Plague (Yersinia pestis)
|Common Name(s)||Plague; Black Death; Bubonic Plague|
|Scientific Name(s)||Yersinia pestis|
|Physical Attributes||gram-negative coccobacillus, facultatively anaerobic bacillus|
|Geography||Africa, Asia, South America|
|Mode(s) of Transmission||
|Likely BW Form(s)||Aerosol (in pneumonic form)|
|Host(s)||Human; rodents; animals|
|Vector/Dormant Form||Fleas, esp. the Oriental Rat Flea|
|Incubation Period||2-10 days (Bubonic); 2-3 days (Pneumonic)|
|Vaccine||Formalin-killed vaccine no longer avaliable in US|
|Treatment||Antibiotics: oral medications are a tetracycline (such as doxycycline) or a fluoroquinolone (such as ciprofloxacin); injection or intravenous of streptomycin or gentamicin antibiotics|
Plague is a zoonotic disease caused by Yersinia pestis, a worldwide bacteria. Under natural conditions, humans become infected as a result of contact with rodents, and their fleas. The transmission of the gram-negative coccobacillus is by the bite of the infected flea, Xenopsylla cheopis, the oriental rat flea, or Pulex irritans, the human flea. Under natural conditions, three syndromes are recognized: bubonic, primary septicemia, or pneumonic. In a biological warfare scenario, the plague bacillus could be delivered via contaminated vectors (fleas) causing the bubonic type or, more likely, via aerosol causing the pneumonic plague, the most deadly type.
- In bubonic plague, the incubation period ranges from 2 to 10 days. The onset is acute and often fulminant with malaise, high fever, and one or more tender lymph nodes. In the second stage, Inguinal lymphadenitis (bubo) predominates, but cervical and axillary lymph nodes can also be involved. The involved nodes are tender, fluctuant, and necrotic. A third stage of the disease is often respiratory failure or pneumonia.
- Bubonic plague may progress spontaneously to the septicemia form with organisms spread to the central nervous system, lungs (producing pneumonic disease), and elsewhere. The mortality is 50 percent in untreated patients with the terminal event being circulatory collapse, hemorrhage, and peripheral thrombosis (blood clot). Speticemia can spread from person to person through the Pulex irritans, the man-borne flea, and death can occur within hours.
- In primary pneumonic plague, the incubation period is 2 to 3 days. The onset is acute and fulminant with malaise, high fever, chills, headache, myalgia (muscle pain), cough with production of a bloody sputum, and toxemia. The pneumonia progresses rapidly, resulting in dyspnea (shortness of breath), stridor (laryngeal obstruction), and cyanosis (bluish or purplish tint to the skin). In untreated patients, the mortality is 100 percent with the terminal event being respiratory failure, circulatory collapse, and a bleeding diathesis (tendency). Pneumonic plague produces higher mortality and morbidity and unlike the other forms of plague, pneumonic plague is transmittable from person to person.
The World Health Organization (WHO) reports 1,000 to 3,000 cases of plague worldwide every year. An average of 5 to 15 cases occur each year in the western United States. These cases are usually scattered and occur in rural to semi-rural areas. Most cases are of the bubonic form of the disease. Naturally occurring pneumonic plague is uncommon, although small outbreaks do occur. Both types of plague are readily controlled by standard public health response measures.
In cases where bubonic type is suspected, tularemia adenitis, staphylococcal or streptococcal adenitis, meningococcemia, enteric gramnegative sepsis, and rickettsiosis need to be ruled out. In pneumonic plague, tularemia, anthrax, and staphylococcal enterotoxin B (SEB) agents need to be considered. Continued deterioration without stabilization effectively rules out SEB.
Plague may be spread from person to person by droplets. Strict isolation procedures for all cases are indicated. Streptomycin, tetracycline, and chloramphenicol are highly effective if begun early. Significant reduction in morbidity and mortality is possible if antibiotics are given within the first 24 hours after symptoms of pneumonic plague develop.
A formalin-killed Y. pestis vaccine is produced in the United States and has been extensively used. Efficacy against flea-borne plague is inferred from population studies, but the utility of this vaccine against aerosol challenge is unknown.To maintain immunity, boosters every 1-2 years are required. Live-attenuated vaccines are available elsewhere but are highly reactogenic and without proven efficacy against aerosol challenge.
Scientists have hypothesized that a mutation in the CCR5 gene, which confers a certain percentage of the population with natural immunity to the HIV virus, also confers immunity to the Yersinia pestis bacteria.
As of the mid-1990s, the vaccine is no longer avaliable in the US.
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