How viruses cause disease?

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  • Viruses gain access to the host through skin and mucous membranes, and via the respiratory, gastrointestinal, and genital tracts.
  • Their virulence or lack of it may be determined by very small mutations in the genome.
  • Viral infection of cells may result in lysis, fusion and syncytium formation, the appearance of inclusion bodies, or, in some instances, transformation to cells with characteristics of malignancy.
  • Infections caused by viruses are localized at or near the site of entry or generalized to involve one or more target organs.

How viruses cause disease

  • In generalized infections a common pattern of spread during the incubation period is site of entry? local lymph nodes? primary viraemia? liver, spleen, bone marrow? secondary viraemia? target organ.
  • In humans, viral infections follow various basic patterns: acute non-persistent, acute followed by persistent latent infection, and chronic with continued shedding of virus.
  • Very rarely, papovavirus, measles virus, and prions cause long-lasting, fatal disease of the CNS.
  • During the course of infection, viruses are shed from the primary site of multiplication, or—with the exception of the CNS—from target organs, and are then free to infect other susceptible hosts.
  • The Ro number is the average number of secondary cases generated by one primary case in a susceptible community; it may be useful in predicting the course of an epidemic.

How viruses cause disease?

About Author

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Sagar Aryal, PhD

Dr. Sagar Aryal is a microbiologist, researcher, and science communicator from Nepal. He is also co-founder and Research Head of the Department of Natural Products at the Kathmandu Research Institute for Biological Sciences (KRIBS), where he leads research on natural product discovery and microbial biodiversity. Dr. Aryal earned his Ph.D. in Microbiology from Tribhuvan University, Kathmandu, Nepal, in 2025, supported by a DAAD Research Grant and a University Grants Commission (UGC) Nepal Ph.D. Fellowship. His research interests include Actinomycetes, Myxobacteria, microbial taxonomy, and natural products, particularly the discovery of bioactive compounds with potential pharmaceutical applications. He isolated and identified Nocardia nepalensis, a novel bacterial species from Nepal, contributing to understanding microbial diversity in the region. Dr. Aryal has published more than 16 research articles in international journals and contributed three book chapters to established academic publications. He has presented scientific research findings and developed international research collaborations through visits to more than 18 countries across Asia, Europe, North America, and Oceania. From 2023 to 2025, he served as the American Society for Microbiology (ASM) Young Ambassador to Nepal. Since December 2025, he has served as an Editorial Board Member of Scientific Reports, a Nature Portfolio journal. In recognition of his scientific contributions, Dr. Aryal received the NAST Science and Technology Youth Award 2025 from the Nepal Academy of Science and Technology. He previously received the Frs. Locke and Stiller Research Award (LSRA) for the 2017-2018 cycle from St. Xavier's College, Kathmandu, and a Nepal Academy of Science and Technology (NAST) Research Grant for 2017-2018. Alongside his scientific career, Dr. Aryal has more than 15 years of experience in blogging, content writing, and search engine optimization (SEO).