral diseases is to practice good personal hygiene. Wash your hands often, cover your mouth when you cough or sneeze, and limit your interactions with people who show symptoms of a respiratory condition. Gastrointestinal viral diseases affect your digestive tract.

The viruses that cause them are contagious and usually lead to a condition called gastroenteritis , also called the stomach flu. Gastrointestinal viruses are shed in the stool during bowel movements.

You can also get the virus from sharing utensils or personal objects with someone who has a virus. In many cases, they resolve on their own within a day or two. In the meantime, drink plenty of fluids to replace those lost from diarrhea or vomiting. You can prevent gastrointestinal viral diseases by washing your hands often, especially after using the bathroom. Wiping down contaminated surfaces and not sharing personal items or eating utensils can also help.

Many exanthematous viruses are spread through respiratory droplets from the cough or sneeze of someone with the virus. Other exanthematous viral diseases, such as chickenpox and smallpox, can be transmitted by coming into contact with fluid in broken skin lesions. Chikungunya virus is spread through a mosquito bite and cannot be transmitted from person to person.

Treating exanthematous viral diseases focuses on managing symptoms. Fever-reducing medications, such as acetaminophen, can help with some of the more bothersome symptoms. Measles, rubella, chickenpox, shingles, and smallpox can all be prevented through vaccination. You can reduce your risk of a chikungunya virus infection by protecting yourself from mosquito bites. Learn more about viral rashes. The hepatic viral diseases cause inflammation of the liver, known as viral hepatitis.

The most common types of viral hepatitis are hepatitis A, B, and C. It is worth noting that diseases caused by other viruses, such as cytomegalovirus and the yellow fever virus, can also affect the liver.

Hepatitis B and C can be transmitted from person to person through bodily fluids. Sharing items that come in to contact with blood, such as needles or razors, can also spread the virus. Hepatitis B can be spread through sexual contact. Treatments for hepatitis B, C, and D focus on managing symptoms.

If you have any doubt about your symptoms then it's best to take a coronavirus test which will help you establish whether or not you need to isolate. The second is more like a prickly heat rash that pops up all over the body, although more common on the elbows, knees and the backs of hands and feet. A GP in London previously warned that kids with Omicron had presented with rashes , but it hadn't been seen as prevalent in adults until recently.

Dr David Lloyd said he had seen about 15 per cent of youngsters with confirmed Omicron cases developing spots. They also suffered with fatigue, headaches and a loss of appetite - which seems to fit with the most common variant symptoms reported so far in adults. Chilblains look similar to Covid toes - which have been a long reported symptom of people contracting other variants of Covid Although in reports it seems children and teens suffer more with the condition.

Data from the app shows people who catch the Omicron variant usually present with symptoms within 48 hours of catching the bug. The viral genome, often with associated basic proteins, is packaged inside a symmetric protein capsid. The nucleic acid-associated protein, called nucleoprotein, together with the genome, forms the nucleocapsid.

In enveloped viruses, the nucleocapsid is surrounded by a lipid bilayer derived from the modified host cell membrane and studded with an outer layer of virus envelope glycoproteins. Morphology: Viruses are grouped on the basis of size and shape, chemical composition and structure of the genome, and mode of replication.

Helical morphology is seen in nucleocapsids of many filamentous and pleomorphic viruses. Helical nucleocapsids consist of a helical array of capsid proteins protomers wrapped around a helical filament of nucleic acid.

The number and arrangement of the capsomeres morphologic subunits of the icosahedron are useful in identification and classification. Many viruses also have an outer envelope. The entire genome may occupy either one nucleic acid molecule monopartite genome or several nucleic acid segments multipartite genome.

The different types of genome necessitate different replication strategies. Aside from physical data, genome structure and mode of replication are criteria applied in the classification and nomenclature of viruses, including the chemical composition and configuration of the nucleic acid, whether the genome is monopartite or multipartite.

Also considered in viral classification is the site of capsid assembly and, in enveloped viruses, the site of envelopment. Viruses are inert outside the host cell.

Small viruses, e. Viruses are unable to generate energy. As obligate intracellular parasites, during replication, they fully depend on the complicated biochemical machinery of eukaryotic or prokaryotic cells. The main purpose of a virus is to deliver its genome into the host cell to allow its expression transcription and translation by the host cell. A fully assembled infectious virus is called a virion. The simplest virions consist of two basic components: nucleic acid single- or double-stranded RNA or DNA and a protein coat, the capsid, which functions as a shell to protect the viral genome from nucleases and which during infection attaches the virion to specific receptors exposed on the prospective host cell.

Capsid proteins are coded for by the virus genome. Because of its limited size Table the genome codes for only a few structural proteins besides non-structural regulatory proteins involved in virus replication. Capsids are formed as single or double protein shells and consist of only one or a few structural protein species. Therefore, multiple protein copies must self assemble to form the continuous three-dimensional capsid structure. Self assembly of virus capsids follows two basic patterns: helical symmetry, in which the protein subunits and the nucleic acid are arranged in a helix, and icosahedral symmetry, in which the protein subunits assemble into a symmetric shell that covers the nucleic acid-containing core.

Some virus families have an additional covering, called the envelope, which is usually derived in part from modified host cell membranes. Viral envelopes consist of a lipid bilayer that closely surrounds a shell of virus-encoded membrane-associated proteins. The exterior of the bilayer is studded with virus-coded, glycosylated trans- membrane proteins. Therefore, enveloped viruses often exhibit a fringe of glycoprotein spikes or knobs, also called peplomers.

In viruses that acquire their envelope by budding through the plasma or another intracellular cell membrane, the lipid composition of the viral envelope closely reflects that of the particular host membrane. The outer capsid and the envelope proteins of viruses are glycosylated and important in determining the host range and antigenic composition of the virion.

In addition to virus-specified envelope proteins, budding viruses carry also certain host cell proteins as integral constituents of the viral envelope.

Virus envelopes can be considered an additional protective coat. Larger viruses often have a complex architecture consisting of both helical and isometric symmetries confined to different structural components.

Viruses are classified on the basis of morphology, chemical composition, and mode of replication. The viruses that infect humans are currently grouped into 21 families, reflecting only a small part of the spectrum of the multitude of different viruses whose host ranges extend from vertebrates to protozoa and from plants and fungi to bacteria.

In the replication of viruses with helical symmetry, identical protein subunits protomers self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path.

Such nucleocapsids form rigid, highly elongated rods or flexible filaments; in either case, details of the capsid structure are often discernible by electron microscopy. In addition to classification as flexible or rigid and as naked or enveloped, helical nucleocapsids are characterized by length, width, pitch of the helix, and number of protomers per helical turn. The most extensively studied helical virus is tobacco mosaic virus Fig. Many important structural features of this plant virus have been detected by x-ray diffraction studies.

Figure shows Sendai virus, an enveloped virus with helical nucleocapsid symmetry, a member of the paramyxovirus family see Ch. The helical structure of the rigid tobacco mosaic virus rod. About 5 percent of the length of the virion is depicted. Individual 17,Da protein subunits protomers assemble in a helix with an axial repeat of 6. Each more Fragments of flexible helical nucleocapsids NC of Sendai virus, a paramyxovirus, are seen either within the protective envelope E or free, after rupture of the envelope.

The intact nucleocapsid is about 1, nm long and 17 nm in diameter; its pitch more An icosahedron is a polyhedron having 20 equilateral triangular faces and 12 vertices Fig. Lines through the centers of opposite triangular faces form axes of threefold rotational symmetry; twofold rotational symmetry axes are formed by lines through midpoints of opposite edges. An icosaheron polyhedral or spherical with fivefold, threefold, and twofold axes of rotational symmetry Fig.

Icosahedral models seen, left to right, on fivefold, threefold, and twofold axes of rotational symmetry. These axes are perpendicular to the plane of the page and pass through the centers of each figure.

Both polyhedral upper and spherical lower forms more Viruses were first found to have symmetry by x-ray diffraction studies and subsequently by electron microscopy with negative-staining techniques.

In most icosahedral viruses, the protomers, i. The arrangement of capsomeres into an icosahedral shell compare Fig. This requires the identification of the nearest pair of vertex capsomeres called penton: those through which the fivefold symmetry axes pass and the distribution of capsomeres between them.

Adenovirus after negative stain electron microscopy. A The capsid reveals the typical isometric shell made up from 20 equilateral triangular faces. The net axes are formed by lines of the closest-packed neighboring capsomeres.