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Viral disease is the sum of the effects of viral replication on the host and the host's subsequent immune response against the virus. [3] Viruses are able to initiate infection, disperse throughout the body, and replicate due to specific virulence factors. [2] There are several factors that affect pathogenesis.
Coronavirus disease 2019 (COVID-19) is a contagious disease caused by the coronavirus SARS-CoV-2. In January 2020, the disease spread worldwide, resulting in the COVID-19 pandemic . The symptoms of COVID‑19 can vary but often include fever, [ 7 ] fatigue, cough, breathing difficulties , loss of smell , and loss of taste .
Transmission and life-cycle of SARS-CoV-2 causing COVID-19. Coronaviruses vary significantly in risk factor. Some can kill more than 30% of those infected, such as MERS-CoV, and some are relatively harmless, such as the common cold. [49] Coronaviruses can cause colds with major symptoms, such as fever, and a sore throat from swollen adenoids. [91]
SARS-CoV-2 is the seventh known coronavirus to infect people, after 229E, NL63, OC43, HKU1, MERS-CoV, and the original SARS-CoV. [105] Like the SARS-related coronavirus implicated in the 2003 SARS outbreak, SARS‑CoV‑2 is a member of the subgenus Sarbecovirus (beta-CoV lineage B). [106] [107] Coronaviruses undergo frequent recombination. [108]
Mutations have produced many strains (variants) with varying degrees of infectivity and virulence. [9] COVID-19 vaccines were developed rapidly and deployed to the general public beginning in December 2020, made available through government and international programmes such as COVAX, aiming to provide vaccine equity.
Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. [1] The pathogenicity of an organism—its ability to cause disease—is determined by its virulence factors.
Scanning electron micrograph of SARS virions. Severe acute respiratory syndrome (SARS) is the disease caused by SARS-CoV-1. It causes an often severe illness and is marked initially by systemic symptoms of muscle pain, headache, and fever, followed in 2–14 days by the onset of respiratory symptoms, [13] mainly cough, dyspnea, and pneumonia.
Coronavirus diseases are caused by viruses in the coronavirus subfamily, a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, the group of viruses cause respiratory tract infections that can range from mild to lethal.