* Humans are the primary reservoir for Streptococcus pneumoniae. This means that pneumococci are most commonly found in the throats and noses of healthy people. When a person with pneumococci sneezes or coughs, they can spread the bacteria to others through respiratory droplets.

* Humans have a high susceptibility to pneumococcal infection. This means that even if a person is only exposed to a small amount of pneumococci, they can still become infected.

* Pneumococci can cause a variety of infections in humans, including pneumonia, meningitis, and sepsis. These infections can be life-threatening, especially in young children and the elderly.

There are a few reasons why pneumococci are not as likely to affect animals other than humans.

* Animals have different respiratory systems than humans. This means that pneumococci are not as easily able to colonize the throats and noses of animals.

* Animals have different immune systems than humans. This means that animals are better able to fight off pneumococcal infection.

* Animals are not as likely to be exposed to pneumococci. Animals are not as social as humans, and they do not spend as much time in close contact with each other. This means that they are less likely to come into contact with pneumococci.

As a result of these factors, pneumococci are primarily a human pathogen.