Viral Infections and Associated Factors That Promote Acute Exacerbations of Asthma

Kim, Chang-Keun; Callaway, Zak; Gern, James E.

All EVs, including poliovirus, circulate mostly in the summer and fall in temperate and year-round in tropical climes. 52 There are more than 100 nonpolio human EVs, with the newer numbered ones being classified into 4 species, EV-A, EV-B, EV-C, and EV-D. EV-D includes 3 serotypes known to cause disease in humans: EV-D68, EV-D70, and EV-D94. 53 Although EV-D68 is not new, having first been isolated in 1962 from a small group of US children with lower respiratory tract infection, it has emerged in the past decade as an important respiratory pathogen, with reports from North America, Europe, and Asia. Its association with severe respiratory disease is of special note in children with asthma. 19 Exactly how it is able to cause lower respiratory tract disease is currently unknown because the virus binds specifically to cell receptors found predominantly in the upper respiratory tract; 54 however, additional mediators are required for EV-D68 to enter cells. 55 There is evidence that recent strains of EV-D68 that are associated with lower respiratory tract infection may have gene mutations that influence antigenicity or trophism for lower airway cells.