Tracking a Live Yersinia pestis Infection with Bioluminescence

The day has finally arrived when an experimental infection can be tracked real-time over the entire course of the infection. Developing a natural history of a rapidly lethal infectious disease has been a challenge because individual variation clouds the progression and individuals can only be studied after death.

The traditional method to study these infections involves infecting many animals so that cohorts of animals can be sacrificed at set time points, have their organs harvested and bacterial load of the organ determined. Some of the flaws of this method are that the right organs may not be selected to survey and individual variation in infection progression means that wide variation may be found at the time points.

Tracking the progression of an infection with bioluminescence allows the infection to run its full course within each experimental animal, rather than taking cohorts at time points. Elizabeth Carniel’s lab at the Institut Pasteur in Paris created bioluminescent Yersinia pestis, and after doing all the controls to ensure a consistent signal under all growth conditions, demonstrated that a live bubonic plague case can be tracked real-time until  death .

In the first figure below the mouse was sacrificed before septicemia set in to correlate the external signals with specific organs. The bioluminescent Y. pestis was injected at the midline near the navel into the linea alba, a tendon-like covering of the abdominal muscles, to simulate a flea bite. Signals represent the injection site, lymph nodes, and the spleen and liver.

Identifying the bioluminescent signals by dissection. 1. axillary lymph nodes, 2. liver, 3. injection site, 4. inguinal lymph node, and 5. spleen. (Nham et al, 2012)

For 74% of the animals injected, the infection followed the same spread pattern. In all the animals the injection site was lit up from the first day. From there it spread to the inguinal lymph node and then surprisingly to the axillary lymph node. The signal then concentrated in the spleen and liver before it becomes completely systemic. Nham et al (2012) note that the signal completely covers the animal from the their ears to the tails. Confirmation of septicemia came from Y. pestis isolated from blood after the death of the animal. Death occurred on average by the sixth day, coming very quickly after septicemia.

Progression of a bubonic plague infection (Nham et al, 2012)

Some of the mice provided clues on how the bioluminescence jumped from the inguinal node to a axillary node. As the linear glow below suggests, they found a lymph vessel that connects the inguinal node to the axillary node. It is consistent with Y. pestis spreading to linked lymph nodes. Confirmation of the lymph vessel linking the inguinal and axillary nodes is shown by bioluminescence and by dye injected dissected mouse in the figure below.

Identification of the lymph vessel connecting inguinal and axillary lymph nodes. (Nham et al, 2012)

The signal next appears under the diaphragm in areas consistent with the liver and spleen (shown in the first figure). This would not necessarily be a direct line from the axillary lymph node to the spleen and liver but that the spleen and liver became infected at about the same time as the axillary node. Colonization of the liver and spleen are related to their blood clearing functions and are indications of a very early phase of septicemia too low to yield systemic bioluminescence.  Death occurred on average by the sixth day, coming very quickly after septicemia.  Nham et al (2012: 5) report that their “results revealed two important phenomena: (i) the variations in the kinetics of bacterial spread were essentially attributable to the length of time the signal remained limited to the injection site, and (ii) as soon as the signal reached lymph nodes, the disease progressed very rapidly, leading to the animal death within two days.” Time between the injection site and first lymph node varied from one to seven days.

The 26% of mice that did not follow this pattern died rapidly with symptoms of a direct septicemic infection (skipping lymph node signals entirely). This suggests that they either hit a blood vessel at the injection site or may have penetrated the abdominal cavity with the injection.

This study is an important first step in developing the method. From here there are many studies than could be done including the effect of changing individual genes on virulence and progression.

Reference:

Nham, T., Filali, S., Danne, C., Derbise, A., & Carniel, E. (2012). Imaging of Bubonic Plague Dynamics by In Vivo Tracking of Bioluminescent Yersinia pestis PLoS ONE, 7 (4) DOI: 10.1371/journal.pone.0034714

Primary Pneumonic Plague Transmission in the USA, 1900-2009

Pneumonic plague is a difficult phenomenon to model. We really don’t have much data from the modern medical era. Hinckley et al. (2012) argue that most of the data studied to date has been biased by taking it from well-established epidemics. To better study all transmission conditions, they gathered all of the cases of primary pneumonic plague in the United States between 1900 and 2009. Their data set, divided into pre- and post-antibiotic era, is really what interests me the most.

The demographics of the two eras tell very different stories. There were 60 cases before 1943, 92% of which occurred in California, 86% in three epidemics (San Francisco 1904, Oakland 1919, and Los Angles 1924). A full 83% of these cases came from documented human contact. After 1943, there have only been 14 cases from south-western states. Of these, 64% came from animal contact and another 21% from laboratory exposure. None of the post-1943 set obtained the infection from human contact. Obviously, the use of antibiotics is not the only difference between these two sets. Sheer number of cases and source of infection are very different.

In both data sets, the overwhelming number of cases failed to transmit the infection. In the antibiotic era, there have been no documented cases of human-to-human transmission of pneumonic plague in the US. On the other hand, in the pre-antibiotic era, where most cases come from epidemics, 8% of the cases transmitted to two or more people.

When it comes to pneumonic plague, antibiotics are not the panacea that is usually implied. In the antibiotic era, the mortality rate was “only 36%”, down from 92% in the pre-antibiotic era. So in other words, pneumonic plague today has approximately the same mortality rate as smallpox. Comforting.

Their models suggest that in the vast majority of instances pneumonic plague quickly reaches extinction due to poor transmission with traditional control measures. The important caveat is that super spreading events early in the outbreak can lead to an explosive increase in case numbers. In one case from 1924 Los Angles, one man transmitted pneumonic plague to 26 others. With the primary concern in the United States being bioterrorism,  response planning for a large plague outbreak will continue with the goal of identifying and containing super spreaders as soon as possible, while knowing that most cases will fail to transmit to anyone.

Reference:

 Hinckley AF, Biggerstaff BJ, Griffith KS, & Mead PS (2012). Transmission dynamics of primary pneumonic plague in the USA. Epidemiology and infection, 140 (3), 554-60 PMID: 21733272

Contagions Round-up 19: Loads of Links for Year’s End

Since my usual fare is not very festive, I’m going to wrap up this year with round-ups and similar stuff.

Holiday Posts

Fungal art from sciencingsara.tumblr.com h/t to The Febrile Muse

A Schooner of Science brings us the science of holly.

Geoffrey Chaucer Hath a Blog brings us a holiday update and some holiday riddles.

Jonathan Jarrett of A Corner of Tenth Century Europe brings us a Christmas Charter madlib if you have any disposable land to unload.

Carl Pyrdum of Got Medieval brings us the war on Christmas,  Uther’s Christmas Knight, and a new medieval marginalia. He also has a guest post by Sir Ten-to-Three on Christmas Past.

Puff the Mutant Dragon brings us the history and science of the Poinsettia.

William Eamon of the Labrynth of Nature brings us the story of Johannes Kepler and the Star of Bethleham.

Continuity of history and science

Continuing with  history of science, Kate Stidham of the group blog Wonders and Marvels tells us about a 17th century text called the Compleat Midwife Practice and its complicated authorship and Lauren Renaud tells us about how the dental woes of the Sun King led to the profession of dentistry.

The History of Vaccines Blog brings us news that mammalian cell lines will be used to produce new influenza vaccines, replacing the 50-year-old egg method. This is also covered by Vincent Rancello of the Virology Blog who argues that this is not the direction we need to be going and also a post on the Megavirus, the largest virus ever found.

Puff the Mutant Dragon also brings us up to date on the recent controversy over lab-bred avian flu and fears that it is a biosecurity risk.

Jennifer Frazer of The Artful Amoeba has a post on the toxic vapors produced by red-tides in the Gulf of Mexico and another on  brain-eating amoebas.

Michael Walsh of Infectious Landscape brings us up-to-date on Amoebaosis of the GI system, sometimes referred to as amoebic dysentery. At his Germscape microblog, Michael Walsh has posted several recent maps on malaria epidemiology, the most recent one can be found here but browse the last several posts for more on malaria. He has also posted the 2011 map of West Nile virus transmission in the European Union.

Maryn McKenna of Superbug has been busy with her bad bugs. Lets start with a good post on the dangers of sleeping with your pet, then on the FDAs failure to stop agricultural antibiotic abuse, and wind up with fecal transplants.

Anthropology

Anthropologist Kate Clancy of Context and Variation writes an important post on the role of science blogging in academia.

Krystal D’Costa of Anthropology in Practice is thinking about toys and finding marbles, and why we deny the sick role.

Patrick Clarkin has an interesting post on the growth differences in growing up in North Korea and South Korea and a post on the opportunity costs of war.

Katy Meyer of  Bones Don’t Lie writes about height variation in medieval Italy, on her frustration over a lack of aging standards for human remains, and about cranial modification (or the original cone heads) and still no discussion of the Huns!!!

Medieval Miscellany

I wrote about an outbreak of plague in Lombardy in the 560s on my blog Heavenfield.

Tim Clarkson of Senchus asks if Merlin really existed?

Mak Wilson of Badonicus writes a two-part post on the mysterious Attacotti people of Roman Britain. Part two is here.

Guy Halsall of Historian on the Edge revisits good ole King Chilperic.

Jonathan Jarrett of A Corner of the Tenth Century brings us a little propaganda stamped right into coinage during the Investiture Controversy.

Esmerald’s Cumbrian History and Folklore explains the relationship between folklore of elf-shot by mermaids and some of our modern medical terms.

Have a Happy New Year and I’ll be back with new content after the New Year.