Epilogue • 279ondary hosts can be as disparate as rabbits, camels, and humans. The plague
microbe Yersinia pestishas been able to adapt to a wide variety of mammals.
The virtually inaccessible burrows of its wild rodent hosts are scattered
throughout the globe. The host usually becomes infected by fleabites and in
rare cases from contact with the soil. Fleas serve as vectors by feeding on in-
fected rodents and transferring the bacteria to new hosts. This happens when
uninfected rodents share nests or burrows with infected ones. Even if exter-
minators reached these remote areas and destroyed their occupants, the bac-
teria could survive for years in the den of the dead animals. The arrival of the
next occupiers of the nests would trigger a new epizootic, potentially leading
to a human epidemic.^33
As the twenty-first century begins, we are on the threshold of a new rela-
tionship with this dread disease. The early microbe hunters, led by Pasteur
and Koch and their protégés Alexandre Yersin and Shibasaburo Kitasato,
laid the groundwork by identifying the microbe. The twentieth century fol-
lowed with a detailed mapping of its cycle of transmission, the development
of effective vaccines and antibiotics, and the sequencing of the DNA of Yer-
sinia pestis.
But is it certain that this Yersinia pestisof the third plague pandemic also
caused the two plague pandemics that preceded it? Some skeptics suggest an
entirely different pathogen, such as the Ebola virus or anthrax, as the micro-
bial source of early plague visitations.^34 Yet it seems impossible that Ebola
could maintain itself during such large-scale epidemics. In Africa, Ebola at-
tacks have wound down after an initial wave of cases. Similarly, anthrax is
not able to create a sizable bubo and would probably not leave such large
numbers dead in the streets as are described in seventeenth-century ac-
counts. Anthrax bacteria can be found in the soil, and spores can exist on the
hair or wool of animals (causing so-called “wool-sorters disease”), but the
pathogen is most lethal in an airborne spore form. Human mortality from
anthrax infection is not as great as with plague; furthermore, it cannot be
passed from person to person.
Most microbiologists remain convinced that the causative plague organ-
ism,Yersinia pestis,has been the same in all pandemics. Testing this belief,
Dr. Julian Parkhill and his colleagues at the Sanger Center in Cambridge
have decoded the complete DNA sequence of Yersinia pestis.Genetically,
this microbe has remained extremely constant through time.^35
These scientific findings fit well with the repeated description, across cen-
turies, of the same symptoms appearing on plague victims. The symptoms
described by William Boghurst, Nathaniel Hodges, and Gideon Harvey in