Germs Chapter 2, The common viruses

Last week I was first in line at my hospital to receive this year's influenza vaccine. Flu shots must be given every year as influenza virus strains change frequently. Influenza virus is capable of antigenic drift and antigenic shift. Think of people who alter their appearance by dying their hair or wearing disguises. This would represent antigenic drift. Now imagine if a criminal could change his or her DNA. That would be similar to antigenic shift. Human and animal influenza strains can swap genetic material and recombine to form novel strains against which, we poor humans, have no immunity. Remember last year's H1N1, the swine flu. Strains that appear in the southern hemisphere and in Asia are used to make the new vaccine for any given year. All health care workers, teachers, first responders, transportation workers, people with chronic medical conditions and those who believe in an ounce of prevention, should get yearly flu shots.

Most upper and lower respiratory tract infections are caused by viruses. These life forms are little more than a piece of DNA or RNA inside an envelope. They require the cellular mechanisms of another higher life form to replicate. The list of respiratory viruses includes influenza and parainfluenza viruses. Parainfluenza is the leading cause of croup. Is there anything more frightening to a parent than waking in the night to the sounds of your child having a cough like a seal's bark and the stridor (loud audible inspiratory and sometimes expiratory sound) that is croup?

Adenovirus, coronavirus and rhinovirus are among the hundreds of viral strains that cause colds. The symptoms of the common cold are familiar: sneezing, coughing, congestion, disturbed sleep and general misery. Differentiating between colds and the flu can be tricky. In general influenza has all the symptoms of a cold but is accompanied by high fever, severe body aches (even your hair seems to hurt), severe sore throat and lasts greater than a week.

RSV is a particularly nasty respiratory virus. The S stands for syncytial. RSV spreads cell to cell down the respiratory tract along intracytoplasmic bridges, e.g. syncytia. RSV cause bronchiolitis and viral pneumonia in infants and toddlers. Their small airways can become plugged by the RSV infection and lead to low oxygen levels. A somewhat effective anti-viral medication is administered to those children with RSV and low oxygen levels. Endotracheal intubation and respiratory support may become necessary.

The gastrointestinal tract is the other target of common human viral infections. Enteroviruses include coxsackie virus, echovirus and poliovirus. Thankfully poliovirus, which lead to paralysis is not seen except in a few countries in the world, because of nearly universal immunization with oral polio vaccine. In addition to the vomiting and diarrhea of gastroenteritis, enteroviruses can cause "hand, foot and mouth" disease. They are also the cause of many cases of viral myocarditis. I recently treated a young man, 16 years of age, for fever, body aches and headaches. His blood work was unremarkable. I suspected Lyme disease and sent off the blood test. Two days later he returned with his mother because he developed a dry cough and had become very short of breath. A chest x-ray revealed an enlarged heart and congested lungs. My partner, who is very adept at ultrasound, showed me that the patient's heart chambers were dilated and hypokinetic and that there was a small amount of fluid in the pericardial sac. We transfered this young man to a pediatric hospital and the offending agent was an enterovirus.

Most patients with viral gastroenteritis do well with sips of clear fluids and a slow progression of their diet. High fevers, weakness, lethargy, dry mucous membranes, decreased urine output and a sunken appearance (in infants) of the fontanel (soft spot on the top of the head) should alert the patient or the parent that dehydration is occuring and an ER visit is necessary.

Rotavirus, norovirus and Norwalk-like virus are all capable of causing localized and severe out breaks of gastroenteritis. Their have been episodes of hundreds of people on a cruise ship coming down with norovirus gastroenteritis. How would you like to be the ship's doctor and nurse on that cruise? An effective and relatively safe vaccine is now available to prevent rotavirus.

Herpes viruses deserve a section of their own. Cold sores, chicken pox, shingles, genital herpes, mononucleosis, and roseola are all diseases caused by members of the family of herpes viruses. Although most cases of herpes infection are self limited, this group of viruses can last a lifetime. Shingles is a recurrence of herpes zoster. The chicken pox infection one had as a child may cause you to harbor the virus in a dormant state in the nervous system. When this dormant virus awakens, it causes a rash and severe pain along a nerve in the body. This can occur anywhere from the face to the toes. Herpes simplex 1 and 2 can cause recurrent painful sores in the mouth and/or genitals. The practice of orogenital sex has blurred the distinction between these 2 strains and the regions they afflict.

Vaccination is our best weapon against viral infections. Mumps, measles, "German measles", chicken pox, hepatitis B, influenza, polio and rotavirus vaccines have saved countless lives and made childhood much less dangerous. There is no evidence that vaccinations cause autism. I would urge all parents to follow the recommendations of the American Academy of Pediatrics with regards to immunizations for their children. To my fellow older folk, there is a vaccine for herper zoster, that is recommended at age 60 to decrease the incidence and intensity of shingles. I highly recommend that you receive this vaccine.

The next chapter of Germs will deal with the deadlier viruses that bedevil humans.