3 main forms of human plague are distinguished. In general symptoms include fever, headache, chills, and weakness. Other symptoms are dependent on the form of the disease:

1. Bubonic plague is the most common form, with up to 96% of cases. Typical are the large painful swellings of the lymph nodes. If untreated, the disease is fatal in almost half of the cases. The name Black Death typically refers to bubonic plague and refers to the fact that skin and other tissues may turn black and die, especially on fingers, toes, and the nose.
2. Septicemic plague can develop as a complication from bubonic plague or pneumonic plague, or as primary sepsis. It results in  shock and bleeding into skin and other organs. If left untreated, the disease is almost always fatal.
3. Pneumonic plague is the least common but most dangerous form of plague. It can develop as a complication from bubonic plague or septicemic plague, or as primary pneumonic plague. Patients develop progressive pneumonia resulting in respiratory failure and shock. If no adequate treatment is started within 24 hours after the onset of symptoms, the disease is almost always fatal. 

Humans get infected through the bite of infected fleas, through unprotected contact with infectious body fluids or contaminated materials or by inhalation of respiratory droplets from a patient with pneumonic plague.

In Belgium, plague is diagnosed at the National Reference Laboratory, located at Sciensano’s Zoonotic bacterial diseases unit. The NRL is responsible for providing specific information regarding sample handling, type of matrices, and pertinent tests. It performs isolation from clinical samples and molecular diagnosis (PCR).

Plague remains present in many regions of the world, particularly in Africa (in rural areas), but also in the Far East, Central Asia, and North and South America. Since the 1990s, most human cases have occurred in Africa. The 3 most endemic countries are the Democratic Republic of Congo, Madagascar, and Peru. No cases have been reported in Belgium in more than 80 years.

Early diagnosis and subsequent treatment are essential for survival and reduction of complications. Antibiotics and supportive therapy are effective if started on time. 

Plague in animals usually occurs as a flea-borne disease of small wild animals such as rodents. It is believed that plague bacteria circulate in low levels in rodent populations. These rodents and their fleas are long-term reservoirs for the bacteria. Also larger animals such as for example dogs, cats and foxes can become infected and develop clinical signs.