What is plague?
Plague is a bacterial disease, caused by Yersinia pestis, which primarily affects wild rodents. It is spread from one rodent to another by fleas. Household pets such as cats, infested with fleas, have also been implicated. The disease occurs naturally in Asia, Africa, South America and the United States. Globally, there are about 2000 cases reported per year to WHO, however the true number is likely to be higher. Plague is a notifiable disease in Ireland.

How can you catch plague?
People most commonly acquire plague when they are bitten by a flea that is infected with the plague bacteria. People can also become infected from direct contact with infected tissues or fluids while handling an animal that is sick with or that has died from plague. Finally, people can become infected from inhaling respiratory droplets after close contact with humans with pneumonic plague. Poor hygiene conditions can favour contact between humans and rats carrying fleas in affected areas.

What are the different types of plague?
Bubonic plague: Patients develop sudden onset of fever, headache, chills, and weakness and one or more swollen, tender and painful lymph nodes (called buboes). This form is usually the result of an infected flea bite. The bacteria multiply in the lymph node closest to where the bacteria entered the human body. If the patient is not treated with appropriate antibiotics, the bacteria can spread to other parts of the body.

Septicemic (blood stream) plague: Patients develop fever, chills, extreme weakness, abdominal pain, shock, and possibly bleeding into the skin and other organs. Septicemic plague can occur as the first symptoms of plague, or may develop from untreated bubonic plague. This form results from bites of infected fleas or from handling an infected animal.

Pneumonic plague: Patients develop fever, headache, weakness, and a rapidly developing pneumonia with shortness of breath, chest pain and cough. Pneumonic plague may develop from inhaling infectious droplets or from untreated bubonic or septicemic plague that spreads to the lungs. Pneumonic plague is the most serious form of the disease with a rapid course and high fatality rate. It is the only form of plague that can be spread from person to person (by infectious droplets).

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

Is there a treatment for plague?
Plague can be effectively treated with antibiotics provided treatment is commenced early. If left untreated, especially the pneumonic form, the infection can result in death in almost 90% of cases. However with timely antibiotic treatment, the mortality rate is reduced to less than 10%. In some circumstances, antibiotics can also be given to close contacts of patients to help prevent them from developing the disease.

Is there a vaccine?
There are no vaccines against plague currently available. New plague vaccines are in development but are not expected to be commercially available in the immediate future.

How do you prevent plague?
Reduce contact with fleas and potentially infected rodents and other wildlife in areas affected by plague. Use repellent if you think you could be exposed to rodent fleas during activities such as camping, hiking, or working outdoors in areas affected by plague. Products containing DEET can be applied to the skin as well as clothing and products containing permethrin can be applied to clothing (always follow instructions on the label) to prevent flea bites.

Important to remember
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.

Last updated: 27 November 2014