JKIMSU, Vol. 10, No. 2, April-June 2021 ISSN 2231-4261 REVIEW ARTICLE Emerging and Re-emerging Viral Infections in the 21st Century: Microbiological and Public Health Perspectives Mohan Bilikallahalli Sannathimmappa1*, Vinod Nambiar1, Rajesh Patil2 1Department of Microbiology and Immunology, College of Medicine and Health Sciences, National University of Science and Technology, Sultanate of Oman, 2Department of Microbiology, Travancore Medical College, Kollam-691020 (Kerala) India Abstract: Pathogens, especially viruses and bacteria are known worldwide have resulted in considerable loss of to have great potential to emerge and evolve for human life [1]. At the fundamental level, emerging thousands of years and it seems to be a never-ending diseases are those whose incidence in humans have process. In the last couple of decades, many viruses increased in the past two decades and re- have reemerged, and several novel viruses have emergence is the reappearance of a known disease emerged from animals and birds, posing a serious after a significant decline in incidence [1-3]. RNA threat to human health and the global economy. Amongst these pathogens, RNA viruses were found to viruses are more frequently associated with be more pathogenic and are more frequently associated emerging and reemerging viral diseases. The key with emerging viral diseases. This is because they have factors (Fig. 1) associated with the emergence of the capabilities to adapt rapidly to changing local and such diseases are evolution of infective agents, global environments. The ability to undergo mutation, increasing human population growth and genetic assortment, and recombination, unavailability globalization, changes in human behavior and their of effective vaccines, and lack of herd immunity are habitat, increased domestic and international the compounding factors for the emergence of new travel, unplanned urbanization, deforestation, diseases and reemergence of old viral diseases. This climate changes, and agricultural evolution [3-4]. article outlines virus characteristics, source and Emerging infections are linked to either emergent transmission of infection, recent outbreaks, and impact of a new virus due to genetic variation (mutation or on human health, laboratory diagnosis, and preventive strategies of the prominent epidemic and pandemic recombination) or because of adaptation of the viral diseases that occurred globally in the 21st century. animal virus in humans. Additionally, it could be due to the introduction of a new infectious agent in Keywords: Coronaviruses, RNA viruses, Emerging a determined geographic area [3-5]. In contrast, re- infections, Epidemic, Pandemic emergent infections generally originate by Introduction: reactivation of quiescent reservoirs or because of The emergence of novel viral infections and reappearance of previously circulating viruses that reemergence of several old viral diseases pose a have spread to other regions [3]. From the begin- serious threat to human health and life [1-2]. The st ning of 21 century, several major outbreaks of frequent continued outbreaks of viral infections Ó Journal of Krishna Institute of Medical Sciences University 1 JKIMSU, Vol. 10, No. 2, April-June 2021 Mohan Bilikallahalli et al. emerging and re-emerging viral diseases (Fig. 2) encephalitis) especially in Asia were the prominent with a varying degree of severity ranging from emerging and reemerging viral diseases (Table 1: mild to highly fatal have been reported from Basic characteristics of common emerging/ different regions of the world [2]. Amongst, several reemerging viral diseases) recorded so far in the coronavirus diseases of animal origin (Severe 21st century [1-2]. The World Health Organization Acute Respiratory Syndrome (SARS), Middle- (WHO) and the Centers for Disease Control and East Respiratory Syndrome (MERS), and the Prevention (CDC), the two major health present ongoing pandemic Coronavirus disease organizations have put a greater emphasis on 2019 (COVID-19), Ebola in West Africa, Zika in control of these infectious diseases [6]. This article South America, H7N9 in China and many Asian focusses on recent global epidemic and pandemic countries, H1N1 influenza worldwide, Nipah in viral diseases that occurred in the 21st century with India, and several arbovirus diseases (Dengue, special attention to virus characteristics, reservoir, Chikungunya, Kyasanoor Forest Disease, Crimean and mode of transmission, impact on human Congo Hemorrhagic Fever (CCHF), Japanese health, diagnosis, and prevention strategies. Urbanization Globalization Climate changes Natural disasters Immunosuppression Genetic changes: Mutation Population density and genetic recombination International travel Resistance to anti-viral Nutrition agents and disinfectants Fig. 1: Contributing Factors for Emergence of Viral Infections Ó Journal of Krishna Institute of Medical Sciences University 2 JKIMSU, Vol. 10, No. 2, April-June 2021 Mohan Bilikallahalli et al. Marburg Ebola, a severe Largest global pandemic hemorrhagic fever hemorrhagic fever of 21st century is the outbreak due to outbreak caused by ongoing COVID-19 Dengue outbreak Marburg virus Ebola virus occurred in caused by SARS CoV-2. Yellow fever outbreak with all serotypes (MARV) occurred in Outbreak of H1N1 2013-16 in West Africa characterized by It was originated at occurred in 2000- West-Africa (Angola) (swine-flu) in with an alarmingly high hemorrhage and fever China and has spread to 2010 in Americas. in 2004-5 with a very Mexico occurred in CFR of 75% was noticed in Brazil in almost every country and The CFR was 2-5% high CFR of 90% 2009-10 with a 2016-17. The CFR was so far has resulted in > 1 CFR ≈ 3-9% ≈ 35% million deaths across the globe. 2000 2002 2004 2005 2009 2012 2013 2015 2016 2018 2019 2020 An outbreak of viral MERS CoV outbreak SARS-CoV outbreak encephalitis caused in 2012-13, originated in China Zika virus outbreak in by Nipah virus Lassa fever outbreak Chikungunya virus originated at Saudi has spread to many 2015-16, originated in occurred in South- reported in Nigeria in outbreak particularly Arabia spread across Asian Countries and Brazil (South America) India (Kerala) in 2020. As on October, in India and other many Middle-Eastern resulted in ≈ 800 resulted in many cases 201 8 with a CFR of 2020, > 1000 lab Asian countries countries. The CFR deaths with CFR of microcephaly in ≈90% confirmed cases occurred in 2005-6 ≈ 34 9.5% was % babies born to infected including 232 deaths with a CFR ≈ 4.5% pregnant ladies. with CFR of ≈21 % Fig. 2: Timeline of Emerging and Reemerging Viral Diseases of 21st Century Table 1: Basic Characteristics of Common Emerging/Reemerging Viral Diseases of 21st Century Causative agent Disease Family/Genus Natural/Reservoir Transmission References SARS-CoV-2 COVID-19 Coronaviridae / Coronavirus Bats/pangolins Human-human 7, 8 Animal-human (initial transmission) SARS -CoV SARS Coronaviridae / Coronavirus Bats/palm civets Human-human 8,9 Animal-human (initial transmission) MERS-CoV MERS Coronaviridae / Coronavirus Bats/camel Human-human 8, 10 Animal-human Nipha virus Nipha virus encephalitis Paramyxoviridae / Henipavirus Pteropus bats (fruit bats) Human-human 11 Direct contact with animals, Ingestion of contaminated fruits Zika virus Zika virus disease Flaviviridae / Flavivirus Mosquitoes/ monkeys Mosquito bite, sexual contact, 12 mother-fetus, blood transfusion Ebola virus Ebola virus disease Filoviridae / Ebolavirus Fruit bats/non-human primates Human-human 13 CCHF virus Crimean Congo Hemorrhagic Bunyaviridae/ Nairovirus Ticks Tick bite, contact with infected 14, 15 fever blood/ tissues/ body fluids of infected animals/human Marburg virus Marburg virus disease Filoviridae/ Marburgvirus Fruit Bats Human-human 16 (Rousettus aegyptiacus) Lassa virus Lassa fever Arenaviridae /mamma arenavirus Multimammate rats Rodents-human 17 West-Nile virus West-Nile virus encephalitis Flaviviridae/ Flavivirus Mosquitoes/ Birds Mosquito bite 18 Ó Journal of Krishna Institute of Medical Sciences University 3 JKIMSU, Vol. 10, No. 2, April-June 2021 Mohan Bilikallahalli et al. Coronavirus Diseases: Coronaviruses are a large group of enveloped CoV, SARS-CoV-2 (beta coronaviruses), hCoV- RNA viruses that belong to Coronaviridae family. NL-63, and hCoV-229E (alpha coronaviruses) They carry a surface glycoprotein projection, have been documented in human infection. resembling solar crowns, therefore being termed However, hCoV-HKU1, hCoV-NL63, hCoV- “coronaviruses”. They possess a single stranded 229E, and hCoV-OC43 are circulating in humans positive sense non-segmented RNA genome that since they were recognized and are mainly has a great potential to undergo high rate of genetic associated with mild upper respiratory and mutation and recombination [7]. Fig. 3 depicts the gastrointestinal infections, accounting for classification of coronaviruses. There are 4 approximately 5-30% of common cold [8]. Within subtypes (alpha, beta, gamma, and delta), among a couple of decades in the 21st century, there have which alpha and beta coronaviruses gained much emerged three highly pathogenic and dangerous attention due to their ability to cause human coronaviruses of animal origin namely SARS- infection [8]. To date, 7 coronaviruses namely CoV, MERS-CoV, and SARS-CoV-2. hCoV-OC43, hCoV-HKU1, SARS-CoV, MERS- Order: Nidovirales Family: Coronaviridae Subfamily: Coronavirinae Genus: Coronavirus Alpha coronavirus Beta coronavirus Gamma coronavirus Delta coronavirus • hCoV-229E • SARS-CoV •