Journal of Tropical Diseases & Public Health

Plague

Plague is a serious infectious disease caused by the bacterium Yersinia pestis. This zoonotic disease primarily affects rodents but can be transmitted to humans through flea bites, direct contact with infected animals, or respiratory droplets from an infected person. Plague has a historical significance due to its association with several pandemics, notably the Black Death in the 14th century.

Types of Plague

There are three main forms of plague, each characterized by different clinical manifestations:

• Bubonic Plague:
  • The most common form, characterized by swollen and painful lymph nodes (buboes) near the site of infection, usually after a flea bite.
  • Symptoms include fever, chills, weakness, and swollen lymph nodes.
• Septicemic Plague:
  • This occurs when the infection spreads to the bloodstream. It can develop from untreated bubonic plague or occur on its own.
  • Symptoms include high fever, chills, abdominal pain, and potentially skin necrosis (blackened skin due to tissue death).
• Pneumonic Plague:
  • The most severe form, involving infection of the lungs. It can develop from bubonic plague if the bacteria spread to the lungs or through respiratory droplets from an infected person.
  • Symptoms include severe respiratory distress, coughing up blood, and difficulty breathing.

Transmission

• Flea Bites: The primary mode of transmission. Fleas that have fed on infected rodents can bite humans and transmit the bacteria.
• Direct Contact: Handling tissues or fluids from infected animals can lead to infection.
• Respiratory Droplets: In the case of pneumonic plague, the bacteria can spread through coughs or sneezes from an infected person, allowing for human-to-human transmission.
• Inhalation of Contaminated Particles: Inhalation of aerosols containing the bacteria can also lead to infection.

Symptoms

Symptoms typically appear 2 to 6 days after exposure and vary depending on the type of plague:

• Bubonic Plague:
  • Sudden onset of fever and chills
  • Swollen, painful lymph nodes (buboes), usually in the groin, armpit, or neck
  • Headache and fatigue
  • Muscle aches

• Septicemic Plague:
  • High fever and chills
  • Abdominal pain
  • Nausea and vomiting
  • Skin changes, such as darkening or gangrene in extremities
  • Shock and potential organ failure in severe cases

• Pneumonic Plague:
  • Severe cough with bloody sputum
  • Difficulty breathing
  • Chest pain
  • High fever and chills

Diagnosis

• Clinical Evaluation: Healthcare providers assess symptoms and medical history.
• Laboratory Tests: Diagnosis is confirmed through laboratory tests, which may include:
  • Blood cultures to detect Yersinia pestis in the blood.
  • Swab tests of buboes or respiratory secretions.
  • PCR (Polymerase Chain Reaction) testing to detect bacterial DNA.

Treatment

• Antibiotics: Prompt treatment with antibiotics is critical and effective against all forms of plague. Commonly used antibiotics include:
  • Streptomycin
  • Gentamicin
  • Doxycycline
  • Ciprofloxacin

• Supportive Care: May be necessary in severe cases, including hydration and management of shock.
• Timely Treatment: Early diagnosis and treatment can significantly reduce the risk of complications and death.

Prevention

• Avoiding Contact with Rodents: Reducing exposure to areas where rodents are prevalent.
• Control of Flea Populations: Implementing measures to control fleas on pets and in the environment.
• Personal Protective Measures: Using gloves and masks when handling potentially infected animals or tissues.
• Public Health Surveillance: Monitoring and controlling outbreaks in endemic regions.

Global Impact and History

• Historical Pandemics: The most notable outbreak of plague was the Black Death in the 14th century, which killed an estimated 25 million people in Europe.
• Modern Cases: Plague is still present in parts of Africa, Asia, and the Americas, with sporadic outbreaks occurring.
• Recent Cases: Plague remains a notifiable disease in many countries. The Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) continue to monitor and respond to plague outbreaks.

Prognosis

• Mortality Rates: If untreated, bubonic plague has a mortality rate of about 30% to 60%. septicaemia and pneumonic plagues can be fatal if not treated quickly.
• Outcomes with Treatment: With appropriate antibiotic therapy, the mortality rate for bubonic plague drops to less than 15%, while pneumonic plague can still be highly fatal if not treated within 24 hours.

Zoonotic Importance

• Reservoir Hosts: The primary reservoirs for Yersinia pestis are wild rodents (e.g., rats, squirrels) and other small mammals. Fleas serve as vectors, transferring the bacteria from animals to humans.
• Ecosystem Impact: Understanding the ecology of plague is important for preventing outbreaks, particularly in areas where human populations encroach on wildlife habitats.