Date: Thursday, 7 December 2023
Time: 4:00 PM Rwandan time (UTC+2)
Physical Venue: Conference Room ICTP-EAIFR, Einstein Building, UR-CST Campus, Fifth floor.
On-line Platform Zoom: please, register here
Non-communicable disease among the poor in Rwanda has a very different face than that seen in middle- or
high-income populations. While Rwanda has enjoyed rapid economic growth and political stability in recent years,
most of the population survives on subsistence agriculture. Bare foot farmers suffer from Podoconiosis, a nontransmissible Elephantiasis type of neglected tropical disease (NTD) according to WHO; In Rwanda its severity
compares to other prevalent diseases such as asthma, as assessed by its disability-adjusted life year DALY (000’s)
value of 47.6, with higher risk among women and genetically susceptible individuals. Podoconiosis is a
lymphoedemia, of the lymph vessels leading to feet and legs swelling. It is caused by chronic exposure during
early childhood to high-altitude irritant volcanic soils. Since beginning in the 1960s, massive migration of mainly
cultivators replaced in the affected areas the indigenous hunter-gathering tribe. Subsequently, land use pattern
changed drastically, from forest dominated to subsistence agriculture on volcanic soils were cultivated. While the
period of mass cultivation coincides with the appearance of the disease in the area, climate change may exacerbate
it through loss of soil organic matter and thus bioavailable soil irritant mineral particles, which penetrate the skin
of the foot, migrate into lymphatic vessels where they are taken up by macrophages and induce inflammation
with subsequent fibrosis.
Podoconiosis etiology was first described in the 1970s by Dr. Ernest W. Price, a British surgeon living in Ethiopia,
working in a leprosarium. Studying with electron microscopy the lymph nodes and vessels of patients affected by
the disease, he showed the presence of silicon, aluminum both in the phagosomes of macrophages and adherent
to the surface of lymphocytes, a finding we recently confirmed (and extended, e.g. to titanium) by advanced LIBS
spectro-microscopic measurements. Bare foot farming occurs throughout the tropics without known occurrence
of such a disease, and thus minerals typical of lateritic soils such as kaolinite or iron and aluminum oxides are
poor candidates for such an uptake. Among minerals naturally present in volcanic soils, (such as allophane,
halloysite), only one has the asbestos-like morphology that could favor such a skin uptake: Imogolite, with its 1
nm wide nanotubes morphology. We will discuss the conditions leading to such an irritant mineral, by discussing
volcanic soil (andosol) pedogenesis, physical-chemical, but also microbial, processes leading to their growth on
pumice, and possibly volcanic ashes. We will also discuss some microbial co-infection, recently demonstrated by
a Cameroon-Germany team, as well as some specific imogolite properties (e.g. hydrophobicity) which could lead
to this uptake. Finally, we will compare skin potential exposure to natural nanotubes (imogolite) with that to
modern nanotechnology, nanowires, good candidates for future touch-screens.
Abstract
Non-communicable disease among the poor in Rwanda has a very different face than that seen in middle- or
high-income populations. While Rwanda has enjoyed rapid economic growth and political stability in recent years,
most of the population survives on subsistence agriculture. Bare foot farmers suffer from Podoconiosis, a nontransmissible Elephantiasis type of neglected tropical disease (NTD) according to WHO; In Rwanda its severity
compares to other prevalent diseases such as asthma, as assessed by its disability-adjusted life year DALY (000’s)
value of 47.6, with higher risk among women and genetically susceptible individuals. Podoconiosis is a
lymphoedemia, of the lymph vessels leading to feet and legs swelling. It is caused by chronic exposure during
early childhood to high-altitude irritant volcanic soils. Since beginning in the 1960s, massive migration of mainly
cultivators replaced in the affected areas the indigenous hunter-gathering tribe. Subsequently, land use pattern
changed drastically, from forest dominated to subsistence agriculture on volcanic soils were cultivated. While the
period of mass cultivation coincides with the appearance of the disease in the area, climate change may exacerbate
it through loss of soil organic matter and thus bioavailable soil irritant mineral particles, which penetrate the skin
of the foot, migrate into lymphatic vessels where they are taken up by macrophages and induce inflammation
with subsequent fibrosis.
Podoconiosis etiology was first described in the 1970s by Dr. Ernest W. Price, a British surgeon living in Ethiopia,
working in a leprosarium. Studying with electron microscopy the lymph nodes and vessels of patients affected by
the disease, he showed the presence of silicon, aluminum both in the phagosomes of macrophages and adherent
to the surface of lymphocytes, a finding we recently confirmed (and extended, e.g. to titanium) by advanced LIBS
spectro-microscopic measurements. Bare foot farming occurs throughout the tropics without known occurrence
of such a disease, and thus minerals typical of lateritic soils such as kaolinite or iron and aluminum oxides are
poor candidates for such an uptake. Among minerals naturally present in volcanic soils, (such as allophane,
halloysite), only one has the asbestos-like morphology that could favor such a skin uptake: Imogolite, with its 1
nm wide nanotubes morphology. We will discuss the conditions leading to such an irritant mineral, by discussing
volcanic soil (andosol) pedogenesis, physical-chemical, but also microbial, processes leading to their growth on
pumice, and possibly volcanic ashes. We will also discuss some microbial co-infection, recently demonstrated by
a Cameroon-Germany team, as well as some specific imogolite properties (e.g. hydrophobicity) which could lead
to this uptake. Finally, we will compare skin potential exposure to natural nanotubes (imogolite) with that to
modern nanotechnology, nanowires, good candidates for future touch-screens.
