Smallpox is a highly infectious disease caused by the Variola virus, spread by respiratory tract droplets or by direct contact with skin lesions. It has no known animal reservoir and is passed from one human to another.
Initial symptoms include high fever, fatigue, head and back pains followed by a characteristic rash particularly affecting the face, arms and legs. Flat red lesions become pus filled and form crusts in the second week. The death rate may reach 30% of those infected.
Smallpox is the only human pathogen which has been eradicated globally through a program of mass vaccination. It is our best example of herd immunity in the protection of a population. The last naturally acquired case was reported in Somalia in 1977 and in 1979 WHO announced the worldwide eradication of smallpox.
By international agreement, all stores of the live smallpox virus were destroyed except for those in very secure laboratories in the USA and in Russia. However, the current interest in smallpox arises from the uncertainty of world supplies of the virus and any potential use in biological warfare/terrorism.
Smallpox has been considered as a biological weapon posing the highest potential risk to any target population, but other viruses with a similar genetic structure, such as monkey pox or camel pox, may be genetically modified and represent a more accessible weapon to a potential terrorist.
Smallpox is a vaccine-preventable disease.
The last major European outbreak of smallpox was in 1972 in Yugoslavia, after a pilgrim from Kosovo returned from the Middle East, where he had contracted the virus.
The last naturally occurring case of the more deadly Variola major was detected in October 1975 in a two-year-old Bangladeshi girl and the last naturally occurring case of indigenous smallpox (Variola minor) was diagnosed in a hospital cook in Merca, Somalia, in 1977. The last case of smallpox in the world occurred in Birmingham, England in 1978 in a laboratory accident. No cases of smallpox have been reported from anywhere in the world since then.
No routine vaccination is required for travellers.
In December 2004, health officials from the Group of Seven nations and Mexico called for an international stockpile of smallpox vaccines to be established.
A global stockpile of live attenuated smallpox vaccine, donated by WHO member states, is managed by WHO. In 2005 it had enough vaccine to cover 10% of the world population, and 1 in 8 countries had enough to cover 100% of their own populations. In 2013, WHO estimated that the WHO stockpile (600-700 million doses) plus national stocks would be sufficient for an epidemic.
Smallpox has been known since ancient times and has been recorded in the earliest Egyptian, Indian and Chinese writings. There is no biblical reference to smallpox, but historians attribute a devastating plague in North Africa and Europe to smallpox, at about the time of the birth of Mohammad in 570AD.
The disease was first referred to as variola by Rhazes in 910AD. Crusaders (1096 to 1291) reintroduced smallpox to Europe after returning from the Levant.
Slave ships from Africa carried the disease to the West Indies and Central America and Spanish Conquistadors spread the disease from Mexico to South American resulting in the deaths of 3.5 million Aztec Indians. In 1562, Queen Elizabeth I survived an attack at the age of 29.
Epidemics occurred in England and in European cities and made its first appearance in southern Africa in 1713 and in Australia in 1789. New Zealand was not infected until the arrival of a Mormon missionary in 1913.
Epidemics occurred regularly in North America, where people of all ages were affected. In Europe, the disease affected mainly children. During the Franco-Prussian War (1870-71), the French Army which did not believe in vaccination lost 23,400 soldiers, whereas the Germans who did vaccinate, lost only 278 dead.
In 1966, there were approximately 10 -15 million cases of smallpox in more than 50 countries, and 1.5 – 2 million people died from the disease each year.
In 1965, international efforts to eradicate smallpox were revitalised with the establishment of the Smallpox Eradication Unit at the World Health organisation and a pledge for more technical and financial support from the campaign’s largest donor, the United States. Endemic countries were supplied with vaccines and kits for collecting and sending specimens, and the bifurcated needle made vaccination easier. An intensified effort was led in the five remaining countries in 1973, with concentrated surveillance and containment of outbreaks.
Smallpox was declared eradicated in 1980 following a global immunisation campaign led by the World Health Organization.
Crude forms of vaccination against smallpox were first practised in China and India in the Middle Ages. Various methods of ‘variolation’ were practiced by early Chinese and Persian physicians and became a common practice in the Ottoman Empire. It was first reported to the Royal Society of London in 1700.
Edward Jenner, an English doctor, formalised the process of vaccination, using cowpox virus – the first generation smallpox vaccine – in 1798.
During the 19th century, the cowpox virus was replaced by the vaccinia virus, genetically distinct but from within the same family as cowpox.
The existing smallpox vaccine is a live preparation of vaccinia virus, which offers protection against monkeypox, as well as smallpox. The virus is prepared from vesicles on the skin of calves or from chick embryos. Extensive use of the vaccinia vaccine commenced in Australia in 1917 and was phased out in the 1970s.
This original vaccine has recently been re-enlisted in the USA where defence and other essential personnel have been vaccinated. Supplies have also been obtained by other countries, including Australia, but are not generally available.
Batches of smallpox vaccines have been exempted from TGA regulations so that an Australian stockpile might be established. Presumably, the 200,000 doses purchased by the Federal Government will be offered to key personnel in the event of any real or expected biological warfare scenario.
A new vaccine, called MVA, which contains a weaker form of the virus and is therefore potentially less dangerous, is undergoing human trials.