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

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

Plague is subject to Australian quarantine.

Infectious agent

Yersinia pestis is the plague bacillus.

Identification

Clinical features
Plague is an acute, severe bacterial infection usually transmitted through a flea bite and most commonly presents as bubonic, pneumonic or septicaemic forms.

Initial symptoms are often non-specific and may include fever, chills, muscle aches, nausea and lethargy.

Bubonic plague is the most common form. It is characterised by swelling and inflammation of the local lymph nodes (buboes) draining the site of the flea bite or elsewhere. The nodes are tender, firm and fixed, and may suppurate in the second week.

Pneumonic plague may be primary due to respiratory transmission from an external source, or secondary as a complication of bubonic plague. Onset of primary plague pneumonia is usually abrupt with high fever, tachycardia and headache. Cough develops within 24 hours. Sputum is mucoid at first and then becomes bright red and foamy. Chest X-rays show a rapidly progressing pneumonia.

All forms of plague infection may progress to septicaemic plague with bloodstream spread around the body, including to the meninges. This includes some with no preceding localising signs or buboes. Sepsis may lead to disseminated intravascular coagulation (DIC).

Method of diagnosis
Visualisation of characteristic ‘safety-pin’ ovoid gram-negative organisms in material aspirated from buboes, sputum or CSF is highly suggestive of plague infection.

Fluorescent antibody (FA) testing or antigen capture ELISA is more specific and particularly useful in sporadic cases.

Seroconversion using the passive haemagglutination (PHA) test is also highly suggestive of recent infection.

The diagnosis is confirmed by culture and identification of the organism from bubo aspirates, the blood, CSF or sputum.

Incubation period

The incubation period is from one to seven days. For primary plague pneumonia it is one to four days.

Public health significance & occurrence

Y. pestis is not endemic in Australia but it is widely distributed around the world.
The World Health Organization (WHO) reports 1000 to 3000 cases of plague every year. Plague is endemic in some parts of South East Asia including parts of Indonesia, Burma and Vietnam. Wild rodent plague exists in areas of the USA, South America, Africa, Central and South East Asia.

Untreated bubonic plague has a case fatality rate of about 50–60%. Case fatality rates are significantly higher for pneumonic and septicaemic plague.

Given that techniques for mass production and aerosol dissemination are well described the threat of a bio-terrorist attack using plague is a potential public health concern.

Reservoir

No enzootic (animal) reservoir exists in Australia. In affected countries wild rats and other rodents are the natural reservoir. Other animal reservoirs include ground squirrels (especially in North America), rabbits, hares and domestic cats.

Plague bacteria are killed within a few hours of exposure to sunlight although they may persist for several weeks in water and on moist grains and pulses.

Mode of transmission

Plague is most commonly transmitted from rodent to human by the bite of an infected flea, especially the oriental rat flea Xenopsylla cheopis.

Respiratory droplets from people or domestic pets with plague pharyngitis or pneumonia may also transmit plague. Unprotected handling of plague infected animal tissues or laboratory specimens are also possible aerosol routes for plague transmission.

If plague bacteria were to be used as a bioterrorist agent, it would most likely be spread in the form of an aerosol or an aerosolised powder. This would result primarily in pneumonic plague. A deliberate release of infected fleas is also possible.

Period of communicability

Infected fleas may remain infectious for months.

Bubonic plague is not usually transmitted from person to person unless there is direct contact with pus from suppurating buboes.

Pneumonic plague may be highly communicable under appropriate climatic conditions.
Patients are usually no longer infectious after receiving 48–72 hours of appropriate antibiotic treatment.

Susceptibility & resistance

Everyone is susceptible to infection. The disease does not always confer protective immunity.

Control measures

Preventive measures
A vaccine is available against plague that provides some short term protection. It may be recommended for laboratory workers handling plague specimens and visitors to epidemic areas but should not be relied upon as the sole prevention measure.

The vaccine is not protective against primary pneumonic plague.

Control of case
Hospitalise the case in a single room.

Treatment usually consists of gentamicin or doxycycline. Consult the current version of Therapeutic guidelines: antibiotic (Therapeutic Guidelines Limited).

Use an appropriate insecticide to rid the patient (including clothing and baggage) of fleas.

For cases with bubonic plague, if there are no respiratory symptoms contact precautions are indicated until the completion of at least three days of appropriate antibiotic therapy with clinical improvement.

For patients with pneumonic plague, isolate the case to prevent droplet spread and use respiratory precautions until the completion of at least three days of appropriate antibiotic therapy with clinical improvement.

Disinfect all sputum and purulent discharges and soiled articles concurrently.

Use respiratory and contact precautions during the handling, and autopsy, of bodies of patients suspected, or confirmed of dying from plague.

Control of contacts
Contacts of the case should be identified, examined for and, if appropriate, disinfested of fleas. Contacts are placed under surveillance to detect symptoms of early infection for six days from the last exposure. Close contacts of confirmed or suspected pneumonic plague cases should also be given chemoprophylaxis (doxycycline or ciprofloxacin) supervised by an experienced physician.

Control of environment
As currently there is no enzootic plague in Australia, the greatest risk of infection is associated with overseas travel.

Any suspected local sources of infection should be investigated and managed as a public health emergency (see Outbreak measures, below).

Special settings
The control measures described above apply to all settings.

Outbreak measures

A single case of plague constitutes an outbreak and should be considered as a public health emergency.

If one or more cases are found with no history of travel to an endemic plague area, a deliberate release of plague bacteria must be considered.

If a focus of infection is identified, outbreak control measures should include:

• active case finding
• alerting medical practitioners
• alerting specialist treatment centres
• release of appropriate public information
• instigation of intensive flea control around the focus in expanding circles of control
• destruction of rodents within affected areas
• control of contacts (as described above) including field workers involved in environmental control measures.

International measures

Governments are required to notify WHO and adjacent countries of the first cases of plague in any area previously free of the disease within 24 hours of diagnosis, in accordance with International Health Regulations.

Measures applicable to ships, aircraft, land transport and international travellers arriving from plague areas are specified in the International Health Regulations 1969, third annotated edition 1983, WHO, Geneva.

Prior to departure from an area where there is an epidemic of pulmonary plague, those suspected of significant exposure should be placed under surveillance to detect symptoms of early infection for six days from the last exposure.

On arrival of a suspected infected ship or aircraft, travellers should be disinfested of fleas and kept under symptom surveillance for six days from the date of arrival.

Additional sources of information

• Australian Government Department of Health and Ageing fact sheet
• Centers for Disease Control and Prevention, Atlanta USA, Public health emergency preparedness and response