The Biblical definition of the word “plague” is anything that causes affliction, troubles, calamity, or any contagious epidemic disease that is deadly. The medical definition of “plague” is a bacterial infection caused by the bacterium “Yersinia pestis.”The plague is attributed to three major pandemics: Justinian’s Plague, 542-546 AD, killed 100 million people in Europe, Asia, and Africa; the Black Death in the 1300s, killed about a third of Europe’s population (The pandemic resulted in 50 million deaths in Europe, Asia, and Africa); the Third Pandemic started in Canton and Hong Kong during the late 1800s. (Ships carried the illness to five continents, and 13 million people died in India alone.)
Some scientists claim the Black Death and other epidemics were too widespread and developed too rapidly for fleas and rats to have been the carriers. Some historians claim there is no mention of a die-off of rats, which typically happens before a plague epidemic.
Plague is a vector-borne illness, which means that it requires a living host to transmit the disease. The most common vector of transmission is a specific species of flea called Xenopsylla cheopis. Commonly known as the Oriental rat flea, Xenopsylla cheopsis primarily feed on rodents. The bacteria can live in fleas, rodents, humans, and cats.
The anatomy of the Oriental rat flea makes it extremely suited to carry the plague. Its digestive system can become blocked by large quantities of plague bacteria. When this happens and the flea bites a host, it often regurgitates plague-infected blood into the wound. Other fleas, like the human flea “Pulex irritans” may still transmit the plague by transferring bacteria found on its stylet, which is a puncturing organ. After the infected flea bites the host, the bacteria suppress the body’s immune response. They also utilize specific proteins to protect themselves from the antigens produced by the immune system.
The bacteria then travel to the nearest lymph node via white blood cells Once the bacteria reach a lymph node, they multiply. The lymph node begins to swell due to the proliferation of bacteria and the endotoxins in the cell walls of the bacteria. In a few days, the node becomes a painful, egg-sized bubo (an infected, swollen lymph gland). The body’s natural defense system mounts an attack on the invading pathogens resulting in a high fever, chills, muscle pain, and weakness.
If the patient is not given the appropriate antibiotics, the bacteria can spread to other parts of the body. Without treatment, the death rate of the bubonic plague is 60 percent.
Septicemic plague, which does not always produce buboes, can result from touching (with an open wound) the infected blood of an animal while skinning it or as a complication of bubonic plague. In rare cases, it is the first symptom of the plague. Symptoms are fever, chills, extreme weakness, abdominal pain, shock, and possible bleeding of the skin and other organs. Skin and other tissues may turn black and die, especially on fingers, nose, and toes. Untreated, it has a death rate of 30-100 percent.
Pneumonic plague is the most serious form of the disease and is the only form that can spread from person to person. Pneumonic plague may develop from inhaling infectious droplets or may develop from untreated bubonic or septicemic plague. Symptoms are fever, headache, weakness, and rapidly developing pneumonia with shortness of breath, chest pain, cough bloody or watery mucus. This form may lead to respiratory failure and shock. Untreated, the mortality rate is nearly 100 percent and can be fatal in 24 hours. Cats can contract pneumonic plague and can transmit the disease to humans when they cough or sneeze.
Secondary pneumonic plague, which is the result of bubonic plague, is not considered as contagious as primary pneumonic plague.
Treatment is most effective with 24 hours of showing symptoms. Most diagnostic procedures include asking about exposure to rodents, looking for buboes, blood work, and smears from bodily fluids. A new 15-minute test has been developed to look for a specific molecule in the bacteria’s cell wall. The three most common antibiotics used are streptomycin, tetracycline, and gentamicin.
There are 1-7 cases a year in the American Southwest. The prairie dog is the leading host of the flea that carries bubonic plague in the U.S. Do not be alarmed the next time you learn of an outbreak of the plague. Thanks to modern medicine, the odds of a pandemic, are slim.