Mycobacterium bovis, also called M. tuberculosis var. bovis, is a bacterium belonging to the M. tuberculosis complex (i.e., MTBC) and which can cause through zoonotic transmission another form of human tuberculosis (Tb). It is above all the agent of bovine tuberculosis (i.e., bTb) which affects not only cattle (wild or farmed) but also a large diversity of other wild mammals worldwide. An increasing number of infected animal cases are being discovered in many regions of the world, thus raising the problem of tuberculosis transmission, including to humans, more complex than previously thought. Efforts have been made in terms of vaccination or culling of populations of host carrier species, such as the badger for example, however leading to consequences of greater dispersion of the infectious agent. M. bovis shows a more or less significant capacity to persist outside its hosts, particularly in the environment under certain abiotic and biotic conditions. This bacillus can be transmitted and spread in many ways, including through aerosol, mucus and sputum, urine and feces, by direct contact with infected animals, their dead bodies or rather via their excreta or by inhalation of aerosols, depending on the host species concerned.

In this paper, Calenge and his collaborators (Callenge et al. 2024) benefited from a national surveillance program on M. bovis cases in wild species, set up in 2011 in France, i.e., Sylvatub, for detecting and monitoring M. bovis infection in European badger (Meles meles) populations. Sylvatub is a participatory program involving both national and local stakeholder systems in order to determine changes in bTb infection levels in domestic and wild animal species. This original work had two aims: to describe spatial disease dynamics in the three clusters under scrutiny using a complex Bayesian model; and to develop indicators for the monitoring of the M. bovis infection by stakeholders and decision-makers of the program. This paper is timely and very comprehensive.

In this cogent study, the authors illustrate this point by using epidemiological surveillance to obtain large amounts of data (which is generally lacking in human epidemiology, but more dramatically lacking in animal epidemiology) and a highly sophisticated biostatistical analysis (Callenge et al. 2024). It is in itself a demonstration of the current capabilities of population dynamics applied to infectious disease situations, in this case animal, in the rapidly developing discipline of disease ecology and evolution. One of the aims of the study is to propose statistical models that can be used by the different stakeholders in charge, for instance, of wildlife conservation or the regional or State veterinary services to assess disease risk in the most affected regions.

References

Assel AKHMETOVA​, Jimena GUERRERO​, Paul McADAM, Liliana CM SALVADOR​, Joseph CRISPELL​, John LAVERY​, Eleanor PRESHO​, Rowland R KAO​, Roman BIEK​, Fraser MENZIES​, Nigel TRIMBLE​, Roland HARWOOD​, P Theo PEPLER, Katarina ORAVCOVA​, Jordon GRAHAM​, Robin SKUCE​, Louis DU PLESSIS​, Suzan THOMPSON​, Lorraine WRIGHT​, Andrew W BYRNE​, Adrian R ALLEN. 2023. Genomic epidemiology of Mycobacterium bovis infection in sympatric badger and cattle populations in Northern Ireland. Microbial Genomics 9: mgen001023. https://doi.org/10.1099/mgen.0.001023

Roman BIEK, Anthony O’HARE, David WRIGHT, Tom MALLON, Carl McCORMICK, Richard J ORTON, Stanley McDOWELL, Hannah TREWBY, Robin A SKUCE, Rowland R KAO. 2012. Whole genome sequencing reveals local transmission patterns of Mycobacterium bovis in sympatric cattle and badger populations. PLoS Pathogens 8: e1003008. https://doi.org/10.1371/journal.ppat.1003008

Clément CALENGE, Ariane PAYNE, Edouard REVEILLAUD, Céline RICHOMME, Sébastien GIRARD, Stephanie DESVAUX. 2024. Assessing the dynamics of Mycobacterium bovis infection in three French badger populations. bioRxiv, ver. 3 peer-reviewed and recommended by Peer Community In Infections. https://doi.org/10.1101/2023.05.31.543041

Marc CHOISY, Pejman ROHANI. 2006. Harvesting can increase severity of wildlife disease epidemics. Proceedings of the Royal Society, London, Ser. B 273: 2025-2034. https://doi.org/10.1098/rspb.2006.3554

Shannon C DUFFY, Sreenidhi SRINIVASAN, Megan A SCHILLING, Tod STUBER, Sarah N DANCHUK, Joy S MICHAEL, Manigandan VENKATESAN, Nitish BANSAL, Sushila MAAN, Naresh JINDAL, Deepika CHAUDHARY, Premanshu DANDAPAT, Robab KATANI, Shubhada CHOTHE, Maroudam VEERASAMI, Suelee ROBBE-AUSTERMAN, Nicholas JULEFF, Vivek KAPUR, Marcel A BEHR. 2020. Reconsidering Mycobacterium bovis as a proxy for zoonotic tuberculosis: a molecular epidemiological surveillance study. Lancet Microbe 1: e66-e73. https://doi.org/10.1016/S2666-5247(20)30038-0

Jean-François GUEGAN. 2019. The nature of ecology of infectious disease. The Lancet Infectious Diseases 19. https://doi.org/10.1016/s1473-3099(19)30529-8

Brandon H HAYES, Timothée VERGNE, Mathieu ANDRAUD, Nicolas ROSE. 2023. Mathematical modeling at the livestock-wildlife interface: scoping review of drivers of disease transmission between species. Frontiers in Veterinary Science 10: 1225446. https://doi.org/10.3389/fvets.2023.1225446

David KING, Tim ROPER, Douglas YOUNG, Mark EJ WOOLHOUSE, Dan COLLINS, Paul WOOD. 2007. Bovine tuberculosis in cattle and badgers. Report to Secretary of State about tuberculosis in cattle and badgers. London, UK. https://www.bovinetb.info/docs/RBCT_david_%20king_report.pdf  

Robert MM SMITH , Francis DROBNIEWSKI, Andrea GIBSON, John DE MONTAGUE, Margaret N LOGAN, David HUNT, Glyn HEWINSON, Roland L SALMON, Brian O’NEILL. 2004. Mycobacterium bovis Infection, United Kingdom. Emerging Infectious Diseases 10: 539-541. https://doi.org/10.3201/eid1003.020819 

Understanding the ecological and evolutionary factors underlying the spread of new fungal pathogen populations can inform the development of more effective management strategies. In plant pathology, pathogenicity is generally presented as having two components: ‘virulence’ (qualitative pathogenicity) and aggressiveness (quantitative pathogenicity). Changes in virulence in response to the deployment of new resistant varieties are a major driver of the spread of new populations (called pathotypes, or races) in modern agrosystems, and the genomic (i.e. proximal) and eco-evolutionary (i.e. ultimate) factors underlying these changes are well-documented [1,2,3]. By contrast, the role of changes in aggressiveness in the spread of pathotypes remains little known [4].

The study by Cécilia Fontyn and collaborators [5] set out to characterize changes in aggressiveness for isolates of two pathotypes of the wheat leaf rust (Puccinia triticina) that have been dominant in France during the 2005-2016 period. Isolates were genetically characterized using multilocus microsatellite typing and phenotypically characterized for three components of aggressiveness on wheat varieties: infection efficiency, latency period, and sporulation capacity. Using experiments that represent quite a remarkable amount of work and effort, Fontyn et al. showed that each dominant pathotype consisted of several genotypes, including common genotypes whose frequency changed over time. For each pathotype, the genotypes that were more common initially were replaced by a more aggressive genotype. Together, these results show that changes in the genetic composition of populations of fungal plant pathogens can be associated with, and may be caused by, changes in the quantitative components of pathogenicity. This study also illustrates how extensive, decade-long monitoring of fungal pathogen populations, such as the one conducted for wheat leaf rust in France, represents a very valuable resource for research.

REFERENCES

[1] Brown, J. K. (1994). Chance and selection in the evolution of barley mildew. Trends in Microbiology, 2(12), 470-475. https://doi.org/10.1016/0966-842x(94)90650-5

[2] Daverdin, G., Rouxel, T., Gout, L., Aubertot, J. N., Fudal, I., Meyer, M., Parlange, F., Carpezat, J., & Balesdent, M. H. (2012). Genome structure and reproductive behaviour influence the evolutionary potential of a fungal phytopathogen. PLoS Pathogens, 8(11), e1003020. https://doi.org/10.1371/journal.ppat.1003020

[3] Gladieux, P., Feurtey, A., Hood, M. E., Snirc, A., Clavel, J., Dutech, C., Roy, M., & Giraud, T. (2015). The population biology of fungal invasions.Molecular Ecology, 24(9), 1969-86. https://doi.org/10.1111/mec.13028

[4] Fontyn, C., Zippert, A. C., Delestre, G., Marcel, T. C., Suffert, F., & Goyeau, H. (2022). Is virulence phenotype evolution driven exclusively by Lr gene deployment in French Puccinia triticina populations?. Plant Pathology, 71(7), 1511-1524. https://doi.org/10.1111/ppa.13599

[5] Fontyn, C., Meyer, K. J., Boixel, A. L., Delestre, G., Piaget, E., Picard, C., Suffer, F., Marcel, T.C., & Goyeau, H. (2022). Evolution within a given virulence phenotype (pathotype) is driven by changes in aggressiveness: a case study of French wheat leaf rust populations. bioRxiv, 2022.08.29.505401, ver. 3 peer-reviewed and recommended by Peer Community in Infections.  https://doi.org/10.1101/2022.08.29.505401

​​Diptera-borne pathogens rank among the most serious health threats to vertebrate organisms around the world, particularly in tropical areas undergoing strong human impacts – e.g., urbanization and farming –, where social unrest and poor economies exacerbate the risk (Allen et al. 2017; Robles-Fernández et al. 2022). Although scientists have acquired a detailed knowledge on the life-history of malaria parasites (Pacheco and Escalante 2023), they still do not have enough information about their insect vectors to make informed management and preventive decisions (Santiago-Alarcon 2022).

In this sense, I am pleased to recommend the study of Vantaux et al. (2023), where authors conducted an experimental and theoretical study to analyzed how the diversity of blood sources (i.e., human, cattle, sheep, and chicken) affected the fitness of the human malaria parasite – Plasmodium falciparum – and its mosquito vector – Anopheles gambiae s.l.

The study was conducted in Burkina Faso, West Africa. Interestingly, authors did not find a significant effect of blood meal source on parasite development, and a seemingly low impact on the fitness of mosquitoes that were exposed to parasites. However, mosquitoes’ feeding rate, survival, fecundity, and offspring size were negatively affected by the type of blood meal ingested. In general, chicken blood represented the worst meal source for the different measures of mosquito fitness, and sheep blood seems to be the least harmful. This result was supported by the theoretical model, where vectorial capacity was always better when mosquitoes fed on sheep blood compared to cow and chicken blood. Thus, the knowledge generated by this study provides a pathway to reduce human infection risk by managing the diversity of farm animals. For instance, transmission to humans can decrease when chickens and cows represent most of the available blood sources in a village.

These results along with other interesting details of this study, represent a clear example of the knowledge and understanding of insect vectors that we need to produce in the future, particularly to manage and prevent hazards and risks (sensu Hoseini et al. 2017).

REFERENCES

Allen T., et al., Global hotspots and correlates of emerging zoonotic diseases. Nat. Commun. 8, 1124. (2017). https://doi.org/10.1038/s41467-017-00923-8

Hosseini P.R., et al., Does the impact of biodiversity differ between emerging and endemic pathogens? The need to separate the concepts of hazard and risk. Philos. Trans. R. Soc. Lond. B Biol. Sci. 372, 20160129 (2017). https://doi.org/10.1098/rstb.2016.0129

Pacheco M.A., and Escalante, A.A., Origin and diversity of malaria parasites and other Haemosporida. Trend. Parasitol. (2023) https://doi.org/10.1016/j.pt.2023.04.004

Robles-Fernández A., et al., Wildlife susceptibility to infectious diseases at global scales. PNAS 119: e2122851119. (2022). https://doi.org/10.1073/pnas.2122851119

Santiago-Alarcon D. A meta-analytic approach to investigate mosquitoes’ (Diptera: Culicidae) blood feeding preferences from non-urban to urban environments. In: Ecology and Control of Vector-borne Diseases, vol. 7 (R.G. Gutiérrez-López, J.G. Logan, Martínez-de la Puente J., Eds). Pp. 161-177. Wageningen Academic Publishers. eISBN: 978-90-8686-931-2 | ISBN: 978-90-8686-379-2 (2022).

Vantaux A. et al. Multiple hosts, multiple impacts: the role of vertebrate host diversity in shaping mosquito life history and pathogen transmission. bioRxiv, ver. 3 peer-reviewed and recommended by Peer Community in Infections (2023). https://doi.org/10.1101/2023.02.10.527988

Trypanosoma lewisi is an atypical trypanosome species. Transmitted by fleas, it has a high prevalence and worldwide distribution in small mammals, especially rats [1]. Although not typically thought to infect humans, there has been a number of reports of human infections by T. lewisi in Asia including a case of a fatal infection in an infant [2]. The fact that the parasite is resistant to lysis by normal human serum [3] suggests that many people, especially immunocompromised individuals, may be at risk from zoonotic infections by this pathogen, particularly in regions where there is close contact with T. lewisi-infected rat fleas. Indeed, it is also possible that cryptic T. lewisi infections exist but have hitherto gone undetected. Such asymptomatic infections have been detected for a number of parasitic infections including the related parasite T. b. gambiense [4]. 
 
Despite the fact that T. lewisi parasites pose a risk to human health, very little is known about their population structure, reproductive mode, population size or dispersal. In the article [5], Ségard et al. presented the first attempt at examining the population structure of the parasite. They developed microsatellite markers and used them to analyse a small set of samples from West Africa and Southeast Asia. Although the number of microsatellite markers is not very high and they encountered problems of PCR amplification especially of the southeast Asian samples, they did provide preliminary data that hints at a clonal population structure with rare recombination and suggests population subdivisions occurring at a scale that is equal, and probably smaller than a neighborhood of several houses with a short generation time. These are very interesting preliminary findings that will need to be validated using a larger cohort with more markers or by whole genome sequencing.
 

References

[1] Hoare CA (1972) The trypanosomes of mammals. A zoological monograph. The trypanosomes of mammals. A zoological monograph.

[2] Truc P, Büscher P, Cuny G, Gonzatti MI, Jannin J, Joshi P, Juyal P, Lun Z-R, Mattioli R, Pays E, Simarro PP, Teixeira MMG, Touratier L, Vincendeau P, Desquesnes M (2013) Atypical Human Infections by Animal Trypanosomes. PLOS Neglected Tropical Diseases, 7, e2256. https://doi.org/10.1371/journal.pntd.0002256

[3] Lun Z-R, Wen Y-Z, Uzureau P, Lecordier L, Lai D-H, Lan Y-G, Desquesnes M, Geng G-Q, Yang T-B, Zhou W-L, Jannin JG, Simarro PP, Truc P, Vincendeau P, Pays E (2015) Resistance to normal human serum reveals Trypanosoma lewisi as an underestimated human pathogen. Molecular and Biochemical Parasitology, 199, 58–61. https://doi.org/10.1016/j.molbiopara.2015.03.007

[4] Büscher P, Bart J-M, Boelaert M, Bucheton B, Cecchi G, Chitnis N, Courtin D, Figueiredo LM, Franco J-R, Grébaut P, Hasker E, Ilboudo H, Jamonneau V, Koffi M, Lejon V, MacLeod A, Masumu J, Matovu E, Mattioli R, Noyes H, Picado A, Rock KS, Rotureau B, Simo G, Thévenon S, Trindade S, Truc P, Reet NV (2018) Do Cryptic Reservoirs Threaten Gambiense-Sleeping Sickness Elimination? Trends in Parasitology, 34, 197–207. https://doi.org/10.1016/j.pt.2017.11.008

[5] Ségard A, Roméro A, Ravel S, Truc P, Gauthier D, Gauthier P, Dossou H-J, Sylvestre B, Houéménou G, Morand S, Chaisiri K, Noûs C, De Meeûs T (2022) Development of nine microsatellite loci for Trypanosoma lewisi, a potential human pathogen in Western Africa and South-East Asia, and preliminary population genetics analyses. Zenodo, 6460010, ver. 3 peer-reviewed and recommended by Peer Community in Infections. https://doi.org/10.5281/zenodo.6460010