Can Napoleon's skin disease and treatment be identified from paleoproteomic analyses of his last bathtub (1821)?

Abstract

The French Emperor Napoleon I died on the island of Saint Helena in the South Atlantic Ocean on 5 May 1821 at the age of 51, 6 years after being deported from France. In the final months of his life, he spent several hours each day in his bathtub at the Longwood estate, to treat a skin disease that was either acquired during the siege of Toulon (1793) or during the Egyptian Campaign (1798–1799).¹

A previous study on the residual deposits found in the bathtub of Marat (historical figure of the French Revolution 1743–1793) showed its importance in conducting retrospective dermatological diagnoses.² In order to better contextualize Napoleon's health, we collected residues still present in the joints of the emperor's metal bathtub, that is part of the collection of Longwood House, under the authority of the French Ministry of Foreign Affairs. Microscopic samples of the metal and mineral residues present in and around the crevices of the metal joints were collected during the mission for the purposes of toxicological and elemental dosages (inductively coupled mass spectrometry) apart from dry swabs for the purpose of metaproteomics.

Due to the lack of a precise clinical description of Napoleon I's dermatological lesions,³ no specific infectious agent was sought. We aimed to create the most complete possible reconstruction of skin microbiome and identification of possible pathogenic infectious agents by broad-spectrum screening. On the toxicological level, the elements favoured for analysis were those with dermatological therapeutic tropism (lead, arsenic, mercury, antimony and copper).

Toxicological and elemental dosages (Table 1) highlight the high concentration of sulphur and arsenic, indicative of a probable use of seawater with added arsenic (and sulphur?). These elements were, in the pharmacopoeia of the first quarter of the 19th century, used as medication for dermatological diseases, reminding one of the ‘scabies’ caught by Napoleon almost 25–30 years prior to his death and which was never completely cured.^{4, 5} Arsenic and sulphur usually come from orpiment (As2S3) and/or realgar (As4S4) but may also originate from the volcanic soil of Saint-Helena Island. However, the presence of this element does not appear frequently.⁶

A new method of paleoproteomic study has made it possible to highlight the presence of several taxa.⁷ Human proteins—mainly of dermatological origin—(Homo sapiens) were detected apart from peptides from other species (Tables 2 and 3): Rhagoletis zephyria (fruit fly), Arachis hypogaea (peanut), Penicillium antarcticum originally discovered on the Windmill Islands off Antarctica and several species of Aspergillus type fungus (Aspergillus steynii linked to the maceration of barley and paprika, Aspergillus glaucus linked to leather, wool, cereals, sweet foods and meat, and Aspergillus cristatus linked to the maceration of tea bricks from Fuzhuan, China).

During the course of the study, we also found some traces of bacteria: Azospirillum palustre (peat bog bacteria), Azospirillum humicireducens (soil bacteria), Marinomonas communis (marine bacteria), Amycolatopsis cihanbeyliensis (bacteria present in salt mines), Streptomyces lonarensis (salt water bacteria), Microbacterium aerolatum (aerial bacteria), Flavobacterium tegetincola (ice and mud bacteria), Flavobacterium cerinum (soil bacteria), Bacillus idriensis (bacteria present in septic context), Paenibacillus sp. 18JY21-1 (soil bacteria), Amycolatopsis xylanica (soil bacteria) and Rhodobacteraceae bacterium KLH11 (marine bacteria).

These elements make it possible to confirm the use of seawater (or salt from salt marshes) in Napoleon's bathtub for therapeutic reasons, likely in combination with other medicinal materials such as peat bog, mud, barley and/or paprika and black tea. Each of these substances has been described in the 18th/19th century in the context of dermatological care, either through direct application on the skin or use in bath water.^{8, 9}

Additionally, the presence of Bacillus idriensis raises questions about the potential cause of death of Napoleon I. This Gram-positive bacillus has indeed been previously linked to an infected newborn¹⁰ and has real pathogenic potential.¹¹ Its presence might indicate skin infection (or superinfection) that affected Napoleon at the time of his death. However, it must be noted that its usual presence in the soil could also indicate potential contamination (of sea water and/or residues used in the bathtub therapy) and therefore should put the results of this study into perspective.

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