Plague

Plague, the disease caused by the bacteria Yersinia pestis (Y. pestis), has had a profound impact on human history. In AD 541, the first great plague pandemic began in Egypt and swept across the world in the next four years. Population losses attributable to plague during those years were between 50 and 60 percent.

In 1346, the second plague pandemic, also known as the Black Death or the Great Pestilence, erupted, and within five years had ravaged the Middle East and killed more than 13 million in China and 20–30 million in Europe (one third of the European population).

Advances in living conditions, public health and antibiotic therapy make such natural pandemics improbable, but plague outbreaks following an attack with a biological weapon do pose a serious threat.

Plague is one of very few diseases that can create widespread panic following the discovery of even a small number of cases. This was apparent in Surat, India, in 1994, when an estimated 500,000 persons fled the city in fear of a plague epidemic.

In the 1950s and 1960s, the U.S. and Soviet biological weapons programs developed techniques to directly aerosolize plague particles, a technique that leads to pneumonic plague, an otherwise uncommon, highly lethal and potentially contagious form of plague. A modern attack would most probably occur via aerosol dissemination of Y. pestis, and the ensuing outbreak would be almost entirely pneumonic plague.

More than 10 institutes and thousands of scientists were reported to have worked with plague in the former Soviet Union.

Given the availability of Y. pestis in microbe banks around the world; reports that techniques for mass production and aerosol dissemination of plague have been developed; the high fatality rate in untreated cases; and the potential for secondary spread; a biological attack with plague is a serious concern.

An understanding of the epidemiology, clinical presentation and the recommended medical and public health response following a biological attack with plague could substantially decrease the morbidity and mortality of such an event.

A plague outbreak that develops after the use of a biological weapon would follow a very different epidemiologic pattern than a naturally occurring plague epidemic.

The size of a pneumonic plague epidemic following an aerosol attack would depend on a number of factors, including the amount of agent used, the meteorological conditions and the methods of aerosolization and dissemination.

A group of initial pneumonic cases would appear in about 1–2 days following the aerosol cloud exposure, with many people dying quickly after symptom onset. Human experience and animal studies suggest that the incubation period in this setting is 1 to 6 days.

A 1970 World Health Organization assessment reported that, in a worst-case scenario, a dissemination of 50 kg of Y. pestis in an aerosol cloud over a city of five million might result in 150,000 cases of pneumonic plague, with 80,000–100,000 people requiring hospitalization and 36,000 expected to die.

There are no effective environmental warning systems to detect an aerosol cloud of plague bacilli, and there are no widely available rapid diagnostic tests of utility. The first sign of a bioterrorist attack with plague would most likely be a sudden outbreak of patients presenting with severe symptoms.

A U.S.-licensed vaccine exists and in a pre-exposure setting appears to have some efficacy in preventing or ameliorating bubonic disease. The mortality of untreated pneumonic plague approaches 100 percent.

Research and development efforts for a vaccine that protects against inhalationally acquired pneumonic plague are ongoing. A number of promising antibiotics and intervention strategies in the treatment and prevention of plague infection have yet to be fully explored experimentally.

Given the fact that naturally occurring antibiotic resistance is rare and the lack of confirmation of engineered antibiotic resistance, the Working Group on Civilian Biodefense at the School believes initial treatment recommendations should be based on known drug efficacy, drug availability, and ease of administration.

People with household or face-to-face contacts with known pneumonic cases should immediately initiate antibiotic prophylaxis and, if exposure is ongoing, should continue it for seven days following the last exposure.

In addition to antibiotic prophylaxis, people with established ongoing exposure to a patient with pneumonic plague should wear simple masks and should have patients do the same.

 Copyright © 2001 The Johns Hopkins University on behalf of its Center for Civilian Biodefense Studies. All rights reserved.