The global distribution and the risk prediction of relapsing fever group Borrelia: a data review with modelling analysis

Abstract

Background: The recent discovery of emerging relapsing fever group Borrelia (RFGB) species, such as Borrelia miyamotoi, poses a growing threat to public health. However, the global distribution and associated risk burden of these species remain uncertain. We aimed to map the diversity, distribution, and potential infection risk of RFGB.

Methods: We searched PubMed, Web of Science, GenBank, CNKI, and eLibrary from Jan 1, 1874, to Dec 31, 2022, for published articles without language restriction to extract distribution data for RFGB detection in vectors, animals, and humans, and clinical information about human patients. Only articles documenting RFGB infection events were included in this study, and data for RFGB detection in vectors, animals, or humans were composed into a dataset. We used three machine learning algorithms (boosted regression trees, random forest, and least absolute shrinkage and selection operator logistic regression) to assess the environmental, ecoclimatic, biological, and socioeconomic factors associated with the occurrence of four major RFGB species: Borrelia miyamotoi, Borrelia lonestari, Borrelia crocidurae, and Borrelia hermsii; and mapped their worldwide risk level.

Findings: We retrieved 13 959 unique studies, among which 697 met the selection criteria and were used for data extraction. 29 RFGB species have been recorded worldwide, of which 27 have been identified from 63 tick species, 12 from 61 wild animals, and ten from domestic animals. 16 RFGB species caused human infection, with a cumulative count of 26 583 cases reported from Jan 1, 1874, to Dec 31, 2022. Borrelia recurrentis (17 084 cases) and Borrelia persica (2045 cases) accounted for the highest proportion of human infection. B miyamotoi showed the widest distribution among all RFGB, with a predicted environmentally suitable area of 6·92 million km², followed by B lonestari (1·69 million km²), B crocidurae (1·67 million km²), and B hermsii (1·48 million km²). The habitat suitability index of vector ticks and climatic factors, such as the annual mean temperature, have the most significant effect among all predictive models for the geographical distribution of the four major RFGB species.

Interpretation: The predicted high-risk regions are considerably larger than in previous reports. Identification, surveillance, and diagnosis of RFGB infections should be prioritised in high-risk areas, especially within low-income regions.

Funding: National Key Research and Development Program of China.

Figure 1:. Flow diagram of the literature review

RFGB = relapsing fever group Borrelia.

Figure 2:. RFGB species infection in animals, vectors, and humans, from publications searched from Jan 1, 1874, to Dec 31, 2022

(A) Overall number of publications on RFGB detection in vectors (blue), animals (yellow), and humans (red). (B) Number of publications on RFGB species stratified by host types with year of first reporting for each RFGB species. (C) Chord diagram between RFGB species and host types. In panels B and C, the names of species with human infection records are marked in red. B=Borrelia. RFGB=relapsing fever group Borrelia.

Figure 3:. Spatial distribution of RFGB species on a global scale

(A) New World or Old World distributed RFGB species. New World countries are marked in grey. (B) RFGB species with worldwide distribution. The names of RFGB species with human infection records are marked in red. RFGB=relapsing fever group Borrelia.

Figure 4:. Global distribution of RFGB detection events in vectors and hosts

(A) Vectors. (B) Animals. (C) Humans. (D) Number of human and host infection occurrence locations (after removing duplication) for each RFGB species, stratified by continent. RFGB=relapsing fever group Borrelia.

Figure 5:. Vectors and numbers of animal species from which each RFGB species was detected

(A) RFGB species detected in vectors, including 71 tick species, most of which further classified by genus. Vectors with documented human bites are marked in blue; RFGB species with documented human infections are marked in red. (B) RFGB species detected in animals classified by genus, including wildlife and domestic animals. The total number of animal species in each genus with detected RFGB species is shown inside the matrix when it is greater than 1. The names of RFGB species with human infection records are marked in red. RFGB=relapsing fever group Borrelia.