Why are some viruses specific to humans and not animals?
Viruses use specially-adapted mechanisms to enter and infect the cells of their host organisms. And these mechanisms will neccessarily be different, depending what the host is. For example, plant viruses have to have a way of getting past the cellulose Cell Wall – while animal viruses don’t have that problem. Bacteria-infecting viruses (bacteriophages) have to similarly penetrate the peptidoglycan cell wall. Some viruses bind specific proteins on the cell-surface, and which protein is bound is different from virus species to virus species. If the protein is one that is common to many different species of host organism, then the virus will be able to infect many different species. OTOH, if the protein bound is only found in (for example) humans, then the virus will only be able to infect human cells. Similarly, if the protein is onkly found on certain cell and tissue types, then the virus will only be able to infect those (which is why the common cold viruses infect your lungs, throat,
