Plague

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 biosecurity measures.

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 is the only form of plague that can be spread from person to person. It may occur due to respiratory transmission from an external source, or secondary as a complication of bubonic plague. The onset of primary pneumonic plague 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.

Rarely, other presentations of plague may be seen such as pharyngeal plague from ingesting contaminated food or drink. This form of plague can lead to sore throat, fever and painful lymph nodes.

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.

Diagnosis

Diagnosis is confirmed through laboratory testing such as:

• isolation of Yersinia pestis from culture of an appropriate clinical specimen
• detection by a validated molecular method such as polymerase chain reaction and antigen detection
• serology may support retrospective diagnosis when paired specimens demonstrate a significant rise in antibody titre.

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.

In Victoria, testing is available through the Microbiological Diagnostic Unit Public Health Laboratory and any requests for testing should be discussed with them prior to specimen collection.

Treatment should not be delayed while awaiting laboratory confirmation.

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 usually 1–7 days. Primary pneumonic plague typically has a shorter incubation period of 1–3 days.

Public health significance and occurrence for plague

Yersinia pestis (Y. pestis) is not endemic in Australia but occurs in certain parts of the world.

Plague is endemic in parts of Africa, the Americas and Asia, with most human cases reported in the Democratic Republic of the Congo and Madagascar. Sporadic cases also occur in the western United States and other endemic regions.

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.

Given that techniques for mass production and aerosol dissemination are well described, the threat of bioterrorism using plague is a potential public health concern. If plague were to be used as a bioterrorism 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.

Reservoir of Yersinia pestis

No enzootic (animal) reservoir for Y. pestis exists in Australia. In affected countries, wild rodents are the natural reservoir. Other susceptible animal species 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. Transmission can also occur from direct contact with infected animals including body fluids and tissues.

Respiratory droplets from people or domestic pets with plague pharyngitis or pneumonic plague may also transmit plague.

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 can spread from person to person through respiratory droplets during close contact. Patients with pneumonic plague are generally considered no longer infectious after at least 48 hours of effective antibiotic therapy and clinical improvement.

Susceptibility and resistance to plague

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

Control measures for plague

Preventive measures

There is no readily available vaccine. Preventive measures include reducing exposure to fleas, rodents and other animals, using flea control for pets in endemic areas and wearing gloves when handling potentially infected animals.

Control of case

Cases of plague should be isolated in a single room ideally with negative pressure and managed under standard and transmission-based precautions with advice from public health authorities, an infectious diseases specialist and infection prevention and control expert.

Antibiotic treatment is highly effective if used early. Antibiotic therapy should be provided in line with the Therapeutic Guidelines and in consultation with an Infectious Disease specialist. Further guidance is available from the USCenters for Disease Control and Prevention (CDC).

Standard and droplet precautions are required for all suspected and confirmed cases of plague, including handling of bodies and autopsies, until pneumonic plague has been excluded. Airborne precautions should be used for any aerosol generating procedures.

• For bubonic plague without respiratory symptoms and a clear chest x-ray, standard precautions should be used.
• For pneumonic plague, standard and droplet precautions should continue to be used.
• For septicaemic plague, standard and transmission-based precautions should be used based on clinical manifestations and transmission risk.

Precautions are generally required until at least 48 hours after commencing appropriate antibiotic therapy and based on clinical improvement and laboratory results. Decisions to step down precautions should be based on advice from an infectious diseases specialist and infection prevention and control expert.

An appropriate insecticide should be used to rid the patient (including their clothing and baggage) of potentially infected fleas. Disinfect all soiled articles.

Control of contacts

People who may have had shared exposures to potentially infected flea, rodents and other animals or close contact with cases of pneumonic plague should be identified, assessed and advised to monitored for fever and other symptoms of plague for 7 days after their last exposure.

People with close, sustained exposure to a person or animal with suspected or confirmed pneumonic plague, or with direct high-risk exposure to infectious tissues or fluids, should receive prompt post-exposure antibiotic prophylaxis in consultation with an infectious diseases specialist and public health authorities. Doxycycline or ciprofloxacin are commonly recommended option. Guidance is available from the Therapeutic Guidelines and the US CDC.

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, an urgent investigation should be undertaken to identify the source of infection.

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.