Key messages

  • Plague is an ‘urgent’ notifiable condition that must be notified immediately to the department by medical practitioners and pathology services. It is also subject to Australian quarantine.
  • Plague is an acute, severe bacterial infection usually transmitted through a fleabite.
  • Y. pestis – the infectious bacterium – is not endemic in Australia but is widely distributed around the world.
  • A vaccine is available that provides some short-term protection against plague. However, it is not commercially available in most countries.

Notification requirement for plague

Plague is an ‘urgent’ notifiable condition and must be notified by medical practitioners and pathology services immediately by telephone upon initial diagnosis (presumptive or confirmed). Pathology services must follow up with written notification within 5 days. 

Plague is subject to Australian quarantine.

This is a Victorian statutory requirement.

Infectious agent of plague

Yersinia pestis is the plague bacillus.

Identification of plague

Clinical features

Plague is an acute, severe bacterial infection usually transmitted through a fleabite. It most commonly presents in bubonic, pneumonic or septicaemic form.

Initial symptoms are often nonspecific and may include fever, chills, muscle aches, nausea and lethargy.

Bubonic plague is the most common form worldwide. It is characterised by swelling and inflammation (buboes) of the local lymph nodes draining the site of the fleabite 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. The 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 also lead to disseminated intravascular coagulation.

Diagnosis

Visualisation of characteristic ‘safety-pin’ ovoid Gram-negative organisms in material aspirated from buboes, sputum or cerebrospinal fluid (CSF) is highly suggestive of plague infection.

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

Seroconversion detected using the passive haemagglutination test is also highly suggestive of recent infection.

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

Incubation period of Yersinia pestis

The incubation period is 1–7 days. For primary plague pneumonia, it is 1–4 days.

Public health significance and occurrence for plague

Y. pestis is not endemic in Australia but is widely distributed around the world.

The World Health Organization (WHO) reports 1,000 to 3,000 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 United States, South America, Africa and Central and South-east Asia.

Untreated bubonic plague has a case-fatality rate of about 50–60 per cent. 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 bioterrorist attack using plague is a potential public health concern.

Reservoir of Yersinia pestis

No enzootic (animal) reservoir for Y. pestis 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 of Yersinia pestis

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 is also a possible aerosol route for plague transmission.

If plague bacteria were to be used as a bioterrorism agent, they 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 of plague

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 72 hours of appropriate antibiotic treatment.

Susceptibility and resistance to plague

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

Control measures for plague

Preventive measures

A vaccine is available that provides some short-term protection against plague. It may be recommended for laboratory workers handling plague, but is not commercially available in most countries.

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.

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

For cases with bubonic plague with no respiratory symptoms, contact precautions are indicated until the completion of at least 3 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 3 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 to have died from plague.

Control of contacts

Contacts of the case should be identified, examined for fleas and, if appropriate, disinfested of fleas. Contacts are placed under surveillance to detect symptoms of early infection for 6 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 there is currently 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 for plague’).

Special settings

The control measures described above apply in all settings.

Outbreak measures for plague

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
  • releasing appropriate public information
  • instigating intensive flea control around the focus in expanding circles of control
  • destroying rodents within affected areas
  • controlling 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 the International Health Regulations (WHO, Geneva, 2005).

Measures applicable to ships, aircraft, land transport and international travellers arriving from plague areas are specified in the International Health Regulations.

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 early symptoms of infection for 6 days from the last exposure.

On the arrival of a suspected infected ship or aircraft, travellers should be disinfested of fleas and kept under symptom surveillance for 6 days from the date of arrival.

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