There are a number of reasons that smallpox was easily eradicated from the wild. For these same reasons, it would be easy to eradicate it again if the need arose, thus limiting the threat of the virus being used by terrorists. Smallpox is an extremely contagious disease. Close contact with a person or infected clothes is often enough to catch it. Combined with the fact that it has an overall mortality rate of about 30%, and those who survive are scarred for life or are left with side effects such as blindness, it would seem that terrorists getting a hold of smallpox is very dangerous. This is not necessarily the case, as can be seen by the relative ease it was to eradicate smallpox. Apart from perhaps causing some panic, re-released smallpox could be wiped-out by widespread vaccination programs.
Smallpox eradication is one of the greatest achievements of our modern age. It is the first time that a disease has been completely eliminated by organized human efforts. It shows the incredible power and potential of immunization. Almost certainly the main reason why it was possible to eradicate smallpox was the global initiative towards wiping it out. A vaccine was discovered by Edward Jenner in 1796, but in fact Chinese, Indian and Persian cultures used variolation (deliberately infecting a person with dried scabs from previously infected humans, thus vaccinating them) for a long time. Thus only once a global target to eliminate smallpox was set, along with proper funding, was it possible to wipe the disease out.
Several characteristics of the smallpox virus contributed to it being eradicated. The virus is essentially a single, very stable serotype which is important because there is no fear of mutations. Thus vaccination works and doesn’t have to worry about combating new strains of the virus. Smallpox is caused by Variola, a brick shaped virus with multiple envelopes and a core that contains linear double-stranded DNA of about 180,000 base pairs.
This is an enormous size for a virus, in fact it’s the largest known, and over 150 genes have been identified. This may seem to increase the likelihood of mutations occurring in the genome, but this is not exactly the case. Uniquely among DNA viruses, pox viruses replicate in the cytoplasm. Thus the virus carries a large number of virus coded proteins to substitute host cell functions, such as making its own reliable RNA polymerase and DNA polymerase.
The end nucleotides of the double-stranded DNA are covalently closed by a hairpin loop, and the key genes are in the middle of the genome. Thus essential sections of the genome are well protected against cellular enzymes, ensuring the virus replicates unerringly. Once smallpox was eliminated, it never naturally reoccurred in humans again. This is because humans are the only hosts that this virus can affect. There is no animal reservoir for the virus to hide in and resurface later when vaccine use declines. Other forms of the pox virus exist in various other animals, but these are host dependent and are not harmful to humans. In fact, catching other forms of pox, such as cowpox, would vaccinate a person from smallpox. Thus there are no concerns of smallpox creeping back into the world from the wild.
Smallpox is only contagious/infectious once symptoms such as severe rash and lesions appear, ensuring that the virus doesn’t spread unchecked. The symptoms are very clear and unique to smallpox. Smallpox can be diagnosed based on the patient’s clinical signs and symptoms. The disease can be definitively diagnosed by isolation of the virus from the blood or lesions, or by identification of antibodies in the blood made in response to the virus.
The diagnosis of smallpox needs to be made in specialized laboratories with appropriate testing techniques and measures to protect the laboratory workers. Once an outbreak occurs, it is relatively easy to isolate and vaccinate those exposed, thereby preventing the spread of the virus. Thus the global initiative to eradicate smallpox was aided by the fact that anybody infected with the virus was quickly identified. Thus small outbreaks of the virus were quickly stamped out by local vaccinations.
Live variola is currently only knowingly held in two laboratories in the world. While these remain alive, there will always be a chance for the virus to escape by accidental means or by terrorists. The threat of the virus if terrorists get a hold of it may not be as severe as the media attempt to make the public think. Smallpox vaccination is known to only be effective up to 5 years, thus placing all but the select few who work with the virus at risk from infection. However, due to symptoms being easily detectable and because of accessible vaccinations, if terrorists were to release the variola virus, it could be rapidly stamped out by local vaccinations.