Emerging viruses like SARS-CoV-2 spark global epidemics through specific biological processes. The correct answer to the multiple-choice question is A, B, and C. Option D does not contribute, as viruses require host cells for replication.

Correct Answer

A, B, and C: Mutation of existing virus, Jumping of existing virus from current to new hosts, Spread of virus in the new host population.

SARS-CoV-2 emerged in late 2019, likely from bats via an intermediate host, leading to a pandemic. These processes—mutation, zoonotic spillover (host jumping), and subsequent transmission—enable viruses to infect humans and proliferate. This combination explains most viral epidemics, including HIV, Ebola, and influenza pandemics.​

Option Explanations

Mutation of Existing Virus (A)

RNA viruses like coronaviruses have high mutation rates due to error-prone replication, generating variants with enhanced transmissibility or immune evasion. SARS-CoV-2 mutations, such as D614G in the spike protein, improved infectivity early in the pandemic. This process creates diversity for adaptation but alone does not cause epidemics without host access.​

Jumping to New Hosts (B)

Zoonotic transmission occurs when viruses cross species barriers, often via close human-animal contact. SARS-CoV-2 likely jumped from bats to humans, possibly through pangolins, exploiting similar ACE2 receptors. Such spillovers initiate outbreaks in immunologically naive populations.​

Spread in New Host Population (C)

Once in humans, sustained person-to-person transmission via respiratory droplets amplifies epidemics. SARS-CoV-2’s high R0 (reproduction number) and global travel fueled its pandemic spread. This phase turns isolated cases into widespread disease.​

Replication Outside a Host (D)

Viruses are obligate intracellular parasites and cannot replicate without host cell machinery. No known process allows extracellular replication, making this option incorrect. SARS-CoV-2, like all viruses, requires infected cells for propagation.​