![]() ![]() If a mosquito capable of spreading yellow fever bites an infected monkey, the mosquito can then give the disease to humans. Yellow fever, for example, infects humans, but can also infect monkeys. ![]() Some diseases have an animal reservoir, meaning they can infect other species besides humans. Second, only humans can transmit and catch smallpox. Workers from the World Health Organization found smallpox patients in outlying areas by displaying pictures of people with the smallpox rash and asking if anyone nearby had a similar rash. In addition, the time from exposure to the initial appearance of symptoms is fairly short, so the disease usually can’t spread very far before it’s noticed. First, the disease is highly visible: smallpox patients develop a rash easily recognized. Smallpox was a good candidate for eradication for several reasons. The last case of wild smallpox occurred in Somalia in 1977. “Ring vaccination” meant anyone who could have been exposed to a smallpox patient was tracked down and vaccinated as quickly as possible, effectively corralling the disease and preventing its further spread. Smallpox eradication was accomplished with focused surveillance-quickly identifying new smallpox cases-and ring vaccination. Coordinated efforts rid the world of a disease that once killed up to 35% of its victims, and left others scarred or blind. To date, only one infectious disease that affects humans has been eradicated.* In 1980, after decades of efforts by the World Health Organization, the World Health Assembly endorsed a statement declaring smallpox eradicated. ![]() If a particular disease is eliminated worldwide, it’s considered eradicated. Polio, for example, was eliminated in the United States by 1979 after widespread vaccination efforts. When a disease stops circulating in a region, it’s considered eliminated in that region. ![]()
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