What organism(s) can cause the extinction of the human race?

Homo sapiens sapiens

The beauty of being human is that, unlike other organisms, we have the ability to alter our own fates, for better or worse. In the face of a global plague (bacterial, viral, social, or otherwise), we could find a cure. In a state of absolute peace, we could destroy everything. In either case, we would have nobody to blame but ourselves, whether for willful action or willful neglect.

Humankind's infinite capacity to solve problems counterbalanced with infinite destructive capacity is one of the greatest ironies of all time. Many of the best stories are based on that theme.

Bacteria that are harmful to humans (many aren't): streptococcus (strep throat); anthrax; etc.

The more we increase population density, the greater the possibility of spreading diseases. That's why we get vaccinations, but not everyone gets vaccinations in every country.

Ironic that the smallest organisms with considerably the least intelligence can wipe us out. Go Earth.

Human itself

Mosquitoes, with their disease spreading capabilities they're already responsible for more human deaths world wide than any other animal.

Viruses. If you want to consider them organisms....

Most like Homo sapiens ... people themselves.

HIV and/or Ebola virus.

smallpox

aids and other diseases that has no cure. and US

sure!