Final answer:
Viruses typically infect specific hosts and cell types due to their ability to bind to cell-surface receptors that differ among species. Host specificity and viral mutation play key roles in how viruses can potentially jump to new species, monitored closely to prevent epidemics. Some viruses can infect a broad range of hosts, while others are highly specific.
Step-by-step explanation:
Most viruses are highly specialized and tend to infect only specific hosts or even specific types of cells within those hosts. This characteristic is known as being host-specific, meaning a virus is generally specific to one or a small number of species. Despite this specificity, the sheer diversity of viruses means that virtually every living organism has its own set of viruses that may attempt to infect its cells. Even the simplest prokaryotic organisms, like bacteria, can be attacked by specific viruses known as bacteriophages.
For a virus to infect a new host species, certain conditions must be met. The virus needs to be able to bind to cell-surface receptors on the host cell, which often differ significantly among species. If the virus undergoes mutations that allow it to bind to a new host's receptors, it can potentially start an infection in a new species. This can occur in environments such as swine and poultry farms, where animals are in close contact with humans and other species. This interspecies transmission is closely monitored by scientists to prevent global epidemics.
Viruses like the human influenza virus have a narrow host range and bind to specific receptors on host cells, which are different across various species. For instance, a virus that can infect humans might not be able to infect other animals such as chickens due to these chemical differences in cell-surface receptors. Some viruses have a broader host range, like the cucumber mosaic virus, which can infect thousands of different plant species, often being transmitted through vectors like insects or through direct contact between plants.