Plague: Past, Present, and Future.
Given its history, plague is often classified as a problem of the past. However,
it remains a current threat in many parts of the world, particularly in Africa,
where both the number of cases and the number of countries reporting plague
have increased during recent decades. Following the reappearance of plague
during the 1990s in several countries, plague has been categorized as a
Plague is endemic in a variety of wildlife rodent species worldwide in a wide range
of natural habitats, with commensal rats only sometimes playing a role as “liaison”
hosts, carrying plague between the sylvatic reservoir and people. Various other
animal-to-human transmission pathways have been documented. Human plague
may be contracted from (1) being bitten by the fleas of wildlife rodent species in
rural settings or of commensal rodents that move freely between villages and the
forest habitats occupied by reservoir hosts; rodents' movements have become
more frequent as human activity has fragmented the forest ; (2) eating infected
animals such as guinea pigs in Peru and Ecuador or camels that contract the disease
from rodent fleas in Central Asia and the Middle East ; or (3) handling cats infected
through the consumption of plague-infected rodents in Africa or the United States.
Human-to-human transmission also occurs, either directly through respiratory
droplets or indirectly via flea bites.
Over the last 20 years, there have been 1,000 to 5,000 human cases of plagues
and 100 to 200 deaths reported to the World Health Organization each year. However,
because of poor diagnostic facilities and underreporting, the number of cases is
almost certainly much higher. Over the years, there has been a major shift in cases
from Asia to Africa, with more than 90% of all cases and deaths in the last five
years occurring in Madagascar, Tanzania, Mozambique, Malawi, Uganda, and
the Democratic Republic of the Congo (DRC). Most are cases of bubonic plague
contracted through contact with infected rodents and fleas. However, outbreaks
of pneumonic plague still occur: the most recent large one was in October and
November 2006 in DRC, with hundreds of suspected cases, and a smaller outbreak
arose just across the border in nearby Uganda in February 2007. In December
2004 there was a pneumonic outbreak in a miners' camp in DRC, probably imported
by an infected human who had travelled from an endemic zone. One pneumonic case
even arrived in Kisangani, a large city several hundred kilometers away. So even
rapid-reaction medical teams may not be sufficient to stop plague from spreading
quickly over long distances before it is detected and managed.
In Africa, poor rural communities typically live in close proximity to rodents, which
are widely hunted and eaten in many plague-endemic areas. Superstitions, lack of
money, and distance from health facilities often lead to delays in seeking health
care and receiving treatment. The public health system in large parts of Africa is
poorly organized and equipped, and political crisis and social disorganization
impede improvements. Finally, anthropogenic changes to the landscape and to
patterns of human mobility are increasingly favoring contact between
plague-reservoir and peridomestic rodents, and between people from
plague-endemic and previously unaffected regions.
Plague cannot be eradicated, since it is widespread in wildlife rodent reservoirs.
Hence, there is a critical need to understand how human risks are affected by the
dynamics of these wildlife reservoirs. For example, the likelihood of a plague
outbreak in North American and Central Asian rodents, and the resulting risk to
humans, is known to be affected by climate. Recent analysis of data from
Kazakhstan shows that warmer springs and wetter summers increase the
prevalence of plague in its main host, the great gerbil. Such environmental
conditions also seem to have prevailed during the emergence of the Second
and Third Pandemics—conditions that might become more common in the future.
Outbreaks are usually tackled with a fire-fighting approach. Teams move into an
infected area to kill fleas with insecticides, treat human cases, and give
chemoprophylaxis to exposed people. Many experts have argued that this
crisis-management approach is insufficient as the outbreak is likely to be on the
wane by the time action is taken. Informed, pre-emptive decisions about plague
management and prevention before outbreaks occur would certainly be more
sustainable and cost-beneficial. There has been some recent progress, such as
development of rapid diagnosis tools, some challenging of accepted dogma about
the dynamics of sylvatic plague in the United States and in Central Asia, and the
identification of predictive critical rodent abundance thresholds for plague in
Kazakhstan. What is striking, though, is our lack of understanding of this high-profile
disease in even the best-studied foci, particularly in Africa: often, we do not
even know the natural reservoir of the bacilli.
Finally, we should not overlook the fact that plague has been weaponized throughout
history, from catapulting corpses over city walls, to dropping infected fleas from airplanes,
to refined modern aerosol formulations. This type of research on the weaponized use of
plague was carried out from before World War II until the 1990s and fueled a fear of
biological warfare that may actually have stimulated research into surveillance and
response strategies. More recently, however, fear of small-scale bioterrorism and the
desire of governmental authorities to more fully control all access to plague materials
risks stifling the research on plague ecology, epidemiology, and pathophysiology that is
required to improve its clinical management in endemic areas. Terrorist use of an
aerosol released in a confined space could result in significant mortality and widespread
panic, and no one would wish plague weaponized knowledge and material to fall into
terrorist hands. However, the need for scientifically sound studies on the dynamics of
infection, transmission, outbreak management, and improved surveillance and
monitoring systems has never been greater.
Plague may not match the so-called “big three” diseases (malaria, HIV/AIDS, tuberculosis)
in numbers of current cases, but it far exceeds them in pathogenicity and rapid spread under
the right conditions. It is easy to forget plague in the 21st century, seeing it as a historical
curiosity. But in the opinion of these writers, plague should not be relegated to the sidelines.
It remains a poorly understood threat that we cannot afford to ignore.
Stenseth, Nils Christian, Bakyt B. Atshabar, Mike Begon, Steven R. Belmain, Eric Bertherat, Elisabeth Carniel, Kenneth L. Gage, Herwig Leirs, and Lila Rahalison. "Plague: Past, Present, and Future." PLOS Medicine (January 15, 2008): n. pag. Journals.plos.org. PLOS. Web. 20 Mar. 2016.
Consider the sentence in lines 81-83:
Plague may not match the so-called “big three” diseases (malaria, HIV/AIDS, tuberculosis) in numbers of current cases, but it far exceeds them in pathogenicity and rapid spread under the right conditions.
What does the word "pathogenicity" mean?