A bubo is a painfully swollen, inflamed lymph node, typically in the groin, armpit, or neck, that develops when bacteria from a nearby infection site travel through the lymphatic system and multiply inside the node. The term is most famously associated with bubonic plague, but buboes can also form from sexually transmitted infections like chancroid and lymphogranuloma venereum, or from animal-borne bacteria such as cat scratch disease and tularemia. Understanding what causes a bubo, what it looks and feels like, and how it gets treated is useful because a swollen lymph node of this severity almost always signals an infection that needs medical attention.
How a Bubo Forms
Lymph nodes are small, bean-shaped structures scattered throughout your body that act as filters for your immune system. When bacteria enter through a wound, bite, or mucous membrane, they drain into the nearest lymph node. In most infections, the node swells mildly as immune cells ramp up their response, and the swelling resolves on its own. A bubo is something more aggressive: the bacteria overwhelm the node’s defenses, multiply inside it, and trigger intense inflammation that can lead to the node filling with pus, a condition called suppuration. In severe cases, the node can become necrotic, meaning the tissue inside begins to die.
The location of the bubo tells you a lot about how the infection entered. A bubo in the groin usually means the bacteria came in through the leg, foot, or genitals. A bubo in the armpit points to an entry site on the arm or hand. A bubo in the neck suggests the infection entered through a scratch, bite, or wound on the head, face, or upper body. This anatomical logic is one of the main reasons clinicians pay close attention to where swollen lymph nodes appear.
Plague and the Most Famous Bubo in History
The word “bubo” entered common vocabulary because of bubonic plague, the disease caused by the bacterium Yersinia pestis. During the fourteenth-century Black Death, plague killed more than a third of Europe’s population, roughly 25 million people, and the hallmark symptom was suppurative buboes: hot, swollen lumps in the groin, armpit, or neck that could grow to the size of an egg or larger.1PubMed Central. History of the Plague: An Ancient Pandemic for the Age of COVID-19 These plague buboes could turn black and necrotic, rotting away the surrounding tissue, or they could rupture and discharge large amounts of pus.2PubMed Central. A Deadly Path: Bacterial Spread During Bubonic Plague
The typical chain of events in bubonic plague starts with a flea bite. Fleas living on infected rodents carry Y. pestis in their gut, and when a flea bites a human, the bacteria enter through the skin. They travel through the lymphatic vessels to the nearest lymph node, where the immune response is systematically dismantled. Y. pestis is remarkably good at suppressing the host’s defenses, injecting toxins directly into immune cells and essentially shutting down the normal inflammatory response before reprogramming the lymph node into a bacterial incubator.3Immunity. Yersinia pestis Targets Lymph Nodes to Direct the Essential Events of Systemic Pathogenesis Once the bacteria overwhelm the node, the infection can spill into the bloodstream, leading to septicemic plague and, if it reaches the lungs, pneumonic plague, both of which carry much higher mortality rates than the bubonic form alone.
Plague is not just a relic of medieval history. It remains a zoonotic disease maintained in nature by rodent populations and transmitted primarily by fleas.4PubMed Central. Human case of bubonic plague resulting from the bite of a wild Gunnison’s prairie dog during translocation from a plague-endemic area Active plague foci still exist in parts of Africa (particularly Madagascar and the Democratic Republic of the Congo), Central and East Asia, and the Americas. In Latin America, cases and natural foci persist in Bolivia, Brazil, Ecuador, and Peru.5PubMed Central. Where Does Human Plague Still Persist in Latin America? Researchers continue to study Y. pestis strains from endemic rodent reservoirs in China and across Central Asia to understand how the bacterium evolves and spreads.6PubMed Central. Draft genome sequences of Yersinia pestis isolates from natural foci of endemic plague in China Even the western United States sees a handful of human cases each year, usually linked to contact with prairie dogs, ground squirrels, or their fleas.
Sexually Transmitted Infections That Cause Buboes
Plague is dramatic, but in many parts of the world, the most common reason a person develops a bubo is a sexually transmitted infection. The two main culprits are chancroid and lymphogranuloma venereum (LGV).
Chancroid is caused by the bacterium Haemophilus ducreyi. It produces painful genital ulcers, and because the bacteria drain into the inguinal (groin) lymph nodes, painful buboes often follow within a week or two of the initial sore.7Clinics in Dermatology. Chancroid These buboes can become fluctuant, meaning they feel soft and fluid-filled as pus accumulates inside the node. In some outbreaks, more than half of chancroid patients develop buboes that need some kind of drainage in addition to antibiotics.
LGV is caused by specific strains of Chlamydia trachomatis. Unlike regular chlamydia, which rarely causes noticeable lymph node swelling, the LGV strains are aggressive invaders of lymphatic tissue. The classic presentation is a painless genital ulcer that goes unnoticed, followed weeks later by large, tender inguinal buboes. LGV buboes can form interconnected abscesses with draining sinuses if left untreated, and they’re sometimes the first symptom a patient actually brings to a doctor.
Both chancroid and LGV are more common in tropical and subtropical regions, though LGV has seen a resurgence in high-income countries in recent years, particularly among men who have sex with men. Anyone with a painful groin lump and a recent history of unprotected sexual contact should be evaluated for these infections specifically, since treatment regimens differ depending on the pathogen.
Cat Scratch Disease and Other Animal-Borne Causes
You don’t need to encounter plague-carrying fleas or have an STI to develop a bubo. Cat scratch disease (CSD) is one of the more common causes of significant lymph node swelling in otherwise healthy people, especially children and adolescents. It’s caused by the bacterium Bartonella henselae, which cats carry in their blood (often without any symptoms of their own) and transmit to humans through scratches or bites.8PubMed Central. Treatment-Resistant Femoral Lymph Node Abscess Caused by Cat Scratch Disease: A Case Confirmed by Polymerase Chain Reaction
The typical CSD bubo appears one to three weeks after a scratch or bite, in the lymph node region that drains the wound site. A scratch on the hand might produce an axillary (armpit) bubo, while a scratch on the neck could cause cervical lymph node enlargement that mimics other conditions, making diagnosis tricky.9PubMed Central. Cat Scratch Disease – The Inconspicuous Cause of Cervical Lymphadenopathy In one reported pediatric case, an 11-year-old boy developed bilateral swollen cervical lymph nodes with the largest bubo reaching 3 to 5 centimeters across, alongside a papular rash on the nape of the neck, and testing confirmed high antibody levels against B. henselae.10Indian Journal of Case Reports. Pediatric cat-scratch disease: An illness hidden among lymphadenitis
CSD buboes can occasionally suppurate and form abscesses, and ultrasound imaging sometimes reveals necrotic tissue inside the node.11PubMed Central. Sonographic Evaluation of an Inguinal Bubo from Bartonella henselae: A Case Report Most cases resolve on their own or with a course of antibiotics, but some prove stubborn enough to require surgical drainage.
Tularemia, caused by the bacterium Francisella tularensis, is another animal-borne infection that produces buboes. The ulceroglandular form, which is the most common presentation, starts with a skin ulcer at the bite or contact site and progresses to enlarged, sometimes liquefying lymph nodes in the draining region. Cervical lymphadenopathy is a frequent manifestation.12PubMed Central. Vector-Borne Tularemia: A Re-Emerging Cause of Cervical Lymphadenopathy Tularemia is transmitted through tick bites, handling of infected animals (especially rabbits), and occasionally through contaminated water or aerosols. It’s found across much of the Northern Hemisphere and is classified as a potential bioterrorism agent because of how infectious F. tularensis is in aerosolized form.
What a Bubo Looks and Feels Like
A bubo is not the same thing as a mildly swollen gland you might notice during a cold. The swelling tends to be more pronounced, often 2 to 10 centimeters in diameter depending on the cause, and the node is usually tender to the touch or outright painful. The overlying skin can become red, warm, and stretched taut. In many cases, the area around the bubo is visibly swollen enough that the patient notices it before any other symptom.
As the infection progresses, a bubo can become fluctuant. At this stage, pressing on it reveals a fluid-filled quality rather than a firm, rubbery texture. This means pus has accumulated and the node may be on the verge of spontaneously draining through the skin. Plague buboes have a particularly grim progression: they can turn dark or purplish-black as tissue dies, and they may rupture if untreated, releasing infectious material. Buboes from chancroid and LGV don’t typically discolor this dramatically, but they can grow quite large and cause significant pain in the groin area that makes walking difficult.
Fever, chills, fatigue, and body aches commonly accompany a bubo regardless of the underlying cause. In plague, the fever tends to spike rapidly and severely. In CSD, the fever may be low-grade and accompanied by general malaise. Sexually transmitted buboes often come with concurrent genital symptoms like ulcers or discharge, though LGV’s initial ulcer can be so mild it goes unnoticed.
How Buboes Are Treated
Treatment depends entirely on the underlying cause, which is why getting a proper diagnosis matters so much. But there are two broad components to managing a bubo: killing the bacteria causing the infection and dealing with the bubo itself.
Antibiotics are the first-line treatment for every bubo-causing infection. For plague, the standard options include streptomycin, gentamicin, doxycycline, and ciprofloxacin. Treatment needs to begin as early as possible because untreated bubonic plague has a mortality rate in the range of 30 to 60 percent, dropping dramatically with prompt antibiotics. For chancroid, a single dose of azithromycin or a course of ceftriaxone typically clears the infection. LGV requires a longer course of doxycycline, usually three weeks. CSD often resolves without antibiotics in immunocompetent people, though azithromycin can speed recovery and is generally prescribed for more severe cases. Tularemia responds to aminoglycosides like gentamicin or streptomycin, or to fluoroquinolones in milder cases.
When a bubo becomes fluctuant and full of pus, antibiotics alone may not be enough. The collected fluid creates a walled-off abscess that drugs can’t penetrate well. Traditionally, clinicians used needle aspiration, inserting a needle to draw out the pus, sometimes repeating the procedure multiple times. Research during a chancroid epidemic found that incision and drainage was more effective, since patients who had their buboes aspirated frequently needed repeat procedures.13PubMed. Incision and drainage versus aspiration of fluctuant buboes in the emergency department during an epidemic of chancroid Incision and drainage resolves the issue in one visit in most cases, though it does leave a small wound that needs aftercare.
For non-fluctuant buboes (those that are swollen and tender but haven’t yet filled with pus), antibiotics are often sufficient on their own. The node gradually shrinks over days to weeks as the infection resolves. Warm compresses can help with comfort, and over-the-counter pain relievers manage the tenderness. Patients are generally advised not to squeeze or try to pop a bubo at home, since this can introduce additional bacteria or spread the existing infection.
Distinguishing a Bubo From Ordinary Swollen Lymph Nodes
Lymph nodes swell for all kinds of reasons, and most of the time the cause is benign. A viral upper respiratory infection, a skin infection, or even a minor scrape can make nearby lymph nodes temporarily enlarge. These reactive nodes are usually small (under a centimeter), mildly tender, and resolve on their own within a couple of weeks.
A bubo is different in several ways. The swelling is larger and more dramatic, typically more than 2 centimeters. The pain is often disproportionate to what you’d expect from a cold or minor infection. And there’s usually a clear infectious cause visible nearby: a bite wound, a genital ulcer, a skin lesion, or a recent flea bite in an endemic area. The key red flags that should prompt medical evaluation include rapid enlargement of a lymph node over days rather than weeks, skin changes over the node like redness or warmth, fever that accompanies the swelling, and a visible wound or lesion in the area that the lymph node drains.
Clinicians evaluating a potential bubo will ask about recent animal contact, travel history (especially to plague-endemic regions), sexual history, and occupational exposures. Imaging with ultrasound can help determine whether the node is simply enlarged or has become suppurative with necrotic tissue inside.11PubMed Central. Sonographic Evaluation of an Inguinal Bubo from Bartonella henselae: A Case Report Blood cultures, serologic testing, and sometimes biopsy of the node itself help identify the specific pathogen.
Who Is Most at Risk
Risk depends on which bubo-causing pathogen you’re exposed to. For plague, the highest risk belongs to people living in or traveling to areas with active rodent plague foci, particularly in sub-Saharan Africa, Madagascar, parts of South America, and rural areas of Central Asia and China.5PubMed Central. Where Does Human Plague Still Persist in Latin America? Occupational risk groups include wildlife biologists handling wild rodents, veterinarians in endemic areas, and occasionally hikers or campers who disturb rodent burrows. One documented case involved a wildlife worker bitten by a prairie dog during a translocation operation.4PubMed Central. Human case of bubonic plague resulting from the bite of a wild Gunnison’s prairie dog during translocation from a plague-endemic area
For STI-related buboes, risk tracks with sexual behavior. Chancroid is now relatively rare in high-income countries but remains common in parts of Africa, the Caribbean, and South Asia, particularly where access to prompt treatment is limited. LGV has become more prevalent in urban centers in North America and Europe, with outbreaks primarily affecting men who have sex with men.
Cat scratch disease is most common in children and young adults who own cats or spend time around kittens. Kittens are more likely to carry B. henselae than adult cats, and they’re also more likely to scratch during play. Immunocompromised individuals face a higher risk of developing severe or disseminated CSD, where the infection spreads beyond the local lymph node to organs like the liver and spleen.
Tularemia risk is tied to tick exposure, hunting and handling wild game (especially rabbits), and in rarer cases, exposure to contaminated water sources. Cases cluster in rural and semi-rural areas across North America, Europe, and parts of Asia.
When Buboes Become Dangerous
Most buboes, treated appropriately, resolve without lasting damage. The exceptions are worth knowing about. Plague buboes can rapidly progress to septicemia if the bacteria escape the node into the bloodstream. This shift from bubonic to septicemic plague can happen within hours, and septicemic plague is fatal in the majority of cases without immediate treatment. This is why any suspected plague case is treated as a medical emergency.
Even in less immediately dangerous infections, a bubo that goes untreated or is treated inadequately can become a chronic draining sinus. LGV is particularly notorious for this: untreated inguinal buboes from LGV can form what’s called a “groove sign,” where the lymph nodes above and below the inguinal ligament both enlarge and create a visible crease in the groin. Late-stage LGV can cause permanent lymphatic damage, leading to chronic genital swelling from impaired lymph drainage.
Cat scratch disease buboes occasionally resist standard antibiotic therapy. In such cases, an abscess forms that requires surgical drainage, and even after drainage, healing can take weeks.8PubMed Central. Treatment-Resistant Femoral Lymph Node Abscess Caused by Cat Scratch Disease: A Case Confirmed by Polymerase Chain Reaction For most patients with healthy immune systems, though, the long-term outcome is excellent once the infection is cleared. The lymph node returns to its normal size over weeks to months, and recurrence is rare because the immune system typically develops lasting protection against the specific bacterium.