 Once introduced into an individual of a new host species, the pathogen may  acquire the ability to infect other individuals of the same species, allowing it to spread through the new host population.
<meaning-changed>  Once introduced into an individual of a new host species, the pathogen may  acquire the ability to infect other individuals of the same species, allowing it to spread through the new host population.
 Once introduced into an individual of a new host species, the pathogen may cause disease for the new host and/or acquire the ability to infect other individuals of the same species, allowing it to spread through the new host population.