Emerging and reemerging respiratory viral infections up to Covid-19 (original) (raw)

TURKISH JOURNAL OF MEDICAL SCIENCES

Introduction Infectious diseases that increase in incidence and tend to spread geographically within decades can be defined as emerging infections. Pathogens of these infections appear for the first time or they have existed previously and spread rapidly among the population and new geographical areas. The emergence of novel human pathogens and reemergence of several diseases is of particular concerns of the current century [1]. There is a dominance of zoonotic infections, mostly originating in wildlife, among emerging health threats with a rate of 70%. Pathogens first emerge in themselves and rapidly mutate, which result in a transmission in humans with subsequent dissemination. According to the extent of the transmission, epidemic outbreaks may occur and progress to a pandemic. Diseases that reappear after a significant decline are called as reemerging diseases. Reemergence may occur due to a breakdown in public health measures or the appearance of new strains of organisms [2]. Respiratory infections with epidemic and pandemic potential that cause a global burden have plagued people since the beginning of human history. In this review, the epidemic and pandemic, emerging and reemerging respiratory viruses are summarized in Table. Most emerging viruses come from animals and are zoonotic or vector-borne diseases belonging to the families Orthomyxoviridae, Paramyxoviridae, Picornaviridae, Coronaviridae, Adenoviridae, and Herpesviridae. Community-acquired respiratory viruses are critical pathogens such as influenza, respiratory syncytial virus, adenovirus, parainfluenza virus, human coronavirus, human metapneumovirus, rhinovirus, enterovirus, cause millions of deaths and hospitalizations around all over the world every year [3,4]. In the last century, influenza originated avian, and swine, severe acute respiratory syndrome-coronavirus (SARS-CoV) and the Middle East respiratory syndromecoronavirus (MERS-CoV) were the most damaging respiratory infections for human being all over the world [5]. These emerging viral respiratory infections derived from the animal world [6]. Mutations in the genetic material of RNA viruses accumulate in years and produce new strains of the viruses with new antigenic properties resulting in a transmission in humans [7]. The probability of pandemics with new viruses would be high in the future as this type of mutations will reoccur. The other mechanism of a virus is reassortment which means that the host is infected with 2 different strains of viruses (animal and human viruses) than a new generation of a new virus with mixed genetic materials is developed and causes new pandemics [7]. Bird and swine influenza viruses obtain new gene segments through a reassortment with human strains.