Mycetoma is a chronic infection of the skin and underlying tissue caused by certain bacteria or fungi that enter the body through a break in the skin, typically a thorn prick or small wound on the foot. It produces painless swelling that slowly grows over months or years, eventually forming open channels that drain pus containing tiny sand-like particles called “grains.” Around 10,000 new cases are reported worldwide each year, though the true number is likely much higher due to underreporting.
How Mycetoma Gets Into the Body
The organisms that cause mycetoma live in soil and on vegetation in warm, dry climates. When a person steps on a thorn, scrapes their skin on rough ground, or sustains any minor puncture wound, the bacteria or fungi can be pushed beneath the skin surface. The foot is the most common site because many people in endemic areas walk barefoot or in open sandals, but mycetoma can develop on the hands, back, or any body part exposed to contaminated material.
Once inside, the organisms form colonies deep in the tissue. They multiply slowly, building dense clusters (the “grains”) surrounded by layers of inflammatory and scar tissue. Over time, the infection spreads outward through the soft tissue, and if left untreated, it can invade muscle and bone.
Two Types With Different Causes
Mycetoma falls into two categories depending on whether the infection is bacterial or fungal, and the distinction matters because treatment is completely different for each.
Actinomycetoma is caused by filamentous bacteria, most commonly species of Nocardia, Actinomadura, and Streptomyces. This form tends to respond to long courses of antibiotics, often combinations that include trimethoprim-sulfamethoxazole as a backbone. Treatment typically lasts at least 12 months, sometimes longer, and may involve cycles of injectable antibiotics for resistant cases. Actinomycetoma is the dominant form in Mexico and parts of Latin America.
Eumycetoma is caused by true fungi, with Madurella mycetomatis being the most common species worldwide. Fungal mycetoma is harder to treat. Antifungal medications are less effective than antibiotics are against the bacterial form, and surgery plays a larger role. Eumycetoma predominates in Sudan and much of Africa.
Where Mycetoma Is Found
The disease clusters along what’s known as the “mycetoma belt,” a band of tropical and subtropical territory that stretches roughly between the Tropics of Cancer and Capricorn. Countries with the highest reported case counts include Sudan and Mexico, but endemic areas also span Chad, Ethiopia, India, Mauritania, Senegal, Somalia, Venezuela, Thailand, and Yemen. These regions share a common climate pattern: short rainy seasons followed by long dry stretches that encourage the growth of thorny bushes, the very vegetation responsible for most inoculating injuries.
Most affected individuals are young men between 20 and 40 who work in agriculture, herding, or other outdoor occupations. Poverty is a major driver. Limited access to footwear, delayed medical care, and scarce diagnostic facilities all allow the disease to progress before it’s identified.
What Mycetoma Looks and Feels Like
The hallmark of mycetoma is a triad of three features: a painless, firm lump beneath the skin; multiple sinus tracts (small tunnels) that open to the surface; and discharge from those openings containing the characteristic grains. The grains can be white, yellow, red, brown, or black depending on the causative organism, and their color helps doctors determine what type of mycetoma is present.
Early on, the only sign may be a small, hard nodule on the foot or lower leg that doesn’t hurt. Because there’s no pain, people often ignore it for months or even years. Gradually the lump grows, the overlying skin develops draining openings, and the foot or affected area becomes visibly swollen and deformed. Pain typically only appears once the infection has reached bone or when a secondary bacterial infection develops on top of the original one.
How It’s Diagnosed
Doctors can often suspect mycetoma from its appearance alone, especially in someone from an endemic region. Examining the color and structure of the discharged grains under a microscope helps distinguish bacterial from fungal disease, which is the single most important diagnostic step because it dictates treatment.
Imaging adds valuable information about how deep the infection has spread. Ultrasound and MRI can reveal a pattern known as the “dot-in-circle sign,” where small round pockets of inflamed tissue appear surrounded by fibrous walls, with a dark central spot representing the grain itself. This pattern is seen in up to 80% of people with mycetoma and is considered highly specific to the disease. X-rays are useful for detecting bone involvement in advanced cases.
Several other conditions can look similar. Bacterial bone infections, tuberculosis of the skin, certain fungal infections like chromoblastomycosis and sporotrichosis, and even some cancers such as soft-tissue sarcoma or Kaposi sarcoma can mimic the appearance of mycetoma. Lymphatic swelling from other causes can also be confused with it. Grain identification and imaging together usually clarify the diagnosis.
Treatment and What to Expect
For actinomycetoma, the standard approach is a prolonged course of combination antibiotics. The most established first-line regimen uses trimethoprim-sulfamethoxazole taken orally for a minimum of 12 months, often paired with a second antibiotic. Treatment continues until the infection is fully cleared, which can take well beyond a year. When the disease involves bone or doesn’t respond to oral medications, doctors may add cycles of injectable antibiotics. Bacterial mycetoma generally has a better outlook than the fungal form when caught reasonably early.
Eumycetoma is more stubborn. Antifungal medications are given for extended periods, but cure rates are lower. Surgery is frequently needed alongside drug therapy, ranging from excision of the infected tissue to wider removal when bone is involved.
For both types, surgery is indicated when the lesion is small and well-contained (where complete removal may be possible) or when the disease is massive and the goal is to reduce the infection load so medications can work more effectively. In the most advanced cases, where the infection has recurred after multiple surgeries, hasn’t responded to prolonged drug treatment, or has caused life-threatening complications like sepsis, amputation may be the only remaining option. This is one reason early diagnosis matters so much: a disease that starts as a painless lump can, over years of neglect, result in the loss of a limb.
Prevention in Endemic Areas
Because mycetoma enters through skin wounds, the most straightforward preventive measure is wearing protective footwear. Closed shoes or boots significantly reduce the chance of thorn pricks and soil contact. In farming communities where the disease is most common, promoting consistent use of shoes is a public health priority, though economic barriers make this harder than it sounds. Early attention to any persistent, painless lump on the foot or lower leg, particularly after a thorn injury, can make the difference between a treatable infection and one that has already reached bone.
The WHO recognizes mycetoma as a condition of significant concern in its neglected tropical diseases program. The global burden remains poorly quantified because surveillance systems in most endemic countries are limited, and many cases are never formally diagnosed. Improved awareness, both among affected communities and among healthcare workers in non-endemic countries who may encounter it in travelers or immigrants, is one of the most practical tools available for reducing the disability this disease causes.