As recently reported by the world organisation for animal health, 60% of infectious diseases are zoonotic with a significant part associated to ticks. Ticks can transmit various pathogens such as bacteria, viruses and parasites. Among pathogens known to be transmitted by ticks, Ehrlichia ruminantium is an obligate intracellular Gram-negative bacterium responsible for the fatal heartwater disease of domestic and wild ruminants (Allsopp, 2010). E. ruminantium is transmitted by ticks of the genus Amblyomma in the tropical and sub-Saharan areas, as well as in the Caribbean islands. It constitutes a major threat for the American livestock industries since a suitable tick vector is already present in the American mainland and potential introduction of infected A. variegatum through migratory birds or uncontrolled movement of animals from Caribbean could occur (i.e. Deem, 1998 ; Kasari et al 2010). The disease is also a major obstacle to the introduction of animals from heartwater-free to heartwater-infected areas into sub-Saharan Africa and thus restrains breeding programs aiming at upgrading local stocks (Allsopp, 2010).

In this context, it is essential to develop control strategies against heartwater, as developing effective vaccines, for instance. Such an objective requires a better understanding of the early interaction of E. ruminantium and its host cells and of the mechanisms associated with bacterial adhesion to the host-cell. In this study, the authors. studied the role of E. ruminantium membrane protein ERGA_CDS_01230 in the adhesion process to host bovine aortic endothelial cells (BAEC).

After successfully producing the recombinant version of the protein, Pinarello et al (2022) followed the in vitro culture of E. ruminantium in BAEC and observed that the expression of the protein peaked at the extracellular infectious elementary body stages. This result would suggest the likely involvement of the protein in the early interaction of E. ruminantium with its host cells. The authors then showed using flow cytometry, and scanning electron microscopy, that beads coated with the recombinant protein adhered to BAEC. In addition, they also observed that the adhesion protein of E. ruminantium interacted with proteins of the cell's lysate, membrane and organelle fractions. Additionally, enzymatic treatment, degrading dermatan and chondroitin sulfates on the surface of BAEC, was associated with a 50% reduction in the number of bacteria in the host cell after a development cycle, indicating that glycosaminoglycans might play a role in the adhesion of E. ruminantium to the host-cell. Finally, the authors observed that the adhesion protein of E. ruminantium induced a humoral response in vaccinated animals, making this protein a possible vaccine candidate.

As rightly pointed out by both reviewers, the results of this study represent a significant advance (i) in the understanding of the role of the E. ruminantium membrane protein ERGA_CDS_01230 in the adhesion process to the host-cell and (ii) in the development of new control strategies against heartwater as this protein might potentially be used as an immunogen for the development of future vaccines.

References

Allsopp, B.A. (2010). Natural history of Ehrlichia ruminantium. Vet Parasitol 167, 123-135. https://doi.org/10.1016/j.vetpar.2009.09.014

Deem, S.L. (1998). A review of heartwater and the threat of introduction of Cowdria ruminantium and Amblyomma spp. ticks to the American mainland. J Zoo Wildl Med 29, 109-113.

Kasari, T.R. et al (2010). Recognition of the threat of Ehrlichia ruminantium infection in domestic and wild ruminants in the continental United States. J Am Vet Med Assoc. 237:520-30. https://doi.org/10.2460/javma.237.5.520

Pinarello V, Bencurova E, Marcelino I, Gros O, Puech C, Bhide M, Vachiery N, Meyer DF (2022) Ehrlichia ruminantium uses its transmembrane protein Ape to adhere to host bovine aortic endothelial cells. bioRxiv, 2021.06.15.447525, ver. 3 peer-reviewed and recommended by Peer Community in Infections. https://doi.org/10.1101/2021.06.15.447525

High-throughput sequencing (HTS) has revealed an incredible diversity of microorganisms in ecosystems and is also changing the monitoring of macroorganism biodiversity (Deiner et al. 2017; Piper et al. 2019).  

The diagnostic of plant pathogens and the identification of pests is gradually integrating the use of these techniques, but there are still obstacles. Most of them are related to the reliability of these analyses, which have long been considered insufficient because of their dependence on a succession of sophisticated operations involving parameters that are sometimes difficult to adapt to complex matrices or certain diagnostic contexts. The need to validate HTS approaches is gradually being highlighted in recent work but remains poorly documented (Bester et al. 2022).

In this paper, a large community of experts presents and discusses the key steps for optimal control of HTS performance and reliability in a diagnostic context (Massart et al. 2022). It also addresses the issue of costs. The article provides recommendations that closely combine the quality control requirements commonly used in conventional diagnostics with newer or HTS-specific control elements and concepts that are not yet widely used. It discusses the value of these for the use of the various techniques currently covered by the terms "High Throughput Sequencing" in diagnostic activities. The elements presented are intended to limit false positive or false negative results but will also optimise the interpretation of contentious results close to the limits of analytical sensitivity or unexpected results, both of which appear to be frequent when using HTS.

Furthermore, the need for risk analysis, verification and validation of methods is well illustrated with numerous examples for each of the steps considered crucial to ensure reliable use of HTS. The clear contextualisation of the proposals made by the authors complements and clarifies the need for user expertise according to the experimental objectives. Some unanswered questions that will require further development and validation are also presented.

This article should benefit a large audience including researchers with some level of expertise in HTS but unfamiliar with the recent concepts of controls common in the diagnostic world as well as scientists with strong diagnostic expertise but less at ease with the numerous and complex procedures associated with HTS.

References

Bester R, Steyn C, Breytenbach JHJ, de Bruyn R, Cook G, Maree HJ (2022) Reproducibility and Sensitivity of High-Throughput Sequencing (HTS)-Based Detection of Citrus Tristeza Virus and Three Citrus Viroids. Plants, 11, 1939. https://doi.org/10.3390/plants11151939

Deiner K, Bik HM, Mächler E, Seymour M, Lacoursière-Roussel A, Altermatt F, Creer S, Bista I, Lodge DM, de Vere N, Pfrender ME, Bernatchez L (2017) Environmental DNA metabarcoding: Transforming how we survey animal and plant communities. Molecular Ecology, 26, 5872–5895. https://doi.org/10.1111/mec.14350

Massart, S et al. (2022) Guidelines for the reliable use of high throughput sequencing technologies to detect plant pathogens and pests. Zenodo, 6637519, ver. 3  peer-reviewed and recommended by Peer Community in Infections. https://doi.org/10.5281/zenodo.6637519

Piper AM, Batovska J, Cogan NOI, Weiss J, Cunningham JP, Rodoni BC, Blacket MJ (2019) Prospects and challenges of implementing DNA metabarcoding for high-throughput insect surveillance. GigaScience, 8, giz092. https://doi.org/10.1093/gigascience/giz092

The paper titled "Celebrating the 20th Anniversary of the First Xanthomonas Genome Sequences – How Genomics Revolutionized Taxonomy Provided Insight into the Emergence of Pathogenic Bacteria Enabled New Fundamental Discoveries and Helped Developing Novel Control Measures – A Perspective from the French Network on Xanthomonads" by Ralf Koebnik et al. (2023) is an insightful contribution to the field of genomics and its application in understanding pathogenic bacteria, particularly Xanthomonas. This comprehensive review offers a unique perspective from the French Network on Xanthomonads, underscoring the significant advancements in taxonomy, pathogen emergence, and development of control strategies due to genomic research.

One of the paper's main strengths is its thorough exploration of how genomics has revolutionized our understanding of Xanthomonas and other pathogenic bacteria. It sheds light on the evolution and emergence of these pathogens, contributing significantly to the development of novel and effective control measures. The authors' detailed account of the historical progress and current state of genomics in this field highlights its pivotal role in guiding future research and practical applications in managing bacterial diseases.

Moreover, the paper emphasizes the importance of collaborative efforts and the sharing of knowledge within scientific networks, as exemplified by the French Network on Xanthomonas. This approach not only enriches the study but also serves as a model for future collaborative research endeavors.

In conclusion, the work of Koebnik et al. is a valuable resource for researchers, policymakers, and practitioners in the field of plant pathology and genomics. It not only provides a comprehensive overview of the advances in genomics related to Xanthomonas but also illustrates the broader impact of genomic studies in understanding and managing pathogenic bacteria.

References

Ralf Koebnik, Sophie Cesbron, Nicolas W. G. Chen, Marion Fischer-Le Saux, Mathilde Hutin, Marie-Agnès Jacques, Laurent D. Noël, Alvaro Perez-Quintero, Perrine Portier, Olivier Pruvost, Adrien Rieux, And Boris Szurek (2024) Celebrating the 20th anniversary of the first Xanthomonas genome gequences – How genomics revolutionized taxonomy, provided insight into the emergence of pathogenic bacteria, enabled new fundamental discoveries and helped developing novel control measures – A perspective from the French network on Xanthomonads. Zenodo ver. 3, peer-reviewed and recommended by Peer Community in Infections. https://doi.org/10.5281/zenodo.8223857

            Parasites represent the most diverse and adaptable ecological group of the biosphere (Timm & Clauson, 1988; De Meeûs et al., 1998; Poulin & Morand, 2000; De Meeûs & Renaud, 2002). The human species is known to considerably alter biodiversity, though it hosts, and thus sustains the maintenance of a spectacular diversity of parasites (179 species for eukaryotic species only) (De Meeûs et al., 2009). Among these, the five species of malaria agents (genus Plasmodium) remain a major public health issue around the world. Plasmodium falciparum is the most prevalent and lethal of these (Liu et al., 2010). With a pick of up to 2 million deaths due to malaria in 2004, deaths decreased to around 1 million in 2010 (Murray et al., 2012), to reach 619,000 in 2021, most of which in sub-Saharan Africa, and 79% of which were among children aged under 5 years (World Health Organization, 2022). 

            As stressed by Taconet et al. (2023), reduction in malaria deaths is attributable to control measures, in particular against its vectors (mosquitoes of the genus Anopheles). Nevertheless, the success of vector control is hampered by several factors (biological, environmental and socio-economic), and in particular by the great propensity of targeted mosquitoes to evolve physiological or behavioral avoidance of anti-vectorial measures.

            In their paper Taconet et al. (2023) aims at understanding what are the main factors that determine the evolution of insecticide resistance in several malaria vectors, in relation to the biological determinisms of behavioral resistance and how fast such evolutions take place. To tackle these objectives, authors collected an impressive amount of data in two rural areas of West Africa. With appropriate modeling, Taconet et al. discovered, among many other results, a predominant role of public health measures, as compared to agricultural practices, in the evolution of physiological resistance. They also found that mosquito foraging activities are mostly explained by host availability and climate, with a poor, if any, association with genetic markers of physiological resistance to insecticides. These findings represent an important contribution to the field and should help at designing more efficient control strategies against malaria.

References

De Meeûs T, Michalakis Y, Renaud F (1998) Santa Rosalia revisited: or why are there so many kinds of parasites in “the garden of earthly delights”? Parasitology Today, 14, 10–13. https://doi.org/10.1016/S0169-4758(97)01163-0

De Meeûs T, Prugnolle F, Agnew P (2009) Asexual reproduction in infectious diseases. In: Lost Sex: The Evolutionary Biology of Parthenogenesis (eds Schön I, Martens K, van Dijk P), pp. 517-533. Springer, NY. https://doi.org/10.1007/978-90-481-2770-2_24

De Meeûs T, Renaud F (2002) Parasites within the new phylogeny of eukaryotes. Trends in Parasitology, 18, 247–251. https://doi.org/10.1016/S1471-4922(02)02269-9

Liu W, Li Y, Learn GH, Rudicell RS, Robertson JD, Keele BF, Ndjango JB, Sanz CM, Morgan DB, Locatelli S, Gonder MK, Kranzusch PJ, Walsh PD, Delaporte E, Mpoudi-Ngole E, Georgiev AV, Muller MN, Shaw GM, Peeters M, Sharp PM, Rayner JC, Hahn BH (2010) Origin of the human malaria parasite Plasmodium falciparum in gorillas. Nature, 467, 420–425. https://doi.org/10.1038/nature09442

Murray CJ, Rosenfeld LC, Lim SS, Andrews KG, Foreman KJ, Haring D, Fullman N, Naghavi M, Lozano R, Lopez AD (2012) Global malaria mortality between 1980 and 2010: a systematic analysis. The Lancet, 379, 413–431. https://doi.org/10.1016/S0140-6736(12)60034-8

Poulin R, Morand S (2000) The diversity of parasites. Quarterly Review of Biology, 75, 277–293. https://doi.org/10.1086/393500

Taconet P, Soma DD, Zogo B, Mouline K, Simard F, Koffi AA, Dabire RK, Pennetier C, Moiroux N (2023) Physiological and behavioural resistance of malaria vectors in rural West-Africa : a data mining study to address their fine-scale spatiotemporal heterogeneity, drivers, and predictability. bioRxiv, ver. 4 peer-reviewed and recommended by Peer Community in Infections. https://doi.org/10.1101/2022.08.20.504631

Timm RM, Clauson BL (1988) Coevolution: Mammalia. In: 1988 McGraw-Hill yearbook of science & technology, pp. 212–214. McGraw-Hill Book Company, New York.

World Health Organization (2022) World malaria report 2022. Geneva: World Health Organization; 2022. Licence: CC BY-NC-SA 3.0 IGO. https://iris.who.int/bitstream/handle/10665/365169/9789240064898-eng.pdf?sequence=1.

Thanks to the coordinated and sustained efforts of national control programs, the World Health Organization (WHO), bilateral cooperation and nongovernmental organizations, the incidence of Human African Trypanosomiasis (HAT), better known as sleeping sickness, has drastically decreased during the last two decades (WHO, 2023a). Indeed, between 1999 and 2022, the reported number of new cases of the chronic form of sleeping sickness (Trypanosoma brucei gambiense) fell by 97% (from 27 862 to 799), and the number of newly reported cases of the acute form of HAT (Trypanosoma brucei rhodesiense) fell by 94% (from 619 to 38) (WHO, 2023b). These encouraging trends led the WHO to target this debilitating and highly fatal (if untreated) vector-borne parasitic disease for elimination as a public health problem by 2020, and for interruption of transmission (zero case) by 2030 (WHO, 2021, WHO, 2023a). However, the disease is persisting in many foci, and even some cases of resurgence have been documented after unfortunate events such as war or pandemics (Moore et al., 1999; Sah et al., 2023. Simarro et al). Although effective control measures, diagnosis and treatment are complex and require specific skills (WHO, 2023), especially in a context which animal reservoirs, including hidden reservoirs, can contribute to the maintenance/persistence of infection (Welburn and Maudlin, 2012; Camara et al., 2021). Vector control therefore appears as a viable alternative to accelerate sleeping sickness transmission interruption, and WHO has identified some critical actions for HAT elimination, including the coordination of vector control and animal trypanosomiasis management among countries, stakeholders and other sectors (e.g. tourism and wildlife) through multisectoral national bodies to maximize synergies (WHO, 2021).

The paper by Kagbadouno and Collaborators (2024) uses microsatellite markers genotyping and population genetics tools to investigate the impact of 11 years of tiny target-based vector control on the population biology of Glossina palpalis gambiensis in Boffa, one of the three active sleeping sickness foci in Guinea (Kagbadouno et al., 2012). Although vector control significantly reduced the apparent densities of tsetse flies (and therefore the human exposure to the vector) as well as the prevalence and incidence of the disease in the Boffa HAT focus (Courtin et al., 2015), no genetic signature of vector control was observed as no difference in population size, before and after the onset of the control policy, was found. The authors then provided national programs and implementing partners with indications on the actions to be taken to (i) maintain the achievements of vector control (thus avoiding rebound/resurgence as was experienced in the past (Franco et al., 2014), and (ii) accelerate the momentum towards elimination by for example combining these vector control efforts with medical surveys for case detection and treatment, in line with WHO recommendations (WHO, 2021). 

References

Camara M, Soumah AM, Ilboudo H, Travaillé C, Clucas C, Cooper A, Kuispond Swar NR, Camara O, Sadissou I, Calvo Alvarez E, Crouzols A, Bart JM, Jamonneau V, Camara M, MacLeod A, Bucheton B, Rotureau B. Extravascular Dermal Trypanosomes in Suspected and Confirmed Cases of gambiense Human African Trypanosomiasis. Clin Infect Dis. 2021 Jul 1;73(1):12-20. https://doi.org/10.1093/cid/ciaa897

Courtin F, Camara M, Rayaisse JB, Kagbadouno M, Dama E, Camara O, Traore IS, Rouamba J, Peylhard M, Somda MB, Leno M, Lehane MJ, Torr SJ, Solano P, Jamonneau V, Bucheton B (2015) Reducing human-tsetse contact significantly enhances the efficacy of sleeping sickness active screening campaigns: a promising result in the context of elimination. PLoS Neglected Tropical Diseases, 9. https://doi.org/10.1371/journal.pntd.0003727

Franco JR, Simarro PP, Diarra A, Jannin JG. (2014) Epidemiology of human African trypanosomiasis. Clin Epidemiol. 6:257-75. https://doi.org/10.2147/CLEP.S39728

Kagbadouno, M. S., Séré, M., Ségard, A., Camara, A. D., Camara, M., Bucheton, B., ... & Ravel, S. (2023). Population genetics of Glossina palpalis gambiensis in the sleeping sickness focus of Boffa (Guinea) before and after eight years of vector control: no effect of control despite a significant decrease of human exposure to the disease. bioRxiv, ver. 2 peer-reviewed and recommended by Peer Community in Infections. https://doi.org/10.1101/2023.07.25.550445

Kagbadouno MS, Camara M, Rouamba J, Rayaisse JB, Traoré IS, Camara O, Onikoyamou MF, Courtin F, Ravel S, De Meeûs T, Bucheton B, Jamonneau V, Solano P (2012) Epidemiology of sleeping sickness in boffa (Guinea): where are the trypanosomes? PLoS Neglected Tropical Diseases, 6, e1949. https://doi.org/10.1371/journal.pntd.0001949 

Moore A, Richer M, Enrile M, Losio E, Roberts J, Levy D. Resurgence of sleeping sickness in Tambura County, Sudan. Am J Trop Med Hyg. 1999 Aug;61(2):315-8. https://doi.org/10.4269/ajtmh.1999.61.315

Sah R, Mohanty A, Rohilla R, Padhi BK. A resurgence of Sleeping sickness amidst the COVID-19 pandemic: Correspondence. Int J Surg Open. 2023 Apr;53:100604. https://doi.org/10.1016/j.ijso.2023.100604

Welburn SC, Maudlin I. Priorities for the elimination of sleeping sickness. Adv Parasitol. 2012;79:299-337. https://doi.org/10.1016/B978-0-12-398457-9.00004-4

World Health Organization, 2021. Ending the neglect to attain the Sustainable Development Goals: a road map for neglected tropical diseases 2021–2030. World Health Organization, Geneva, Switzerland. ISBN: 978 92 4 001035 2. 196p. 

World Health Organization, 2023a. Trypanosomiasis, human African (sleeping sickness): key facts. Accessed at https://www.who.int/news-room/fact-sheets/detail/trypanosomiasis-human-african-(sleeping-sickness) on February 19, 2023.

World Health Organization, 2023b. Human African Trypanosomiasis, (sleeping sickness): the global health observatory. Accessed at https://www.who.int/data/gho/data/themes/topics/human-african-trypanosomiasis on February 19, 2023.