Global Maps of Avian Leukosis Viruses: Research Trends and Themes Based on Networking

Simple Summary Avian leukosis viruses (ALVs) are important veterinary viruses. Given the medicinal and economic significance of ALV infections in poultry, we explored and compiled data from the Web of Science (Core Collection) database. According to scientific data, there are limited bibliometric studies on ALV research. We aimed to find research trends and themes, the influential journals, authors, countries, institutions, and worldwide collaborative networking of countries on ALV research. Recent developments in networking science and bibliometric tools have paved the way to visualize and map scientific outputs. We utilized the bibliometric tools VOSviewer and Biblioshiny software to construct and map research trends and themes for Avian Leukosis Viruses. Our findings revealed that Chinese and American research institutions produced the majority of papers during the study time period. The Journal of Virology and Avian Diseases appeared as the preferable journal/source for publications. Apart from the avian leukosis virus and the ALV-J, the important keywords mentioned were avian leukosis virus subgroup j, chicken, and retrovirus. The bibliometric analysis revealed substantial findings on ALV research, with a strong research response from the USA and China. Abstract Avian leukosis virus (ALV) has a tremendous adverse impact on the poultry industry. Since its discovery, research on different aspects of ALV have been published. Due to the vast academic emphasis and economic importance of the ALV infection in poultry worldwide, this bibliometric analysis explored the scientific output associated with ALV utilizing the Web of Science (Core Collection) database. The relevant data were collected using the search query “AVIAN LEUKOSIS VIRUS”, further refined by document types (article, book chapter, and proceedings paper). Finally, 1060 items with full records were imported in Plaintext and tab-delimited formats. The data analysis was carried out using MS Excel, VOS viewer, and R (Biblioshiny) software. Chinese and American research institutions produced the majority of papers during study time period. The Journal of Virology and Avian Diseases appeared as the favorite journal/source for publications. Apart from the avian leukosis virus and the ALV-J, the important keywords mentioned included avian leukosis virus subgroup j, chicken, and retrovirus. The analysis revealed substantial findings on ALV research, with a strong research response from the USA and China.


Introduction
Avian leukosis viruses (ALVs) are important veterinary viruses economically and medically and are classified based on sequence similarities. These belong to the alpharetrovirus genus of the subfamily orthoretrovirinae in Retroviridae [1][2][3]. Based on their endogenization and transmission mode, ALVs are categorized into endogenous and exogenous avian retroviruses. All oncogenic ALVs fall into the exogenous category of ALV [3] and are causative of severe commercial losses in the poultry industry [4,5]. In chicken, the exogenous ALVs include subgroups A, B, C, D, J, and K, while subgroup E belongs to endogenous ALV [1,[5][6][7]. The research on avian retroviruses is not new in the scientific world, as it dates back more than a century [4,8,9], and still, scientists are exploring its enigma. Until now, no effective vaccine has been available for ALV infection [10].
Bibliometric studies pave our understanding to determine the scientific impact and research trends. Several indices (indexes), including co-occurrence, citations, and keywords, are widely used in scientometrics to highlight research productivity, collaboration networks, and trends. Scientists use different algorithms and methods to decipher broad dimensions of bibliometric studies [11][12][13]. The bibliometric metadata of scientific publications has been mathematically used for the quantitive analysis of a specific topic's yearly or total research publications. This method helps to determine the quality of studies, analyze the main areas of research, and also helps to predict future research directions [14]. The network science and bibliometric studies combine to make research more interactive, allowing users to visualize worldwide scientific activity and create maps-the current study utilized bibliometric and networking tools to decipher the ALV research. Our aim was to find out research trends and themes, the influential journals, authors, countries, institutions, and worldwide collaborative networking of countries on the ALV research. According to scientific data, there are limited bibliometric studies on ALV research.
Furthermore, the co-author network analysis helps to explore and quantify research and development collaboration among authors, institutes, and countries [15]. In these graphical visualizations of the co-author network, the authors are nodes interconnected through co-authored scientific publications, which are the edges between these nodes. The level of betweenness density of each author node specifies their connectivity [14].

Data Mining
We collected published datasets indexed in Thompson's Institute for Scientific Information Web of Science (WOS core collection) with a timeframe of 1999-2022. We searched with the keyword "AVIAN LEUKOSIS VIRUS". The full citation information, including the authors' names, organizational affiliations, the publication year, and the sum of citations, was chronicled as a bibliographical corpus in Plaintext and tab-delimited formats [16].

The Inclusion and Exclusion Criteria of Data
The inclusion criteria were: a clear correlation with ALV and a focus on avian subjects. We included pertinent avian leukosis virus articles; review papers; books; editorials; letters; and conference proceedings. Moreover, publications in other languages available on WOS (Core Collection) were also included in our research. Our search did not include studies in other databases, such as Scopus and PubMed.

Bibliometric Analysis
Bibliometric analysis is a new approach to identifying current trends in the field of scientific publications. Over the course of a decade, this study examined publication patterns (top 10 prolific countries and journals), publish themes and trends (top keywords for avian leukosis virus, research focus, and data), scientist contributions, global collaborations, and co-citing references in avian leukosis virus (ALV) research, where "Total Link Strength (TLS)" is an essential feature of bibliometric analysis, as it infers the connectivity among various terms that occur together. The impact factors (IFs) of the journals/sources were manually added from the journal citation report (JCR) (Clarivate Analytics, Philadelphia, United States, available from https://jcr.clarivate.com/) accessed on 26 August 2022 [17]. The VOSviewer software version 1.6.17 [18], MS Excel, and RStudio (Biblioshiny) were utilized to analyze and visualize our dataset.

Results
Overall, 1060 studies available on the WOS (Core Collection) were included in the recent study with a timespan of 1999-2022; the publication type, annual publication numbers, and total of citations were also investigated. The total citations of these articles were 22,117, and the average sum of citations per article was 20.87. The h-index of these publications was 67. This data set comprises original articles (966; 91.13%) and review articles (64; 6.03%). Most of the publications were in English (1049; 98.96%), followed by Hungarian (3; 0.28%), as shown in Table 1. A sum of 54 countries scientifically contributed to the ALV literature globally. These findings reveal that the USA contributed significantly (444; 41.88), followed by China (419; 39.52%) and England (76; 7.17%). The dataset reveals that Virology (314) and Veterinary Sciences (305) are the chief research areas in the ALV research.  Table 2 shows the ten leading research journals/sources that published scientific literature on ALV research. The Journal of Virology (impact factor 4.50) appeared as a leading journal/source (140 publications and 4574 citations), followed by Avian Diseases (66 publications and 1180 citations) and Avian Pathology (60 publications and 1307 citations) ( Figure 1).  IF = impact factor of journals/sources; TP = total production; TC = total citations; TLS = total link strength.  Table 3 reveals the ten prominent countries and institutions producing ALV publications globally. Only three countries produced more than 50 publications. According to the study, behind the United States of America (USA), which had 443 articles, China came in second with 419 publications (citations 4997, TLS 86), and England followed in third with 76 publications (citations 1981, TLS 69). The findings reveal that the USA had contributed more to scientific ALV-related publications ( Figure 2a). Still, the overlay visualization indicates that during the past decade, China has emerged as the knowledge hub for ALV research (Figure 2a).  Table 3 reveals the ten prominent countries and institutions producing ALV publications globally. Only three countries produced more than 50 publications. According to the study, behind the United States of America (USA), which had 443 articles, China came in second with 419 publications (citations 4997, TLS 86), and England followed in third with 76 publications (citations 1981, TLS 69). The findings reveal that the USA had contributed more to scientific ALV-related publications ( Figure 2a). Still, the overlay visualization indicates that during the past decade, China has emerged as the knowledge hub for ALV research (Figure 2a).

Most Cited Documents/Articles
The ALV research is relatively nascent compared with the remaining members of the family Retroviridae; therefore, many aspects of ALV research overlap or depend on the retroviral research dimensions, including DNA integration and endogenous retroviruses. Table 4 describes the top-ten highly cited articles on ALV research. The most cited article,  (Table 4). Development of a flexible and specific gene delivery system for production of murine tumor models

The Authorship Analysis
The citation analysis of scientists/authors was based on the publication count and citations. Out of 3369 authors, only 221 met the default criterion and participated in the scientific ALV research literature worldwide. These authors are in seven clusters, with 12,174 links and 76,335 TLS (Figure 3a,b). Young JAT appeared as a highly cited author, with 1889 citations and 28 documents (Table 5).   The co-authorship network is as much a network depicting academic society as it depicts the structure of our knowledge [15]. Studies on co-authorship networks of authors have gathered the attention of many scholars, not just because of their strong descriptive and synthetic power to define the evolution of scientific research communities but also because social networks play a substantial role in the generation of knowledge and provide a vision of cooperation patterns between individuals [15,19,20]. The analysis reveals the social structure of the networks of the authors/researchers and their connections. This manuscript also reviews the co-authorship network analysis of authors/scientists/researchers (Figure 3c) in ALV research [19]. Current findings reveal Cui Zhizhong as the most co-authored author/researcher (50 articles, 824 total citations, and 226 TLS), followed by Zhao Peng and Wang Xiaomei (Table 5). These findings show that Chinese authors have stronger scientific collaborations in the field of ALV research and the moving of the research hub towards China, which puts more responsibility on Chinese researchers to contribute significantly to the scientific community.  (Table 6). Furthermore, "endogenous retrovirus", "immune response", "innate immunity", and "replication" appeared as the latest hotspots in the ALV research themes.  Occurrence  Total link strength  1  avian leukosis virus  94  101  2  alv-j  77  71  3  avian leukosis virus subgroup j  67  46  4  Chicken  65  96  5  Retrovirus  36  40  6 Subgroup j avian leukosis virus 29 30 7 Marek's disease virus 22 30 8 Marek's disease 21 42 9

Three-Factor Analysis
The three-factor analysis of the association between authors' countries, journals, and institutions/organizations is mentioned in Figure 5, where the author's country is shown on the left, journals/sources in the middle, and author-provided keywords on the right side. It shows that the six journals/sources (Journal of Virology, Poultry Science, Avian Diseases, Avian Pathology, Archives of Virology, and Veterinary Microbiology) that published the ALV literature with the author-provided keywords (avian leukosis virus, avian leukosis virus subgroup J, ALV-J, subgroup j avian leukosis virus) have a strong relationship with

Three-Factor Analysis
The three-factor analysis of the association between authors' countries, journals, and institutions/organizations is mentioned in Figure 5, where the author's country is shown on the left, journals/sources in the middle, and author-provided keywords on the right side. It shows that the six journals/sources (Journal of Virology, Poultry Science, Avian Diseases, Avian Pathology, Archives of Virology, and Veterinary Microbiology) that published the ALV literature with the author-provided keywords (avian leukosis virus, avian leukosis virus subgroup J, ALV-J, subgroup j avian leukosis virus) have a strong relationship with leading countries (China, USA, and the UK, respectively). Figure 5 shows that most US scientists prefer to publish their ALV in the Journal of Virology, and that Avian Disease is the second-most prioritized source. On the other hand, Chinese scientists prefer to publish most of their ALV work in the Poultry Science, Archives of Virology, and Veterinary Microbiology journals.

Discussion
Recently, bibliometric investigations have been utilized more to analyze the scientific research trends and progress in numerous scientific and research domains. The current data analysis represents different dimensions of ALV research, including the leading countries, organizations, and sources/journals producing the literature on ALV. Of these countries, the USA is the leading country in ALV research, closely followed by China. However, during the last decade, China has appeared as the new scientific hub for ALV research. This puts a significant responsibility on Chinese policymakers and researchers to fund more meaningful and citable research [21]. The current findings align with the findings of Al-Jabi and Farooq [22,23], indicating English as the de-facto language, which is also in line with Wiethoelter, Morel, and Yi [24][25][26].
The data analysis regarding authorship and collaborative research patterns reveals that most publications have collaboration ties of authors [15,25,27]. This collaborative network is also essential for health innovation due to its application in interdisciplinary research [19]. The authors from China were the most significant contributors to the topic, which does not coincide with Albuquerque and others [28,29], where US researchers were the most frequent contributors to the studies conducted on Zika. Moreover, the articles from the USA were the most cited, followed by China. Shandong Agricultural University was the most cited institution, followed by South China Agricultural University [30]. Considering the country-wise organizations contributing to the theme, it is not astounding that Chinese institutes ranked on top in the ten lading organizations list, followed by the USA organizations. The bibliometric dataset unveiled the most productive journal on ALV research. According to our findings, the Journal of Virology has published more on the ALV topic. The present results coincide with the previous study of Zaib et al. [11], where the Journal of Virology appeared as the most influential journal. These findings contradict the results of Koo [31], who reported that the Journal of Alternative and Complementary Medicine contributed the greatest number of articles on aroma therapy. These findings are also not in line with the study conducted on Campylobacter [32]. The country-collaboration map centering a significant count of the literature published as the result of positive collaborative research between countries, such as the USA and China, agrees with Hossain's bibliometric work [32]. The USA actively participated in collaborative research with the UK and Canada, which matches the previous study [23].
Early studies mainly concentrated on the diagnosis, signs, and subtypes of ALV, but later they prioritized ALV-J more due to the economic losses in the poultry industry. There is inadequate data available for the treatment and vaccine development against ALV infection among poultry flocks. Hence, scientists started to study the immune response, replication, and innate immunity to curb the infection in the host.
The current study has some limitations, such as avian leukosis virus research data collection being limited to the WOS (Core Collection) publication index, whereas other databases such as PubMed, EMBASE, Google Scholar, Dimension, and Scopus were not included. Moreover, gender analysis was not performed to study females' global contribution to the ALV research. Future work in these domains may provide a thorough comparative and cumulative aspect of the ALV literature available on these databases.

Conclusions
Bibliometric analyses are now being undertaken in a variety of scientific domains, but the current study is believed to be the foremost for ALV research. In short, the bibliometric analyses were carried out to better understand and quantify the global research productivity for ALV. China and the United States appear to collaborate with one another, and the rest of the globe, the most, and have the highest research productivities. Regarding publishing output, the Chinese Academy of Sciences (CAS), South China Agricultural University, and Shandong Agricultural University hold the top three spots among research institutions. Moreover, the analysis highlighted that "endogenous retrovirus", "immune response", "innate immunity", and "replication" emerged as the dominant research trends and themes. The preferable journals for publication are the Journal of Virology and Avian Diseases. In general, the current study provides a comprehensive overview of the global ALV research perspective, and therefore can serve as the basis for future research in this field.

Data Availability Statement:
The dataset in the current study comes from the Web of Science (core collection) and is available on its web page. Thomson Reuters does not allow us to make the data freely available. Readers can contact Thomson Reuters to obtain the data (http://thomsonreuters. com/thomson-reuters-web-of-science/, accessed on 1 November 2022).