Podoconiosis is a type of elephantiasis (leg swelling) found in subsistence farming communities in the tropics. It is an unusual disease, triggered not by any bacterium, virus or parasite, but by an abnormal reaction to irritant mineral particles found in soils of volcanic origins.
Many years of walking, ploughing or going barefoot on these clay soils appears to trigger inflammatory changes within the lymph system in the legs, then foot swelling, and after years of exposure to the mineral particles, elephantiasis.
It was the work of Dr Ernest Price, in the 1970s, that established the link between irritant soils and podoconiosis (pdf), but research is still necessary to establish precisely what the mineral trigger is.
Not everyone who lives and works on irritant soils without shoes becomes affected. Studies have shown strong ‘heritability’ of podo susceptibility, and current research is homing in on where the susceptibility genes might lie on the genome.
economic and social consequences
In a 2005 economic study, podoconiosis cost Ethiopia an estimated $208 million per year in lost productivity and medical costs. This level of impact multiplies across the number of endemic countries worldwide. It also has profound social impact – affected individuals are — for a variety of reasons — typically barred from attending school, ostracised from social and religious events, and have difficulty finding marriage partners, marginalizing them with little prospect for a meaningful life as a contributing member of their communities.
The most common cause of elephantiasis in the tropics is lymphatic filariasis (‘LF’), which is responsible for an estimated 14 million people with leg swelling worldwide. Although LF sometimes resembles podoconiosis, there are easy ways of distinguishing between the two:
- LF occurs in low-lying areas (<1500m/5000ft) where mosquitoes can transmit the parasite
- Podoconiosis occurs in highland areas (>1500m/5000ft) where mosquitoes are rarer, and climatic conditions favour intense weathering of volcanic rock into irritant soil
- LF symptoms tend to start in the groin, and the leg swelling is commonly unilateral (occurring most notably in one leg or the other) and descending from the groin area down towards the feet
- Podoconiosis symptoms tend to start in the foot, be bilateral (though asymmetric) and ascending, though swelling is rare above the knee.
Laboratory tests such as the BinaxNOW filariasis rapid antigen test can be used to distinguish LF from podoconiosis where doubt remains.
Field experience and a pilot study suggest the effectiveness of simple, inexpensive lymphoedema management (foot hygiene [washing with water and antiseptic], emollient, bandaging, exercise/massage, and socks & shoes) in reducing swelling, improving clinical appearance and quality of life for podoconiosis patients. A formal trial of this treatment is planned.
Dr Ernest Price, a British leprologist, suggested that podoconiosis was previously common in North Africa (Algeria, Tunisia, Morocco and the Canary Islands) and parts of Europe, but is no longer found in these areas since use of footwear has become the norm.
In highland volcanic areas (>1500m/5000ft), everyday foot washing and use of shoes or boots to protect feet against irritant soil is encouraged to help prevent podoconiosis. Research studies are planned to measure the effectiveness of various means of disease prevention.