9. METHODS OF CONTROL

A. Preventive measures:

The basic objective is to reduce the likelihood of people being bitten by infected fleas, having direct contact with infective tissues and exudates, or of being exposed to patients with pneumonic plague.

1) Educate the public in enzootic areas on the modes of human and domestic animal exposure; the importance of rat proofing buildings, preventing access to food and shelter by peridomestic rodents through appropriate storage and disposal of food, garbage and refuse; and the importance of avoiding flea bites by use of insecticides and repellents. In sylvatic or rural plague areas, the public should be advised to use insect repellents and warned not to camp near rodent burrows and to avoid handling of rodents, but to report dead or sick animals to health authorities or park rangers. Dogs and cats in such areas should be treated periodically with appropriate insecticides.

2) Survey rodent populations periodically to determine the effectiveness of sanitary programs and to evaluate the potential for epizootic plague. Rat suppression by poisoning (see 9B6, below) may be necessary to augment basic environmental sanitation measures; rat control should always be preceded by measures to control fleas. Maintain surveillance of natural foci by bacteriologic testing of sick or dead wild rodents and by serologic studies of wild carnivore and outdoor ranging dog and cat populations in order to define areas of plague activity.

Collection and testing of fleas from wild rodents and their nests or burrows may also be appropriate.

3) Control rats on ships and docks and in warehouses by rat proofing or periodic fumigation, combined when necessary with destruction of rats and their fleas in vessels and in cargoes, especially containerized cargoes, before shipment and on arrival from plague endemic locations.

4) Wear gloves when hunting and handling wildlife.

5) Active immunization with a vaccine of killed bacteria confers some protection against bubonic plague (but not primary pneumonic plague) in most recipients for at least several months when administered in a primary series of 3 doses with doses one and two 1-3 months apart followed by dose three 5-6 months later; booster injections are necessary every 6 months if high risk exposure continues. After the third booster dose, the intervals can be extended to every 1 to 2 years. Immunization of visitors to epidemic localities and of laboratory and field workers handling plague bacilli or infected animals is justifiable but should not be relied upon as the sole preventive measure. Routine immunization is not indicated though for most persons living in enzootic areas such as the western USA. Live attenuated vaccines are used in some countries, but may produce more adverse reactions and there is no evidence that they are more protective.

B. Control of patient contacts and the immediate environment:

1) Report to local health authority: Case report of suspected and confirmed cases universally required by International Health Regulations, Class 1 (see Communicable Disease Reporting). Because of the rarity of naturally acquired primary plague pneumonia, even a single case should inititate prompt consideration by both public health and law enforcement authorities of a bioterrorist/biowarfare exposure.

2) Isolation: Rid patients, and especially their clothing and baggage, of fleas using an insecticide effective against local fleas and known to be safe for people; hospitalize if practical. For patients with bubonic plague (if there is no cough and the chest x-ray is negative) drainage and secretion precautions are indicated for 48 hours after start of effective therapy. For patients with pneumonic plague, strict isolation with precautions against airborne spread is required until 48 hours of appropriate antibiotic therapy have been completed and there has been a favorable clinical response (see 9B7, below).

3) Concurrent disinfection: Of sputum and purulent discharges and articles soiled therewith. Terminal cleaning. Bodies of people and carcasses of animals that died of plague should be handled with strict aseptic precautions.

4) Quarantine: Those who have been in household or face to face contact with patients with pneumonic plague should be provided chemoprophylaxis (see 9B5, below) and placed under surveillance for 7 days; those who refuse chemoprophylaxis should be maintained in strict isolation with careful surveillance for 7 days.

5) Protection of contacts: In epidemic situations where human fleas are known to be involved, contacts of bubonic plague patients should be disinfested with an appropriate insecticide. All close contacts should be evaluated for chemoprophylaxis. Close contacts of confirmed or suspected plague pneumonia cases (including medical personnel) should be provided with chemoprophylaxis using tetracycline (15-30 mg/kg) or chioramphenicol (30 mg/kg) daily in 4 divided doses for 1 week after exposure ceases.

6) Investigation of contacts and source of infection: Search for people with household or face to face exposure to pneumonic plague, and for sick or dead rodents and their fleas. Flea control must precede or coincide with antirodent measures. Dust rodent runs, harborages and burrows in and around known or suspected plague areas with an insecticide labeled for flea control and known to be effective against local fleas. If nonburrowing wild rodents are involved, insecticide bait stations can be used. If urban rats are involved, disinfest by dusting the houses, outhouses and household furnishings; dust the bodies and clothing of all residents in the immediate vicinity. Suppress rat populations by well-planned and energetic campaigns of poisoning and with vigorous concurrent measures to reduce rat harborages and food sources.

7) Specific treatment: Streptomycin is the drug of choice, gentamicin can be used when streptomycin is not readily available; tetracyclines and chioramphenicol are alternative choices. Chioramphenicol is required for treatment of plague meningitis. All are highly effective if used early (within 8-18 hours after onset of pneumonic plague). After a satisfactory response to drug therapy, reappearance of fever may result from a secondary infection or a suppurative bubo that may require incision and drainage.

C Epidemic measures:

1) Investigate all suspected plague deaths with autopsy and laboratory examinations when indicated. Develop and carry out case finding. Establish the best possible facilities for diagnosis and treatment. Alert existing medical facilities to report cases immediately and to use full diagnostic and therapeutic services.

2) Attempt to mitigate public hysteria by appropriate informational and educational releases through the press and news media.

3) Institute intensive flea control in expanding circles from known foci.

4) Implement rodent destruction within affected areas only after satisfactory flea control has been accomplished.

5) Protect all contacts as noted in 9B5, above.

6) Protect field workers against fleas; dust clothing with insecticide powder and use insect repellents daily.

D. Disaster implications: 

Plague could become a significant problem in endemic areas when there are social upheavals, crowding and unhygienic conditions. See preceding and following paragraphs for appropriate actions.

E. International measures:

1) Telegraphic notification within 24 hours by governments to WHO and to adjacent countries of the first imported, first transferred or first non-imported case of plague in any area previously free of the disease. Report newly discovered or reactivated foci of plague among rodents.

2) Measures applicable to ships, aircraft and land transport arriving from plague areas are specified in International Health Regulations. These regulations are being revised, but the new regulations will not be in effect until the year 2002 or after.

3) All ships should be free of rodents or periodically deratted.

4) Rat proof buildings at seaports and airports; apply appropriate insecticide; eliminate rats with effective rodenticide.

5) For international travelers, international regulations require that prior to their departure on an international voyage from an area where there is an epidemic of pulmonary plague, those suspected of significant exposure shall be placed in isolation for 6 days after last exposure. On arrival of an infested or suspected infested ship, or an infested aircraft, travelers may be disinsected and kept under surveillance for a period of no more than 6 days from the date of arrival. Immunization against plague cannot be required as a condition of admission to a territory.

6) WHO Collaborating Centres.

F. Bioterrorism measures:

Y. pestis is distributed worldwide; techniques for mass production and aerosol dissemination are available; and the fatality rate of primary pneumonic plague is high and there is a real potential for secondary spread. For these reasons, a biological attack with plague is considered to be of serious public health concern. A few sporadic cases will likely be missed or at least not attributed to a deliberate bioterrorist act. Any suspect case of plague should be reported immediately by telephone to the local health department. The sudden appearance of many patients presenting with fever, cough, a fulminant course and high case-fatality rate should provide a suspect alert for anthrax or plague; if cough is primarily accompanied by hemoptysis, this presentation favors the tentative diagnosis of pneumonic plague. For a suspected or confirmed outbreak of pneumonic plague, follow the treatment and containment measures outlined in 9B above.