That time of the month again? Oh wait… I meant, it’s that time of the year again huh? It seems that a large portion of the population contracts some type of sickness around the winter time. Surprisingly, the weather has nothing to do with why you get sick so often around the winter. It’s been theorized that individuals contract illnesses more frequently in the winter because there is a greater tendency to stay inside, and with that you are exposed to individuals who are often sick. The common cold is easily transferable because it is an upper respiratory infection caused by rhinovirus, or other viruses. It is more commonly caused by rhinovirus, because there are more than 100 different types of rhinoviruses which all have a human reservoir; meaning they only house their infections within a human host. Additionally, respiratory syncytial virus (RSV) can cause a cold in older children and adults. There are other viruses including influenza A and B, which can cause the “flu” as well. The pathogenesis (the ability to cause disease) of a rhinovirus occurs after the incubation period which is usually 1-2 days after encountering the virus. The rhinovirus attaches to your respiratory epithelial cells and infects the cells by entering and producing multiple copies of itself. The epithelial cells eventually lyse (burst) releasing large numbers of virus particles into your upper respiratory tract (URT). This cycle repeats continuously and the rhinovirus has the ability to infect the overwhelming amounts of epithelial cells present in your pharynx. As cells die, the release of protein signalling molecules called cytokines recruit leukocytes (white-blood cells) to the site of infection. Furthermore, there is inflammation within the URT to localize the site of infection preventing it to spread to other areas of the body.
As the battle between the exponential growth of the virus and the human leukocytes occurs, the symptoms of the common cold are experienced. This includes a scratchy throat, sneezing, nasal discharges, malaise, headache and cough. Often you experience these symptoms because your immune system is trying to battle the virus and clear the infection. The reason you cough and sneeze is due to inactivity of ciliary motion in the URT. When a virus infects a cell, it often inactivates the movement of these tiny hair-like projections on cells which prevent pathogens from entering your lower respiratory tract (LRT). When the ciliary motion (mucociliary escalator) is inactivated due to the increasing amount cell death, the strength of your coughs and sneezes are used to push these pathogens up and out of your URT. A runny nose is also a result of your increased mucus production because your immune system is trying to again contain the infection which can lead to congestion but at the same time it is trying to clear the infection from your nasal cavity. Due to the vast variety of rhinoviruses, there is no vaccine available that can target all types of different rhinoviruses. And with that, there is also no generally accepted treatment except over the counter medication to help with symptoms. To prevent catching the virus, it is recommended to avoid people with the cold, wash hands frequently (not use hand sanitizer), and avoid touching your face.
According to the Nova Scotia Respiratory Watch, there were 21 hospitalized cases of influenza A and B, and 41 cases of RSV observed last week. Only 1 case of rhinovirus was observed because it is not as harmful to a healthy individual and is often cleared within two weeks. Although rhinovirus may not be particularly harmful to a healthy individual, an individual who is immunocompromised (lacks an effective immune system) may be prone to severe symptoms due to the viral nature of the infection. Immunocompromised individuals are more susceptible to secondary infections which are often caused by other pathogens (such as a bacterial infection) hence, becoming more ill.
The lower respiratory tract is sterile and infections in the LRT are often more severe than infections in the URT. Influenza and RSV are both viruses affecting the lower respiratory tract and are far more damaging to the host than rhinovirus. Influenza has an incubation period of roughly 2 days before the onset of symptoms. The symptoms are flu-like and worsen over time with lingering cough, fatigue, and weakness. The pathogenesis of influenza is similar to the rhinovirus as they both multiply within epithelial cells and suppress the mucociliary escalator. However, in the case of influenza, even healthy individuals are more susceptible to a secondary infection which can often lead to death. There are three types of influenza virus; influenza A, influenza B, and influenza C. The letters indicate severity based on the protein coat that the influenza virus possesses. Type A is more severe for humans, as compared to type B and C. Influenza is a unique virus, as it has the ability to change. Influenza has a protein coat which surrounds the genetic material found inside the virus. On the protein coat, influenza has glycoprotein spikes of hemagglutinin (HA) and neuraminidase (NA). The HA and NA glycoproteins are antigens which are often recognised by your immune system as pathogenic. The HA and NA glycoproteins mutate frequently as the virus multiplies over time infecting many individuals. Seasonal influenza occurs because there are mutations that occur commonly within these HA and NA genes that changes the conformation of the antigen proteins and becomes unrecognisable by your immune system. The protein antigens found on the virus in the previous year are completely different from the protein antigens found on the seasonal influenza virus currently, thus making you sick every year. This is known as antigenic drift. The treatment of influenza includes some antiviral mediation, only if it is given at an appropriate time and there are also multivalent vaccines. The current strain of influenza affecting the general population in Nova Scotia includes unsubtyped influenza A, and influenza B. The multivalent vaccine is used against the top three important strains in circulation but a new vaccine is required every year due to antigenic drift. There have been more reported cases for RSV than influenza and rhinoviruses because it is not necessarily more pathogenic but has a different approach as to how it infects its host and the type of symptoms experienced. The RSV infection is of the LRT and is often more damaging to infants, young children, and the elderly. Healthy individuals and older children/adults with RSV experience RSV with similar symptoms to a bad cold. The symptoms experienced by an infected individual would be flu-like with wheezing, difficulty breathing, and possibly fever. RSV can also cause croup which is a high-pitched cough with noisy inhalation due to airway obstruction. The pathogenesis of RSV is slightly different from influenza and rhinovirus because although it may also infect epithelium of the respiratory tract, it causes the bronchioles of the lungs to be partially plugged from the dead sloughed cells of the epithelium. The bronchioles are often plugged with mucus, clotted plasma, and this obstruction is a result of wheezing. The RSV virus has proteins which also allow it to attach and fuse two cells together to hide from the leukocytes of the immune system. Due to the nature of some RSV virus proteins, it can sometimes be fatal for the elderly population that have underlying conditions. Currently, there few effective antiviral medications available for this infection. Many antivirals like ribavirin are only given to people who have contracted severe cases. Additionally, a method has been developed for premature babies to have added protection if they are born in the winter. Doctors will give the premature babies injections of antibodies to RSV so that this vulnerable population develops a passive immunity.
Note!! Antibiotics cannot cure your “common cold”, it only works against bacterial infections!
