http://dx.doi.org/10.4314/sajas.v54i3.09

 

A bibliometric analysis of brucellosis research (1991-2022): Research trends and hotspots

 

 

M. Farooq^I,; A.U. Khan^II,; H. El-Adawy^III; F. Melzer^III; H. Neubauer^III; I. Khan^I; Y.-S. Ho^IV

^IDepartment of Clinical Sciences, University of Veterinary and Animal Sciences, Lahore, Sub-campus Jhang, 35200 Jhang, Pakistan
^IIDepartment of Pathobiology, University of Veterinary and Animal Sciences, Lahore, Sub-campus Jhang, 35200 Jhang, Pakistan
^IIIInstitute of Bacterial Infections and Zoonoses, Friedrich-Loeffler Institute, 07743 Jena, Germany
^IVTrend Research Centre, Asia University, Taichung, Taiwan

 

 

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ABSTRACT

Brucellosis is an important, highly contagious, bacterial zoonotic disease that has economic and public health implications. It is caused by various Brucella species with a wide host range including livestock, wildlife, other terrestrial animals, and humans. Despite the availability of a huge number of publications on brucellosis, no comprehensive bibliometric analysis discussing research trends has been published. Bibliometric studies are important tools to highlight research trends and outputs of the relevant discipline. The current study aimed to highlight the research trends of published brucellosis data (9,022 articles published 1991-2022) from the Web of Science Core Collection database. The relevant data were obtained for the keywords "Brucella", "brucellae", and "brucellosis" and highlight the most research-active countries, institutions, authors, publications, journals, and disciplines. The articles focusing on brucellosis were predominantly published in journals categorized under veterinary sciences, followed by microbiology and infectious diseases. The United States emerged as the leading contributor to brucellosis research articles. The University of Navarra, Spain, and the French National Institute for Agricultural Research (INRA) stood out as the most prolific institutions in this field. The word cluster analysis indicated emerging brucellosis research areas including the development of diagnostic assays, host range (humans, cattle, small ruminants, rodents), and Brucella species (B. abortus, B. melitensis, B. suis and B. ovis). This review indicates the research landscape and future hotspots in brucellosis research that will promote sharing of knowledge and initiate collaborative research under the umbrella of "One Health".

Keywords: research trends, brucellosis, Brucellae, Brucella, zoonosis, bibliometric, citation analysis, Web of Science

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Introduction

Brucellosis is a bacterial zoonosis that causes severe economic losses to the livestock industry. It also poses serious public health risks to humans globally. Brucellosis is caused by gram-negative facultative and intracellular bacterium of the genus Brucella, which is classified as a category B pathogen with bioterrorism potential, as declared by the National Institute of Allergy and Infectious Diseases (NIAID) and the Centre for Disease Control and Prevention (CDC) (Pappas et al., 2006a; Doganay & Doganay, 2013; Cetaruk and Ciccone, 2016). Many developed countries have effectively controlled brucellosis in domestic animals, but sporadic cases are being reported in wildlife. However, brucellosis is still endemic in developing countries, particularly in the Middle East and central Asian and African countries (Boschiroli et al., 2001).

The genus, Brucella, consists of 12 recognised species with six so-called "classical" species, B. melitensis (sheep and goats), B. ovis (rams), B. abortus (bovines), B. canis (canines), B. suis (pigs), and B. neotomae (rodents). Later, B. microti and B. vulpis were isolated from terrestrial wildlife, B. ceti and B. pinnipedialis from marine mammals, B. papionis from primates, and B. inopinata from human breast implants. Brucellae are causing cross-infections in other hosts, especially those in contact with hosts e.g., cohabitation of farm animals. In livestock, brucellosis causes huge economic losses due to reproductive problems e.g., orchitis, stillbirth, weak offspring, repeat breading, infertility or abortion, mastitis, and lameness. Control measures include vaccination, testing, and culling of positive animals (Singh et al., 2015). Brucellosis may spread horizontally via reproductive tract discharges and milk from chronically-infected livestock (Nikokar et al., 2011) and vertically to newborn calves (Kato et al., 2007). Mechanical dissemination may be possible by the consumption or feeding of undisposed placental and foetal material by domestic (dogs and cats) and wild carnivores (Coelho et al., 2015; Wareth et al., 2017).

Brucellosis also poses a severe public health concern that causes acute febrile illness in humans as a result of B. melitensis, B. abortus, and B. suis (Godfroid, 2017). It is transmitted by direct or indirect contact with infected animal discharges, birth products, and consuming contaminated, unpasteurized dairy products (Palanduz et al., 2000). Brucellosis transmission among humans is a rare event but has been reported via sexual intercourse, breastfeeding to infants, bone marrow transplant, and blood transfusion (Lubani et al., 1988; Palanduz et al., 2000; Arroyo-Carrera et al., 2006). In humans, the clinical outcomes are diverse, raising serious concerns among clinicians and scientists regarding both disease pathogenesis and diagnosis. The clinical picture may include intermittent fever, sweating, insomnia, arthritis, infertility, nervous system disorders, and abortion (Megid et al., 2010; Saddique et al., 2019; Jamil et al., 2021).

Usually, brucellosis is diagnosed using serological assays, such as the Rose Bengal plate test (RBPT) and enzyme-linked immunosorbent assay (ELISA) but these assays require the provision of specific equipment that could be challenging in field conditions (El-Diasty et al., 2018; Khan et al., 2020a). Isolation of brucellae from clinical samples and detection of Brucella DNA using molecular assays such as polymerase chain reaction (PCR) is the method of choice for a definitive diagnosis (Khan et al., 2019a). Culture is laborious, time consuming, and poses serious health hazards to laboratory personnel (Khan et al., 2019b; Khan et al., 2020b; Khan et al., 2021). In animals, the control of brucellosis is possible through vaccination, then testing and culling of infected animals. There are no vaccines available for human use but the disease is treated using various antimicrobials alone or in combination, such as rifampicin, doxycycline, aminoglycosides, streptomycin, and quinolones for three to four weeks (Ariza et al., 2007; Khan et al., 2019b).

This bibliometric analysis analysed a total of 10 204 publications associated with brucellosis. The data were harvested from the Science Citation Index Expanded database of the Web of Sciences, the most acknowledged database in bibliometrics. The retrieved data were analysed for country, institution (laboratory), scientific journals, most cited articles, and most productive authors. Based on current analysis, the scientific trends and research hotspots in brucellosis research were identified and described.

 

Materials and Methods

In this study, data were geared using the Clarivate Analytics Web of Science Core Collection (WSCC), through the online edition of the Science Citation Index Expanded (SCI-EXPANDED) (data updated on 3 August, 2023). The system in question catalogues 9 510 academic journals, encompassing citation references spanning 178 categories within SCI-EXPANDED on the Web of Science platform. The journal's impact factor (IF2022) in the Journal Citation Reports (JCR) was reported on June 28, 2023, and documents published in the year 2022 were sourced from SCI-EXPANDED. Keywords Plus is a unique feature in the WSCC, providing additional search terminologies obtained from the article titles cited by authors in their bibliographies and footnotes in the Institute of Science Information (ISI) (now Clarivate Analytics) database, and substantially augments title word and author keyword indexing (Garfield, 1990). Some articles are irrelevant to the search topic and only rely on Keyword Plus (Fu and Ho, 2015). The 'front page' was used as a filter and included the article title, author keywords, and abstract (Wang and Ho, 2011). The "Front page" as a filter in bibliometric research topics published in journals listed in WSCC creates a large difference in bibliometric search (Farooq et al., 2022). This can be avoided by using other unrelated publications for bibliometric analysis.

Quotation marks (" ") and the Boolean operator "or" were used, which ensured the appearance of at least one search keyword in the terms of TI (title), AB (abstract), and AK (author keywords) as 'front page' from 1991-2022 (Giannoudis et al., 2021). The search keywords were: "Brucella", "Brucellae", and "Brucellosis". It is recommended that 'front page': TI, AB, and AK be used as a filter in a bibliometric studies using the Web of Science core Collection when search keywords are single words but not phrases. A total of 10 971 documents were found, including 10 942 documents (99.7% of 10 971 documents) published in SCI-EXPANDED from 1991-2022. This procedure resulted in 10 971 documents, including 9 022 articles with the search keywords on their 'front page' from 1991-2022. The full record in SCI-EXPANDED and the number of citations in each year for each document were checked and downloaded into Excel Microsoft 365 and additional coding was manually performed (Li and Ho, 2008). Functions of Excel Microsoft 365, for example, Count, Concatenate, Filter, Match, look-up, Proper, Rank, Replace, Freeze Panes, Sort, Sum, and Len were applied. The journal impact factors (IF₂₀₂₂) were taken from the Journal Citation Reports (JCR) published in 2022.

The corresponding author in the SCI-EXPANDED database was considered a reprint author but we used the term "corresponding author" in this study as well and the articles containing single authors were considered as both the first and corresponding author simultaneously (Ho, 2012). All corresponding authors, institutes, and countries were considered in multi-corresponding author articles. Articles with corresponding authors in SCI-EXPANDED that had only addresses but no affiliation names were checked out and the addresses were changed to be affiliation names, for example, 19 Rue Rougemont, F-37380 Crotelles, France was changed to Animal Infectiology & Public Health, F-37380 Nouzilly, France; 108-32 Sk 22 D 11 Adnan Suvari Mahalesi Esenyali, Izmir, Turkey was changed to Dr. Behcet Uz Children's Hospital, Department of Infectious Diseases, Izmir, Turkey; and 1 Hollyshaw Terrace, Leeds LS15 7BG, W Yorkshire, England was changed to be University of Leeds, Sch Philosophy, Leeds LS2 9HD, W Yorkshire, UK. The geographic location of the countries was determined as described elsewhere (Usman and Ho, 2020).

Publications were assessed using the following citation indicators:

C_year: the number of citations from Web of Science Core Collection in a year (e.g., C₂₀₂₂ describes citation count in 2022) (Ho, 2012).

TCyear: the total citations from Web of Science Core Collection received from publication year till the end of 2022 (TC₂₀₂₂) (Wang et al., 2011; Wang and Ho, 2011).

CPP_year: average number of citations per publication (CPP₂₀₂₂ = TC₂₀₂₂/TP), TP: total number of publications (Ho, 2013).

Six publication indicators were applied to evaluate the publication performance of countries and institutions (Hsu and Ho, 2014):

TP: total number of articles

IP: number of single country articles (IP_c) or single institution articles (IP_i)

CP: number of international articles (CP_c) or inter-institutional collaborative articles (CP_i)

FP: number of first author articles

RP: number of corresponding author articles

SP: number of single author articles

Six citation indicators related to the six publication indicators (CPP₂₀₂₂) were also applied to evaluate the publication's impact on countries and institutes (Ho and Mukul, 2021). TP-CPP₂₀₂₂: average number of citations per publication (TC₂₀₂₂/TP)

IP-CPP₂₀₂₂: the total TC₂₀₂₂ of all single country articles per the number of single-country articles (TC₂₀₂₂/IP_C) or the total TC₂₀₂₂ of all single institution's articles per the number of single institutions articles (TC₂₀₂₂/IP_I)

CP-CPP₂₀₂₂: the total TC₂₀₂₂ of all internationally collaborative articles per the number of internationally collaborative articles (TC₂₀₂₂/CP_C) or the total TC₂₀₂₂ of all inter-institutional collaborative articles per the number of inter-institutional collaborative articles (TC₂₀₂₂/CP)

FP-CPP₂₀₂₂: the total TC₂₀₂₂ of all first author per the number of first author articles (TC₂₀₂₂/FP)

RP-CPP₂₀₂₂: the total TC₂₀₂₂ of all corresponding-author articles per the number of corresponding-author articles (TC₂₀₂₂/RP)

SP-CPP2022: the total TC₂₀₂₂ of all single-author articles per the number of single author articles (TC₂₀₂₂/SP)

The Y-index was used to evaluate the publication performance of authors. The Y-index is defined as (Ho, 2012; Hsu & Ho, 2014) Y-index (j, h) where j is a constant related to the publication potential, the sum of the first author articles, and the corresponding author articles; and h is a constant related to the publication characteristics, polar angle of the proportion of RP to FP. The greater the value of j, the more the first and corresponding author contributes to the articles.

h = π/2, indicates an author that has only published corresponding-author articles, j is the number of corresponding author articles; π/2 > h > π/4 indicates that an author has more corresponding author articles than first author articles (FP > 0); h = π/4 indicates that an author has the same number of first and corresponding author articles (FP > 0 and RP > 0); π/4 < h < 0 indicates an author with more first author articles than corresponding author articles (RP > 0); h = 0, indicates that an author has only published first author articles; j is the number of first author articles.

 

Results and Discussion

In recent years, Ho's group identified the characteristics of document types based on the average number of citations per publication (CPP_year = TC_year/TP) and the average number of authors per publication (APP = AU/TP) as basic information for document types in a research topic (Nájera & Ho, 2017). Using TC₂₀₂₂ and CPP₂₀₂₂ is advantageous owing to their invariability and ensured repeatability when compared to the number of citations from the Web of Science Core Collection directly (Ho & Hartley, 2016). A total of 10 942 brucellosis publications in SCI-EXPANDED were found for 16 article types (Table 1). This includes 9 022 articles (82% of 10 942 documents) with an APP (average number of authors per publication) of 6.1. The APP of brucellosis articles (6.1) was slightly higher than for other medical related topics, for example 6.0 for Q fever (Farooq et al., 2022), 5.6 for insomnia (Jallow et al., 2020), 5.2 for breast reconstruction (Li et al., 2020), 5.0 for keloid (Chong et al., 2021), and 4.7 for non-union fractures (Giannoudis et al., 2021).

The document type "review" with 611 documents had the greatest CPP₂₀₂₂ value of 48. The CPP₂₀₂₂ of the document type "review" was found to be 2.4 times higher than that of medical-related topics, for example, keloid (2.0 times) (Chong et al., 2021), insomnia (1.4 times) (Jallow et al., 2020), non-union fracture (1.3 times) (Giannoudis et al., 2021), and breast reconstruction (0.86 times) (Li et al., 2020). However, a higher ratio of citations of reviews and articles can be found in Q fever, i.e., 2.7 times (Farooq et al., 2022). In brucellosis research, reviews entitled "The new global map of human brucellosis" (Pappas et al., 2006b) and "Legionella and Legionnaires' disease: 25 years of investigation" (Fields et al., 2002) were the only classic documents with a TC2022 of 1,000 or more (Long et al., 2014) with a TC2022 of 1,300 and 1,147, respectively. Publications can be categorized in two types in WSCC, 178 proceedings, papers, and two book chapters were also classified as document type "article". Therefore, cumulative percentages exceed 100% in Table 1 (Usman & Ho, 2020).

A total of 9 022 brucellosis-related articles were published in 16 languages. The most often used language was English with 8 500 articles (94% of 9 022 articles), followed with great distance by Spanish (140 articles), French (94), Portuguese (89), German (75), Turkish (63), Russian (20), and Hungarian (15). Some other languages that were less often used were Italian (8), Polish (7), Chinese (5), Dutch (2), and one article each for Catalan, Korean, Serbo-Croatian, and Slovak languages, respectively. Non-English articles had less citations with a CPP₂₀₂₂ of 5.3, whereas English articles had a CPP₂₀₂₂ of 21. Non-English articles had an APP of 4.9, whereas English articles had an APP of 6.2.

Characteristics of publication outputs

To understand publications in medical research topics, a relationship between the average number of citations per publication (CPP_year) and article life was proposed (Chuang et al., 2007). The article life with CPP₂₀₂₂ for all 9 022 brucellosis articles and the comparison to medical related topics is displayed in Fig. 1. It took CPPs three full years to reach a peak. Articles related to brucellosis took three full years to reach a peak CPP_year of 2.2. A peak appeared in four and five full years for breast reconstruction of (Li et al., 2020) and child sexual abuse (Vega et al., 2019) research with CPP_year of 3.0 and 4.2, respectively. After the peak, a decrease in CPPyear was generally found. However, articles related to non-union of fractures needed a longer citation life (ten full years) to reach the peak with CPPyear of 2.4.

 

 

The correlation between the annual number of articles (TP) and their citations (CPP_year = TC_year/TP) by year (Ho, 2013) was proposed to understand the impact of publication and development trends in medical related topics in SCI-EXPANDED, including dengue (Ho et al., 2016; Pouris and Ho, 2016), non-union fracture (Giannoudis et al., 2021), keloid (Chong et al., 2021), insomnia (Jallow et al., 2020), and Q fever (Farooq et al., 2022). The 9 022 articles associated with brucellosis were published in SCI-EXPANDED from 1991-2022. The mean value of TC₂₀₂₂ was 20 with 908 as the highest for an article. The distribution of the annual number of articles (TP) and their CPP2022 by year is demonstrated in Figure 2. In 2003, 202 articles had the highest CPP₂₀₂₂ of 43. The current study showed a slight increase in published articles from 1991 (155 articles) to 2022 (431 articles). In addition, a peak of annual publications was found in 2021 with 456 articles. Figure 2 further highlights that almost 16 years were taken for CPPs to reach a plateau. Brucellosis-related articles had a longer life in comparison to other medical related topics, for example non-union fracture with 14 years (Giannoudis et al., 2021), breast reconstruction with 10 years (Li et al., 2020), and child sexual abuse with 8 years (Vega et al., 2019).

 

 

Web of Science categories and journals

The JCR indexed 9 510 journals across 178 Web of Science categories in SCI-EXPANDED in 2022. In 2021, to characterize a Web of Science category of a research topic, the CPP_year and the APP were proposed as basic information (Giannoudis et al., 2021). In total, 1 491 journals associated with 134 Web of Science categories in SCI-EXPANDED have published ~9 003 brucellosis-related articles. The top 10 most productive Web of Science categories with TP, APP, CPP2022, and the number of journals in a category are shown in Table 2. A total of 5 908 articles (66% of 9 003 articles) were published in the top four categories: veterinary sciences (2 497 articles; 28% of 9 003 articles), microbiology (2 081; 23%), infectious diseases (1 492; 17%), and immunology (1 354; 15%). The articles published in the category "immunology" had the greatest CPP2022 of 30, whereas articles in "general and internal medicine" had the lowest CPP₂₀₂₂ of 8.7. The "multidisciplinary sciences" category articles had the largest APP of 8.1, whereas articles in "general and internal medicine" had an APP of 5.0.

Figure 3 shows the trend of brucellosis articles in the four main productive Web of Science categories. The four major disciplines are "veterinary sciences" (TP = 2 497), "microbiology" (TP = 2 081), "infectious diseases" (TP = 1 492) and "immunology" (TP = 1 354). For the last 32 years, there has been a remarkable rise in publications in the disciplines "veterinary sciences" and "microbiology". However, an increasing trend in publication was recorded in the disciplines "infectious diseases" and "immunology". The highest number of publications was seen in the discipline "veterinary sciences" in 2013.

 

 

Table 3 highlights the top 10 most productive journals publishing brucellosis-related research by IF₂₀₂₂, APP, and CPP₂₀₂₂. The top four journals are from the category of "veterinary sciences". The Infection and Immunity (IF₂₀₂₂ = 3.1) published the most articles (294 articles: 3.3% of 9 022 articles). PLoS One (IF₂₀₂₂ = 3.7) with 195 articles had the highest APP of 8.1, whereas those of the Indian Journal of Animal Sciences (IF₂₀₂₂ = 0.4) with 97 articles had an APP of 4.5. Articles in the Journal of Clinical Microbiology (IF₂₀₂₂ = 9.4) with 146 articles had the highest CPP₂₀₂₂ of 50, whereas articles in the Indian Journal of Animal Sciences had a CPP₂₀₂₂ of 2.1. The top five journals had an IF₂₀₂₂ greater than 40, i.e., Lancet (IF₂₀₂₂ = 168.9), Nature Medicine (IF₂₀₂₂ = 82.9), Nature (IF₂₀₂₂ = 64.8), Science (IF₂₀₂₂ = 56.9), and Lancet Infectious Diseases (IF₂₀₂₂ = 56.3).

Publication performances: Countries and institutions

There were 29 articles (0.32% of 9 022 articles) lacking the author's affiliation information in SCI-EXPANDED. A total of 8 993 brucellosis articles were published with author affiliations of 150 countries with a TP-CPP₂₀₂₂ of 20, including 6 849 single-country articles (all authors from the same country) (76% of 8 993 articles) by authors associated with 103 countries with an IP_C-CPP₂₀₂₂ of 18, and 2 146 international collaborative articles (24%) by authors from 147 countries with a CP_C-CPP₂₀₂₂ of 25. The number of citations was increased by international collaborations.

The top 10 most productive countries were assessed based on six publications and related six citation indicators (CPP₂₀₂₂) (Table 4). This data highlighted the dominance of the USA in all publication indicators with a TP of 1 902 articles (21% of 8 993 articles), an IP_C of 1 192 articles (17% of 6 849 single-country articles), a CP_C of 710 articles (33% of 2 146 international collaborative articles), an FP of 1 480 articles (16% of 8 993 first-author articles), an RP of 1 502 articles (17% of 8 954 corresponding-author articles), and an SP of 67 articles (24% of 282 single-author articles). France with TP = 644 articles, CP_C = 375 articles, and RP = 403 articles ranked at the top with a TP-CPP₂₀₂₂ of 37, a CP_C-CPP₂₀₂₂ of 42, and an RP-CPP₂₀₂₂ of 33. The UK with an IP_c of 123 articles, an FP = 222 articles, and an SP = 17 articles ranked top with an IP_C-CPP₂₀₂₂ of 37, an FP-CPP₂₀₂₂ of 35, and an SP-CPP₂₀₂₂ of 73. Furthermore, articles of Iranian, Chinese, and Indian origin had a lower CPP₂₀₂₂.

The author's institutional affiliation may be used to identify the origin of the document. Concerning institutions, 3 030 brucellosis articles (34% of 8 993 articles) had single institutional affiliation with an IP_I-CPP₂₀₂₂ of 19, whereas 5 963 articles (66%) were institutional collaborations with a CP_I-CPP₂₀₂₂ of 20. The institutional collaborations slightly increased the number of citations. The top 10 leading institutions and their associated features are shown in Table 5. The University of Navarra in Spain and the Institut National de la Recherche Agronomique (INRA) in France ranked at the top with a TP of 157 articles (1.7% of 8 993 articles). The University of Navarra in Spain also ranked at the top with a CP_I of 139 articles (2.3% of 5 963 inter-institutional collaborative articles). The Universidade Federal de Minas Gerais (UFMG) in Brazil ranked at the top with an FP of 102 articles (1.1% of 8 993 first-author articles) and an RP of 103 articles (1.2% of 8 861 corresponding-author articles). The United States Department of Agriculture (USDA), and Agricultural Research Service (ARS) in the USA ranked at the top with an IP_i of 44 articles (1.5% of 3 030 single-institution articles). In addition, the King Saud University in Saudi Arabia published 61 articles (rank 26^th), including the greatest SP of 14 articles (5.0% of 282 single-author articles). The Institut National de la Recherche Agronomique (INRA) in France with a TP = 157 articles and a CP_I = 117 articles ranked at the top with a TP-CPP₂₀₂₂ of 47 and an CP_I-CPP₂₀₂₂ of 52. The University of California, Davis in the USA with an IP_I = 15 articles and an FP = 54 articles ranked at the top with an IP_I-CPP₂₀₂₂ of 50 and an FP-CPP₂₀₂₂ of 45. The USDA ARS in the USA with an RP = 74 articles and an SP = 7 articles ranked at the top with a RP-CPP₂₀₂₂ of 44 and an SP-CPP₂₀₂₂ of 46.

Publication performances: Authors

Brucellosis-related articles had an APP of 6.1 with a maximum number of 58 authors for a single article. With the available author information of the 9 015 articles, 72% of articles contained 3-8 authors. A total of 1 345 (15% of 9 015 articles), 1 309 (15%), 1 127 (13%), 1 087 (12%), 856 (9.5%), and 723 (8.0%) were written by groups of 5, 4, 6, 3, 7, and 8 authors, respectively. Recently, the publication characteristics for authors have been based on four publication indicators: TP, FP, RP, and SP. CPP_year as well as Y-index parameters were proposed to be added to the basic information of the author on a research topic (Giannoudis et al., 2021). The top 20 most productive authors with associated characters are given in Table 6. A. Cloeckaert was the most productive author with 116 articles including 27 first-author articles (ranked 2^nd) and 31 corresponding-author articles (ranked 7^th). S. Kim with 91 articles had the most corresponding-author articles (59). J. Godfroid with 86 articles had most four single-author articles. In addition, S.C. Olsen with 77 articles also ranked top in both first-author articles and the single author articles. Compared to the 20 most productive authors, E. Moreno with 70 articles (TP) and a total of TC₂₀₂₂ of 4,290 had the highest CPP₂₀₂₂ of 61 (4 290/70) for the total articles in Brucellosis research. J. Godfroid with a TP of 86, an FP of 12, and an RP of 14 articles, had the highest CPP₂₀₂₂ of 80 and 76 for the first-author articles and the corresponding-author articles, respectively. K. Nielsen with a TP of 71 and SP of 3 articles, had the highest CPP2022 of 77 for the single-author articles. Only nine of the top 20 authors, including S. Kim, S.C. Olsen, A. Cloeckaert, K. Nielsen, S.C. Oliveira, C.F. Chen, R.M. Roop, H. Zhang, and X. De Bolle were found to be the top 20 publication potential authors as evaluated by Y-index. The top 20 most potential authors are evaluated based on the Y-index, which relies solely on the number of articles contributed as first and corresponding author (the most important authors in an article).

The 8 683 brucellosis articles (96% of 9 022 articles) with the information of both first and corresponding authors were investigated based on the Y-index. In total, 28 105 authors contributed to 8 683 brucellosis articles, with 20 359 authors (72% of 28 105 authors) having no first and no corresponding-author article with a Y-index (0, 0). Furthermore, 1 796 (6.4%) authors only published as corresponding authors with h = π/2, whereas 397 (1.4%) authors published more corresponding-author articles with π/2 > h > π/4 (FP > 0). Additionally, 2 810 (10%) authors had published the same number of first author and corresponding-author articles with h = π/4 (FP > 0 and RP > 0); 274 (1.0%) authors published more first-author articles with π/4 > h > 0 (RP > 0); and 2 469 (8.8%) authors published only first-author articles with h = 0.

The distribution of the Y-index (j, h) in polar coordinates of the leading 20 authors with j of 27 or more is indicated in Figure 4, with each point in the coordinate Y-index (j, h) symbolizing single or multiple authors. S. Kim with Y-index (67, 1.436) had the greatest publication performance, followed by S.C. Olsen (64, 0.8478). However, Kim had a lower CPP2022 (Table 6). P.C. Baldi (39, 1.457) and R.M. Roop (39, 1.425) had the same j of 39. The authors are located on the same curve (j = 39), demonstrating similar publication potential with contrasting characteristics of publications (Figure 4) (Ho and Hartley, 2016b). Baldi had a higher ratio of corresponding author to first-author articles with an h of 1.457, followed by Roop with an h of 1.425. Z.L. Chen (27, π/2) and M. Watarai (27, 1.347) were also located on the same curve (j = 27). Chen published only 27 corresponding-author articles with an h of π/2, whereas Watarai had an h of 1.347. Similarly, R. Shome (30, 0.8520), R. Adone (30, 0.7854), Q.M. Wu (28, 1.534), and X. De Bolle (28, 1.494) were positioned on the same curve (j = 30 and 28) with similar publication potential but varying publication features. K. Nielsen (54, π/4) and R. Adone (30, π/4) on the diagonal line (h = π/4), and C.F. Chen (41, π/2) and Z.L. Chen (27, π/2) on the y-axis (h = π/2) demonstrated similar publication characteristics with varying publication potential. Nielsen had a higher publication potential with a j of 54 than Adone (j = 30). C.F. Chen had a higher publication potential, with a j of 41 than Z.L. Chen (j = 27).

 

 

The position of the graph, along the curve or line of origin, shows various author publication potential or characteristics. However, potential bias in authorship analysis may arise due to the same name of authors or different names of the same authors used over time (Chiu & Ho, 2007).

Citation histories of the ten most frequently-cited articles

Wang & Ho reported that the total number of citations from the WSCC since publication year to the end of the year 2022 (TC₂₀₂₂) could be applied to improve bibliometric study by addressing the bias directly using the database (Wang & Ho, 2011). The most cited articles with associated features are shown in Table 7; citation history over time of the most cited articles is presented in Fig. 5.

C2022 = 278 (rank 1^st), TC2022 = 779 (rank 4^th)

This report published by the European Food Safety Authority (EFSA) and The European Center for Disease Prevention and Control highlights the important food-borne, bacterial, zoonotic diseases in the EU. Brucellosis remained in the top 8 List A diseases that must be notified immediately, needing continuous disease surveillance. Human outbreaks were primarily linked to the consumption of cheese. However, the trend of brucellosis endemicity in animals is on a steady decline. Greece reported an almost 10 times higher number of Brucella infections in animals when compared to the EU average. Similarly, Greece and Italy reported more than half of the human brucellosis cases reported in the EU.

2. The European Union summary report on trends and sources of zoonoses, zoonotic agents, and food-borne outbreaks in 2017 (EFSA, 2018)

C₂₀₂₂ = 244 (rank 2^nd), TC₂₀₂₂ = 838 (rank 2^nd)

Although Brucella-associated foodborne illnesses have become a rare event in the EU, Italy and Germany reported human brucellosis cases. In Italy, brucellosis is strongly associated with the consumption of unpasteurized milk. The source of infection, e.g., the consumed food responsible for disease, remained unknown in Germany. The report highlights the importance of the transmission from animals to humans via direct contact, which remains the major source of infection in humans. In comparison to the report of the previous year, the number of Brucella cases in humans continued to decrease. Overall, the EU reported 378 cases, of which only 30% were diagnosed to the species level of causative agent. Of these, B. melitensis remained the major cause of human brucellosis, followed by B. abortus and B. suis. In Greece, Italy, Portugal, and Spain, brucellosis in humans was usually acquired through contact with domesticated sheep, cattle, and goat herds.

3. The European Union summary report on trends and sources of zoonoses, zoonotic agents, and food-borne outbreaks in 2016 (EFSA, 2017)

C₂₀₂₂ = 74 (rank 5^th), TC₂₀₂₂ = 787 (rank 3^rd)

The report highlights that Greece, Italy, and Portugal reported the most Brucella infections in the EU. Brucellosis was endemic in these countries and human infections were associated with the consumption of raw dairy products or direct contact with infected animals. These countries reported little monitoring data from raw products in particular, which were the major source of food-borne human brucellosis. The majority of reported human cases in 2016 had unknown travel history to endemic countries, mainly Iraq, Syria, Somalia, and Turkey. Overall, the number of human infections continued to decline over the years, whereas the share of cases of unknown travel history continued to increase. The data showed a continuous decline in Brucella infections with every passing year from 2012-2015. However, in 2016, this trend was reversed, and the EU reported a 35.2% higher number of cases in comparison to last year, mainly due to a rise in Brucella infections in Italy.

Research foci

The title, abstract, author keywords, and Keywords Plus of an article provide important information regarding conducted research. The analysis of word distribution is useful for evaluating research focus and related developmental trends in the field of specific research. This analysing tool can mitigate shortcomings, such as the incomplete meaning of individual words in titles and abstracts, the small sample size of author keywords, and the indirect relationship between Keywords Plus and research topics (Farooq et al., 2022). This pertinent analysis during the research period provides rough research trends using title, abstract, author keywords, and words in Keywords Plus (Zhang et al., 2010). Table 8 reports the most commonly-used author keywords for brucellosis-related research and their distribution trends over the last 32 years (1991-1998, 1999-2006, 2007-2014, and 2015-2022). The most frequently-used words by authors also indicate that the major focus areas of researchers as "cattle" (most often-investigated host), "serology" (demonstrating a focus on screening of serum samples), "zoonosis", "laboratory diagnosis" (PCR, ELISA), clinical manifestations such as "abortion", "Brucella species" (B. abortus, B. melitensis, B. canis), and "epidemiology".

To highlight the potential research hotspots, the word "cluster analysis" was also performed. Trend analysis concerning the causative agent showed B. abortus (TP = 2 817 articles) remained the focus, followed by B. melitensis (TP = 1 941 articles), B. suis (TP = 648 articles), B. ovis (TP = 513 articles), B. canis (TP = 355 articles), B. ceti (TP = 90 articles), B. microti (TP = 59 articles), and B. pinnipedialis (TP = 52 articles) (Fig. 6). The data suggest the greater interest of the scientific community towards B. abortus and B. melitensis, which also reflects their greater zoonotic potential, demonstrating the serious risk to human health. Humans mainly contract infections from domestic animals infected with B. abortus (cattle) and B. melitensis (sheep and goats). Human infections are also caused by B. suis (pigs) but other brucellae rarely cause infection in humans. Timely and accurate identification of the species causing the disease is important for appropriate therapy and the use of control strategies.

 

 

We investigated the research trends for "diagnosis". Overall, most publications used the keyword "culture" (TP = 1 586 articles), followed by "RBPT" (TP = 1 296 articles), "PCR" (TP = 1 257 articles), "ELISA" (TP = 1 157 articles), complement fixation test "CFT" (TP = 419 articles), simultaneous amplification and testing "SAT" (TP = 268 articles), and multiple-locus variable number tandem-repeat analysis "MLVA" (TP = 106 articles) (Fig. 7). Definitive diagnosis of brucellosis can be achieved by culture isolation and nucleic acid-based molecular identification. However, culture is tedious, time-consuming, and poses serious risks to laboratory personnel and the associated environment. Therefore, bacterial culture requires specific biosafety measures (BSL-3). Serological assays are more practical and are used for routine monitoring and diagnosis of brucellosis, particularly in resource-limited locations. However, the choice of the serological test to be used depends upon the epidemiology of the disease in a particular region, the cost of the test, and the sensitivity and specificity of the test. Serological assays such as RBPT, CFT, SAT, or ELISA are used for screening and/or confirmation. RBPT is a highly-sensitive, cost-effective test that can be performed under field conditions for screening of brucellosis in resource-poor, endemic countries. However, due to its low specificity, this test needs confirmatory tests with high specificity such as ELISA. Thus, RBPT is not recommended for screening in disease-free countries. Instead, assays with high sensitivity and specificity, such as ELISA or CFT, should be used. Additionally, culture-independent molecular diagnostic assays such as PCR [either conventional or quantitative (real-time)] and a multi-locus variable number of tandem repeat assays (MLVA) are being used to characterize and genotype Brucella isolates. PCR is considered a safe and reliable molecular method for the confirmation. MLVA remains the method of choice for genotyping in resource-poor settings and is helpful in characterising the origin of an outbreak and may also help in the development of better prophylaxis. Next Generation Sequencing (NGS) and bioinformatic pipelines will replace MLVA shortly in most developed countries.

 

 

Effective control of infectious diseases, particularly zoonotic pathogens, requires knowledge of their hosts. Brucellae have a wide host range, including domesticated animals and wild aquatic and terrestrial animals. Hence, brucellosis is mainly a disease of domesticated animals. However, it can be maintained in wildlife, which can then be the source of re-emerging infections in humans and livestock. In the current study, the keywords related to "host range" are summarized in Fig. 8 and "human" was most-often used keyword (TP = 2 837 articles), followed by "cattle" (TP = 1 985 articles), "rodents" (TP = 1 336 articles), "sheep" (TP = 906 articles), "goat" (TP = 665 articles), "pigs" (TP = 368 articles), "dogs" (TP = 345 articles), "wildlife" (TP = 303 articles), and "buffalo" (TP = 266 articles).

 

 

The effective control of disease usually depends on circulating pathogens and their host range. Besides the six classical Brucella species infecting cattle, sheep & goats, swine, and humans, in recent years new brucellae have been discovered causing infections in marine and terrestrial animals. This analysis depicts that the predominantly-discussed hosts for brucellae are cattle, rodents, and small ruminants (sheep & goats). Rodents (3^rd most discussed keyword) are mainly used as an experimental model to understand the pathophysiology and host-pathogen interaction of Brucella species. However, rodents are not the primary source of human brucellosis, which is mainly linked to domesticated animals, such as cattle, sheep, and goats (Jamil et al., 2021). Usually, humans contract the infection by direct contact with infected animals or through the consumption of contaminated raw dairy or meat products.

 

Conclusion

The current study highlights the research trends and important developments in the field of brucellosis research. It provides insights on the most influential authors, institutes, countries, publications, and epidemiological aspects of brucellosis. Furthermore, data on Brucella species, host range, and most widely-used diagnostic tests applied in brucellosis research over the last three decades are provided. This analysis will be helpful for the researchers who intend to pursue their careers in brucellosis research in choosing the trending discipline, country, or institute. Furthermore, it will help the relevant researchers to collaborate. We further highlighted the list of journals publishing most articles in this discipline, for the use by the relevant researchers. Additionally, the zoonotic nature of the disease with its wide host range of domestic to wildlife stresses the need for collaboration of physicians, veterinarians, and environmentalists under the umbrella of "One Health" to ensure better global health.

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this paper

Funding

This research received no external funding.

Author Contributions

Data curation, M. F, A. U. K and Y. S. H; Methodology, Y. S. H, M. F and A. U. K. ; Writing - original draft, M. F and A. U. K. and H. E-A.; Writing - review & editing, A. U. K., F. M., H. N., I. K. and H. E-A.

 

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Submitted 30 November 2023
Accepted 21 May 2024
Published 30 September 2024

 

 

Corresponding author: muhammad.farooq@uvas.edu.pk
# Authors with the same symbols contributed equally