What steps are required for a pathogen to infect a novel host species?

Steps are required for a pathogen to infect a novel host species.

A pathogen is defined as an organism causing disease to its host, with the severity of the disease symptoms referred to as virulence.The pathogens can be viruses or bacteria. If the host is humans then these pathogens can enter through nose, sputum, yes or any cut wounds. After entering the host species, the pathogens ejects its genome into the cell of the host for its multiplication. Such type of organisms require the machinery of the host to multiply.The pathogens after multiplying, increases in number and damages tissues and organs of the host thereby causing diseases.

The answer is a because - is an direction