Role of viral respiratory infections in asthma and asthma exacerbations

Abstract

Viral respiratory tract infections are common and usually selflimited illnesses. For patients at risk of asthma, or with existing asthma, viral respiratory tract infections can have a profound effect on the expression of disease or loss of control. New evidence has shown that wheezing episodes early in life due to human rhinoviruses are a major risk factor for the later diagnosis of asthma at age 6 years. For those with existing asthma, exacerbations are a major cause of morbidity, can need acute care, and can, albeit rarely, result in death. Viral respiratory tract infections, predominantly those caused by human rhinoviruses, are associated with asthma exacerbations. There is also evidence that deficiencies in antiviral activity and the integrity of the airway epithelial barrier could make individuals with asthma more likely to have severe viral respiratory infections of the lower airway, and thus increase the risk of exacerbation. In view of the effect of respiratory viruses on many aspects of asthma, efforts to understand the mechanisms and risk factors by which these airway infections cause changes in airway pathophysiology are a first step towards improved treatment.

Figure 1

Role of infections in asthma Infections in early life can be inducers of wheezing or protectors against the development of allergic disease.

Figure 2

Childhood Origins of Asthma (COAST) study design

Figure 3

Risk of asthma at age 6 years in children who wheezed during the first 3 years of life Number at top of bar=odds ratio. HRV=human rhinovirus. RSV=respiratory syncytial virus. *p<0·05 versus no RSV or HRV. †p<0·05 versus RSV only. Reprinted with permission from Jackson and colleagues.

Figure 4

Factors that determine whether a respiratory infection provokes asthma The interaction between the infectious agent and the patient are the purported determinants of the outcome of infection.

Figure 5

Interferon-β mRNA expression from cultured bronchial epithelial cell in response to human rhinovirus-16 Samples were obtained from healthy and asthmatic individuals and then infected in vitro with human rhinovirus (HRV)-16. Vertical bars=95% CI. *(p=004) patients versus controls. Reprinted with permission from Wark and colleagues.

Figure 6

Response to human rhinovirus infection Bronchoalveolar lavage cells were obtained from healthy and asthmatic individuals. FEV₁= forced expiratory volume in one second. Reprinted with permission from Contoli and colleagues.