Plague

Part of the Communicable Disease Control Manual

Chapter last reviewed and updated in May 2012.

Contents


Epidemiology in New Zealand

Twenty-one cases of plague were recorded in New Zealand between 1900 and 1911, but none has been recorded since then. However, both species of rodent flea necessary for the transmission of the plague bacteria Yersinia pestis exist in New Zealand.

More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website.

Case definition

Clinical description

A disease characterised by fever and leucocytosis presenting in one of the following ways:

  • regional lymphadenitis (bubonic plague)
  • septicaemia (septicaemic plague)
  • pneumonia (pneumonic plague).

Laboratory test for diagnosis

Laboratory confirmation requires at least one of the following:

  • isolation of Y. pestis
  • four-fold or greater rise in antibody to Ypestis.

Discuss laboratory testing with the Enteric Reference Laboratory at ESR.

Case classification

  • Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
  • Probable: A clinically compatible illness with a single serological positive test.
  • Confirmed: A clinically compatible illness that is laboratory confirmed.
  • Not a case: A case that has been investigated and subsequently found not to meet the case definition.

Spread of infection

Incubation period

From 1–7 days; may be a few days longer in immunised people who develop illness. Primary plague pneumonia has a shorter incubation period of 1–4 days.

Mode of transmission

Most often transmitted by the bite of infected rodent fleas. Domestic pets or rodents can carry the infected flea into the house. Other potential routes of spread include handling the tissue of an infected animal (especially a rodent or rabbit), contact with pus from suppurating buboes, inhalation of respiratory secretions from infected pets (for example, cats) and inhalation of droplets from coughing cases with pneumonic plague.

Period of communicability

Fleas remain infective for some months. Person-to-person spread in bubonic plague occurs if the lesions are suppurating. The risk of transmission is substantially reduced after 48 hours of antimicrobial treatment. Pneumonic plague may be highly communicable under appropriate climatic conditions, such as overcrowding and cool temperatures.

Notification procedure

Attending medical practitioners or laboratories must immediately notify the local medical officer of health of suspected cases. Notification should not await confirmation.

Management of case

Investigation

Obtain a history of travel, vaccination, flea bites, contact with other human cases, recent hunting or trapping and contact with dead or sick animals.

Ensure laboratory confirmation by culture of blood, aspirated bubo fluid, sputum or cerebrospinal fluid has been attempted.

Restriction

In a health care facility, contact isolation precautions should apply to cases with suppurating buboes, and droplet isolation precautions should apply to cases with pneumonic plague. These precautions should continue at least until 48 hours of antimicrobial agents have been given and the case has clinically improved.

Exclude from work, early childhood service, school and close contact with previously unexposed people until the period of communicability is over.

Treatment

Cases should be under the care of an infectious diseases physician.

Counselling

Advise the case and their caregivers of the nature of the disease and its mode of transmission. Educate about hygiene, especially cough hygiene, hand cleaning and the need to cover discharging buboes with a dressing.

Management of contacts

Every effort should be made to locate contacts and unreported cases or undiagnosed cases.

Definition

All people with unprotected household or face-to-face contact with a case of pneumonic plague during the period of symptoms and until 48 hours after administration of effective antimicrobial therapy.

Investigation

Nil unless symptomatic.

Restriction

Contacts who refuse chemoprophylaxis must be quarantined and carefully observed for 7 days.

Prophylaxis

Options include doxycycline and ciprofloxacin. Standard adult doses are doxycycline 100 mg twice daily or ciprofloxacin 500 mg twice daily for 7 days after exposure ceases. Standard doses for children are doxycycline 2.5 mg/kg orally bd or ciprofloxacin 10 mg–15 mg/kg orally bd (not to exceed 1 g per day) (Health Protection Agency 2008).

Chloramphenicol can be used as an alternative – discuss with an infectious diseases physician.

Counselling

Advise all contacts of the incubation period and typical symptoms of plague. Encourage them to seek early medical attention if symptoms develop.

Other control measures

Identification of source

Look for other cases in the community. Assess pets in the household for infection or flea infestation. Rid cases, contacts and household pets of fleas. Follow intensive flea control with rodent control, if necessary.

If the case may have been acquired locally, liaise with Ministry for Primary Industries staff to investigate potential animal sources of infection.

Disinfection

Clean and disinfect surfaces and articles soiled with sputum or purulent bubo fluid. For further details, refer to Appendix 1: Disinfection.

Health education

In the event of a locally acquired case, consider a media release and direct communication with local parents, early childhood services, schools and health professionals to encourage prompt reporting of symptoms. In communications with doctors, include recommendations regarding diagnosis, treatment and infection control.

Travellers should be advised to avoid sick or dead animals, and rodent nests and burrows. Insect repellent can protect against rodent fleas.

Control rats on ships and docks and in containerised cargoes before shipment to and on arrival from locations endemic for plague.

Reporting

Ensure complete case information is entered into EpiSurv.

Laboratory notification follows the laboratory notification flowcharts from the Direct Laboratory Notification of Communicable Diseases: National guidelines (Ministry of Health 2007).

Immediately notify any suspected or confirmed cases to the Director of Public Health at the Ministry of Health.

The International Health Regulations (IHR) National Focal Point (NFP) in the Ministry must use the IHR Decision Instrument for any event involving cholera, pneumonic plague, yellow fever, viral haemorrhagic fevers, West Nile fever or any unusual or potentially serious public health event, and then notify the World Health Organization if required.

References and further information

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