Host-parasite dynamics examine the evolution of host and parasite populations over time and across different environments. These dynamics are influenced by a combination of biotic and abiotic factors, as well as by evolutionary processes. Co-evolution within host-parasite systems plays a central role, enabling parasites to adapt to their hosts while allowing hosts to develop effective defense mechanisms. According to evolutionary theory, models in disease ecology predict that pathogens involved in infectious diseases co-evolve with their hosts and typically disappear before the host populations become locally extinct [1] [2] .

In the African context, several studies highlight that parasites and pathogens play a decisive role in shaping ecosystem dynamics. Long neglected by classical ecology, they can act as true population regulators by influencing host density, distribution, and behavior [3] . In West Africa, recent molecular and ecological surveys have revealed a wide diversity of infectious agents associated with rodents (bacteria, viruses, protozoa) and demonstrated that host community composition and infection prevalence vary greatly with seasonality, land use, and proximity to human settlements [4] [5] .

In West Africa, rodents play a major role in the transmission of numerous pathogens of medical and veterinary importance. Among these, viruses, particularly Lassa virus, occupy a central position due to their epidemiological impact and wide geographic distribution. Recent studies indicate that transmission dynamics are strongly influenced by host species diversity and their proximity to human settlements [6] . Molecular and eco-epidemiological investigations reveal increased circulation of Lassa virus and other zoonotic agents among various Mastomys and Mus species, suggesting interspecies transmission events and ecological plasticity of the reservoirs. [7] highlights that changes in land use, agricultural expansion, and urbanization promote rodent population growth and increase the risk of human-reservoir contacts. These findings confirm that rodents constitute a critical link at ecological and health interfaces, underscoring the need for integrated surveillance within a One Health framework.

Recent field studies have also revealed major changes in reservoir and zoonotic pathogen dynamics. For example, surveys conducted in Senegal detected several bacterial and protozoan families in wild rodents, emphasizing the potential role of invasive species and landscape modifications in the emergence of new pathogens [4] . Similarly, studies in Nigeria and elsewhere in West Africa have reported an increased prevalence and greater diversity of rodent species carrying Lassa virus, suggesting interspecies transmission events and a broader distribution of viral lineages than previously recognized [8] .

Moreover, intervention and applied ecology studies show that conventional rodent population control strategies (trapping, rodenticides) do not always result in sustainable reductions of viral transmission risk and may sometimes lead to unexpected outcomes such as rapid population recovery, compensatory reproduction, or the persistence of chronic carriers. These findings highlight the need for integrated approaches inspired by the “One Health” framework, combining ecological surveillance, environmental management, and community engagement [9] .

Finally, global environmental changes, habitat fragmentation, agricultural intensification, and climate change, alter the geographic distribution and temporal dynamics of pathogens. Large-scale approaches integrating time series, epidemiological mapping, and reservoir surveys are therefore indispensable to understand the persistence and transmission of zoonotic pathogens in human and animal populations in West Africa. Integrating molecular, ecological, and socio-environmental data is essential for designing more targeted interventions to mitigate spillover risks [5] [9] .

The loss of biodiversity and the degradation of ecosystems, exacerbated by deforestation and agricultural expansion, disrupt ecological balances and promote the emergence of new infectious diseases. Habitat fragmentation reduces the genetic diversity of animal populations, making them more vulnerable to diseases and disrupting natural regulatory mechanisms [10] .

Within this context, the study of rodents and their ectoparasites in Guinea is particularly crucial. Rodents serve as reservoirs for numerous zoonotic pathogens, while their ectoparasites play a central role in transmitting infectious diseases to humans and domestic animals. Understanding the diversity, abundance, and distribution of these hosts and vectors across different ecosystems (bushlands, agricultural fields, villages, orchards, warehouses, and riverbanks) is essential for assessing health risks and designing effective prevention strategies.

General Objective

To assess the impact of rodents and their ectoparasites on the transmission of zoonoses in the Republic of Guinea.

Specific Objectives

Rodents were handled using personal protective equipment (lab coat, gloves, face mask, goggles, visor, helmets) and captured with H.B. Sherman, Formizon, and traditional traps. Sampling and analyses were performed with standard laboratory instruments (scissors, forceps, scales, tubes, syringes, absorbent cotton), disinfection materials (70% alcohol, chlorine, NaCl solution), observation and documentation tools (lamps, magnifying glasses, camera, logbook), as well as molecular analysis equipment, including RNeasy Plus kits, Tissue Lyser LT, and Amplisens Ribo Prep reagents (Qiagen, Hilden, Germany).

Out of a total of 1114 rodents captured, five families were identified through morphometric analysis: Muridae, Soricidae, Nesomyidae, Sciuridae, and Gliridae. The distribution of the various species within these families is presented in Table 1 and Table 2 .

The analysis of this table reveals a high taxonomic diversity among the rodents, with a predominance of Muridae, which is expected in inhabited or agricultural areas. The diversity of families and species highlights the presence of various microhabitats and ecological niches, providing a wide range of hosts for ectoparasites and zoonotic agents. The rodents listed in this table are therefore key indicators for the study of zoonoses, as their variety, abundance, and distribution directly influence parasite dynamics and the transmission of infectious diseases.

The analysis of this table highlights the diversity of identified ectoparasites (7 species, belonging to 2 orders and 7 families) and reflects the strong interactions between rodents, their parasites, and the environment.

Some ectoparasites, such as Xenopsylla cheopis, Ixodes spp., and Ctenocepha-lides felis, are major vectors of zoonotic diseases of medical importance (plague, rickettsioses, borrelioses). This parasitic composition suggests that the studied rodents constitute a significant epidemiological reservoir in Guinea, warranting enhanced surveillance to prevent emerging or re-emerging diseases.

Detailed results on rodent ectoparasite collection and pathogen detection are presented in Table 3 and Table 4 .

A total of 356 ectoparasite infestations were recorded, The distribution of parasites is given as shown in Table 3 . The diversity of collected parasites highlights strong interactions between rodents and hematophagous arthropods, playing a central role in zoonotic disease transmission.

Three parasite-host pairs dominate the dynamics:

Broad-spectrum parasites include Ixodes spp., which was collected from R. rattus, C. gambianus, X. erythropus, and D. rufulus. Its multi-species distribution suggests a role in interspecific circulation of pathogens such as Borrelia and Anaplasma.

Ornithonyssus bacoti infests multiple rodent species (R. rattus, C. gambianus, Mus spp., Mus setulosus, L. sikapusi, L. striatus), highlighting its low host specificity and ability to transmit easily between hosts, including humans.

Nosopsyllus fasciatus affects both commensal species (R. rattus, Mus musculus, Mus spp.) and sylvatic species (C. gambianus, X. erythropus, M. natalensis), confirming its ecological plasticity.

Finally, Rattus rattus is by far the most heavily infested host, harboring over six parasite species with high rates of C. felis, X. cheopis, and P. spinulosa, making it the primary reservoir and vector of ectoparasites in urban and rural environments. Cricetomys gambianus is also highly parasitized, particularly by Hemimerus spp. (host-specific), as well as Ixodes spp. and Nosopsyllus fasciatus, serving as a secondary reservoir of strategic importance. Other rodents (Mus spp., Lophuromys, Dasymys, Lemniscomys, etc.) show lower but diverse infestations, contributing to the eco-epidemiological dispersal of ectoparasites across various habitats (fields, forests, human settlements).

Out of 1114 samples, 55 positive cases were detected, corresponding to a prevalence of 4.98% (See Table 4 ). This indicates that pathogen circulation remains relatively low but not negligible, suggesting the possibility of discreet endemicity.

Rattus rattus is the most affected species (15 positive cases; 1.35%), confirming its central role as a potential reservoir in urban and peri-urban environments.

Cricetomys gambianus shows a prevalence of 0.36%, but harbors a medically important pathogen (Ehrlichia spp.), representing a notable zoonotic risk.

Mus spp. and Mus musculus account for 18 positive cases (1.62%), indicating their active involvement in the dissemination of Borrelia spp.

Borrelia spp. was detected in multiple species (Mus spp., Mus musculus, Rattus rattus, Dasymys rufulus, Lemniscomys zebra), suggesting wide interspecific dispersion.

Mammarenavirus Lassa was detected only in Mastomys natalensis (3 cases, 0.27%), consistent with the recognized role of this rodent as the natural reservoir of Lassa virus.

Leptospira spp. and Anaplasma spp. were sporadically detected in Dasymys rufulus and Lemniscomys striatus, indicating localized eco-epidemiological foci.

Coxiella burnetii (1 case in Xerus erythropus), although rare, is the causative agent of Q fever, a zoonosis of veterinary and human importance.

These results confirm that synanthropic rodents (Rattus, Mus, Mastomys) are the main reservoirs of zoonotic agents. The low but significant detection of pathogens with high public health impact (Lassa, Ehrlichia, Borrelia, Leptospira) reflects a latent risk of transmission to humans, especially in areas with high human-rodent contact.

Our results indicate that the study areas are particularly rich in ecosystems, as evidenced by the diversity of rodent fauna observed. Overall, rodents were closely associated with various vegetation formations, confirming their role as ecological indicators. The composition of the populations during this year of research revealed 18 species captured, a higher number than the 11 species reported by [13] . The Kindia region stands out for its greater species richness, with 16 species identified, surpassing the 12 species inventoried by [14] in the same area. These observations confirm the dynamic and complex nature of small mammal communities in the Republic of Guinea.

Regarding ectoparasites, all collected specimens consisted of mites belonging to the families Ixodidae, Dermanyssidae, and Myobiidae, as well as blood-feeding insects from the families Ceratophyllidae, Haematophiridae, and Pulicidae. In total, 356 ectoparasites were collected and distributed across seven species: Ixodes spp., Ornithonyssus bacoti, Radfordia ensifera, Ctenocephalides felis, Nosopsyllus fasciatus, Polyplax spinulosa, and Xenopsylla cheopis. This result differs from [15] , who collected 539 ectoparasites in Benin but only identified four species. Furthermore, all ticks identified in our study belonged to the genus Ixodes, representing all three developmental stages (larvae, nymphs, and adults), consistent with the findings of [16] in Madagascar, who also reported the coexistence of all three tick stages on small mammals.

The ectoparasite abundances observed on Rattus rattus are comparable to those reported by [14] , who considered this species the most heavily infested host, ahead of Rattus norvegicus and Arvicanthis niloticus. However, our observations differ from those of [17] in Egypt, where Rattus norvegicus was reported as the most abundant. These discrepancies highlight the geographic and ecological variability in the distribution and dynamics of hosts and their ectoparasites.

A key finding of our study is the detection, via PCR, of two positive cases of Lassa mammarenavirus, both from rodent blood and organ samples as well as from homogenates of mites and insects. This discovery is epidemiologically significant, given that confirmed cases of Lassa fever were reported by Guinean health authorities in Yomou in May 2021 and in Guéckédou in April 2022 [18] . These results confirm that rodents play a central role as pathogen reservoirs and, through their ectoparasites, serve as a source of infection for humans.

This situation more broadly illustrates the role of rodents in the transmission of infectious diseases, which is not limited to hemorrhagic fevers but extends to other zoonoses, including mosquito-borne arboviruses such as dengue and chikun-gunya. These diseases, strongly influenced by climatic and environmental conditions, reflect ecological disturbances caused by human activities that facilitate pathogen spread and accelerate biodiversity loss. A comprehensive analysis of our results highlights that the highest-risk areas are Nzérékoré and Kindia, due both to their richness in micromammals and the density of contacts among hosts, parasites, and human populations.

This study revealed the diversity of rodents and their ectoparasites across four natural regions of the Republic of Guinea, confirming their role as reservoirs for several zoonoses. Molecular and bacteriological analyses detected zoonotic pathogens, underscoring the potential for disease transmission between species and to humans. Although the overall health risk appears moderate, the presence of potentially dangerous zoonoses, particularly for exposed professionals, warrants strengthened surveillance. These findings highlight the importance of an integrated “One Health” approach to prevent disease spread, taking into account interactions between wildlife, vectors, and the environment.

Conceptualization: Kolié Bonaventure, Diallo Alpha Oumar Sily, Bah Boubacar Sidy Sily.

Data curation: Kolié Bonaventure, Diallo Alpha Oumar Sily, Bah Boubacar Sidy Sily.

Formal analysis: Kolié Bonaventure, Diallo Souleymane.

Investigation: Kolié Bonaventure, Diallo Alpha Oumar Sily, Sacko Noumouny, Bah Boubacar Sidy Sily, Diallo Souleymane, Diallo Mamadou Gando, Conde Youssouf, Tolno Raphael, Boumbaly Sanaba.

Methodology: Kolié Bonaventure, Diallo Alpha Oumar Sily, Bah Boubacar Sidy Sily, Diallo Souleymane.

Project administration: Diallo Alpha Oumar Sily, Boumbaly Sanaba, Bah Boubacar Sidy Sily.

Supervision: Diallo Alpha Oumar Sily, Boumbaly Sanaba, Bah Boubacar Sidy Sily.

Validation: Kolié Bonaventure, Diallo Souleymane, Diallo Alpha Oumar Sily, Bah Boubacar Sidy Sily, Konaté Daouda.

Visualization: Kolié Bonaventure.

Original draft editing: Kolié Bonaventure, Diallo Souleymane, Diallo Alpha Oumar Sily, Bah Boubacar Sidy Sily, Konaté Daouda.

Writing—review and editing: Kolié Bonaventure, Bah Boubacar Sidy Sily, Diallo Alpha Oumar Sily, Diallo Souleymane, Konaté Daouda.

We express our sincere gratitude to the Guinean government through the Ministry of Higher Education, Scientific Research, and Innovation, the University of Kindia (UK), the Higher Institute of Veterinary Science and Medicine of Dalaba (ISSMV/Dalaba), the Institute of Applied Biology Research of Guinea (IRBAG/ Kindia), the International Center for Research on Tropical Infections in Guinea (CIRIT-Guinea), the Central Research Institute of Epidemiology in Moscow, Russia, and the Laboratory of Applied Research in Natural Sciences (LARASCINA) for their support.