This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
Small pox eradication was successful because of all except - 
Select and explain. 
A. Subclinical cases don't transit disease, B. Highly effective vaccine, C. Lifelong immunity, D. Cross resistance with animal pox
D: Cross resistance with animal pox
Answer: D: Cross resistance with animal pox 
Explanation: <p> Cross-resistance existed with animal pox. Epidemiological reason for smallpox eradication are No known animal reservoir, no long term carrier state,infection provides life long immunity,case detection simple due to characteristic rash,subcliical cases did not transmit the disease,a highly effective vaccine was available,internationalcooperatio. Reference:Park&;s textbook of preventive and social medicine,K.Park,23rd edition,page no:143. <\p>