Plague is often thought of as a disease that occurred in the Middle Ages only, but it is still found in the United States in the Southwest, particularly New Mexico and people die of it every year.
1) caused by infection with Yersinia pestis 2) subtypes – bubonic, septicemic, and pneumonic 3) any subtype can progress in an acute, subacute, or chronic course 4) bubonic plague often converts to septicemic plague
Signs and Symptoms
Bubonic form – abrupt onset of 1) high fever/chills 2) tachycardia 3) headache 4) myalgias 5) enlarged and exquisitely tender femoral, axillary, or inguinal lymph nodes surrounded by edema that suppurate in the second week (buboes) 6) skin lesion at the flea bite site (varies from rash to vesicle to eschar) 7) restlessness/confusion/delirium 8) hepatosplenomegaly Septicemic form – 9) abdominal pain due to mesenteric lymphadenitis 10) sepsis – hypotension, oliguria, renal failure 11) liver and spleen necrosis 12) ecchymoses and petechiae 13) acral gangrene 14) mental confusion and agitation Pneumonic form – abrupt onset of 15) chills/high fever 16) severe headache 17) tachycardia 18) cough developing within 24 hours of onset of fever 19) hemorrhagic sputum (raspberry syrup) 20) tachypnea 21) chest pain
Characteristic Test Findings
Laboratory – 1) White blood cell count 10,000-20,000 per microliter 2) thrombocytopenia (low platelet count) 3) presence of fibrin split products 4) increased AST and ALT 5) increased bilirubin 6) diagnosis is by culture of organism, hemagglutination tests, or ELISA Radiology – 7) on chest radiograph, pneumonic form has rapidly developing pneumonia
1) gram-negative coccobacillus 2) resembles “safety pin” under stain 3) bubonic form has pustules with necrosis and neutrophils 4) septicemic form has lymphadenopathy with necrosis 5) pneumonic form has hemorrhagic and necrotizing bronchopneumonia
virulence factors include – F1 envelope antigen, V antigen, pesticin
1) reservoir is rodent (rats, mice, squirrels, prarie dogs, and occasionally cats) 2) usual vector is via bite of an infected flea, but direct contact with infected animal carcass can transmit the disease 3) transmitted human to human via cough and sprayed droplets 4) 20-25 cases occur in southwest USA each year 5) bubonic form – incubation is 2-5 days, with 50% mortality 6) pneumonic form – incubation is 2-3 days, with mortality almost 100%
1) streptomycin 2) gentamicin 3) tetracyclines
Tips for USMLE
1) the nursery rhyme “ring around the rosy, pocket full of posies, ashes, ashes, we all fall down” is about medieval victims of plague – the rosy ring was the initial rash at the bite site, the pockets were filled with spices and herbs to deodorize the air from the stench of dead bodies, the ashes were the dried blood coughed up, and the fall down was the person’s final collapse and death (okay, probably not going to be on the test 2) think plague if a national park ranger in New Mexico spends two weeks trapping prarie dogs and 3 days later develops a high fever (104 F) and enlarged, extremely tender inguinal lymph nodes.