While many people colloquially refer to seasonal upper respiratory illnesses as "the flu," in reality, the flu is a specific illness caused by the influenza virus. Flu infections typically come on quickly, display rapidly progressing symptoms including headache, fever and respiratory difficulty, and resolve in otherwise healthy patients within a few weeks. There are several characteristics of the flu virus that both identify it to microbiologists and produce some of its defining characteristics.
Genetic Material
Humans, like most other living organisms, encode their genetic information into long molecules called DNA. Specialized cellular machinery reads the DNA and uses it to produce proteins that the organism needs to engage in its various functions. Viruses are somewhat different; while some encode their genetic information on DNA, others use RNA, which is a related molecule.
Knowing whether a virus uses DNA or RNA for its genetic information helps researchers understand its function and find cures or prevent infection. Influenza, notes the Molecular Expressions website maintained by Florida State University, is an RNA virus. This has ramifications on its behavior. For instance, many DNA viruses, like HIV, incubate for long periods of time before causing symptoms. Influenza is much faster-acting.
Mechanism of Infection
Viruses generally only attack specific cell types within the body. Influenza, according to the University of South Carolina School of Medicine, attacks the cells that line the respiratory tract. As the cells become infected, they typically die. This is the combined result of trauma inflicted upon the cells by the virus and trauma inflicted by the body's own immune system, in its attempt to destroy the invading pathogens. As the cells die, they lose their ability to move mucus from the lower reaches of the lungs up toward the throat, causing mucus to accumulate in the small airways. This clogs airways and leads to difficulty breathing, wheezing and the need to cough up sputum.
Susceptibility of Virus
Viruses, unlike bacterial infections, can't be treated with antibiotics. Many viruses are simply not treatable, while others may be prevented with vaccination and ameliorated by antiviral preparations. Influenza infections are well-understood, and researchers have created both vaccinations and antivirals. Typical vaccinations contain killed virus, which can't cause infection, but does introduce the virus to the immune system, explains the University of South Carolina School of Medicine. This means that later exposure to the virus doesn't lead to infection, because the immune system kicks in before the virus can infect cells. Antivirals, like oseltamivir, or Tamiflu, help reduce the ability of the virus to proliferate in cells. They don't prevent infection, but if taken early, they can reduce the severity and duration of illness. Influenza is susceptible to antivirals because of the specific mechanisms through which it binds to cells and reproduces.
