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Causative Agent

Yersinia pestis

Incubation Period

2-6 days

Infectious Period

Throughout duration of illness (pneumonic plague is the most important infectious form).


Transmitted from rats by flea bites, by handling infected animal tissues, or airborne by aerosol from animals or humans with pneumonic plague.


There are natural foci of plague infection of rodents in many parts of the  world. Wild rodent plague is present in central, eastern and southern Africa, South America, the western part of North America and in large areas of Asia. In some areas, contact between wild and domestic rats is common, resulting in sporadic cases of human plague and occasional outbreaks.

In Southeast Asia, Myanmar and Vietnam report the highest number of cases.

Plague should be suspected in anyone with fever and painful lymphadenopathy who has been to an endemic country.

There are three principal clinical presentations:

  • Bubonic plague: initial fever, headache, myalgia followed by painful acute regional lymphadenopathy (pathognomonic bubo), typically involving the inguinal, axillary or cervical regions. If left untreated, rapid progression to septicaemia and secondary plague pneumonia occurs (fatality 50 - 60%).
  • Septicaemic plague: occurs when Y. pestis invades the bloodstream. It can follow bubonic plague or occurs without detectable lymphadenopathy (primary septicaemic plague). Complications include septic shock, disseminated intravascular coagulation, meningitis and multiorgan failure.
  • Pneumonic plague: the least common but the most dangerous and fatal form of the disease. It can develop as a complication of septicaemic plague or be acquired directly by inhalation of aerosols from a human or animal with pneumonic plague. The signs include severe pneumonia, fever, dyspnoea and often haemoptysis. Patients who do not receive treatment within 18 hours of onset of respiratory symptoms are unlikely to survive.

  • Blood, bubo aspirate, sputum/throat swab, necropsy material can be sent for isolation of Y. pestis.
  • Acute and convalescent serology for fourfold rise in titre. A single titre >1:16 is suggestive.
  • Inform the laboratory beforehand so that arrangements can be made to forward samples if necessary to the Department of Pathology, Singapore General Hospital, or other designated sites.

A legally notifiable disease in Singapore. Notify Ministry of Health (Form MD 131 or electronically via CD-LENS) not later than 24 hours from the time of diagnosis. Call MOH Communicable Diseases Surveillance team at: 98171463 immediately on suspicion.

All cases must be managed at the Communicable Disease Centre (CDC).

Gentamicin, streptomycin, chloramphenicol or tetracycline are highly effective if used within hours of presentation.

  • Patients with uncomplicated infection who are promptly treated present no health hazard to others.
  • Those with cough and other signs of pneumonia must be placed in strict respiratory isolation for at least 48 hours after the institution of antibiotic therapy or until the sputum culture is negative.
  • Bubo aspirate and blood must be handled with gloves and aerosolization of these materials should be avoided.
  • Laboratory workers must be alerted to exercise precautions although standard bacteriological techniques that safeguard against skin contact and aerosolization should be adequate.

  • All cases will be isolated at CDC, Tan Tock Seng Hospital.
  • Case investigations will be carried out and contact tracing will be intensified.
  • In the event of death, proper disposal of the body is important.
  • Cases and close contacts, including their clothing and personal belongings, will be disinfected with insecticide dusting.
  • Anti-flea measures and rodent trapping will be increased at the focus of transmission.
  • The public and the World Health Organisation will be informed of all suspected and confirmed cases.
  • The public will be advised to step up measures to prevent rodent infestation in the premises and to avoid contact with rodents (either live or dead).

Consider antibiotic prophylaxis for the following:

  • Persons exposed to patients with pneumonic plague.
  • Persons exposed to bites of wild rodent fleas during an outbreak or to tissues/fluids of a plague-infected animal.
  • Persons travelling to highly endemic area for short duration.

For adults, doxycycline is the best choice (100mg orally bd for 7 days). Trimethoprim-sulfamethoxazole is a suitable alternative.

A formalin-killed plague vaccine has been used for the following groups:

  • Travellers to endemic or hyperendemic areas.
  • Individuals who must live and work in close contact with rodents.
  • Laboratory workers who must handle live cultures of Y. pestis.
  • Military personnel deployed in plague-endemic areas.

This vaccine is not routinely available in Singapore.


  1. Perry RD, Fetherston JD. Yersinia pestis-etiologic agent of plague. Clin Microbiol Rev 1997; 10:35- 66
  2. CDC (Atlanta). Information on plague. Available at: Accessed Aug 2010.
  3. Plague as a biological weapon: medical & public health management. JAMA 2000; 283:2281-90

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