The pathology of non-filarial elephantiasis of the lower legs

Evidence for immune activation in pathogenesis of the HLA class II associated disease, podoconiosis

Available evidences suggest that podoconiosis is triggered by long term exposure of bare feet to volcanic red clay soil particles. Previous genome-wide studies in Ethiopia showed association between the HLA class II region and disease susceptibility. However, functional relationships between the soil trigger, immunogenetic risk factors and the immunological basis of the disease are uncharted. Therefore, we aimed to characterise the immune profile and gene expression of podoconiosis patients relative to endemic healthy controls. Peripheral blood immunophenotyping of T cells indicated podoconiosis patients had significantly higher CD4 and CD8 T cell surface HLA-DR expression compared to healthy controls while CD62L expression was significantly lower. The levels of the activation markers CD40 and CD86 were significantly higher on monocytes and dendritic cell subsets in patients compared to the controls. RNA sequencing gene expression data indicated higher transcript levels for activation, scavenger receptors, and apoptosis markers while levels were lower for histones, T cell receptors, variable, and constant immunoglobulin chain in podoconiosis patients compared to healthy controls. Our finding provides evidence that podoconiosis is associated with high levels of immune activation and inflammation with over-expression of genes within the pro-inflammatory axis. This offers further support to a working hypothesis of podoconiosis as soil particle-driven, HLA-associated disease of immunopathogenic aetiology.

A geochemical and mineralogical characterization of soils associated with podoconiosis

Podoconiosis is a disease that causes swelling and disfiguration of the lower legs found in several developing countries where shoes are not regularly worn. The current model for the etiology of the disease proposes that mineralogical agents enter the lymph system through the skin leading to inflammation that causes swelling of the feet and legs. We collected 125 soil samples from 21 towns associated with podoconiosis, 8 towns unassociated with Podoconiosis as controls, and 3 towns of unknown status. Data collected for each soil sample included color, particle size, mineralogy, and geochemistry to distinguish unique components within the podoconiosis-associated soils. Our results indicate podoconiosis-associated soils are more highly weathered than non-podoconiosis associated soils. The enrichment of kaolinite and gibbsite suggests that these minerals, their surface chemistry, and trace elements associated with them should be prioritized in future podoconiosis research. In addition, we found that color may be a valuable tool to identify soils at greater risk for inducing podoconiosis.

Podoconiosis: Clinical spectrum and microscopic presentations

Background

Podoconiosis is a skin Neglected Tropical Disease (skin NTD) that causes lymphoedema, and affects barefooted subsistence farmers in some tropical countries. The clinical presentation and histopathologic correlates of podoconiosis have been understudied. Here, we systematically document the clinical and histopathologic spectrum of podoconiosis.

Methods

This is a cross-sectional study in Durbete, Ethiopia from February 2018 to October 2019. Dermatologists performed a patient history, physical examination, filariasis test strip, and skin biopsy for histopathologic examination. The results were summarised and a descriptive statistical analysis and Wilcoxon rank sum test with continuity correction was done.

Results

We recruited 289 patients for the study, 178 (61.6%) had stage 1 or 2 podoconiosis, and 111(38.4%) stage 3 to 5 podoconiosis. 188 (64.1%) had a family history of podoconiosis. In 251 (86.9%) patients, both legs were affected by podoconiosis and in 38 (13.1%) only one leg was affected. 220 (77.5%) patients had warty lesions, 114 (39.4%) had nodules. The median number of episodes of Acute Dermato-Lymphangio-Adenitis (ADLA) reported by the patients in the last three months was 2 (interquartile range (IQR) 1–4). Increased episodes of ADLA were significantly associated with stage 3–5 podoconiosis (P = 0.002), while burning pain in the feet was more common in stage 1 or 2 podoconiosis. Stage 3–5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as thickened collagen bundles.

Conclusion

We provide a detailed description of the different clinical patterns, associated clinical findings and the histopathologic spectrum of podoconiosis at different stages of the disease. Our observations should serve as a guide to classifying patients with podoconiosis for prognostic assessment and treatment decision.

Podoconiosis - From known to unknown: Obstacles to tackle

Podoconiosis is a non-filarial and non-communicable disease leading to lymphedema of the lower limbs. Worldwide, 4 million individuals live with podoconiosis, which is accompanied by disability and painful intermittent acute inflammatory episodes that attribute to significant disability adjusted life years (DALYs). Different risk factors like contact with volcanic red clay soil, high altitude (above 1000 m), high seasonal rainfall (above 1000 mm/year) and occupation (e.g., subsistence farmer) are associated with the risk of podoconiosis. Although podoconiosis was described to be endemic in 32 countries in Africa, parts of Latin America and South East Asia, knowledge about related genetics, pathophysiology, immunology and especially the causing molecule(s) in the soil remain uncertain. Thus, podoconiosis can be considered as one of the most neglected diseases. This review provides an overview about this non-filarial related geochemical disease and aim to present perspectives and future directions that might be important for better understanding of the disease, prospect for point-of-care diagnosis, achieving protection and developing novel treatment strategies.

Genetic analysis of endometriosis and depression identifies shared loci and implicates causal links with gastric mucosa abnormality

Evidence from observational studies indicates that endometriosis and depression often co-occur. However, conflicting evidence exists, and the etiology as well as biological mechanisms underlying their comorbidity remain unknown. Utilizing genome-wide association study (GWAS) data, we comprehensively assessed the relationship between endometriosis and depression. Single nucleotide polymorphism effect concordance analysis (SECA) found a significant genetic overlap between endometriosis and depression (P_{Fsig-permuted} = 9.99 × 10^-4). Linkage disequilibrium score regression (LDSC) analysis estimated a positive and highly significant genetic correlation between the two traits (r_G = 0.27, P = 8.85 × 10^-27). A meta-analysis of endometriosis and depression GWAS (sample size = 709,111), identified 20 independent genome-wide significant loci (P < 5 × 10^-8), of which eight are novel. Mendelian randomization analysis (MR) suggests a causal effect of depression on endometriosis. Combining gene-based association results across endometriosis and depression GWAS, we identified 22 genes with a genome-wide significant Fisher's combined P value (FCP_gene < 2.75 × 10^-6). Genes with a nominal gene-based association (P_gene < 0.05) were significantly enriched across endometriosis and depression (P_{binomial-test} = 2.90 × 10^-4). Also, genes overlapping the two traits at P_gene < 0.1 (P_{binomial-test} = 1.31 × 10^-5) were significantly enriched for the biological pathways 'cell-cell adhesion', 'inositol phosphate metabolism', 'Hippo-Merlin signaling dysregulation' and 'gastric mucosa abnormality'. These results reveal a shared genetic etiology for endometriosis and depression. Indeed, additional analyses found evidence of a causal association between each of endometriosis and depression and at least one abnormal condition of gastric mucosa. Our study confirms the comorbidity of endometriosis and depression, implicates links with gastric mucosa abnormalities in their causal pathways and reveals potential therapeutic targets for further investigation.

Involvement of Hookworm Co-Infection in the Pathogenesis and Progression of Podoconiosis: Possible Immunological Mechanism

Podoconiosis is an endemic, non-infectious, geochemical and non-filarial inflammatory cause of tropical elephantiasis. The immunology of podoconiosis is not yet expressly understood. In spite of this, co-infection and co-morbidity with the infectious, soil-transmitted hookworm disease that causes iron deficiency anemia has been found to be predominant among affected individuals living in co-endemic settings, thus creating a more complex immunological interplay that still has not been investigated. Although deworming and iron-rich nutrient supplementation have been suggested in podoconiosis patients living under resource-poor conditions, and it is thought that hookworm infection may help to suppress inflammatory responses, the undisputed link that exists between a non-infectious and an infectious disease may create a scenario whereby during a co-infection, treatment of one exacerbates the other disease condition or is dampened by the debilitation caused by the other. In this paper, we elaborate on the immunopathogenesis of podoconiosis and examine the possible immunological dynamics of hookworm co-infection in the immunopathology of podoconiosis, with a view toward improved management of the disease that will facilitate its feasible elimination.

[Podoconiosis, a society and medical community neglected disease]

Podoconiosis, mossy foot or endemic non-filarial elephantiasis, is a geochemical disease that causes lower limb lymphedema; it is directly related to walking barefoot over soils of volcanic origin, in areas with a high pluviometric annual index. It has a specific geographical distribution, affecting around 5% population in areas where it is endemic. It is debilitating and disfiguring disease, which frequently leads to social margination. Podoconiosis is totally preventable and, once a diagnosis is established, it may improve with simple therapeutic measures.

Podoconiosis: endemic nonfilarial elephantiasis

PURPOSE OF REVIEW

Podoconiosis is a noncommunicable disease producing lymphoedema of the lower limbs; it affects predominantly barefoot agricultural workers in the tropics. Why should this be of interest to a journal of infectious disease? For many years this disease has not been widely recognized as distinct from lymphatic filariasis and yet it may affect about 10% of populations in volcanic tropical highlands. It produces considerable morbidity associated with limb lymphoedema, impacting on economically productive age groups. As it does not fall into the briefs of infectious or chronic disease initiatives of the World Health Organization, it has been difficult to attract funds for research and for the development of community management approaches. The aim of this review is to describe details of the clinical features, management, epidemiological significance and evidence for the underlying aetiology of this poorly understood condition.

RECENT FINDINGS

A recent comprehensive study in Ethiopia by Destas et al. identified a mean zonal prevalence of 5.46% of the population with 64% being in the economically productive age group. Otherwise there are no other contemporary epidemiological publications in this field.

SUMMARY

Podoconiosis is thought to be a geochemical disease induced by the absorption of ultrafine silica particles from the soil (konia) through the skin of the feet (podos) in susceptible individuals, leading to a progressive obliterative endolymphangitis.

The immunopathology of siliconosis. History, clinical presentation, and relation to silicosis and the chemistry of silicon and silicone

Recent evidence confirms the fundamental involvement of the human immune system in the reaction to implantation of silicone-based medical devices. An as yet-to-be particularized epitope of many complex substances sharing siloxane structures is presented through the MHC-II apparatus with development and retention of T cell memory. This memory can be tested for in practical terms using one or more forms of silica, which links the immuno-histopathology and autoimmune attributes of "silicosis" with those of "siliconosis." The lesions of siliconosis are typical of those for persistent antigens and delayed, cell mediated hypersensitivity. The basic descriptive pathology of the reaction to silicone has been known since soon after introduction of silicones in medical procedures, with the exception of some details related to the more recent discoveries on the role of cytokines in the immunopathic process. The clinical consequences of siliconosis are common and can be severe in some individuals implanted with silicone devices.

Studies on filariasis in Bauchi State, Nigeria. 1. Endemicity of human onchocerciasis in Ningi Local Government Area

The endemicity of human onchocerciasis was assessed in eight rural, at-risk communities in Ningi Local Government Area, Bauchi State, Nigeria, between July 1990 and March 1991. Of the 1536 subjects skin-snipped, 334 (21.7%) were positive for Onchocerca volvulus microfilariae. Surprisingly, there was a significant inverse relationship between prevalence and mean microfilarial load (r = -0.608; P < 0.05). Males were more likely to be infected than females (P < 0.01) and cattle rearers (71.0% infected), farmers (49.8%) and fishermen (40.0%) had significantly higher prevalences than students/schoolchildren, housewives or traders (P < 0.001). Pruritus and itchy eyes were recorded in all age groups and appeared in much younger subjects than any other manifestations of the infection. Prevalence and onchocercal blindness were linearly related to intensity of infection. The epidemiological significance of these findings, in terms of a future community-wide programme of long-term chemoprophylaxis with Mectizan, is highlighted.

Endemic Kaposi's sarcoma in Africa and local volcanic soils

Endemic Kaposi's sarcoma (KS) in Africa has been attributed to a geographically-determined environmental factor. Endemic KS, a chronic nodular condition predominantly affecting the feet and legs, is believed to arise in the lymphatic endothelium and is associated with chronic lymphoedema. As such, KS bears a resemblance to podoconiosis (non-filarial elephantiasis). The prevalence of both conditions in highland areas close to volcanoes suggests a shared pathogenetic relationship to exposure to volcanic soils. The lymphatics and lymph nodes of patients with podoconiosis contain particulate alumino-silicates in macrophages consistent with the theory that ultrafine clay minerals are absorbed through the feet. The resulting chronic lymphatic irritation, inflammation, and collagenosis causes obstruction and lymphoedema. The geographical proximity of endemic KS to areas containing volcanic clay minerals, its lympho-endothelial origin, predilection for the feet and legs, and its prevalence among rural peasants and cultivators, suggest a common aetiology. Other features point to the participation of a low-grade, possibly sexually-transmitted, infective agent that becomes more pathogenic in the presence of immunosuppression. Damage to the dermal lymphatics of the feet and legs by absorbed clays could impair local immunity to such an agent. Endemic KS would then occur in exposed individuals who harbour the KS infective agent and are susceptible to the KS phenotype (males).

The possible role of soil particles in the aetiology of non-filarial (endemic) elephantiasis: a macrophage cytotoxicity assay

A link between the incidence of non-filarial elephantiasis and tropical red clay soil has been suggested after epidemiological surveys in Ethiopia and other African countries, although the mode of action of these soils in disease induction is unknown. We have thus investigated the physical composition of soils from both endemic and non-endemic areas of Ethiopia and their effect on the viability of macrophages using in vitro systems. Endemic and non-endemic soils were avidly phagocytosed by the macrophages. Cell shape was seen to change over a 144-hour period, the cells changing from approximately circular to spindle or stellate shape. Both groups of soils were cytotoxic towards the macrophages. Greatest cell death occurred during the first 48-hour period although some cells were viable after 96 hours. The soil groups could be divided by assessing their contents of silicon and aluminium, as well as observing the number of sub-2 micron particles they contained. The present study gives support to the epidemiological studies implicating soils as the cause of non-filarial elephantiasis.

The effects of silica on lymph nodes and vessels--a possible mechanism in the pathogenesis of non-filarial endemic elephantiasis

Non-filarial tropical elephantiasis, which occurs in certain volcanic areas of the world, has been postulated to be an obstructive lymphopathy due to the fibrogenic effects of silica absorbed through the plantar skin of bare-footed people. Animal experiments involving the direct intralymphatic injection of fine silica particles have been carried out in order to assess the extent to which this substance can engender lymphatic obstruction and to determine its main site of action. Intralymphatic silica provoked an immediate and intense macrophage reaction with later fibrosis both within lymph vessels and to a lesser extent within lymph nodes. Lymphography indicated that the consequent obstruction resulted more from the effects of silica on vessels than on nodes.

Effect of immunosuppressive or inflammatory agents on lymphatic dilatation in cats infected with Brugia pahangi

Cats infected with Brugia pahangi were immunosuppressed and the development of lymphatic pathology, as measured xeroradiographically by dilatation of the vessels, in these animals was compared with that of normally infected cats. Individual cats showed wide variations in response. Niridazole and antilymphocyte serum both reduced dilatation, niridazole being particularly effective in the early stages of infection. When silica, used as an inflammatory agent, was injected subcutaneously in conjunction with worm infection lymphatic dilatation developed, this being potentiated in degree and rate of development as compared with control animals. The possible role of a non-filarial inflammatory response in the development of lymphatic dilatation is discussed.

Verrucous and elephantoid lymphedema: morphologic spectrum and terminology

Five patients with varying severities of hyperkeratotic verrucous thickening at the skin illustrate that the condition may occasionally become elephantoid and occurs in some cases of long-standing lymphedema regardless of its cause. The morphologic term "elephantiasis" has been associated with the end of lymphedema, but has been used by different authors to mean different things and has, therefore, become imprecise. The noun "lymphedema" modified by the appropriate adjective is more accurate in describing these skin changes. Under the heading--"elephantiais"--Index Medicus now states--"see lymphedema."

Silica and silicates in femoral lymph nodes of barefooted people in Ethiopia with special reference to elephantiasis of the lower legs

Electron microscopy of femoral lymph nodes of barefooted Ethiopians show the presence of numerous particles of colloid-size and electron-density in the lysosomes of the macrophages in the gland. On diffraction analysis, the particles are found to be amorphous. Elemental microanalysis of the X-ray spectrum indicate the predominance of Si, Al and Fe. In elephantiasics some particles contain silicon alone, presumably silica. The distribution of the Al/Si ratios of the particles in subjects with elephantiasis of the lower legs show a difference from that of non-elephantiasics which is statistically "highly significant" at p less than 0.001. The importance of this as a possible aetiological factor in the disease is discussed. The hypothesis that the disease is discussed. The hypothesis that the disease is a silicosis of the peripheral lymphatics of the lower limbs is supported by the present study.

Man-biting species of Chrysops meigen, Culicoides latreille and Simulium latreille in Ethiopia, with discussion of their vector potentialities

Human filariasis and its vectors are little known in Ethiopia. Wuchereia bancrofti is confined to the western lowlands and cannot be the aetiological agent of elephantiasis in the highlands. Onchocerca volvulus is widespread in the south-western highlands. Loa loa and Dipetalonema perstans are reported here for the first time and appear to be uncommon. Studies were conducted in 1973, mostly near Jimma in Kaffa Province, on potential vectors of all but the first of these parasites. Among Simuliidae, the only blackflies of apparent medical importance were S. woodi ethiopiense and a possibly new member of the S. damnosum complex. The former is less seasonal and much less numerous than the latter, but may be more widespread and important along smaller and higher streams. Onchocerca larvae were recovered from "damnosum", but not from the small number (46) of ethiopiense examined. In August, at the height of the rainy season, the biting-rate of ethiopiense at 1,710 m altitude on the Gilgil Ghibe river reached 9.5/man-hour at 10-1100 hours and about 12/man-hour at 14-1600 hours. At the same time and place, the attack of "damnosum" reached a midday climax of about 1,800/man-hour; this peak could be delayed or suppressed by rain. Another possibly anthropophilic blackfly, S. dentulosum, tended to become most common in December afer the rainy season had passed, but proved incompetent to bite man successfully. The only feasible loiasis vector found in Ethiopia was Chrysops streptobalius; however, this tabanid was not closely associated with man. Up to 34/man-day were caught in watermeadows by the Gojeb river (altitude 1,160 m) in October. Man-biting species of Ceratopogonidae in various parts of Ethiopia were Culicoides fulvithorax, C. grahamii, C. kingi and C. milnei. The first two of these were anthropophilic in lowlands, but apparently not so in highlands. C. milnei was extremely abundant biting man highlands. C. milnei was extremely abundant biting man and domestic animals both indoors and outdg cycle was irregular, usually displaying a succession of ill-define nocturnal peaks; sometimes it attacked in daylight. Up to 35,000 C. milnei per trap-night were caught in light traps. Most of the females entering light traps in a stable were already engorged with blood. It seemed very likely that C. milnei would prove to be of veterinary importance. No firm indication was obtained as to what may transmit D. perstans in Ethiopia.