The COVID-19 pandemic is still at its peak. Reports from China have added to the distress as people have been reported to die of "the Black Death".

A whole village has been sealed in China's inner Mongolia to restrict the spread of the disease. The Black Death or Plague was the deadliest pandemic that killed 75 - 200 million people in the 13th Century [Ref].

What is "The Black Death"?

The "Black Death" is caused by infections caused by species of Yersinia. Eleven different species have been identified, however, the three most important are:

• Yersinia Pestis
• Yersinia Enterocolitica
• Yersinia pseudotuberculosis

'The black death or the plague is a zoonotic disease. It primarily infects animals, however, human transmission occurs via infected rodent fleas. Other modes of transmission in humans may occur in the following ways:

• Inhalation of respiratory secretions from infected animals
• Scratches and bites from infected domestic cats and dogs
• Consumption of contaminated food
• Laboratory or postmortem exposure
• Inhalation of aerosolized droplets from infected humans
• Handling of infected animal tissues and secretions

Cats and dogs can transmit the infection to humans by carrying infected fleas. Infected animals can be identified from their signs and symptoms.

• Fever
• Lethargy
• Anorexia
• Development of Buboes or lymph nodes including cervical mandibular, and inguinal.

About 30 different species of fleas can transmit the disease, however, Xenopsylla cheopis, the oriental rat flea is considered the most efficient flea.

Do you know ...

The human body lice can also transmit plague from human to human

Some epidemiologists considered body lice as the ones responsible for the second plaque pandemic.

Pathogenesis of Yersinia infections:

The pathogenesis of plage involves two distinct steps: Transmission and human response. The bacteria infect the fleas when they feed on an infected host. This is followed by rapid replication of the bacteria in the gut of the flea resulting in blockage of the flea's intestine.

As food can not enter (because of the blockage), the fleas become hungry and start biting aggressively. During feeding, they regurgitate their intestinal contents transmitting the infection.

As low as ten bacteria can cause the disease when inoculated subcutaneously. The bacteria then travel in the lymphatics and an intense inflammatory response occurs resulting in enlarged lymph nodes.

These are also called "Buboes". Bacteremia can occur resulting in a septicemic plague. Other organs frequently get affected. The most important one is the lungs resulting in Pneumonia.

Endotoxemia can cause disseminated intravascular coagulation and fibrin deposition in various tissues. This can cause a purpuric rash and digital gangrene (microthrombi in the small vessels of the hands resulting in a blockage of the blood flow).

What are the symptoms of the Plague:

There are three different types of plagues:

• The Bubonic plague - accounts for about 80% of the cases
• The septicemic plague - accounts for 10 - 20% of the cases, and
• The Pneumonic plague - is very rare.

Bubonic Plague:

• Patients develop a sudden onset of fever, rigors, chills, and headaches. This is followed by the development of enlarged lymph nodes (Buboes) in the affected limbs.
• Patients may report severe pain as the lymph nodes enlarge. Other skin rashes such as purpura, pustules, and eschars can occur on the limbs.
• The lymph nodes may become fluctuant later and result in the dissemination of the infection causing septicemia and shock.

Septicemic Plague:

Patients in the septicemic stage become incredibly ill. Hypotension and shock may result if not timely managed to culminate in disseminated intravascular coagulation and multiple organ failure.

Pneumonic Plague:

Pneumonic plague may be acquired directly from inhaling air droplets or respiratory secretions of infected animals or from laboratory exposure.

This is called Primary Pneumonic Plague. Hematogenous propagation of the illness results in secondary pneumonic plague. Patients develop a sudden onset of cough, chest pain that worsens with deep breaths, and blood in the phlegm.

Patients develop difficulty in breathing and may die rapidly if not treated promptly. Other symptoms may also include pharyngitis and tonsillitis. Meningitis or infection of the covering f the brain may occur causing headaches, drowsiness, and neck pain.

Diagnosis of Plague:

Patients have variable hematologic abnormalities. Important findings include leukocytosis with thrombocytopenia, however, leukopenia may occur. Chest radiographs may show bronchopneumonia, cavitations, effusions, and consolidation.

Sputum may be purulent or bloody. The culture of the infected lymph nodes may be positive in 10 - 13% of the patients. Blood cultures are positive in 27 - 96% of the patient's Gram stain of the peripheral blood may show rod-shaped organisms with wright Giemsa stain in 40% of the patients.

Wayson's staining may stain the organisms that look like "safety pins" because of the bipolar positivity of gram-negative coccobacilli. Rapid diagnostic tests may detect Yersinia Pestis F1 antigen within 15 minutes in the serum or sputum. PCR testing may be done to further classify the species.

Treatment of Plague:

If not treated timely, the death rates are as high as 50 - 90%. The death rate in patients with pneumonic plague is almost 100% if not treated timely. The two most important groups of antibiotics against the infection are:

• Aminoglycoside (Streptomycin and Gentamicin)
• Tetracyclines (Doxycycline and tetracycline)
• Other antibiotics that have been found effective in animal studies include:
  • Quinolones (levofloxacin, moxifloxacin, ciprofloxacin)
  • Chloramphenicol
  • Trimethoprim-sulfamethoxazole (Co-trimoxazole)

Treatment typically lasts 7 to 14 days.Treatment typically lasts 7 to 14 days.

How you can prevent yourself from "The Black Death"?

The best way to avoid getting infected is to avoid getting exposed!

Exposure can be reduced by avoiding contact with infected animals and diseased individuals. The handling of infected and dead animals is one of the strongest risk factors. Exposure can occur at slaughterhouses or veterinary clinics.

Hand washing plays a key role. Handwashing after contact with an exposed person or animal reduces the chances of getting the infection. Rodents and fleas control measures and using insect repellents also reduce the risks of getting the infection.

Pneumonic plague can be prevented by social distancing (1 - 2 meters minimum) and the use of face masks. Post-exposure prophylaxis is recommended in epidemic and endemic areas in individuals who had a face to face contact without masks or proper protection with an exposed individual.

Recommended post-exposure prophylaxis includes:

• 100 mg of doxycycline twice daily for seven days100 mg of doxycycline twice daily for seven days
• Trimethoprin-Sulfamethoxazole may be used for five to seven days in children and pregnant women.
• Levofloxacin 500 mg once daily for 10 days (Alternative to doxycycline)

A killed vaccine is no more commercially available. It was used as two injections administered one month apart and then six-monthly until the time of exposure.

Take-Home Message ...

The world is still fighting COVID-19 infection. Although the same rules of prevention apply here to prevent oneself from "The Black Death", it may be devastating if we face another pandemic. Wash hands frequently, stay home, avoid overcrowding, and report early.