plague

plague
Name	Plague
Field	Infectious disease
Symptoms	Fever, chills, weakness, swollen lymph nodes
Causes	Yersinia pestis
Diagnosis	Blood test, sputum test, aspiration from a bubo
Prevention	Rodent control, antibiotics, vaccine
Treatment	Antibiotics such as streptomycin, gentamicin, doxycycline
Prognosis	Good with early treatment

plague. Plague is a severe infectious disease caused by the bacterium Yersinia pestis. Historically responsible for devastating pandemics, it primarily affects rodents and is transmitted to humans through the bites of infected fleas. The disease manifests in several clinical forms, with bubonic plague being the most common, and remains a public health concern in certain regions today.

Overview

The disease is a zoonosis maintained in animal reservoirs, particularly among wild rodents. The causative agent, Yersinia pestis, was identified in 1894 by the Swiss-French physician Alexandre Yersin during an outbreak in Hong Kong. Plague has been a defining force in human history, most notably during the Black Death in the 14th century, which originated in Asia and spread via trade routes like the Silk Road to Europe, causing immense mortality. The World Health Organization classifies it as a re-emerging disease, with endemic foci in countries including the Democratic Republic of the Congo, Madagascar, and the United States in areas like the Southwest.

Causes and transmission

Infection is caused by the gram-negative bacterium Yersinia pestis. The primary transmission cycle involves fleas, such as the oriental rat flea (Xenopsylla cheopis), which become infected by feeding on rodents like rats, prairie dogs, or ground squirrels that harbor the bacteria. When these rodent hosts die, fleas seek new sources of blood, potentially biting humans. Direct transmission can also occur through handling infected animal tissues, as seen in hunters handling rabbits or carnivores. In its pneumonic plague form, the disease can spread directly between humans via infectious respiratory droplets, a mode of transmission that played a significant role in outbreaks such as the Manchurian plague of 1910-1911.

Symptoms and diagnosis

Symptoms vary by the form of the disease. Bubonic plague, the most frequent, is characterized by the sudden onset of fever, headache, chills, and painfully swollen lymph nodes called buboes, typically in the groin, armpit, or neck. Septicemic plague can occur primarily or secondarily, causing abdominal pain, shock, and gangrene in extremities, sometimes leading to the condition historically called "Black Death." Pneumonic plague affects the lungs, causing cough, chest pain, and hemoptysis. Diagnosis is confirmed by laboratory testing, including culture of samples from blood, sputum, or aspirate from a bubo, with techniques like polymerase chain reaction and immunofluorescence providing rapid identification.

Treatment and prevention

Prompt treatment with antibiotics is essential to reduce mortality. Streptomycin and gentamicin are the drugs of choice, with alternatives including doxycycline, ciprofloxacin, and chloramphenicol. Supportive care in a hospital setting is critical, especially for severe cases. Prevention strategies focus on controlling rodent populations and flea vectors in endemic areas. Public health measures include surveillance, rapid diagnosis, and isolation of patients with pneumonic plague. A vaccine exists but is generally recommended only for high-risk groups like laboratory personnel and those in endemic regions; its use was more widespread historically, such as for troops during the Vietnam War. Early administration of antibiotics as prophylaxis is recommended for close contacts of infected individuals.

Historical impact

Plague has caused some of the deadliest pandemics in recorded history. The Plague of Justinian in the 6th century, centered in the Byzantine Empire under Emperor Justinian I, severely weakened the empire. The most infamous outbreak, the Black Death, swept through Europe, Asia, and North Africa in the mid-14th century, killing an estimated one-third of Europe's population and causing profound social and economic upheaval, contributing to events like the Peasants' Revolt. A third major pandemic began in Yunnan, China in the 1850s, spreading globally via steamships to port cities like San Francisco, Bombay, and Sydney, and leading to the establishment of modern epidemiology and international health regulations.

In modern times

While no longer a global threat, plague persists as a neglected tropical disease in natural foci around the world. Notable recent outbreaks include a significant epidemic in Madagascar in 2017 and periodic cases in the Western United States in states like New Mexico, Arizona, and Colorado. Research institutions like the Centers for Disease Control and Prevention and the Institut Pasteur maintain active surveillance and research programs. The bacterium is also studied for its pathogenesis and potential as a biological weapon, placing it on lists of select agents regulated by agencies such as the Federal Bureau of Investigation. Ongoing ecological studies investigate the effects of climate change on rodent and flea populations in relation to future outbreak risks.

Category:Infectious diseases Category:Zoonoses Category:Neglected tropical diseases