Yersinia pestis can infect the Pawlowsky glands of human body lice and be transmitted by louse bite

An insight into the salivary gland content of the human body louse, Pediculus humanus

Human body lice, Pediculus humanus humanus, are blood-feeding parasites that live in clothing and feed several times per day. Saliva injected during louse feeding induces pruritis and local inflammation in the skin. If untreated, chronic Pediculosis can cause systemic negative health effects. Despite the medical importance of body lice and their longstanding association with humans, characterization of their saliva has been limited. To address this, we extracted RNA and protein from two of the body louse's morphologically distinct sets of salivary glands (Bean-shaped and U-shaped) and generated transcript and protein profiles for each. Additionally, we performed fluorescent staining and confocal microscopy on each gland type to enhance descriptions of their structure and gross cellular architecture. Analysis of body louse salivary gene products and proteins revealed that the overwhelming majority were not closely related to biomolecules of known function, highlighting the organism's unique and understudied saliva composition. Despite the contrasting morphology of the two gland types, there was a high degree of overlap in the salivary products produced. This finding suggests strong Darwinian selection pressure to maintain both salivary gland types, given that it would be simpler to have a single morphologically identical set of glands. Here we present the first next-generation sequencing and proteomic characterization of the human body louse sialome, discuss the potential physiological importance of louse salivary proteins, and consider possible explanations for why lice have a complex salivary gland system despite inordinate redundancy in the protein repertoire of the Bean- and U-shaped salivary glands.

Evolution of the Neopsylla hongyangensis Mitogenome: Insights Into the Mitogenomic Evolution of the Orders Siphonaptera and the Phthiraptera

The evidence that parasitic animals exhibit elevated mitogenomic evolution rates is inconsistent and limited to Arthropoda. Neopsylla hongyangensis Li, Bai et Chen, 1986 (Siphonaptera: Ctenophthalmidae) feeds on the host's blood and is an important medical insect with plague transmission. In this study, we sequenced the N. hongyangensis mitogenome and explored the mitogenomic evolution of Siphonaptera and Phthiraptera, which both belong to the Insecta on warm-blooded animals. The mitogenomes of Siphonaptera are closed-circular double-stranded DNA molecules and exhibit highly conserved structural features. In contrast, the mitogenomes of most Phthiraptera species exhibit extensive fragmentation and comprise multiple minichromosomes. We performed a comparative analysis of nucleotide composition, Ka/Ks ratios, and codon usage patterns in Siphonaptera and Phthiraptera mitogenomes. Compared to Phthiraptera with low locomotory capacity, Siphonaptera with high locomotory capacity have higher AT content, slower evolution, and greater influence from natural selection (i.e., micro-habitat). The mitogenomic evolution of Siphonaptera and Phthiraptera was influenced by locomotory capacity and life history. Phylogenetic analysis based on 13 PCGs showed that Ceratophyllidae, Leptopsyllidae, and Ctenophthalmidae were paraphyletic, and Vermipsyllidae, Hystrichopsyllidae, Pulicidae, and Pygiopsyllidae were monophyletic. This study provides new insights into the phylogenetic relationships and mitogenomic evolution of Siphonaptera.

Plague history, Mongol history, and the processes of focalisation leading up to the Black Death: a response to Brack et al

This essay responds to Brack et al., 'Plague and the Mongol Conquest of Baghdad (1258)? A reevaluation of the sources', which is a critique of our 2021 essay in this journal, 'Plague and the Fall of Baghdad (1258)'. We argue that Brack and colleagues have misunderstood our investigation as an attempt to pinpoint the exact timing of the outbreak of plague connected with the Mongol siege of Baghdad, and so believe that an altered timeframe invalidates our suggestion that plague was involved. Taking this opportunity to revisit the state of plague historiography in western Asia, we address four issues: (1) why Mongol historiography has, until recently, avoided the question of plague's late mediaeval resurgence within the Mongol Empire and why the 'new genetics' of plague now makes the question unavoidable; (2) why reconstruction of the biological processes of 'focalisation' is now the most urgent question in plague historiography since it constitutes what we call the prodromal stage of the Black Death pandemic; (3) how a newly informed biological perspective on disease history can allow a more sensitive reading of past observers' reports of epidemics; and finally, (4) what a plausible scenario might look like for plague's presence in western Asia and the eastern Mediterranean region in the late-thirteenth and early-fourteenth centuries as an emerging zoonotic disease with occasional epizootic and human outbreaks, before the more catastrophic outbreaks of the 1340s commonly referred to as 'the Black Death'.

Differential pathogenicity and lethality of bubonic plague (1720-1945) by sex, age and place

COVID-19 brought back to the attention of the scientific community that males are more susceptible to infectious diseases. What is clear for other infections-that sex and gender differences influence both risk of infection and mortality-is not yet fully elucidated for plague, particularly bubonic plague, although this knowledge can help find specific defences against a disease for which a vaccine is not yet available. To address this question, we analysed data on plague from hospitals in different parts of the world since the early eighteenth century, which provide demographic information on individual patients, diagnosis and course of the disease in the pre-antibiotic era. Assuming that the two sexes were equally represented, we observe a worldwide prevalence of male cases hospitalized at any age, a result which seems better explained by gender-biased (thus cultural) behaviours than biological sex-related factors. Conversely, case fatality rates differ among countries and geographic macro-areas, while globally, lethality appears slightly prevalent in young females and older adults (regardless of sex). Logistic regression models confirm that the main risk factor for bubonic plague death was the geographical location of the cases and being older than 50 years, whereas sex only showcased a slight trend.