Giving the Plague no Quarter in Madagascar


Plague, for very good reasons, is something that will always capture headlines and panic individuals. It is an infectious disease that entirely disrupted civilization on multiple occasions and has become the stuff of legends involving everyone from Roman emperors to Nostradamus. Indeed for most of human history plague, caused by a bacteria that spreads from rodents via the bite of flea, was an existential threat, until it was tamed by scientific discoveries that discovered its origin and its susceptibility to antibiotic therapy. In many parts of the world, this taming of plague has made it a non-issue but a new outbreak on the African island nation of Madagascar has some worrying characteristics that merit swift action to extinguish what could become a larger problem. 

In Madagascar, close to 700 individuals have been infected with 57 succumbing to the infection. What makes this outbreak particularly notable, despite occurring in a country that has hundreds of annual plague cases, is that many of the cases are of the pneumonic form. This form of plague, which involves infection of the lungs, is the form that can be transmitted between humans through coughs and sneezes in little droplets that travel about 3 feet. Also, cases are occurring in urban areas giving the bacteria more opportunity to find new hosts. 

These factors have prompted public health agencies to take prompt actions including the creation of a treatment center and the delivery of antibiotics. So far, the risk of international spread is low -- despite an importation to the Seychelles. However, in the wake of Ebola it is crucial, even in low international risk situations and with effective antibiotic therapies, to not allow infectious diseases to any breathing room 

The Dog Gave Me Plague

The recent detailing of the 4-person cluster of plague cases that occurred in Colorado in 2014 is a fascinating look at how plague, in the modern age, can still cause substantial morbidity. 

People forget that plague is endemic in parts of the US that are west of the "plague line" and we have a handful of cases each year in the US. What was special about this cluster was the involvement of a dog and possible human-to-human transmission in one instance. Additionally, half of the cases of pneumonic plague were mild and didn't require hospitalization, a fact that calls into question the common conception of plague as a universally severe illness.

The index mammal in this outbreak was a dog who was euthanized for an illness that caused bloody-tinged cough. This was subsequently diagnosed as plague and the property on which he lived had inactive prairie dog burrows and rabbits--known means for how the dog may have acquired its fatal affliction.

Didn't realize there was a  movie  with this title, unfortunately its anti-vivisection.

Didn't realize there was a movie with this title, unfortunately its anti-vivisection.

What happened next illustrates the concept of One Health, an approach to medicine and public health in which animal and human health issues are integrated, perfectly: 3-4 contacts of the dog became ill with plague. Of the 4 human cases, 3 had very close contact with the ailing dog and the remaining patient had some contact with the dog but also close contact with the dog's owner, raising the prospect that human-to-human transmission occurred--a phenomenon that hasn't occurred in the US for 70 years.

So, it's time to add spreading plague to the long litany of things, including their favorite pastime of eating homework, to blame on dogs 

Would Gerbils Obey the Pied Piper?

Rats are considered an unavoidable bane of urban life and have been generally associated with filth, disease, and pestilence. One of the most ominous events--The Black Death and the following European plague outbreaks--they have been linked to may not actually have involved them (they would blame it on the fleas anyway).

A new study suggests another rodent might have been to blame: the gerbil (actually the great gerbil from Asia). In this study, Schmid and colleagues looked at climatological data contained in tree rings in Europe and Asia (the traditional home of plague) to determine if such conditions were conducive to rat populations. The study attempts to unravel a few paradoxes regarding plague in Europe: what was the rodent reservoir that allowed plague to persist there (which disappeared in the late 19th century when plague outbreaks tapered off) and was plague something that seeded Europe at the time of The Black Death and persisted in rodent populations there? 

What the evidence presented in this paper suggests is that tree ring data in Europe from the time of known plague outbreaks do not support a climate suitable for rat populations to thrive. However, tree ring data from Asia do show a correlation with a climate conducive to gerbil population booms followed by  busts, forcing resident fleas to look for alternate hosts (i.e. humans and other animals, including rats). This finding is at odds with the traditional view that attributes the presence of plague in an infected European rat reservoir.

The authors speculate that repeated introductions of plague to Europe from Asia occurred to produce each plague outbreak--a finding that may absolve the rat of its role in perpetuating Europe's plague outbreaks. 

This study shouldn't dissuade people from having gerbils as pets as it is not applicable to captive gerbils. Similarly, it shouldn't encourage people to have rats as pets (don't forget about rat bite fever). 

What the study does do, at least for me, is provide another great concretization of how infectious diseases affect and are effected by absolutely everything: animal population, international trade, seasons, and, in the case of the Black Death, perhaps the structure of Western society. 


The "Laptop of Doom" & the Threat of Bioterrorism

Commenting on the ongoing Ebola outbreak, I often note that all the novel medications and vaccines being put in trials are the result of a recognition, post-anthrax, that Ebola could be a potential bioweapon. Almost 13 years have passed since Amerithrax and many have forgotten about the sense of alarm and calamity that gripped the nation in October of 2001. 

The specter of bioterrorism is in the headlines again with the revelation that a laptop found in Syria contained information about using plague as bioweapon. 

Unlike anthrax, plague--caused by the bacterium Yersinia pestis--can be transmissible from person-to-person.

Plague, like anthrax and Ebola, is also classified in the highest priority category (A) and has a long history of use as a bioweapon that stretches back to the times of The Black Death, when a Tartar commander catapulted plague-stricken corpses into the city of Caffa.

In the modern era, the bioweapons programs of the Soviets (and the US) also sought to weaponize plague. One fact that would delimit plague's effectiveness, however, is the fact that it is easily treatable with antibiotics and, upon exposure, prompt administration of antibiotics can abort infection. 

The lesson I draw from the discovery of this laptop is that, despite an absence from the headlines, the threat of bioterrorism is itself not absent. 

Is that Justinian's Plague Caught in-between Your Teeth?

Justinian's Plague, long thought to be the result of infection with Yersinia pestis, was responsible for killing approximately 50 million individuals in 541. Justinian's plague represented the 1st pandemic of plague and was followed about 800 years later by the more famous 2nd plague pandemic, The Black Death. 

In 576, about 35 years following this outbreak, the Roman Empire fell and some historians credit the plague's decimation of the population with weakening the already ailing Empire to the point where it was unable to fend off barbarian attacks (see Justinian's Flea). 

Using a remnant of a tooth found in a burial pit in Germany that dates from the time of Justinian, a research team was able to extract the DNA of the plague bacillus from dental pulp confirming that Y.pestis indeed was the culprit organism. 

It's interesting to imagine what the fate of the world would have been had this plague not occurred. I tend to think that the Roman Empire was already on a death spiral and the plague may only have served to hasten its fall.

Epidemics and their impact on history are a fascinating topic and one of the reasons the subject provides endless enjoyment for me.