The plague is back. No, not Ebola, but rather infection with the dreaded bacterium, Yersinia pestis. An outbreak in Madagascar, where the disease is endemic, already has involved more than 100 people and killed almost half. The plague made a brief appearance in China earlier this year and continues in the U.S. with a few cases annually.

The current Madagascar outbreak is of particular concern for two reasons. First, cases have arrived in the capital, Antananarivo, a city of more than 2 million located in the center of the island. As was demonstrated with Ebola, once any infection enters a city, the opportunity for spread is greatly heightened, owing to the dense concentration of people, the paucity of clean air and water, and likelihood that vermin are nearby.

The second concern about the current Madagascar outbreak is that cases of pneumonic plague, a highly contagious and lethal form, have been seen. As I described in an article over the summer when the fatal case in China was diagnosed, plague has three distinct clinical forms. First, bubonic (rhymes with pneumonic but is altogether different) is a local infection sequestered in a lymph node. After an infectious flea bites a person and transmits the infection, the bacteria are carried to the closest upstream lymph node where (hopefully) the infection is contained, even without antibiotics. A patient with bubonic is ill with fever and headache, as well as the large lymph node (or bubo) in the appropriate spot, but not contagious.

Many plague infections, unfortunately, are not contained in the local lymph but rather spill into the bloodstream, causing the second manifestation of plague, septicaemic (or bloodborne) disease. This form often overwhelms the infected person, causing perturbations in clotting and blood vessels that lead to black, devitalized toes and fingers (and feet and toes for some) giving the Black Death its alarming name. Though devastating for the individual, this form is not that large a public health concern.

Spread happens easily, however, and epidemics are propagated when the third form of plague occurs: pneumonia plague. This too is a particularly lethal type with the added problem that once the bacteria heavily invade the lung, causing the pneumonia, an infected person can spread infection simply by coughing at the next person. The eccentric plague suits of the Middle Ages were developed in order to protect the wearer from contracting plague in this manner.

At the root of the trouble is the rat. Though the fleas (Xenopsylla cheopis) on the rat are the actual transmitters of infection, it is the presence of rats, lots and lots of rats, rats crawling out of and into everything, that are the reservoir. And in a city with large slums and poor sanitation, rats can thrive easily, fleas and all, to spread the plague. Given this threat, it is worth recalling the still-important municipal job of rat catcher, a role once held by the Pied Piper of Hamelin as well as Jack Black, Her Majesty’s rat-catcher. Their absence in impoverished cities leads to the rat overrun that sets up the perfect conditions for the plague—which makes the existence of the American Fancy Rat and Mouse Association, a group that promotes rats as household pets, even more difficult to comprehend.

The reason the collision of rats, urban crowding and squalor, and a highly contagious infectious disease is not more alarming as a potential Ebola version 2.0 is simple: antibiotics. We have several effective antibiotics both to treat the plague for those infected, but more importantly for protection of the public, to give to uninfected people who are exposed to an infectious patient. The availability of prophylactic antibiotics further removes the fear quotient for loved ones and healthcare workers called to care for someone sick with plague. Contacts can work in close contact with infectious patients with impunity knowing that the antibiotic will prevent disease acquisition.

There is only one problem with this efficient approach to disease control—a problem very familiar to healthcare in the US: antibiotic resistance. Antibiotic resistant and multiply resistant strains of plague have been described several times over the past decade including particularly resistant forms in Madagascar. Thus the problem of excess—too much antibiotic used for all the wrong indications—year after year, is having an impact in Madagascar, an area of the world where excess is unknown. And this is where the plague outbreak does resemble Ebola—as a grim reminder of the consequences of our global interconnectedness.