Common colds are frequent illnesses in both children and adults; on average, adults report 2.5 episodes per year. The common cold is caused by a variety of respiratory viruses, such as human rhinoviruses, coronaviruses, human enteroviruses, respiratory syncytial virus, parainfluenza viruses, or influenza viruses. Rhinoviruses are the most common cause of respiratory tract infections in individuals of all ages. In adults, rhinoviruses cause approximately 50% of common colds and up to 90 % of colds during the autumn epidemic season.
Colds comprise a syndrome of symptoms, typically with nasal complaints, cough, sore throat, and sometimes constitutional complaints, like headache, malaise, and fever, but about 12–32 % of human rhinoviruses infections in children of less than 4 years are asymptomatic. Pre-school children can experience an upper respiratory infection up to 8 to 12 times per year that might lead to wheezing, otitis media, bronchiolitis, exacerbations of asthma, CF, or COPD and aggravate allergic reactions.2
Although initially believed that HRV infection was limited to the upper airways, replicating virus was found in ciliated epithelial cells of the lower respiratory tract. Infected cells appear in patches, and only 10 % of the ciliated cells produce viral proteins and RNA.2
Environmental factors, in particular ambient air temperature and humidity, may contribute to the observed seasonal variation of respiratory viruses and the resulting respiratory tract infections. Both temperature and humidity may independently or jointly contribute to the risk of human rhinovirus (HRV) infections, either through altered survival and spread of viruses in the environment or due to changes in host susceptibility. Evidence suggests that inhalation of cold and dry air lowers the upper airways temperature and dries the mucosal membrane and may cause pathophysiological responses that contribute to increase the host susceptibility to viral infections.3
Cough is a protective reflex to prevent aspiration and can be triggered by a multitude of stimuli. The commonest form of cough is caused by upper respiratory tract infection and has no benefit to the host. Cough causes a plethora of complications affecting the cardiovascular, gastrointestinal and respiratory systems, with far-reaching psychological, neurological and musculoskeletal effects.
Despite the resolution of the majority of cold symptoms within 2 weeks, cough can persist for some time thereafter. Unfortunately, the mechanism of infectious cough brought on by pathogenic viruses, such as human rhinovirus, during colds, remains elusive despite the extensive work that has been undertaken.
The development of effective cold preventives is hampered by the multiplicity of viruses and the complex interplay between host and virus. For decades, intense research has focused on applications of broad-spectrum antivirals like interferons (α, β, or γ), capsid binding proteins, or soluble receptors directed against rhinoviral infection and/or replication. Some therapies showed efficacy in clinically induced infections but failed to significantly prevent colds in larger field studies that included multiple types of respiratory viruses. Nasal applications of interferons showed good preventative efficacy but were typically accompanied by adverse reactions like nasal bleeding.1
Currently, the Food and Drug Administration (FDA) has approved prophylactic drugs for respiratory syncytial virus, including palivizumab and ribavirin, administered along with symptomatic treatment and supportive care. While palivizumab, a humanized monoclonal antibody directed against the F protein RSV, effectively prevents RSV infection, it is expensive and ineffective in the management of an established RSV infection. Ribavirin is limited due to the side effects.4
Another method for preventing cold infections is to modulate the immune system. Prophylactic treatment with Echinaforce drops produced by A. Vogel Bioforce AG, Switzerland over 4 months appeared to be beneficial for many reasons.1
- Safety and Efficacy Profile of Echinacea purpurea to Prevent Common Cold Episodes: A Randomized, Double-Blind, Placebo-Controlled Trial
M. Jawad, 1 R. Schoop, 2 ,* A. Suter, 2 P. Klein, 3 and R. Eccles 1 Evid Based Complement Alternat Medv.2012; 2012
- Mechanism of human rhinovirus infections. Dieter Blaas and Renate Fuchscorresponding author. Mol Cell Pediatr. 2016 Dec; 3: 21.
- A Decrease in Temperature and Humidity Precedes Human Rhinovirus Infections in a Cold Climate. Tiina M. Ikäheimo,1,2,*† Kari Jaakkola,1,3,† Jari Jokelainen,4,5 Annika Saukkoriipi,6 Merja Roivainen,7 Raija Juvonen,8 Olli Vainio,2,9,10 and Jouni J.K. Jaakkola1,2 Virusesv.8(9); 2016 Sep