Flu, also called influenza, is a viral infection of the nose, throat and lungs, which are part of the respiratory system. The viruses that cause influenza are divided into four categories named with letters. Influenza A is the most common type. The others are influenza B, C and D.
Influenza A viruses are further divided into subtypes. These subtypes are grouped based on two proteins on the surface of the viruses. One protein is called hemagglutinin (H) and the other is neuraminidase (N). There are many H and N subtypes and each one is numbered. H1N1 flu is a subtype of influenza A.
Each influenza subtype includes many different strains of influenza virus. Not all strains infect people. Subtypes of influenza A viruses currently found in people are strains of H1N1 and H3N2. Each year's flu vaccine includes varieties of these strains and influenza B.
Common Cold
There's [currently] no cure for the common cold. Most cases of the common cold get better without treatment within 7 to 10 days. But a cough may last a few more days.
What Is a Cold?
Colds are minor infections of the nose and throat caused by more than 200 different viruses. Rhinovirus is the most common cause, accounting for 10 to 40 percent of colds. Other common cold viruses include coronavirus and respiratory syncytial virus (RSV).
What causes the common cold?
A cold is caused by any one of several viruses that causes inflammation of the membranes that line the nose and throat. It can result from any one of more than 200 different viruses. But, the rhinoviruses causes most colds.
Common human coronaviruses, including types 229E, NL63, OC43, and HKU1, usually cause mild to moderate upper-respiratory tract illnesses, like the common cold.
Seven human coronaviruses (HCoVs) have been so far identified, namely HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1, severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV) and the novel coronavirus (2019-nCoV, a.k.a. SARS-CoV-2). Unlike the highly pathogenic SARS-CoV, MERS-CoV, and 2019-nCoV, the four so-called common HCoVs generally cause mild upper-respiratory tract illness and contribute to 15%–30% of cases of common colds in human adults, although severe and life-threatening lower respiratory tract infections can sometimes occur in infants, elderly people, or immunocompromised patients. In this article, we review the molecular virology of these common HCoVs, and summarize current knowledge on HCoV-host interaction, pathogenesis, and other clinically relevant perspectives.
Rhinoviruses are the most frequent cause of the common cold. In the United States, children have an average of two rhinovirus infections each year, and adults have an average of one. Most rhinovirus infections are mild, but they can cause severe illness, especially in people with weakened immune systems, asthma, or other underlying medical conditions. Rhinoviruses are commonly detected in children hospitalized for respiratory illness.
There are many different rhinovirus types. Rhinoviruses are part of the same virus group as Non-polio Enteroviruses, and have some similar properties to Enterovirus D68.
Respiratory syncytial virus, or RSV, is a virus that infects the lungs and respiratory tract causing cold-like symptoms. It's so common that most children have been infected with it by the time they're 2 years old. The virus can also infect adults. Self-care measures are usually all that's needed to relieve discomfort.
