How is the plague transmitted and what are the methods of prevention and treatment?

Plague Transmission, Prevention, and Treatment

Plague is primarily transmitted to humans through the bite of infected fleas from rodents, direct contact with infected animal tissues, or inhalation of infectious respiratory droplets, with prompt antibiotic treatment being essential for survival, particularly with streptomycin as the drug of choice for plague. 1

Transmission Mechanisms

Plague is caused by the bacterium Yersinia pestis and has three main transmission routes:

1. Flea-borne transmission (most common - 78% of US cases):

   • The Oriental rat flea (Xenopsylla cheopis) and other flea species become infected after feeding on infected rodents 1
   • When rodent populations die during epizootics, fleas seek alternative hosts, including humans 1
   • This route typically leads to bubonic plague, characterized by swollen lymph nodes (buboes) 1

2. Direct contact transmission (20% of US cases):

   • Contact with infected animal tissues or bodily fluids 1
   • Particularly common with handling infected wild or domestic animals 1
   • Can lead to bubonic or septicemic plague 1

3. Respiratory droplet transmission (2% of US cases):

   • Inhalation of infectious droplets from humans or animals with pneumonic plague 1
   • Most dangerous form with nearly 100% fatality if untreated 1
   • Person-to-person transmission occurs primarily through close contact (within 6.5 feet) with symptomatic individuals 1, 2
   • Most cases of pneumonic plague in the US have been linked to exposure to infected cats 1, 3

Clinical Presentations

1. Bubonic Plague (80-90% of cases):

   • Incubation period: 2-6 days 1
   • Characterized by acute regional lymphadenopathy (buboes) 1
   • Additional symptoms: fever, chills, malaise, headache 1
   • Untreated fatality rate: 50-60% 1
   • With treatment: 13% fatality rate 1

2. Pneumonic Plague:

   • Incubation period: 1-3 days 1
   • Symptoms: severe pneumonia, high fever, dyspnea, hemoptysis 1
   • Requires treatment within 18 hours of symptom onset for survival 1
   • Nearly 100% fatal if untreated 1

3. Septicemic Plague:

   • Can be primary or secondary to bubonic plague 1
   • Characterized by bloodstream infection without lymphadenopathy 1
   • Symptoms: fever, gastrointestinal symptoms 1
   • Higher fatality rate than bubonic plague 1
   • Complications: septic shock, coagulopathy, meningitis 1

Prevention Methods

1. Environmental and Personal Protection:

   • Avoid rodent-infested areas, especially where dead rodents have been reported 1
   • Apply insect repellents containing DEET to skin and clothing 1
   • Use appropriate insecticides in homes and surrounding areas 1
   • Treat pets with insecticides to prevent flea infestation 1
   • Reduce food and shelter available to rodents near human dwellings 1

2. Occupational Precautions:

   • Laboratory workers should follow biosafety level 2 precautions 1
   • Veterinary personnel should wear gloves, eye protection, and take respiratory precautions when examining potentially infected animals 1
   • Animal workers should avoid handling sick or dead rodents 1

3. Post-Exposure Prophylaxis:

   • Prophylactic antibiotics for close contacts of pneumonic plague patients 1
   • Isolation of confirmed pneumonic plague patients under droplet precautions until sputum cultures are negative 1

4. Vaccination:

   • Limited efficacy, especially against pneumonic plague 1
   • Recommended only for laboratory personnel routinely exposed to Y. pestis 1
   • May be considered for persons with regular contact with wild rodents in endemic areas 1

Treatment

Antimicrobial Therapy:

• Streptomycin: First-line treatment for plague 4

  • Dosage for plague: 2 grams daily in two divided doses intramuscularly
  • Minimum treatment duration: 10 days
  • Administered intramuscularly in the upper outer quadrant of the buttock or mid-lateral thigh

• Early antibiotic treatment is critical, especially for pneumonic plague where treatment must begin within 18 hours of symptom onset 1

• Supportive care as needed for complications such as septic shock, respiratory failure, or meningitis 1

Important Considerations

• Diagnostic Challenges:

  • Plague is often misdiagnosed initially as severe pneumonia or other infections 5
  • High index of suspicion needed for patients with relevant travel history to endemic areas 3

• Public Health Response:

  • Plague is a reportable disease requiring immediate notification of public health authorities 6
  • Contact tracing and prophylaxis for close contacts of pneumonic plague cases 1

• Mortality Risk:

  • Without treatment, bubonic plague has a 50-60% fatality rate 1
  • Pneumonic plague is almost always fatal without prompt treatment 1
  • Even with treatment, plague carries significant mortality risk, emphasizing the importance of early diagnosis and intervention 1, 5