Smallpox was a systemic disease, officially eradicated since 1979 (WHO), caused by infection with the Variola major virus, whose only reservoir was infected humans.
The transmission of Clostridioides difficile can be patient-to-patient, via contaminated hands of healthcare workers or by environmental contamination.
HIV is a virus which attacks the immune system and causes a lifelong severe illness with a long incubation period. The end-stage of the infection, acquired immunodeficiency syndrome (AIDS), results from the destruction of the immune system.
Pertussis, also known as whooping cough, is a highly contagious acute respiratory infection, caused by the bacterium Bordetella pertussis. The disease is characterised by a severe cough, which can last two months or even longer.