Smallpox (Orthopoxvirus variola) is the first human disease considered to be globally eradicated. All of the following factors played a huge role in its eradication EXCEPT for . a. the existence of an inexpensive, effective vaccine
b. the removal of animal reservoirs in nature
c. rapid diagnosis due to obvious signs and symptoms
d. the fact that there are no asymptomatic carriers, so the disease is always diagnosable