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CBRNE - Plague

Author: Demetres G Velendzas, MD, Attending Staff, Department of Emergency Medicine, Manchester Memorial Hospital, Eastern Connecticut Health Network
Coauthor(s): Susan Dufel, MD, FACEP, Program Director, Associate Professor, Department of Traumatology and Emergency Medicine, Division of Emergency Medicine, University of Connecticut School of Medicine
Contributor Information and Disclosures

Updated: May 2, 2007

Introduction

Background

The plague has caused more fear and terror than perhaps any other infectious disease in the history of humankind. It has laid claim to nearly 200 million lives and has brought about monumental changes, such as the end of the Dark Ages and the advancement of clinical research in medicine.

Although still debated by historians, the plague has been responsible for at least 3 great pandemics and multiple epidemics in history. The first spread occurred from the Middle East to the Mediterranean basin during the fifth and sixth centuries AD, killing approximately 50% of the population in these areas. The second pandemic afflicted Europe between the 8th and 14th centuries, destroying nearly 40% of the population. The third pandemic started in approximately 1855 in China, and, although it has been mostly controlled, it is still ongoing.

Alexandre Yersin isolated the plague bacillus, developed an antiserum to combat the disease, and postulated its connection with fleas and rats during the epidemic of 1894. The plague bacillus was named Yersinia pestis in his memory.

Pandemics have succeeded in entrenching the plague in every major continent, with the possible exception of Australia. Unlike smallpox, the plague never will be eradicated. It lives in millions of animals and on billions of fleas that reside on them. It is a disease of the desert, the steppes, the mountains, and the forest.

Although, the plague has been considered a disease of the Middle Ages, recent interest has been spurred by concerns over its use as a potential biological weapon. Aerosolized Y pestis, causing primary pneumonic plague, has been recognized by bioterrorism experts as having one of the highest potentials for adverse public health impacts.

In addition to the concern over its use in acts of terrorism, there are further reasons that may cause a dramatic increase in the number of plague cases worldwide in the years to come. One reason may be the climatic change brought about by global warming. This change is ideal for increasing the prevalence of Y pestis in the host population. A recent study has estimated a more than 50% increase in the plague host prevalence with an increase of 1 degree centigrade of the temperature in spring.¹ Another reason may be the increasing population explosion worldwide, which is bringing humans into ever-increasing contact with wildlife. Lastly, the dramatic population increase will contribute to conditions of overcrowding and poor sanitation—conditions ripe for plague hosts and vectors to flourish in.

Pathophysiology

The etiologic agent of the plague is Y pestis, a facultative anaerobic, intracellular, gram-negative bacillus.

The organism can be transmitted from a host to a human via the bite of a vector, via close contact with infected tissue or body fluids, and via direct inhalation of the bacterium. Currently, the most common form of transmission involves the bite of a vector infected by a host. Infection through an inhalational route would be of concern if the bacillus was aerosolized.

More than 200 different rodents and species can serve as hosts. These include domestic cats and dogs, squirrels, chipmunks, marmots, deer mice, rabbits, hares, rock squirrels, camels, and sheep.

The vector is usually the rat flea, Xenopsylla cheopis. Thirty different flea species have been identified as able to carry the plague bacillus. Other carriers of plague include ticks and human lice.

Rodents resistant to the infection form an enzootic stage that ensures the long-term survival of the bacillus. Occasionally, the infected animals are not resistant to the disease and die. This is known as an epizootic stage and ensures the spread of the organism to new territory. A sylvatic stage occurs when humans are infected from wild animals.

Three forms of the plague exist: bubonic plague, pneumonic plague, and septicemic plague. The bubonic form of the plague involves the pathognomonic "bubo" and is caused by deposition of the bacillus in the skin by the bite of an infected vector. If the vector is a flea, bacillus proliferates in the flea's esophagus, preventing food entry into the stomach. To overcome starvation, the flea begins a blood-sucking rampage. Between its attempts to swallow, the distended bacillus-packed esophagus recoils, depositing the bacillus into the victim's skin.

The bacillus invades nearby lymphoid tissue, producing the famous bubo, an inflamed, necrotic, and hemorrhagic lymph node. Spread occurs along the lymphatic channels toward the thoracic duct, with eventual seeding of the vasculature. Bacteremia and septicemia ensue. The bacillus potentially seeds every organ, including the lungs, liver, spleen, kidneys, and rarely even the meninges.

The most virulent form, pneumonic plague, results from direct inhalation of the bacillus, which occurs from close contact of infected hosts or from aerosolized bacteria such as may occur if used as a biological weapon. A severe and rapidly progressive multilobar bronchopneumonia ensues with subsequent bacteremia and septicemia. Secondary pneumonic plague is caused when an infected patient seeds his or her lungs and airways.

The third type of plague is a primary septicemic plague. This is hypothesized to occur when the bacillus is deposited in the vasculature, bypassing the lymphatics. Early dissemination with sepsis occurs but without the formation of a bubo. This usually is observed in bites to the oral, tonsillar, and pharyngeal area and is believed to occur because of the vascularity of the tissue and short lymphatic distance to the thoracic duct.

Frequency

United States

An average of 10-15 cases per year have been reported during the last few decades. One of the largest animal foci of the plague worldwide is found west of the 100th parallel, in states such as New Mexico, Arizona, Colorado, Utah, and California. Only one case of imported plague has been reported since 1926. Most cases occur during the warmer months of the year. In 2006, 13 human plague cases were reported in the United States, the most since 1994.

International

From 1967-1993, the World Health Organization has reported an annual average of 1666 cases of the plague. The number of actual cases is probably much higher, given the failure of many countries to diagnose and report the plague. Most cases occur in the developing countries of Africa and Asia. Recent outbreaks of the plague have occurred in Vietnam, in India, and in 2006 from the northeastern part of the Democratic Republic of the Congo.

Mortality/Morbidity

• Bubonic plague has a 1-15% mortality rate in treated cases and a 40-60% mortality rate in untreated cases.
• Septicemic plague (primary or secondary) has a 40% mortality rate in treated cases and 100% mortality rate in untreated cases.
• Pneumonic plague (primary or secondary) has 100% mortality rate if not treated within the first 24 hours of infection.

Sex

More than 50% of cases occur in males.

Age

Approximately 50% of cases occur in persons younger than 20 years.

Clinical

History

In general, after an incubation period of 1-6 days, the history suggests a severe and rapidly progressive sepsis.

• Recent travel in the Southwestern and Pacific Coast regions of the United States, particularly in New Mexico, Arizona, California, and Utah, should raise suspicion of a fleabite. Although imported plague is rare, similar suspicion should exist for any recent travel to endemic areas outside the United States. Fewer than 10% of patients recall a prior fleabite.
• Close contact with any potentially infected host or rural environment should raise suspicion for the plague. Historically, the rat has been believed to be the main plague host; however, currently in the United States, the ground and rock squirrels are the most common hosts. In recent years, the domestic cat has emerged as a prominent host that transmits the plague to veterinarians.
• A sudden increase in the incidence of severe pneumonia in previously healthy individuals should raise concern for pneumonic plague.
• Symptoms
  
  
  • Fever
  • Chills
  • Myalgias
  • Sore throat
  • Headache
  • Weakness
  • Malaise
  • Enlarged, painful, swollen lymph node
  • Abdominal pain - Only presenting symptom more common in a patient presenting with septicemic plague (primary blood-borne plague) versus one presenting with bubonic plague
  • Nausea, vomiting (bloody at times)
  • Constipation, diarrhea, and black or tarry stools
  • Gastrointestinal complaints (may precede a bubo)
  • Cough, which may be productive of bloody sputum
  • Shortness of breath
  • Stiff neck (if meningitic infiltration by plague bacillus has occurred)

Physical

In general, after an incubation period of 1-6 days, the plague presents with the physical findings of severe and rapidly progressive sepsis with or without features of pneumonia. Multiple organ involvement occurs. Pneumonic plague may present only as a severe pneumonia.

• Temperature of 37-40.9°C, tachycardia, tachypnea, and hypotension, if in late septic shock
• Inguinal bubo (60%), axillary (30%), cervical (10%), or epitrochlear (10%) (Bubo is usually no greater than 5 cm, extremely tender, erythematous, and surrounded by a boggy hemorrhagic area; patient often flexes, abducts, and externally rotates the hip near an involved inguinal node to reduce pain at the site.)
• Dermatologic findings
  • A maculopapular lesion may be found at the site of the fleabite; however, such lesions commonly are found at autopsy implying that, in the United States, the diagnosis often is not determined until it is too late.
  • Acral cyanosis, ecchymosis, petechiae, and digital gangrene are seen with Y pestis septicemia (from disseminated intravascular coagulation [DIC]).
  • The medieval epithet "Black Death" is thought to have originated from the deeply cyanotic skin, ecchymoses, and/or acral necrosis associated with terminal septicemic and pneumonic plague.
  • The initially rose-colored purpuric lesions most likely gave rise to the child's nursery rhyme "Ring Around the Rosy."
    • "Ring around the rosy" - Rose-colored purpuric macules (may be caused by the Y pestis enzyme that acts alternately as a plasminogen activator or coagulase at various temperatures or may be due to DIC)
    • "Pocket full of posies" - Sweet-smelling flowers that those tending the sick would carry to ward off the stench of disease
    • "Ashes, ashes" - Impending mortality or "A-choo, a-choo" - The sneezing and coughing of pneumonic plague
    • "All fall down" - Death
  • Rare cases of ecthyma gangrenosum–like lesions and carbuncles due to blood-borne Y pestis have been described.
• Diffuse crackles, diffuse areas of dullness to percussion (secondary to patchy consolidation of pneumonic plague), and hemoptysis
• Diffuse abdominal tenderness, with or without guarding, splenomegaly, hematochezia, or heme-positive stools
• Nuchal rigidity and diffuse muscle and joint tenderness
• Various degrees of mental status changes, ranging from mild confusion or agitation to delirium and coma
• Seizures
• Bleeding from any body site or cavity (eg, hematemesis, hematochezia, hemoptysis)
• Gangrene and necrosis of areas such as the digits, penis, and nares (ascribed to peripheral thrombosis secondary to DIC)
• Pharyngitis culture positive for Y pestis has been seen in endemic areas in household contacts of those with bubonic plague. These patients also have associated cervical lymphadenopathy.

Causes

The etiologic agent is Y pestis, a facultative anaerobic, intracellular, gram-negative bacillus. The following are some epidemiologic factors that suggest an increased likelihood of infection with the plague:

• Rural or nonurban residency, especially in geographic areas with known plague foci
• Contact with sick animals, small rodents, or other possible hosts
• Wilderness activities (eg, camping, hiking, sleeping on ground, hunting)
• Fleabite
• Recent plague in the community
• Occupation as a veterinarian
• Summer months
• Sudden influx of previously healthy patients with severe pneumonia, especially if geographically clustered

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