Black death

Depending on its mode of transmission and which part of the body the plague bacteria infects, plague can be of three types:

Bubonic plague spreads through the bite of flea (often the Oriental/tropical rat flea or Xenopsylla cheopis) infected with Yersinia pestis bacteria. These fleas commonly infest rodents like rats, squirrels and rabbits—though they have been found on over 200 mammalian species by some accounts.

In bubonic plague, the bacteria use the lymphatic system to get around—the bacilli quickly move from the bite site to the nearest lymph nodes (usually in the armpits or groin) where they multiply rapidly causing the node to fill up with bacteria and appear swollen. This swollen mass is called a bubo.

Bubonic plague can also be transmitted by coming in contact with the dead bodies of plague victims (human and animal). It can also be transmitted through close contact with buboes—the bacteria-filled nodes. Human fleas (Pulex irritans) and body lice can also spread the disease from one person to another.

Septicaemic plague occurs when Yersinia pestis reaches the bloodstream. The bacteria can travel with the fleas (carried into households and other human-populated areas by rats, squirrels and other common rodents), or by coming in contact with the dead bodies of people and animals who died of the plague, or they could enter the bloodstream through an open wound to cause this type of plague. The lymphatic system is connected to the bloodstream through the subclavian vein—research has suggested that this route may be one way in which the bacteria reach the bloodstream.

Pneumonic plague occurs when Yersinia pestis affects the lungs. This is the most fatal type of plague. Human-to-human transmission of pneumonic plague is possible through respiratory droplets: when an infected person coughs, sneezes or talks loudly, they can release droplets into the air. Most of these droplets travel a short distance before falling to the ground. Some of these droplets remain airborne for longer and cover more distance. If these droplets enter the nose, mouth or eyes of a healthy person, they can transmit the infection. There are a few more things to keep in mind when it comes to pneumonic plague: if bubonic plague reaches the lungs, it can turn into pneumonic plague—which is much more deadly and acts even faster.

In February 2002, 16 cases of pneumonic plague (including four deaths) were reported from a village in Simla, Himachal Pradesh. The outbreak was contained by giving prophylactic antibiotics (chemoprophylaxis) to people who had come in contact with the patients, to the residents of the villages (Hat Koti) and the neighbouring village and to doctors and health workers. Both villages, all patient transport vehicles, etc., were also fumigated.

Pneumonic plague is so deadly that it typically kills the patient before he/she can transmit the disease to many people—the R-naught, or how many people can be infected by a diseased person on average, for pneumonic plague is around 1.3.

Each of these three types of plague has slightly different symptoms and outcomes. Read on for more.

The incubation period of the plague is between one and seven days—that is, it takes up to a week after exposure to the bacteria for symptoms to show. Bubonic plague, or the plague that caused Black Death and the 1994 outbreak in India, has the following symptoms:

• Fever
• Chills
• Myalgia (muscle pain)
• Nausea and vomiting
• Headaches

Buboes, the characteristic sign of bubonic plague, are inflamed and painful lymph nodes, usually in the armpit and groin area (though they can be present in lymph nodes anywhere in the body).

The symptoms of septicaemic plague (fever, chills, weakness, stomach ache, shock and possible bleeding) and pneumonic plague (fever, weakness, shortness of breath, chest pain, cough and blood in mucus) are different from bubonic plague in some important respects.

The bacteria that causes bubonic plague (Yersinia pestis) infects fleas which in turn infest roughly 200 mammalian species, including rats, squirrels, rabbits, wild rodents, prairie dogs and cats.

The fleas get infected when they bite an animal with the plague bacteria. The bacteria now grow in the food pipe (oesophagus) of these fleas, until the bacteria completely block the fleas' food pipe. Now, the fleas can’t feed without vomiting up the bacteria into a new host first. Once the flea bites a human host, the bacteria travel to the lymph nodes where they grow exponentially.

There are over 131 types of fleas that commonly spread the bubonic plague; chief among them is the Oriental rat flea.

Symptoms start showing up one to seven days after the flea bite. A person with bubonic plague is most infectious towards the end of the disease period (as opposed to pneumonic plague where the person’s condition could worsen suddenly, and the patient could die within 24 hours after contracting the bacterial infection).

Black Death specifically refers to an outbreak of bubonic plague in the Middle Ages—1347-51 (some science historians say it went on till 1353). Here’s what we need to know about the bubonic plague today:

• Black Death or bubonic plague is a bacterial infection.
• It is a zoonotic disease, meaning that it jumped from animals to people at some point in history. Scientists say that this point in history could be anywhere from 5,000 to 10,000 years ago. The Plague of Justinian in 541-542 AD may have been the first plague epidemic—it is said that 25-50 million people may have died in this outbreak, most of them in Constantinople—then a powerful empire—and parts of North Africa.
• Bubonic plague is also a vector-borne disease. Which means that it has a carrier that transmits the infection—the flea. As this flea can feed on roughly 200 species of mammals, it can get around quite quickly. That said, bubonic plague is most commonly associated with rats (those who de-skin infected rabbits and squirrels without gloves can also be infected). Since rats can get into homes, on-board ships and practically everywhere, the plague can travel with them.
• Bubonic plague is a fulminant disease, meaning it sets in quickly and can be severe and even lethal. Left untreated, 30-60% of patients with bubonic plague die (the mortality for pneumonic plague is even higher at nearly 100%; remember than bubonic plague can travel to the lungs and become pneumonic plague).
• Bubonic plague bacteria enter the body through the skin’s dermis layer. Most of the bacteria doesn’t go beyond the skin. A small fraction of “dissemination competent bacteria” escapes from the skin into the lymph vessels “immediately after inoculation”. According to research published in Trends in Microbiology, a peer-reviewed journal, Yersinia pestis bacteria possibly reach the lymph nodes too quickly for the immune system to put up an adequate response. Next, the bacterium multiplies “at remarkably high rates”. The bacteria then leave the lymph node and enters the bloodstream (possibly when lymph nodes burst or via the subclavian vein) and cause sepsis and septicaemic plague.
• Bubonic plague is endemic to India and countries like the Democratic Republic of Congo, Madagascar, Peru and China even today. Between 2010-15, the World Health Organization received reports of 3,248 confirmed cases of bubonic plague across the world. However, an outbreak in Madagascar in 2017 saw cases rising over 2,000 within weeks.

Scientists have argued that bubonic plague outbreaks are linked to:

• Historical events like the beginning of agriculture settlements when people started clearing forests for farming and making granaries to store grain. Wild rodents that lost their habitat and mice in search of food started living closer to human settlements and domesticated animals, making people more prone to the disease.
• International travel, especially for war and trade, contributed to the spread of the plague bacteria to nearly all part of the world.
• Disasters like floods, earthquakes and famine do two things: bring more rodents to human settlements in search of food. Some disasters kill off rats and other rodents—some scientists have proposed that with fewer rats and rodents to feed on, fleas turn to humans for their blood meals, thereby causing a spike in infections.

In 1994, the flooding in Surat brought the rats out of the open drains. In part, this is what triggered the outbreak in parts of the western, central and northern parts of India that year.

The World Health Organization recommends the following steps to prevent and contain the spread of bubonic plague and manage any future outbreaks:

Bubonic plague is treatable with antibiotics, provided it is diagnosed early. This may sometimes be difficult as the early symptoms of plague can be quite generalised. However, buboes are a characteristic feature of bubonic plague. If you experience painful swelling in your lymph nodes, you should see a doctor without losing any time.

The doctor will do a physical examination. If you live in an area (or have recently travelled to an area) where the bubonic plague is endemic or if your doctor wants to confirm or rule out the bubonic plague, he/she may recommend a sputum test or blood test. Fluid from the swollen lymph node may also be tested.

The doctor may start antibiotics quickly (sometimes before the test results come back), if he/she suspects infection with Yersinia pestis. Some of the antibiotics used for treating bubonic plague are:

• Septromycin
• Gentamicin
• Doxycycline
• Ciprofloxacin
• Levofloxacin
• Moxifloxacin
• Chloramphenicol

Please note that you should not take any antibiotics without a prescription from a doctor.