Bibliometrics is a quantitative research method that uses mathematical and statistical methods to review and describe published literature in a particular field (25). This research method can obtain and analyze important information such as the details of publication authors, keywords, journals, institutions, countries, and references. The results will help to understand the development trend of a scientific field, research focus, and researcher cooperation relationships (26). Furthermore, the use of computer technology to present results graphically and visually can help to uncover hidden relationships within the data and make the results more comprehensive (27).

Data visualization technology is a very important research method and means in bibliometrics. VOSviewer and CiteSpace are two commonly used data visualization analysis software programs. Using VOSviewer, a large-scale bibliometric map can be constructed to reflect the importance of items such as authors, keywords, institutions, and the strength of relationships with adjacent items through label views, density views, cluster density views and scatter views (28). CiteSpace is a Java application for analyzing and visualizing co-citation networks. It can divide a time interval into several time slices, from which individual co-citation networks can be obtained to highlight the main changes between adjacent time slices (29). Moreover, CiteSpace can detect and visualize trends and changes in science over time. It can be used to explore the dynamics of a profession, that is, the mapping of temporal changes from its knowledge base to the research frontier (30). Therefore, VOSviewer version 1.6.18 and CiteSpace version 6.1.R6 were used in this study to conduct a bibliometric analysis of ASF-related academic publications. In addition, BiblioShiny, a software package running in R language, and an online analysis platform of bibliometrics were used as complementary methods in this study.

This study delimits the scope of analysis, employs a strict literature search strategy, and selects the Web of Science (WoS) as the data source. The WoS includes relevant material from a wide range of research fields and is a high-quality digital database that is widely accepted by researchers around the world (31). It exceeds other databases in functionality and complexity, with historically greater coverage (32).

The Web of Science Core Collection (WoSCC) was selected as the data source for this particular study. The Science Citation Index Expanded was chosen, and the retrieval strategy was to use “African swine fever” as the subject search term to guarantee the comprehensive and precise retrieval of data. Additionally, the time horizon was set from January 1, 2003, to December 31, 2022. The initial search identified 2,132 relevant articles, including all document types. Considering the completeness of the literature information, the literature types were selected as articles and review articles, and the language was restricted to English for ease of analysis. Finally, 1,885 valid papers were obtained. Retrieved publications were exported as plain text files with “full record and cited references”, which were uploaded to the VOSviewer and CiteSpace for analysis under the name “download_X.txt”. The selection process is detailed in Figure 1.

The 1,885 articles used in this study come from 7,621 authors affiliated with 2,021 institutions in 111 countries/regions. These articles were published in 338 journals and cited 46,521 references from 12,358 journals. The number and the cumulative number of papers published in different periods can reflect the development trend of this research field. In the past two decades, the temporal distribution of 1,885 articles in the ASF research field is shown in Figure 2. Although the annual publication volume did not change much before 2013, which was < 40, on the whole, the number of publications in this field is on the rise. The number of publications has increased significantly, especially after 2018. More than 150 articles were annually published for four consecutive years from 2019 to 2022, and the increase was large. In 2018, ASF spread to China, the world's largest pig breeder, sparking a research boom among researchers in this field. Linear regression analysis was carried out on the publication time of the literature and the annual cumulative number of publications, R² = 0.9629. The model fitting effect is good, which is in line with the scientific exponential growth law proposed by Price, that is, various scientific indicators increase approximately exponentially with time (33). This shows that the relevant research on ASF is currently in a period of rapid development, and the speed of achievement output and literature publication is also accelerating.

To understand the representative scholars and main research teams, this paper studies the top 11 scholars with the number of publications, as shown in Table 1. Sandra Blome, a virologist from the Friedrich Loeffler Institute in Germany, published the most papers over the past two decades (75 articles, 3.98%, 25.37 average citation per article). Linda Dixon of the Pirbright Institute in the UK was second in the number of publications (64 articles, 3.40%, 64.66 average citation per article). Carmina Gallardo, a Spanish scholar from the European Union Reference Laboratory for ASF, ranked third (55 articles, 2.92%, 50.53 average citation per article). Based on the WoS, the H-index is a useful indicator to assess the impact and productivity of certain countries/regions, institutions, or scientists in an academic field (34). It can be simply expressed as H publications were cited no less than H times. For example, a scientist with an H-index of 30 means that he has 30 papers that have been cited at least 30 times. It has mostly become an objective measure of scientific achievement. According to statistics, the top 3 authors for the H-index in this study are Linda Dixon (H-index = 40), Carmina Gallardo (H-index = 34), and José Manuel Sánchez-Vizcaíno (H-index = 30). Dr. Sandra Blome is responsible for the Germany National Reference Laboratories for African and classical swine fever. Her research focuses on the pathogenesis of viral infectious diseases such as classical swine fever and ASF (35, 36), especially the mechanism of virus–host interaction and the development of vaccines (37). Dr. Linda Dixon's research focuses on the functional genomics of ASFV(1) and the mechanisms of immune evasion and pathogenesis (38), and her research team has also been committed to the research and development of effective vaccines (39). Dr. Carmina Gallardo's main expertise is in ASF research, mainly involving new diagnostic tools, molecular epidemiology, epidemic control strategies and vaccine research (40, 41). Professor Sánchez-Vizcaíno's research has been vital in the fight against various animal diseases, such as ASF, African horse sickness, and classical swine fever. His work has enabled the development of new techniques, quick and accurate diagnostic tools, innovative epidemiologic approaches, and novel vaccine strategies (42, 43).

To highlight the collaboration between the core authors in the field, authors with more than 5 publications are visualized in Figure 3. The size of each node in the figure represents the number of articles published by each author, and the thickness of the connecting line represents the strength of cooperative publishing between authors. Each color represents a cluster, and authors whose nodes are of the same color cooperate closely. We can see that the authors have formed multiple research groups based on their cooperative relationships, indicating that scholars in this field have a certain consensus basis on ASF. Overall, the representative scholars in this field are mainly from Europe and the United States, and they have formed their cooperation networks, and the communication and cooperation between the groups are relatively close. Although Chinese scholars also performed well in this field, only many small cooperative clusters were formed, and no good cooperation network has formed between the various groups.

Statistics on the journals that published the literature show that articles on ASF research have been mainly published in 338 journals in the past two decades. By setting the minimum number of documents to 5, we obtained the co-occurrence map of journals as shown in Supplementary Figure S1. The more published articles, the brighter the color. Conversely, the smaller the number of publications, the darker the color. The top 10 journals published a total of 824 articles, accounting for 43.71%. Table 2 shows the top 10 journals in terms of publication volume, which are mainly professional journals in the field of veterinary sciences and virology, and some interdisciplinary comprehensive journals. Journals that have published more than 100 articles about ASF in the past two decades include Transboundary and Emerging Diseases (203, accounting for 10.77%, 21.85 average citation per article, Q1), Viruses-Basel (137, accounting for 7.27%, 11.77 average citation per article, Q2), and Frontiers in Veterinary Science (106, accounting for 5.62%, 8.66 average citation per article, Q1). In particular, Transboundary and Emerging Diseases and Frontiers in Veterinary Science are the top journals in the field of veterinary sciences. The former favors content on novel scientific approaches to the causes, control and prevention of cross-border and emerging diseases. The latter is the third most cited journal in the field, covering almost all veterinary sciences such as animal infectious diseases, genomics, veterinary public health, and the exploration of new treatments. The journal with the most average citation is Virus Research, with a total of 50 articles published and an average of 60.20 citation per article, indicating that this journal has received more attention in the field of ASF research. Its publications consist primarily of original research papers in the field of viral molecular science, review articles, and special issues on specific topics. Book reviews, editorials and conference presentations are also occasionally accepted.

Among the top 10 journals with the most publications related to ASF, Journal of Virology had the highest impact factor (IF 2021 = 6.549), followed by Virus Research (IF 2021 = 6.286) and Viruses-basel (IF 2021 = 5.818), and these three journals belong to Q2 of Journal Citation Reports (JCR) virology category. In addition, the three journals with the highest H-index are: Transboundary and Emerging Diseases (H-index = 36) followed by Journal of Virology (H-index = 33) and Virus Research (H-index = 32), their published articles related to ASF had an important influence on this field. The publishing regions of the top 10 most productive journals are all from Europe or the United States, while the Netherlands and Switzerland have 3 each and the United States has 2, indicating that journals from Europe and the United States have been instrumental in advancing this field of research.

To understand the contribution and cooperation of various countries/regions in the field of ASF research, we analyzed the number of publications of 111 countries/regions that have been identified. First, VOSviewer was used to visualize the top 20 countries/regions with the most publications, and then SCImago Graphica version 1.0.23 is used to visualize the geographical distribution, as shown in Figure 4A. The nodes in the figure represent the number of articles published by the countries, and the larger the node is, the more articles are published by the country. The line represents the strength of the association, and the thicker the line is, the greater the number of published articles in cooperation between the two countries. The colors of the nodes represent different clusters, and the cooperation between countries of the same color is relatively close. It can be seen in the figure that countries with high publication volume form four obvious clusters, indicating that there is a stable cooperative relationship between countries. The top 10 countries/regions by publication volume are presented in Table 3. Through the analysis of the data and the visual map, it can be seen that China published the most articles in the field of ASF (401, 4,965 citations, 12.38 average citation per article), but the frequency of cooperation with other countries is not high, and the citation per article are relatively low. The second-ranked United States (353, 7,872 citations, 22.30 average citation per article), third-ranked Spain (312, 11,387 citations, 36.50 average citation per article), and fourth-ranked United Kingdom (252, 9,661 citations, 38.34 average citation per article) have more collaborative publications, indicating that they have frequent academic exchanges in this field.

To further show the contribution of each country/region in the field of ASF research, we also counted the distribution of the corresponding author's country/region. China remains the most productive country (374, accounting for 19.84%), followed by the United States (238, accounting for 12.63%) and Spain (224, accounting for 11.88%). In addition, SCP represents the number of publications co-authored by authors from the same country, whereas MCP represents the number of papers co-authored with authors from multiple countries. According to the MCP ratio, Poland, as well as China, have a limited level of international collaboration, whereas Kenya is the most engaged as shown in Figure 4B.

The publications on ASF research included contributions from 2,021 institutions. According to the number of publications statistics, Table 4 presents the top 10 producing institutions. The top 10 institutions each contributed 718 publications, accounting for 38.09%. Institutions in Europe, Africa, North America, and Asia have made outstanding contributions in this field, indicating that ASF is a global problem that has attracted great attention from scientists all over the world. Although the Chinese Academy of Agricultural Sciences has the most publications (115 papers), the number of citation per article is low (16.30 times). The top H-index value at the Pirbright Institute (H-index = 32) and the highest number of citation per article at the University of Pretoria (43.08 times). The VOSviewer presented the knowledge graph of the institutional collaboration network. By setting the minimum number of documents for one institution as 5, the cooperative network graph of 222 institutions was obtained in Figure 5. There is deep and extensive cooperation between European and American scientific research institutions, while Chinese scientific research institutions cooperate more with domestic institutions. In general, although Chinese scientific research institutions have many publications, the average citation number of articles and the H-index value are not high, and the degree of international cooperation needs to be improved. Among the top 10 institutions, three are from Spain, indicating that the country's scientific institutions have made an outstanding contribution. In addition, scientific institutions in African are an important force in the field of ASF research.

The behavior of papers citing other papers can be regarded as the flow of knowledge among different research topics and the process of knowledge reorganization to produce new knowledge (44). Citation analysis can be used to evaluate the scientific value and influence of publications in a particular field of research and has a significant impact on the discussion, practice, and future research in this area (45). Moreover, co-citation analysis of cited journals helps to understand key scientific journals in related fields. To understand the most frequently cited papers in the ASF research field and the journals that publish them, as well as the internal relations between them, to obtain the knowledge base source of the research field. In this study, 46,521 references from 12,358 journals were used as data sources to analyze co-cited literature and the journals in which it was published.

ASF has been present on the earth for more than 100 years since it was reported for the first time in 1921. In the past 100 years, ASF has caused serious social and economic consequences around the world. To date, there are still many problems in research in this field that urgently need to be solved. Therefore, it has received extensive attention from many scholars around the world. So this is a hot study that is constantly being updated. Based on the information of 1,885 papers on ASF from January 1, 2003 to December 31, 2022, obtained from the WoSCC, this study reviewed the development of this field employing a bibliometric system and visualized the research results through VOSviewer and CiteSpace. We identified the core journals in the field, revealed important authors, contributions of institutions, highly productive countries and their collaborative networks, and explored the keywords, co-cited literature, etc. We also found research hotspots at different times, and keywords involved in these research hotspots are presented.

From the 1,885 published articles related to ASF retrieved from the WoSCC, the number of published articles increased from 16 in 2003 to 400 in 2022. The number of publications on ASF research has increased rapidly over time, indicating that the field is receiving increasing attention. Some renowned scholars have emerged in the research field of ASF, and some author cooperation networks have been established, which play a vital role in promoting the advancement of this field. At present, the author with the most articles on ASF research was Sandra Blome from the Friedrich Loeffler Institute, while Linda Dixon of the Pirbright Institute is the most influential author. The journals that publish ASF-related papers are mainly journals in the professional fields of veterinary science and virology, many of which are top journals in the field of veterinary science. The journal Transboundary and Emerging Diseases has published the most publications in this area, it has great academic influence and high professional recognition in the field of industry segmentation. This also hinted at the ASF research has a high professional level in the field of veterinary science. China ranked first in the number of articles published. In 2018, the first ASF epidemic occurred in China and caused a serious impact, which may have caused a research boom among scholars. Another fact is that although China has the most publications, it is not dominant in this field. European countries and the United States have higher H-index and more citation per paper. Similarly, the international cooperation rate of Chinese scholars is much lower than that of scholars from Kenya, South Africa, France, and other countries from the perspective of multi-country cooperation. This shows that Chinese scholars are very important participants in this research field and have great potential for development, but they still need to strengthen cooperation with foreign research institutions and further improve the research level of ASF through complementary advantages. According to the survey of institutions, the Chinese Academy of Agricultural Sciences has contributed the most articles, while the Pirbright Institute has contributed many high-impact articles. And more, the output and quality of scientific institutions in Spain in the field of ASF research are impressive.

Keywords are indicative words that relate to the content of the research topic, which can reflect the research hotspots to a certain extent. The analysis of the literature related to ASF conducted via CiteSpace revealed important keywords, such as “gene,” “epidemiology,” “transmission,” “replication,” “protein,” “identification,” “virulence,” “protection,” “outbreak,” “cell,” “risk factor,” “macrophage,” “sequence,” etc. With the deepening and development of research, the keywords “transmission,” “identification,” “virulence,” “replication,” and “gene” continued to break out until 2022. It reflects that the research related to these keywords is the latest hotspot in the field of ASF.

It can be inferred from the high frequency keywords such as “epidemiology,” “transmission,” “wild boar,” “domestic pig,” and “outbreak” that a significant area of study for ASF is epidemiological research. Molecular biology is commonly employed by researchers as a pivotal tool for the epidemiological investigation of ASF to analyze the characteristics of viral genes and study the dynamic information of the disease. By collecting ASFV strains from domestic pigs and wild boars, researchers have been able to track the genetic variability of ASFV strains over time and understand the distribution of different genetic variants of the virus (54). Genotyping and phylogenetic analysis of ASFV can be used to determine the likely origin of the virus and to differentiate it from closely related strains (55). Furthermore, when combined with the phylogeographic approach, we can gain a more intuitive understanding of the transmission modes and dynamics of ASF. This information can then be utilized to implement targeted control strategies in specific regions to prevent the spread of this disease (56). The keywords “virus,” “protein,” and “virulence” suggested that the research hotspots were also related to the pathogen of ASF. ASFV is a complex nucleocytoplasmic large DNA virus. The uniqueness and complexity of its structure may be the factors that make it difficult to control (57). Therefore, the study of ASFV structure and protein function is also an important direction in this field. By studying the cryo-EM structure of the ASFV virion, scholars have revealed its important protein structure and the basis of assembly, opening a new way for the development of the ASF vaccine (7, 57, 58). It has also been found that the protein–protein interaction mechanism between ASFV and host pigs is important for studying potential drug targets and predicting the direction of antiviral drugs (59). By understanding the structure and function of certain ASFV proteins, we can gain insight into how to block the development of this virus, as well as provide dissimilar diagnostic strategies to amplify the level of diagnosis (60–62). Additionally, the study on the infection and immune response mechanisms of ASFV is also a crucial research direction, as evidenced by the clustered keywords such as “macrophages,” “infected cells,” “replication,” “immunologics,” and “mechanisms” (as outlined in Supplementary Table S1). The development of ASF may be due to virus-induced changes in the host's immune system, allowing the virus to better adapt to it (63). The mechanisms by which ASFV evades or inhibits the innate immune system involve the regulation of various complex signaling pathways (64). For example, through the inhibition of interferon regulatory factor-3 activation and stimulating interferon gene phosphorylation, the ASFV Armenia/07 virulent strain is capable of impeding the synthesis of IFN-β in porcine alveolar macrophages, thereby evading the host's immune responses (65). Moreover, certain genes of ASFV can regulate the replication of the virus within the host organism. Scholars found that ASFV with deletion of the CD2v and MGF360-505R genes caused significantly less cytopathic effects and apoptosis in PAMs than wild-type ASFV (66). The keywords “recombinant antigen,” “rDNA technology,” “immunization,” and “vaccinology” (shown in Supplementary Table S1) reflect the research focus on vaccines study. Despite the remarkable achievements in ASF research in recent years, we have to face the reality that there is currently not universally accepted safe and reliable ASF vaccine regimen. At present, although researchers have made many explorations into vaccine adjuvants, vaccination methods, and doses, inactivated ASFV vaccines still cannot achieve good protective effects (37, 67). The vaccine research program for ASF is more focused on live attenuated virus vaccines and subunit vaccines. The efficacy of live attenuated vaccines has been established, and research strategies include deleting specific genes, naturally attenuated virus isolates, and cell passages. However, their safety profile is not without risk (68–70). Side effects have been found in vaccinated animals (5). The protective effects of subunit vaccines are also inconsistent due to various reasons, such as vaccination methods and antigen strategies used (71, 72).

It is equally important that the co-citation analysis shows highly co-cited references and highly co-cited journals, which is helpful for subsequent scholars to quickly understand the core knowledge structure and sources of the research field. In conclusion, this study conducted a systematic and comprehensive review of ASF related studies based on the WoS database using a bibliometric approach. Through a quantitative and visual review of ASF research, researchers can accurately grasp the development dynamics and potential trends of ASF research.