Microbiology
A little gram-negative rod (aka coccobacillus) that can have bipolar staining. Y. enterocolitica, Y. frederiksenii, Y. intermedia, Y. kristensenii, Y. pestis, Y. pseudotuberculosis and others.
It may be misidentified by some automated systems and delay the diagnosis (Pubmed).
Epidemiologic Risks
Y. pestis is found in burrowing rodents. From the CDC web site: "In North America, plague is found from the Pacific Coast eastward to the western Great Plains and from British Columbia and Alberta, Canada southward to Mexico. Most of the human cases occur in two regions; one in northern New Mexico, northern Arizona, and southern Colorado, another in California, southern Oregon, and far western Nevada." It came to the US from Asia with the advent of the steamship. The first outbreak was in San Francisco where the city fathers tried to cover up the problem.
Plague is classically spread by fleas, in the US over 50% are from animal exposure (Pubmed).
Also found in SE Asia, Africa (especially Madagascar) and China. In Africa, increased rainfall presages plague. Rain means plants means food for rodents means a booming rodent population and with it comes death from plague. And Hanta.
There was a cluster of pneumonic plague in China when a dog gave it to its master, who then gave it to 12 others.
In Madagascar the Asian house shrew Suncus murinus is the reservoir (PubMed), so Petruchio was just trying to keep Padua from getting plague from Kate (explanation for the Shakespeare impaired).
Dogs and cats are common vectors in the US. They kill a rodent, or just sniff the prairie dog (PubMed), get plague and pass it on to their owners. Cats are more likely to get and give pneumonic plague (PubMed). So avoid the coughing cat, it may be hacking up more than a hairball.
In modern Uganda, history repeats itself with an unusual number of dead rats a harbinger of outbreaks where 1 in 4 dies (PubMed).
Nice historical review. This organism has been plaguing humans for millennia. Get it? Plaguing? I am soooooo clever.
Y. enterocolitica, Y. pseudotuberculosis: a wide variety of domestic and wild animals.
Syndromes
Y. pestis: plague (review). Three clinical presentations:
1) Bubonic plague: enlarged, tender lymph nodes, fever, chills, and prostration.
2) Septicemic plague: fever, chills, prostration, abdominal pain, shock and bleeding into skin and other organs, a purpura fulminans syndrome, a similar presentation can also be caused by Capnocytophagia canimorsis, N. meningitis, and S. pneumoniae (especially in the asplenic).
3) Pneumonic plague: fever, chills, cough, and difficulty breathing; rapid shock and 100% fatal in 72 hours if antibiotics are delayed more than 18 hours after the onset of respiratory symptoms. Infectious: put in respiratory isolation (CDC web site).
Y. enterocolitica, Y. pseudotuberculosis: diarrhea, sepsis in compromised hosts and those with iron overload states, and pharyngitis.
Y. enterocolitica can cause transfusion sepsis, usually from old pints (blood, not beer). It multiplies nicely in cold and needs iron, which occurs after a couple of weeks as the red cells start to break down (PubMed).
Y. pseudotuberculosis: mesenteric adenitis; can mimic acute appendicitis. And in the Far East a Scarlet-Like Fever syndrome (PubMed).
Treatment
Y. pestis: for historical reasons, in order of preference, gentamicin, streptomycin, doxycycline /tetracycline, OR chloramphenicol are the recommended agents, however, I bet all aminoglycosides, piperacillin, quinolones and third-generation cephalosporins will work (although not suggested), one of which most people will get for empiric sepsis anyway.
Oral ciprofloxacin was effective in Africa, but I would start with iv in the US (PubMed)
There was a naturally occurring strain with multiple resistance (chloramphenicol, streptomycin, and tetracycline, sulfonamides and tetracycline) in Madagascar (PubMed), and bioterrorism strains will likely be resistant as well.
Y. enterocolitica, Y. pseudotuberculosis: aminoglycosides, doxycycline, piperacillin, and quinolones.
Notes
There is an interesting book "The Biology of Plagues" that makes a compelling argument that the black death of the middle ages was NOT due to Y. pestis. However, when they have dug up patients from plague pits, it is the DNA of Y. pestis they find in the pulp of teeth.
On the basis of dental pulp, it was responsible for Plague of Justinian and "Y pestis lineages that caused the Plague of Justinian and the Black Death 800 years later were independent emergences from rodents into human beings (PubMed)."
Y. pestis may be used for bioterrorism. Back in the 16th century, there was a plan to use "a liquid made from the spleens and buboes of plague victims" (aka Mountain Dew) as a weapon to end a siege (PubMed).
An agent of bioterrorism, the Soviets probably bioengineered a strain to be resistant to antibiotics, which has also occurred naturally in Madagascar.
Curious Cases
Relevant links to my Medscape blog
Last Update: 11/29/19.