The disease is typically endemic in low-income countries where people live and walk barefoot and are persistently in contact with irritant alkaline volcanic clay soils. The disease is geographically restricted to countries with highland areas (more than 1500 meters, 5000 feet, above sea level) and associated with high annual rainfall (more than 1500 mm, 59.1 inches) and with mean annual land surface temperatures of 19°C-20°C (66.2°F-68°F). These geological features are found in tropical regions of Africa (the highest disease incidence is in Ethiopia), Central and South America, and northwestern India, where the use of footwear may not be common practice. Historically, podoconiosis was eradicated in European countries (such as France, Ireland, and Scotland) when footwear became the norm.
Approximately 4 million people are affected by podoconiosis worldwide. Ethiopia has the largest number of podoconiosis patients, with an estimated 1 million Ethiopians affected by the disease. In endemic areas, podoconiosis is reportedly more prevalent than HIV infection, tuberculosis, malaria, and filarial elephantiasis.
Farmers, goldmine workers, potters, and weavers are at high risk for developing the disease. There is no sex predilection, and most affected individuals are aged 16-45 years. The economic impact to the community from podoconiosis is significant. There is an enormous loss of productivity, because it affects individuals who are in their most productive age range. Despite its significant socioeconomic impact on individuals and countries as a whole, podoconiosis receives little attention from local health authorities because of its lack of immediate threat to life. In 2011, the World Health Organization (WHO) listed podoconiosis as one of the 20 neglected tropical diseases.
The pathogenesis of podoconiosis is poorly understood. It is postulated that mineral particles from the soil penetrate through and irritate the skin of the foot. They are phagocytized by lymphatic macrophages, eliciting an intense inflammatory response that leads to cutaneous fibrosis and lymphedema from blockage of the lymphatic vessels. However, this does not explain why only a portion of the people exposed to the same irritant soils develop the disease. Other suggested predisposing factors are familial heritability (siblings have a 5 times higher chance of contracting the disease than the general population), genetic susceptibility (HLA-DQA1, HLA-DQB1, HLA-DRB1), or micronutrient deficiencies.
The clinical presentation of podoconiosis depends on the degree and chronicity of exposure to the irritant soils. Typical cutaneous lesions involve both feet asymmetrically and ascend and progress up to the knees. Clinical features of the early stage of podoconiosis are itching and burning sensation of the foot, splaying of the forefoot, plantar edema with lymph oozing, increased skin markings, hyperkeratosis with the formation of moss-like papillomas, and rigid toes. The late stage of the disease is characterized by multiple hard, leathery nodules, giving rise to severe elephantiasis disfigurement of the lower legs.
I89.0 – Lymphedema, not elsewhere classified
251490001 – Lymphedematous hyperkeratosis
- Filarial elephantiasis – Skin lesions usually extend to the thigh and groin. Occurs in lowland regions where mosquito vectors could transmit disease. The immunodiagnostic assay for Wuchereria bancrofti is a useful tool for diagnosis of filariasis.
- Lepromatous lymphedema – There is loss of sensation to the feet and toes, presence of thickened nerves, or trophic ulcers. Hands could be involved.