Ward's World Activity Guides

Coronavirus (continued) Many wild animals have been surveyed since SARS-CoV-1 was isolated in 2003. In addition to coronaviruses, bats continue to harbor some of the most diverse and highly pathogenic viruses, such as Ebola, Nipah, Hendra, and rabies viruses. Bats are found everywhere on Earth, with the exception of Antarctica, and ac- count for 20% of all mammals. They play an important role in ag- riculture by pollinating fruit trees and controlling insect popula- tions (for example, mosquitoes). In Asia, more than 50 species of bats are hunted and eaten by low-income populations. Bats also are used in traditional medicine, and their guano (excrement) is harvested to use as fertilizer for jackfruit, eggplant, papaya, and other economically important crops. Bats are capable of sustained flying speeds up to 160 km per hour (99 miles per hour) for hours at a time, achieving long dis- tances that aid virus transmission. Because they possess remark- ably strong antiviral immune responses and limited self-damaging inflammatory responses, bats rarely exhibit disease symptoms. Bats are being increasingly recognized as flying germ factories for zoonotic diseases that become lethal when they jump to humans. Undoubtedly, the conditions at some geographic locations will be ideal for spillover and a potential epidemic. Coronaviruses are masters of RNA recombination What determines whether a coronavirus will jump to hu- mans? Interestingly, the mutation rate of SARS-CoV-1 has been estimated to be consistent with that of other viruses that have RNA genomes. The viral RNA genome has a high-fidelity rate, undergoing 0.17 mutations per genome per day or 2 mutations per human passage (few errors occur during viral replication). Coronaviruses are masters of RNA recombination, which is a genetic mechanism whereby two different viral RNA genomes hybridize and exchange regions of RNA at precise locations. Coronavirus genomes undergo RNA recombination at high frequencies during replication. In doing so, the integrity of the RNA is preserved (replacing any mistakes made during rep- lication). In addition, coronaviruses can pick up novel genes, enabling them to adapt to a new host. RNA recombination can occur between the same and different coronavirus genomes (and between host RNA, which is less common). The RNA region that codes for the S protein is located in the most variable region of the coronavirus genome. RNA recom- bination events resulting in S-protein mutations are typical examples of how viral genomic changes allow a coronavirus to adapt and attach to a host receptor, enabling the coronavirus to infect a different species. In addition, changes in other loca- tions of the coronavirus genome can increase its adaptability to new hosts, or the genome may incorporate host/cellular RNA into its genome that codes for an accessory factor that permits its replication in a different species. Thus, it is more apparent than ever that emerging coronaviruses are a serious threat. Fig. 4: Primary and intermediate hosts of human coronaviruses showing cross-species transmission. No concrete evidence exists about the intermediate host (or hosts) of HCoV NL63 and HCoV HKU1. The years of isolation or emergences of each viral strain are also indicated. (Credit: Teri Shors) + ward ' s science 5100 West Henrietta Road • PO Box 92912 • Rochester, New York 14692-9012 • p: 800 962-2660 • wardsci.com

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