It’s that time of year. The time for festivities and family, for shopping and holiday buzz, and for influenza and other respiratory illnesses to gain popularity. It’s cold and flu season.
With all the discussion about Ebola and how it’s transmitted, it is always interesting—and even wise—to think about how other more common viruses affect and infect the population.
The Common Cold
Coronaviruses can be a common cause of mild-to-moderate upper respiratory tract illnesses, often referred to as the "common cold." Symptoms include fever, runny nose, cough, and sore throat. More severe infection can result in pneumonia. Young children are most likely to get the disease. However, adults can contract the viruses, and people have multiple coronavirus infections during their lifetimes.
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There are six different coronaviruses that can infect humans with four types being the most common. The other two coronaviruses are SARS-CoV and MERS-CoV, which can cause much more severe disease as demonstrated in the 2002 outbreak of SARS-CoV, and the ongoing outbreak of MERS-CoV in the Middle East. Most coronaviruses only infect an individual species, but SARS-CoV and MERS-CoV are unique in that they can infect certain animals as well as humans.
Spread of coronaviruses occurs through airborne transmission (coughing, sneezing, etc.) and direct contact of virus, including through contaminated surfaces (think doorknobs, remote controls, etc).
Cough, Cough, Cough
Human parainfluenza virus (HPIVs) can cause upper and lower respiratory tract disease in the spring, summer, and fall. Infant and young children are most likely to contract the virus, but any age can become infected. Older adults with weak immune systems are particularly susceptible. Like coronavirus, individuals can become infected with HPIVs multiple times during their life. There are four members of this family of viruses (1-4). It is commonly known as the cause of croup.
Human metapneumovirus (hMPV) is a relatively more recently identified virus first described to cause infection in young children. However, more extensive research of this virus has identified it to be an important cause of lower respiratory tract disease in adults, particularly those with advanced age, weakened immune system, and underlying cardiopulmonary disease. Like most respiratory viruses, it is transmitted through direct contact of contaminated surfaces and persons as well as through airborne droplets. The highest incidence typically occurs in winter and early spring, although summer outbreaks have been noted. Reinfection can occur throughout life.
Respiratory syncytial virus causes and infection typically associated with infants and young children and occurring during the fall and winter. However, it should be noted that elderly individuals and those with weakened immune systems or underlying lung/heart disease can become infected.
Viruses can be a common cause of community-acquired pneumonia (CAP). Both RSV and hMPV can cause classic symptoms of an upper respiratory infection, including cough, runny nose, sore throat, and fever. However, these 2 viruses may often manifest simply as an exacerbation of underlying chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF) without the classic symptoms typically associated with a virus infection.
No discussion of fall and winter virus infections would be complete without a discussion of influenza. It is an extremely fined tuned, complex virus that is perfectly built to adapt to the changing immune status of the human population. There are three types of influenza (A, B, C) with A and B causing disease in humans. Each virus has eight gene segments. Each time the gene segments are copied to make offspring, errors are made, which is why there is a different flu vaccine each year. Occasionally, these gene segments re-assort (switch out parts) leading to an influenza virus that no human immune system has seen before, i.e. pandemic.
Birds serve as the reservoir for influenza, but pigs can be infected as well. Reassortment of gene segments becomes particularly important when a bird or pig is infected with both a human virus and a virus specific for their species. These viruses can mix and out comes a new virus that could potentially infect humans.
Fever, cough, and body aches are the classic symptoms of influenza but fever may be absent in the elderly. Symptoms typically begin 2 days after infection, and you can be infectious for 1 day before symptoms began. Adults shed the virus for 5-7 days after symptoms start while children shed for up to 10 days. People with weakened immune systems, such as transplant patients, can shed virus for a much longer period of time.
Influenza can be fatal, particularly for the elderly and those with chronic lung and heart disease. However, a larger number of deaths can occur as a complication of influenza. This could be from exacerbation of underlying heart or lung disease, heart attacks, severe secondary bacterial infections ( Streptococcus pneumonia and Staphylococcus aureus). Although rare, influenza can cause neurologic complications such as seizures and paralysis as well.
Medications are available for influenza, but increasing resistance has been seen. They need to be started within 48 hours of symptom onset to be most effective. Post-exposure medication is given to people at high risk for complications of influenza.
Vaccination is the most pro-active step anyone can take towards preventing influenza. It is now recommended for all persons older than 6 months of age.
People are most familiar with the "flu shot" that contains inactivate/dead virus. It typically contains 3-4 strains of the virus with one being a type B influenza. A high dose vaccine is available to persons older than 65 years, which has been shown to promote a stronger immune response in this population that often responds less effectively to the standard influenza vaccine.
There also is a newer recombinant vaccine that can be given to individuals with severe egg allergy. Anaphylaxis egg allergy remains a contraindication to influenza vaccine. Fortunately, research is ongoing towards the development of a "universal" influenza vaccine that is directed against parts of the virus that change extremely slowly. The FDA is currently studying one of those vaccine candidates. This could eventually lead to a vaccine that is not needed yearly, but rather on a much less frequent time interval.
Last, it should be noted that you CANNOT get influenza from the flu shot. The vaccine does not contain live, or even complete, virus. The symptoms fever, fatigue, and aches persons sometimes experience after receiving the vaccine is simply your body’s immune system being stimulated by the vaccine.
While viruses do not stay alive in the environment for prolonged periods of time, they stay alive long enough on surfaces to be picked up by another host to infect. With all upper respiratory viruses, regular hand washing and avoiding people known to be sick are the most successful strategies to avoid infection.
However, this easier said than done. Humans typically touch their face from 3-18 times per hour. Now think of how many door knobs, counter tops, keyboards, ATM, and shopping carts you touched today. Get the picture? This is why infants and young children are more likely to get viral infections.
Use of common sense principles can help significantly. If you are ill, avoid work or close contact with people who have a weak immune system or chronic medical problems if possible. Try using the back of your hand or your forearm to scratch your face as opposed to your fingers or palms. If you have chronic lung or heart disease and must go out to the store when there is a high prevalence of a virus infection, take along a sanitizing wipe to clean the cart handle or open doors without your hand if possible. Likewise, if you have a friend of loved one in the hospital of long term care facility, wash hands going and coming and try to avoid touching your face while there. Also consider shortened visits, particularly if you have underlying heart and lung disease. Last, get your influenza vaccine!