Smallpox was a severe viral disease that was eradicated worldwide, more than twenty years ago. It is considered to be a likely weapon in a bioterrorist attack since it is a highly contagious virus that can spread through the air and infects upto 30% of the people who are exposed to it.
What is the cause?
It is caused by the Variola virus, belonging to the pox group of viruses. It is known to exist legitimately in only two laboratories in the world – one at CDC Atlanta in USA and the other in Russian State Research Center of Virology and Biotechnology in Koltsovo.
How is it transmitted?
The infection is transmitted by the air-borne route or direct contact, leading to a severe infection with a high fatality rate. Smallpox can spread from person to person and through infected blankets, linens, and clothing. It affects both adults as well as children.
The virus is shed in the respiratory secretions, vesicle fluid and scabs. The patients are most infectious on the second and third day of the fever and remain infectious either until death or till all the scabs fall off after recovery. Close contacts of the patients, especially family members, are at risk of getting infected. The infectious dose is estimated to be as low as 10 to 100 viruses. The patients are infectious after the onset of rash and the maximum risk of passing it on to others lasts till 10 days.
What are the symptoms?
The time period between exposure to the infection and the onset of symptoms is around 10-14 days. At first, it is like the flu - causing fever, nausea, vomiting, headache, and backache. Then, abdominal pain and disorientation can start, along with small, round sores erupting all over the skin.
About 30% of people who become infected will die, and survivors can be left with permanent scars and even blindness if the cornea of the eye is affected.
Which other illnesses resemble smallpox?
Other viral illnesses like chickenpox (caused by the related Varicella zoster virus), widespread herpes simplex, monkeypox and tanapox can be confused with smallpox infection.
How is it diagnosed?
If the virus is deliberately released, the typical clinical picture along with a clustering of cases will point to the diagnosis. The confirmation of the diagnosis rests on demonstration of the virus in vesicle fluid and blood by various tests. The laboratory tests will show a rise in the lymphocyte blood cells and decrease in platelets. The chest x-ray is normal.
What is the treatment?
Once infected, there is no safe cure as none of the current antiviral medications are effective, though a couple of experimental drugs are available for use. The usual treatment is supportive and managing the complications, if any.
Can it be prevented?
Vaccination can prevent smallpox infection. The vaccine modifies the course of the illness and reduces the attack rate by 25-50%, if given within the first four days after exposure.
The World Health Organisation's worldwide vaccination campaign was started in 1967 and ended in 1980 when the disease was officially declared "eradicated". The young population which has not been vaccinated is most at risk in the event of an outbreak.
There are currently about 50 million vaccine doses worldwide. Experts estimate that it would take at least three years before there would be sufficient supply to prevent an epidemic.