Tales of the Plague: The rat, the flea, and the Black Death

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What’s in a plague, that a disease named by any other name would kill as efficiently?

The world is still in the midst of a pandemic with no cure in sight, and here comes another threat – a more familiar one, one that has been rearing its deadly head through history.

And now, it is resurfacing.

Xinhua reported on Sunday 5 July, 2020 that North China’s Inner Mongolia Autonomous Region has one suspected bubonic plague case.

Local authorities in Bayannur on Sunday issued a third-level warning for plague prevention and control that will last until the end of 2020. The commission urged the public to beef up self-protection as the city has the risk of people-to-people infections.  The public was also discouraged from hunting and eating animals that could cause plague infections.

The agency also called the public to report any findings of killed or dead marmots and other animals, and report suspected plague cases, patients who developed high fever without known reasons, as well as patients dying suddenly.

According to the Centers for Disease Control and Prevention, plague is a disease that affects humans and other mammals.

It is caused by the bacterium Yersinia pestis. Humans usually get the plague after being bitten by a rodent flea that is carrying the plague bacterium or by handling an animal infected with plague. The plague is notorious for killing millions of people in Europe during the Middle Ages, for a brief history of plague and pandemics in general.

Today, modern antibiotics are effective in treating plague. Without prompt treatment, the disease can cause serious illness or death.

Oriental rat flea (Xenopsylla cheopis), the primary vector of plague, engorged with blood. Image courtesy of Centers for Disease Control and Prevention (CDC), Atlanta, Ga.
Oriental rat flea (Xenopsylla cheopis), the primary vector of plague, engorged with blood. Image courtesy of Centers for Disease Control and Prevention (CDC), Atlanta, Ga.

Transmission: How one gets infected

The Yersinia pestis maintain their existence in a cycle involving rodents and their fleas. This plague bacteria can be transmitted to humans in the following ways according to a 1992 study by Crook LD on a clinical review of Bubonic plague: flea Bites; contact with contaminated bodily fluids (,i.e. a hunter skinning an infected rabbit without proper protective equipment). Human-to-human transmission is also possible through respiratory droplets, and would sometimes cause the deadliest form once these infected droplets are inhaled, the pneumonic Plague. Scratches and bites from infected domestic animals such as cats can also transmit the plague.

Symptoms

Plague symptoms depend on how the patient was exposed to the plague bacteria. The plague can take different clinical forms, but the most common are bubonic, septicemic, and pneumonic plague.

Bubonic Plague

Patients develop sudden onset of fever, headache, chills, and weakness and one or more swollen, tender and painful lymph nodes (called buboes). This form usually results from the bite of an infected flea. The bacteria multiply in the lymph node closest to where the bacteria entered the human body. If the patient is not treated with the appropriate antibiotics, the bacteria can spread to other parts of the body.

Septicemic Plague

Patients develop fever, chills, extreme weakness, abdominal pain, shock, and possibly bleeding into the skin and other organs. Skin and other tissues may turn black and die, especially on fingers, toes, and the nose. Diarrhea may also be the predominant symptom. Septicemic plague can occur as the first symptom of plague, or may develop from untreated bubonic plague. This form results from bites of infected fleas or from handling an infected animal.

Pneumonic Plague

Patients develop fever, headache, weakness, and a rapidly developing pneumonia with shortness of breath, chest pain, cough, and sometimes bloody or watery mucous. Pneumonic plague may develop from inhaling infectious droplets or may develop from untreated bubonic or septicemic plague after the bacteria spread to the lungs. The pneumonia may cause respiratory failure and shock. Pneumonic plague is the most serious form of the disease and is the only form of plague that can be spread from person to person by infectious droplets.

Swollen lymph glands, termed buboes, are a hallmark finding in bubonic plague. Image courtesy of Centers for Disease Control and Prevention (CDC), Atlanta, Ga.
Swollen lymph glands, termed buboes, are a hallmark finding in bubonic plague. Image courtesy of Centers for Disease Control and Prevention (CDC), Atlanta, Ga.

Diagnosis and Treatment

The most common sign of bubonic plague is the rapid development of a swollen and painful lymph gland called a bubo. The possibility of plague should be strongly considered in febrile patients from endemic areas who have history of exposure to rodents. In many cases, particularly in septicemic and pneumonic plague, there are no obvious signs that indicate plague.

According to the 2014 guidelines on the diagnosis and treatment of bubonic plague published by the Infectious Diseases Society of America (IDSA), diagnosis is made by taking samples from the patient, especially blood or part of a swollen lymph gland, and submitting them for laboratory testing and culturing of the bacteria.

Plague is a very serious illness, but is treatable with commonly available antibiotics. The earlier a patient seeks medical care and receives treatment that is appropriate for plague, the better their chances are of a full recovery.  Based on a 2000 study on bubonic plague by Inglesby TV, etc., historically, streptomycin has been the drug of choice for the treatment of plague, but it has been scarce in the United States.

The FDA has approved the antibiotics levofloxacin and moxifloxacin as alternative treatment for plague. These have also been approved for use as prophylaxis following exposure to Yersinia pestis.

Here’s some assuring news: while outbreaks of the plague may occur every now and then it’s very unlikely that this will become an epidemic because of the availability of effective treatment (antibiotics). Before the age of antibiotics, the plague is a death sentence. While the plague is not less dangerous now, we do know how to combat it.

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