What is Plague?
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An electron microscope picture of Yersinia pestis- ...........................................................Y. pestis transmits the bubonic type of plague through a flea
the causative bacterial agent of the plague._....................................................................vector often found on rodents. Diamanus montanus is the flea
...................................................................................................................................... .North America is most concerned with.

That's right- the bubonic plague or Black Death is the number one plague killer with over 100 million total deaths.
See some other infectious disease pandemics in this video clip..

What is the Plague?

Plague is a zoonotic reemerging infectious disease caused by the gram-negative bacillus Yersinia pestis. It is transmitted from rodents to fleas which may come in contact with the human population. Y. pestis is a non-motile, non-spore forming coccobacillus (intermediate between a rod shape and a spherical shape). Y. pestis is sensitive to sunlight and cannot survive long outside the host but can live for years in animal carcasses.

Studying the genome of the bacterium, comparing the Black Death strains to the modern strains, they discovered that the genome changed very little.

There are three types:
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The above pictures shows some of the symptoms that occur with each of the three types of plague.

1. Bubonic Plague- This type is characterized by fever and the presence of buboes which is the inflammatory swelling of the lymph nodes found usually in the armpit or groin. It does not spread person to person.

2. Septicemic plague – This plague accounts for 10-15 percent of all cases, is an acute, overwhelming, and progressive bacterium that affects all ages. The rapid replication in the bloodstream leads to severe injuries such as blood clotting, multiple organ failure, and respiratory distress. These symptoms can lead to gangrenous necrosis, or the breakdown and rotting of tissues. It is usually fatal even when treated. It does not spread from person to person.
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Click on picture of hand with gangrenous necrosis to find more about the disease popping up in the US through wild animals.
3. Pneumonic plague – A rapidly developing disease that spread to the lungs via the blood stream have a very high fatality rate. This secondary infection can be spread from person-to-person without the need for a flea vector. This mode requires close contact, moderate humidity, and cool climates to have successful transmission. If left untreated, it is generally fatal within 24 hrs.

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This picture above shows the natural transmission of plague from bubonic plague transmitted from the flea vector to pneumonic plague which is transferred through the air or by person to person contact.

This video above is from Nature describing the bacterium Y. pestis and how remarkably similar the genome from ancient DNA is to modern plague DNA. They suggest that other factors have limited the scale of outbreaks in recent years.

With that said, this current article suggests that the two large pandemics, The Justian Plague (541 AD) and The Black Plague (around 1330 AD) occured with different bacteria, as the fully 2011 sequence of their genomes suggest.

Teacher Resource: Here is a link to another History Channel video showing the transmission and spread of the European outbreak.

Teacher Resource: Here is an interactive quiz related to the Black Death that quickly spread in Europe. The quickness of the spread is one of the reasons why this disease is so potentially dangerous as a biological weapon. It spread entirely throughout Europe in 3 years, killing 25 million lives when all was said and done.

History of Plague in Society

Overall, the plague has killed over 100 million people.

25 million were killed in Europe’s Black Death. Half of the population.

Recently, since 1980, the World Health Organization estimates that the average global number of yearly cases is approximately 1,087. (See World Map)

1894- Alexandre Yersin isolated the bacterial agent and made the connection between rats and plague.

1897 – Masanori Ogata discovered the role of the flea in this disease.

Three major pandemics of plague noted in history:

  1. The Justinian Plague (541-544 AD) The plague spread from Ethiopia into Egypt and from there spread out to the rest of Asia, Africa, and Europe.
  2. The Black Death (1330’s-1340’s) The plague traveled the Silk Road from Asia, entered the Black Sea port of Caffa, and spread throughout Europe, wiping out over half of Europe population (approximately 25 million). Epidemics would continue to pop-up until the 1600’s.
  3. The Asia pandemic- (1855-1900) This pandemic began in China and spread throughout the rest of the world via the steamship.
  4. Currently, the possibility of a fourth pandemic is beginning considered for Africa and India.

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Click on the map above to read a blog describing the recent distrubution of this disease.
In the map above, we see the reemergence of the plague disease with a previous pandemic in the late 1960's and a more recent outbreak in Africa, Madagascar, and India.
The link here from CDC Maps shows the distrubution of plague in the US and around the world.

Here is a news report clip describing a 15 year old boy's death in Asia due to Bubonic Plague. (Notice the reporter keeps refering to the disease as a virus instead of the correct pathogen- bacteria) The outbreak causes fear and panic, one of the goals of a terrorist attack.

Here is an article of a recent outbreak in Madagascar killing at least 42 people, 20 of which happened in a single week. Most cases here were reported as pneumonic plague. Africa is now the leader in plague outbreaks.

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In this map we see that Africa has been facing a large outbreak since 2000. The United States does see sporatic cases usually found in the south western states, especially New Mexico.

A video of couple in New Mexico have the legendary Bubonic Plague.

Here is a 2012 clip of The Dr's show describing the plague still infecting people here in the US.
Here is an article Paul Gaylord's story. Here is an article to the 7 yr old Sierra Jane Downing's story.

Role of Plague in Bioterrorism

The beginning use of bioweapons
1. The first attempt to use the Plague as a bioweapon was during the time of the Black Death (1346-1347). A European conflict occurred at this time between the Tartars and the Genoese sailors. The Tartars were struck with the Plague, so the Tartar commander decided to catapult dead corpses at the Genoese. The plague broke out, due to the rats spreading the disease, causing the Genoese to flee back to Italy.

2. The Japanese army established a secret biological warfare agenda called Unit 731 during World War II. They used the human flea, Pulex irritans, as the delivery vector by placing them in bombs and spray-based systems. It is believed that they used these weapons against China at least three times.

3. The Soviet Union began a biological weapons program, using Y. pestis in the 1970’s-1980’s. They created a genetically engineered, dry, antibiotic resistant form of the bacterium. NO FLEA VECTOR IS NOW NEEDED.

4.Other countries, such as the US, North Korea,China, and Canada has had research programs to work with plague.

5. In the United States, the most important vector to watch out for is Diamanus montanus, a common flea found on ground squirrels and rock squirrels in California.

Here is a link to a 4 minute video describing how the Plague was used as a bioweapon before.

  • Y. pestis, a “critical biological agent” according to the CDC, is one of the most serious agents to cause concern because of its availability around the world, its capacity for mass production and aerosol dissemination, its difficulty to prevent such attacks, its high fatality rates of pneumonic plague, and its potential for secondary spread of the epidemic.
  • The size of an outbreak would depend on the quantity of the agent used, characteristics of the strain, the environmental conditions, and the methods of aerosolization.
  • The World Health Organization (WHO) published a study in 1970 describing a worst scenario case using pneumonic plague in aerosol form. They determined that if a 50 kg (110 lb.) quantity of Y. pestis was dropped on a large city, possibly 36,000 people would be predicted to die from the disease and the greatest concern would be the inhabitants would panic and flee causing further spread of the disease.
  • Following a biological attack, the clinical manifestations would be different than a naturally occurring plague. More likely, the terrorist attack would favor pneumonic plague, rather than bubonic plague.
This is a problem since any vaccination product was discontinued in 1999, which only has the ability to prevent bubonic plague and not pneumonic plague. This would most likely occur through an aerosol spray and would display symptoms within 1-6 days following exposure, killing most who display symptoms. This form of the plague can spread through the air via person to person or aerosol sprays, without any other vector needed.

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Teacher Resource: Click on picture above to see a trailer of a game, Plague Inc:Evolved, simulating an outbreak due to bioterrorism. A great way for students to learn about infectious diseases.

Prevention of an Outbreak

Main ways of disease prevention:
1. Transmission control – Proper sanitation, insecticide use, rodent population control, and public health education are key factors for transmission control. Contact with wild animals, dead or alive, and their feces should be avoided. Fleas should be targeted before rodents.

2. Receive post-exposure treatment if exposed to aerosols. Current recommendations found on the CDC website http://www.bt.cdc.gov/agent/plague/index.asp is 100 mg of doxycycline twice daily for adults and 2.2 mg/kg, to children under 45 kg, orally
twice a day. Oral drugs would be preferred in mass exposures.
*Streptomycin was approved by the FDA for plague and has been the preferred treatment.
*Public health officials have supplies of drugs stored and ready to be sent if a bioterrorist attack occurs.

3. Find a better plague vaccine?? Scientists are currently working on finding a vaccine to prevent the pneumonic plague, a more likely
candidate for bioterror. No plague vaccine is currently available in the US (discontinued in 1999 and only effective with bubonic plague),
although it was previously licensed and given to US troops. If the pneumonic plague is not treated with antibiotics within the first 18 hrs. of the
symptom onset, the patient is likely to die.
WWII troops were vaccinated with a killed form of the plague. Since US troops were vaccinated with the plague only 8 servicemen contracted
the disease during that war even though the disease is endemic in that area. It only prevents the bubonic form, the most common form, of the

4. Build a worldwide surveillance system for infectious disease. See article here. The goal is to stop bioterror agents before they spread.
The Obama administration is creating a project to eliminate the potential loss of life and the economic damage that it would bring. The US
government is committing an extra $45 million to the CDC 2015 budget to help this process in low-income countries.

This is a link to an Animal Planet video describing how The Bubonic Plague is still around in the western United States and the possability out an outbreak still exists.

Here is an article that describes how the US plans for the next global threat of microbes.

See source page for sources related to plague.
All pictures are hyperlinked to their page.