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Smallpox (variola)

Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | International measures | Additional sources of information

Victorian statutory requirement

Smallpox (Group A disease) must be notified immediately by telephone or fax followed by written notification within five days.

Smallpox is included on the Commonwealth Quarantine List and all cases will need to be notified immediately to the State Chief Quarantine Officer.

Smallpox is subject to Australian quarantine.

Infectious agent

Variola virus is a DNA virus of the genus Orthopoxvirus.

The virus used in the live smallpox vaccine is known as the vaccinia virus and is also a member of the genus Orthopoxvirus.


Clinical features
Smallpox is a severe prostrating illness characterised by fever and a macular, papular, vesicular and pustular rash with an observed mortality rate of 30%. There are three major forms. The most common form described below occurs in 90% of cases. The remaining two are known as haemorrhagic and malignant (flat) variants. These both have significantly higher mortality (greater than 95%) and seem to be related to alterations in immune status.

Common smallpox begins with symptoms of fever (100%), headache (90%), backache (90%), chills (60%), vomiting (50%), malaise, prostration and cough. Less commonly pharyngitis and severe abdominal pain are observed. In pale-skinned patients an erythematous rash sometimes accompanies the prodromal phase. This occurs rarely as a petechial rash. This may be misdiagnosed as meningococcal disease, erythema multiforme or measles.

By the second or third day fever begins to descend from its peak (40.5 to 38.5°C) and the eruptive phase begins with the development of rash lesions. These lesions first appear on the buccal and pharyngeal mucosa and then emerge on the face, forearms and hands. The rash spreads down, and within a day the trunk and lower limbs are involved.

Smallpox produces a single crop of lesions which are distributed in a centrifugal pattern: most profuse on the face, more abundant on the forearms and lower legs than the upper arms and thighs, and often involve palms and soles.

Prominent surfaces and areas most exposed to irritation are more heavily involved by the rash. Protected surfaces such as flexures and depressions (axilla) are usually spared.

The eruptive lesions appear as flat discoloured macules that progress to firm papules on the second day of the rash. These are typically described as ‘shotty’. They become clearly identifiable as vesicles on the fourth or fifth day of the rash and progress to pustules on day seven.

Day ten commonly sees the pustules at maximal size and the lesions then commence to flatten. Approximately 14 days after rash onset the pustules begin to dry up and crust. Most pustules begin to scab and separate at day 19. Lesions on the palms and soles separate last and typically leave pitted scars.

A patient is no longer infectious once all the scabs have separated from the skin which is usually three to four weeks after the onset of the rash. Recovery results in the complete clearing of the virus from the body and prolonged immunity.

The major differential diagnosis is chickenpox and disseminated herpes simplex infections.

Smallpox may be complicated by secondary bacterial skin infection, corneal scaring, keratitis, arthritis, osteomyelitis, bronchitis, pneumonitis, pulmonary oedema and encephalitis.

Method of diagnosis
The diagnosis of smallpox will be made on the basis of a consistent clinical presentation combined with the results of electron microscopy and PCR testing which will be performed at the National High Security Quarantine Laboratory at Victorian Infectious Diseases Reference Laboratory in Melbourne.

Incubation period

The incubation period is regarded to be seven to 17 days, with a median of 12 days.

Public health significance & occurrence

In 1980 the World Health Organization (WHO) declared smallpox the first communicable disease ever to be globally eradicated. This was a direct consequence of the Global Smallpox Eradication Program which was achieved by a population based smallpox vaccination strategy.

The virus has been retained legally under strict security in two World Health Organization collaborating centres in the USA and the Russian Federation.

The virus is believed to have been part of the bio-weapons research of certain countries and there have been recent concerns that non-state actors may obtain access to the virus for deliberate release.

A single confirmed case of smallpox would prompt a global public health alert from the World Health Organization and would raise the spectre of an intentional release.

Historically variola major has a significant mortality and it would be reasonable to expect a greater impact upon today’s unimmunised and older populations. It is clear that an outbreak would be of extreme public concern requiring action at the highest level of government and involving the mobilisation of significant resources.


Smallpox is a disease only of humans and there are no non-human hosts.

Mode of transmission

The variola virus is most frequently transmitted from an infectious person via direct deposition of large, infective, airborne droplets of saliva onto the nasal, oral or pharyngeal mucosal membranes during close, face to face contact with a susceptible individual.

The generation of infectious fine-particle aerosols provides a possible albeit less common means of smallpox transmission. This may result in the infection of persons involved in non-face to face contact with the case, with the virus carried in aerosols spread by drafts and air-conditioning systems. Such spread is most likely in instances where the case has a significant cough.

Cases may contaminate objects in their environment including their clothing and linen with the large droplets or aerosols during sneezing or coughing and these fomites may serve as a further route of transmission.

Physical contact with a smallpox pustule or crusted scab may also transmit the virus. The virus has been found to survive in scabs for many years, however encased in this form it is not considered to represent a significant infectious risk.

Body fluids are also infectious and care is needed for the disposal of clinical waste.
The variola virus is thought to be unlikely to survive on its own for more than 48 hours when exposed to normal environmental conditions (ambient temperature, usual humidity and sunlight exposure).

During the smallpox era the disease had secondary household or close contact attack rates of up to 80%.

Period of communicability

Patients are not infectious during the asymptomatic incubation period. They become increasingly infectious after onset of fever and this usually results from the release of virus from oropharyngeal lesions.

For the purpose of contact tracing, cases are regarded as infectious 24 hours prior to the recognition of fever, and any contacts identified from this time on need suitable management.

Susceptibility & resistance

Resolved infection confers lifetime immunity.

Pregnant women and those who are immunocompromised are more susceptible to variant forms of smallpox.

It is unclear how long the smallpox vaccine will provide effective immunity but it is unlikely to be more than 10 years. As a result essentially all persons in Victoria and Australia will be regarded as susceptible to smallpox.

Control measures

Preventive measures
The Australian Government Department of Health and Ageing has stockpiled a certain amount of smallpox vaccine which will be accessed under appropriate situations.

In the event of an outbreak, there will be a stepwise process to vaccinate persons who will be required to assist in its containment such as doctors, nurses and ambulance personnel.
All others will be offered vaccination only if they have had contact with a case or form part of a ‘ring vaccination’ control strategy.

Control of case
Any patient that raises a concern of smallpox must be notified to the Communicable Diseases Section of the Department of Health as soon as possible such that a mobile smallpox care team can be dispatched to provide a swift and expert provisional diagnosis, and to implement suitable patient care and public health management.

All such patients (and their possessions) should be placed in the best available form of isolation as soon as possible. They should have limited contact with any persons other than those directly involved in their care, who must wear personal protective equipment. Any air conditioning should be turned off immediately.

All persons in contact with the case or those sharing the same airspace (hospital or practice staff, other patients etc) should be requested to remain in a safe area until the smallpox care team arrives and makes an assessment. They may need to be given access to smallpox immunisation in the short term and their details, including contact numbers, will be essential to collect. This should be commenced as soon as practicable. The smallpox care team will advise about infection control matters including disinfection and provide information to those present.

Cases will be categorised as possible, suspected, probable or confirmed, depending upon the epidemiology, clinical presentation and the results of electron microscopy and PCR testing of vesicular fluid.

All confirmed and probable cases will be managed in the treatment ward of the smallpox care centre where they will receive optimal health care by staff who have been successfully immunised, whilst maintaining appropriate isolation precautions for the community.

Those who meet the possible or suspected criteria will be placed in the observation ward of the smallpox care centre.

Control of contacts
The strategy of ring vaccination will be used in the control of any smallpox outbreak. This means that all contacts of a case will be immunised (category A and B, see below) and as an extra precaution, those persons with ongoing household contact with category A contacts, during the formal monitoring period, will also be offered access to the vaccine.

Category A, primary contacts
These are persons who are likely to be exposed to the virus through large droplets or contaminated fomites. They include:

  • Household contacts. All usual residents and any visitors who had spent more that one hour at the address during the infectious period.
  • Face to face contacts (within two metres) during the infectious period. This will include work and social settings as well as unvaccinated health care and emergency services personnel.
  • Fomite contact. All persons with direct contact with clothing or articles that have been used by infectious cases of smallpox.

Actions required

  • Urgent vaccination, preferably before day three but up to day seven.
  • Active surveillance for 17 days after the last exposure
    • Daily reporting of the contact by phone to the Department of Health will be required
    • Details of oral temperature and presence of constitutional symptoms
    • If there is failure to contact, the Department will actively follow up cases by phone or in person.
  • Restriction of movement from seven days after first exposure until 17 days after last exposure.
    • Avoid contact with unvaccinated persons
    • During this time contact must stay away from school and work
    • Remain within local area as defined by the Department
  • If symptomatic, category A cases need to stay at home and immediately contact the Department.
    • A category A contact who develops fever will be regarded as a possible case and transferred immediately to the observation ward of the smallpox care centre
    • A category A contact who develops fever and rash will be regarded as a probable case and transferred immediately to the treatment ward of the smallpox care centre.
  • Outside the restricted period category A contacts will need to stay within the local area until their vaccination site is completely healed and their formal monitoring period is over.

Category B, primary contacts
These contacts are less likely to have been exposed to the virus than Category A contacts.

They include:

  • All persons who have shared a room or other enclosed spaces with the case whilst infective and not meeting the criteria of category A contacts
    • These may include those who have visited the same premises or travelled on the same public transport (trains, planes or buses) or who have shared the same floors of buildings or the same air conditioning space with an infectious case.

Action required for category B contacts

  • Vaccinate unless contraindicated
  • Commence passive surveillance:
    • Details will be taken by the Department of Health and information provided as to nature of smallpox and actions to be taken if symptoms develop (fever, rash or constitutional symptoms).
    • If symptoms develop they must immediately contact the Department and remain at home, avoiding contact with all unvaccinated persons.
    • Surveillance will continue until 17 days after the last exposure to the virus.
  • Restricted movement:
    • Category B contacts will not be allowed to travel abroad until their vaccination site is completely healed and their formal surveillance period is over.
    • No other restrictions of activity are required unless the case is unwell.
  • If symptomatic they will be admitted to the smallpox care centre:
    • Category B contacts who develop fever will be classified as possible cases and transferred to observation ward of the smallpox care centre.
    • Category B contacts who develop fever and vesicular rash will be classified as probable cases and transferred to the treatment ward.

Secondary contacts
These are persons who will have ongoing household contact with category A contacts during the formal monitoring period. As such they are at risk of exposure to the virus if the primary contact becomes symptomatic. Secondary contacts would be expected to include usual household residence of category A contacts, together with any visitors to the household who expect to spend extended periods of time there, during the formal monitoring period.

Actions required for secondary contacts

  • Vaccinate unless contraindicated:
    • If immunisation is contraindicated then the secondary contact will need to avoid contact with the primary contact until the vaccination site is completely healed.
  • Passive surveillance and no restriction of movement:
    • There are no monitoring or restriction requirements necessary unless the primary contact becomes symptomatic. If they become confirmed with smallpox, then the secondary contacts will be reclassified as a category A contact and will need to be managed accordingly.

Unimmunised primary contacts
These are primary contacts (both category A and B) who fail to respond to the vaccine after three days, who are vaccinated later than three days after first exposure to the virus, or who refuse to be vaccinated.


  • Limited options are available for the pharmacological management of persons vaccinated late. The smallpox response team’s infectious disease specialist may suggest the use of vaccinia immune globulin or cidofovir in very limited circumstances.
  • Category A primary contacts who are categorised as unimmunised, will be required to remain in isolation accommodation until the incubation period has elapsed.
  • Category B primary contacts will be managed as if they were a category A contact (active surveillance, restricted movement from day seven after first exposure to day 17 after last exposure, see above).

Control of environment
All persons in contact with a case of smallpox must wear the appropriate personal protective equipment (PPE) and in order to limit any further spread, this will be removed and the person required to shower on leaving the infected area. This PPE includes gloves, theatre cottons with head cover, disposable apron, eye protection, foot wear such as overshoes, and a P2 respiratory mask.

Until the smallpox care team arrives, the possibly infected area should be cordoned off and access limited to those already present and those required for urgent medial care. The case of concern should be isolated as best as possible and all others should remain within a safe distance of the cordoned off area. Information and all care should be afforded all persons involved, with particular attention being made to advise that the earliest possible access to the vaccine will provide the best possible outcome if the case in fact proves to be smallpox.

The smallpox care team will advise on suitable decontamination processes and the disposal of possibly infectious materials. This will be in accordance with the Guidelines for the smallpox outbreak, preparedness, response and management.

As the virus is transmitted through infectious respiratory droplets and bodily fluids or contaminated clothing, dressings, linen, towels or clinical waste, every effort must be made by relevant staff to limit spread through these routes. Air conditioning must be isolated or turned off and the time documented. Any object that enters the infected area must remain there until disinfected or disposed of appropriately. This includes all linen, dressings and disposable eating utensils and medical notes.

Outbreak measures

Smallpox management will be framed in one of the five Australia response codes detailed below.

Australian response codes for smallpox

  • Response code 0: Smallpox remains eradicated – no credible threat of a release
  • Response code 1: Imminent threat or a case overseas
  • Response code 2: One case or a cluster of related cases in Australia
  • Response code 3: Unrelated cases or unrelated clusters occurring in Australia
  • Response code 4: Outbreak controlled – no further cases occurring

Emergency plans would be activated in sequence with these codes as outlined in the Australian Government’s Guidelines for the smallpox outbreak, preparedness, response and management. This would include alerts to the community and health providers, roll out of the smallpox vaccination strategy, mobilisation and augmentation of the smallpox care teams, and commissioning of the smallpox care centre.

Special settings
General hospital wards and their emergency department (ED) may be at increased risk of attending to smallpox cases. In order to limit this, all community concerns regarding smallpox need to be notified to the Department of Health immediately. The Department will dispatch a smallpox care team to make an urgent assessment. In this way, cases will be diverted to smallpox care centres without disrupting the working of any hospitals.

However if a case does present to an ED, then activation of the ED infection control procedures should be instituted, such that appropriate action is taken to limit any spread into the broader hospital.

International measures

If there are smallpox cases overseas then the Australian Government may divert all aircraft from that country, to a limited number of airports where screening, immunisation and the appropriate isolation and quarantine measures will be applied as required.

Additional sources of information

  • Australian Government Department of Health and Ageing 2004, Guidelines for smallpox outbreak, preparedness, response and management.
  • Fenner, F 1988, Smallpox and its eradication, World Health Organization.


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