Rat fleas transmit the Yersinia pestis bacteria between infected rodents and humans, causing zoonotic plague. The bacteria can cause three main types of plague - bubonic, pneumonic, and septicemic. Bubonic plague occurs when the bacteria enters through a flea bite and infects lymph nodes, causing swelling. Pneumonic plague develops when the infection spreads to the lungs via droplets. Septicemic plague happens when the infection enters the bloodstream from bubonic or pneumonic plague. Diagnosis involves examining blood, sputum, or infected lymph nodes under a microscope to look for the bacteria.

1. TRANSMISSION
Zoonotic disease (Affects humans and animals)
Rat fleas feeding on infected rodents
Feces of infected fleas
Human infection via skinning, carcasses and droplet
inhalation of infected animals
Flea vectors: Xenopsylla cheopsis, X. astia,
Ceratophyllus fasciatus
Rodent vector in India: gebril, bandicoot
PLAGUE
TYPES & PATHOGENESIS
Bubonic plague
Incubation: 2-5 days
Lymph nodes draining the site of entry of pathogen becomes infected.
Infection at the site of flea bite with minor constitutional symptoms –
pestis minor
Bacilli enters via bites to legs to inguinal lymph nodes are involved –
bubonic groin
Glands enlarge and suppurate
Bacilli enters blood stream causing septicemia
Sometimes hemorrhage on skin, mucosa, Gas gangrene of skin,
fingers, penis
Fatality (untreated)- 30-90%
Pneumonic plague
Sometimes happens during epidemics of bubonic plague
Transmission: droplet infection
Bacilli spreads throughout the lung causing hemorrhagic pneumonia
Cyanosis
Bloody mucoid sputum on coughing(contains large number of bacilli)
Highly infectious, fatal mostly
Septicemic plague
Terminal event in bubonic/ pneumonic plague
Rarely meningitic involvement
No human carrier
Asymptomatic oropharyngeal infection
Other symptoms
Sudden onset of fever, chills, head and body ache, weakness,
vomitting and nausea
TREATMENT
• Streptomycin, Chloramphenicol, Doxycycline
CAUSATIVE AGENT
Bacteria: Yersinia pestis
Gram negative, short bacilli
Primary pathogen of rodents
DIAGNOSIS
• Blood/ sputum/ buboes
• Culture
• Microscopic observation: methylene blue ( Wayson stain)
shows bipolar stained bacilli- “safety pin appearance)
• Antibodies to F1 antigen may be detected by Passive
hemagglutination
• Detection of IgM and IgG ELISA
• Rapid dipstick assay
• PCR
CONTROL
• Vector (rodent and fleas) control
• Vaccine (only for high risk group)
BlackDeath