The bacteria Yersinia pestis causes plague, which can be a life threatening infection if not promptly treated. Plague is called the ‘Black Death’ as it causes skin sores that form black scabs, which killed more than a third of the population of Europe within a few years in the 14th century.
While plague is basically an animal infection, it can get transmitted to adults by the bite of an infected rat flea. This is why people living in areas where there are many rats and fleas are most susceptible to a plague infection.
Humans also get infected by plague when the Y.pestis bacteria enter their body through a crack in the skin, after having direct contact with the meat or blood of an infected animal. Humans also get infected by breathing in Y.pestis bacteria droplets when in close contact with an infected person and through scratches and bites of infected domestic cats.
This is why hunters, veterinarians and people who hike and camp in regions with many animals infected with plague. Sometimes even domestic cats and dogs spread the disease by bringing infected fleas to the house.
Plague occurs in different forms; bubonic, septicemic and pneumonic, which have various and differing symptoms. Bubonic plague is the most common form where victims develop a high fever, chills, headache, extreme weakness and headache after 2-6 days of the flea bite. Prompt treatment with antibiotics helps cure most cases while with improper treatment, the bacteria spreads to the bloodstream wherein the patient develops septicemic plague.
Septicemic plague is the second most common form of plague with symptoms of nausea, diarrhea, abdominal pain, vomiting, severe bleeding problems, sudden bleeding under the skin, blood in urine, scattered bruises and bleeding from nose, mouth and rectum. These bleeding problems can lead to shock, severe breathing difficulties, kidney failure and possibly death. However with the right treatment, most cases survive.
Pneumonic plague is very rare which occurs when the Y.pestis bacteria infects lungs to cause pneumonia. Symptoms include chills, chest pain, rapid breathing, cough that brings up blood, headaches and shortness of breath. The disease can lead to death without the right treatment.
Diagnosis and treatment
If plague is suspected, your doctor will first ask if you have travelled to a place where plague occurs, if you have treated an extremely ill pet, had a flea bite, come in contact with a dead animal or if you have been around wild rodents. Then to confirm the diagnosis, blood or other body fluids will be tested for Y. pestis bacteria infection.
Patients suffering from plague have to be hospitalized where staff will take preventive measures to prevent its spread. Antibiotics are administered intravenously while patients with severe bleeding and breathing problems will be treated in an intensive care unit. While bubonic plague subsides within 2-5 days of proper antibiotic treatment, recovery from septicemic and pneumonic plague takes longer.
Researchers extracted DNA from the teeth of plague victims in London 660 years ago to reconstruct the genome of the bacteria that lead to the Black Death. They were surprised to find that the genetic make-up of these bacteria had not changed at all when compared to modern day strains.
This is part of a new era of research into infectious disease where scientists believe that a better understanding of the evolvement of ancient bacteria will give them an insight into how pathogens change and adapt to new infections.