A bubo is an acute, painful swelling of a lymph node or a cluster of lymph nodes, a specific form of infectious lymphadenopathy. The term originates from the Greek word boubōn, meaning groin, reflecting one of its most common anatomical sites. Historically associated with severe epidemic diseases, it remains a precise medical description for lymphatic inflammation caused by various bacterial infections. A bubo represents a concentrated immune response where the lymph node attempts to fight a large number of invading pathogens.
The Specific Anatomy and Appearance
A bubo is a severely inflamed and enlarged lymph node that is hyper-reactive to an overwhelming localized infection. The afflicted node typically appears as a firm, tender, and visibly raised lump beneath the skin. The overlying skin is often red, warm, and painful.
The swelling is distinct from general lymphadenopathy due to its severity, rapid onset, and tendency to become suppurative (filled with pus). When a bubo reaches this stage, it is described as fluctuant, indicating a soft, wave-like sensation upon palpation. Buboes most frequently develop in the inguinal (groin), axillary (armpit), or cervical (neck) regions, which have dense concentrations of lymph nodes. The location generally corresponds to the body area drained by that node group and is often near where the infection entered the body.
Primary Infectious Causes
The formation of a bubo is a sign of a significant bacterial infection, with causes ranging from rare historical diseases to common sexually transmitted infections. The most famous cause is the bubonic plague, an infection by the bacterium Yersinia pestis, transmitted primarily through flea bites. The bacteria travel from the bite site to the nearest lymph node, where they rapidly multiply, causing the characteristic, often hemorrhagic, bubo. Although modern plague cases are rare, this disease is historically significant.
More common causes today include sexually transmitted infections (STIs) that produce inguinal buboes. Lymphogranuloma venereum (LGV), caused by specific serovars of Chlamydia trachomatis, is a prominent example. This infection typically leads to an often unnoticed genital lesion followed by the delayed development of painful, matted inguinal buboes. Chancroid, caused by the bacterium Haemophilus ducreyi, also frequently results in tender, suppurative inguinal buboes, often accompanied by painful genital ulcers.
Buboes can also be a feature of zoonotic diseases acquired from animals. Cat-scratch disease (CSD), caused by Bartonella henselae and transmitted through a scratch or bite from an infected cat, typically results in a bubo in the lymph nodes nearest the injury site (axilla or neck). Another zoonotic cause is Tularemia, or “rabbit fever,” caused by Francisella tularensis, transmitted by ticks, deer flies, or contact with infected animals. The most common form, ulceroglandular tularemia, results in an ulcer at the inoculation site and a painful, enlarged regional lymph node.
Clinical Diagnosis and Treatment
Identifying a bubo requires a thorough clinical assessment, beginning with a physical examination and a detailed patient history to determine potential pathogen exposure. The physician must determine the underlying cause, as treatment depends on the specific infectious agent. Diagnostic tests often include blood work, such as serology, to detect antibodies against suspected pathogens like Yersinia pestis or Francisella tularensis.
A definitive diagnosis often involves collecting a sample directly from the bubo itself. This procedure, known as needle aspiration, removes fluid or pus from the node for Gram stain, culture, or polymerase chain reaction (PCR) testing to identify the causative organism. This step is particularly important for distinguishing between the various bacterial causes, which guides the selection of the most effective antibiotic.
Treatment focuses on eliminating the underlying infection, typically through a course of specific antibiotics. For plague, immediate treatment with drugs like streptomycin or gentamicin is necessary, while LGV is treated with a prolonged course of doxycycline. If the bubo is large, painful, and fluctuant, surgical management may be required to relieve pressure and prevent spontaneous rupture. However, incision and drainage is generally avoided in cases of LGV or Chancroid to prevent delayed healing; aspiration is the preferred method when drainage is necessary.