Plague

What is plague?
Plague is an acute bacterial infection caused by the organism Yersinia pestis. The disease occurs naturally in Asia, Africa, the US and South America. There are about 2000 cases per year, nearly all in Africa. It was responsible for three large pandemics (world-wide outbreaks) that killed millions of people. In the second pandemic (the Black Death) that began in the fourteenth century, as many as 100 million people lost their lives to plague. Plague is highly infectious. There is concern that plague could be used in a bioterrorist attack where it could be released by aerosol and inhaled or spread by infected vectors (fleas). Person-to-person spread of plague occurs readily. Plague is a notifiable disease in Ireland.

What are the symptoms of plague?
There are three major forms of plague, all of which are uncommon and a further two which are extremely rare.

1. Usually, plague takes the form known as bubonic plague. The bacteria invade the body and cause fever. The lymph nodes swell up and become very painful (this is the bubo). The buboes can range in size from1-10cm in length. Patients are not infectious is this state but many go on to develop pneumonic plague and are then capable of spreading the bacteria.
2. Less frequently, the organism causes pneumonic plague, a form of pneumonia with severe respiratory symptoms, rapidly developing cough and difficulty in breathing.
3. If the bacterium gets into the blood, septicaemic plague results. This has the highest mortality.

The very rare forms are meningitis and pharyngeal plague.

Is there a treatment for plague?
Plague can be very effectively treated with antibiotics, meaning that in treated cases deaths occur in fewer than 5% of cases. If left untreated the infection can result in death in 90% or more of cases.

How can you catch plague?
The natural hosts are small animals such as wild rats. The organism is usually passed to humans through the bite of a flea which has previously fed on an infected animal. Bubonic plague is generally not spread from person-to-person, except through direct contact with any fluids from the swellings. Pneumonic plague can be passed from person to person through the inhalation of droplets from the cough or sneeze of an infected individual.

What is the incubation period of plague?
The incubation period for plague is usually between 1 and 7 days. For plague pneumonia following inhalation it is shorter at 1-4 days.

How can plague be prevented or treated?
Provided the disease is identified in its early stages, it can be treated very effectively with antibiotics. Antibiotics can also be given to close contacts of patients to help prevent them from developing the disease.

 Updated July 2010