The Bubonic Plague, Rodents and Outbreak

A hospital in China's Bayannur reported a herdsman suspected of contracting bubonic plague. It is unclear how the herdsmen contracted the deadly plague. 

Authorities are also investigating the second case of the plague: a 15-year old who had consumed marmot hunted by a dog.

Last year, two people in Mongolia also died from the plague after consuming raw meat of the marmot, the same type of rodent as the suspected second case of this year. 

Authorities have issued a level 3 alert which prohibits hunting and eating of animals that may transmit the plague. The public has also been asked to report suspected cases. The authorities announced that the warning maybe until the end of this year.

Bubonic Plague

For those who are not yet familiar with the bubonic plague or black death, it is a highly infectious disease that exhibits fever, headaches, vomiting, and swollen lymph nodes in infected persons. As the disease progresses, the inflamed lymph nodes turn into open sores filled with pus. As the infection advances to the lungs, it becomes a pneumonic plague, the most virulent form of the disease. Transmission at this point may be transmitted to other humans through droplets in the air. 

At its height in the 14th century, the disease claimed 30 percent to 60 percent of Europe's population and 50 percent of China's population. The plague reduced the world's population by 100 million. 

We have come a long way since the 14th century, but from time to time, flare-ups of bubonic cases come up. In 2017, there were 300 cases in Madagascar, and less than 30 people died. The disease has been studied well enough that "We know how to prevent it. We are also able to treat patients who are infected with effective antibiotics," Dr. Shanti Kappagoda, an infectious diseases doctor at Stanford Health Care, said.

How did the bubonic plague come about?

A gene sequencing study revealed that The Plague emerged from China more than 2,000 years ago. Scientists believe that the plague bacillus reached Crimea in 1346 and most likely spread on black rats that traveled on merchant ships.

Yersinia pestis, the bacteria that causes the plague is found in small mammals and their fleas. The disease spreads from bites of fleas from infected rodents like mice, rats, rabbits, squirrel, chipmunks, voles, and rabbits.

According to the CDC, even in the U.S., scientists believe that the plague exists in an enzootic cycle: it just there involves rodents and fleas. Still, it is kept at low rates, making these rodents and fleas the long-term reservoir for the bacteria. 

When the bacteria infect other species, epizootic occurs. But when the outbreak affects humans as when plague epizootic happens, many rodents die, causing the fleas to seek other hosts, including humans. 

Modes of Transmission

One can get the bubonic plague in three ways:

Flea bites. The bite of an infected flea transmits the plague bacteria. When infected rodents die, the infected flea looks for other hosts or sources of blood. People and animals exposed to areas where the rodents recently died are at risk of the flea bite transmission. Dogs and cats may also be carriers of the infected fleas at home. 

Contact with the plague-infected fluid or tissue. This includes hunting, consuming, and handling of tissue of the infected animals.

Infectious droplets. Cough droplets in the air of a contaminated person can cause pneumonic plague.

Cats are particularly susceptible to the plague as they can get infected by eating infected rodents. Plague-infected cats can pass the disease to its owners or veterinarians by transmitting its cough or droplets in the air. In recent decades in the United States, contacts with infected cats have caused several cases of human plague.