Mycetoma has a worldwide distribution but this is extremely uneven. It is endemic in many tropical and subtropical regions. The African continent seems to be the area of the highest prevalence. It prevails in the mycetoma belt, which includes Sudan, Somalia, Senegal, India, Yemen, Mexico, Venezuela, Columbia, Argentina and others.
In Africa, mycetoma is most frequently seen in Sudan, Senegal, Mauritania, Kenya, Niger, Nigeria, Ethiopia, Chad, Cameroon, Djibouti and Somalia. In Asia, it has been extensively reported from India and Yemen. However, mycetoma has been reported in many temperate regions as well. Cases were reported from the United Kingdom, most of those afflicted were immigrants who probably contracted the infection overseas and the pale grain eumycetoma was the most common type. There are few reports on mycetoma from the United States, Ceylon, Germany, Egypt, Turkey, Philippines, Japan, Lebanon, Thailand, Saudi Arabia, Tunisia and Iran.
Areas where mycetoma prevails are relatively arid zones with a short rainy season of 4 - 6 months with the rainfall of 50 to 1000 mm per year, a relative humidity of 60 - 80% and fairly constant temperatures of 30 - 37 0C day and night. This is followed by a dry season of 6 - 8 months with a relative humidity of 12 - 18%, day temperatures of 45 – 600C and night temperatures of 15 - 180C.
The geographical distribution of the individual mycetoma organism shows considerable variations, which can be convincingly explained by climatic factors. These factors include the temperature, humidity and the rainfall and the latter is the most relevant factor.
Adapted from: van de Sande WWJ (2013) Global Burden of Human Mycetoma:
A Systematic Review and Meta-analysis. PLoSNegl Trop Dis 7(11): e2550. doi:10.1371/journal.pntd.0002550
Madurella mycetomatis, which is the commonest cause of fungal mycetoma, predominates in the tropical areas of Africa and India with a rainfall of 250-500 mm per year. Whereas, Streptomyces somaliensisis seen more often in the Middle East, Central and West Africa and the arid region adjacent to the Sahara desert with a rainfall of 50 to 100 mm per year. However, it is sometimes seen in areas with higher rainfall as in Mexico.
Actinomadura pelletierii is more prevalent in the relatively humid areas where the rainfall ranges from 250 to 1000 mm per year. Nocardiae are usually the causative organisms of mycetoma in temperate regions.
The mycetoma belt encases an area of forest trees and savannah. The dominant plants being various species of Acacia in addition to a variety of other thorny trees like Balanytesaegyptica and other thorny bushes, all these plants are armed with strong thorns.
There is an association between mycetoma pathogenesis and thorns. The penetrating thorns facilitate the entry of the organism into the subcutaneous tissue as it lives saprophytically on or inside the thorn. This was documented in serial sections of thorns removed from two mycetoma patients. In these patients, the thorns cells contained many fungal elements in different stages of development were reported. From one of them, Leptosphaeriasenegaliensiswas isolated and Pyrenochaetaromeroifromin the other. The presence of thorns in the vicinity of the mycetoma granuloma had been observed histologically and during surgery. Thorns may have the ability to produce the granuloma and probably they provide an appropriate nucleus for the development of the mycetoma organism. The fact that the disease is common among rural people who go barefooted is in line with these observations. However, in many patients there is no history of local trauma at the mycetoma site.