Research into Neospora caninum-What Have We Learnt in the Last Thirty Years?

Abstract

Background: Neospora caninum has been recognised world-wide, first as a disease of dogs, then as an important cause of abortions in cattle for the past thirty years. Over that time period, there have been improvements in the diagnosis of infection and abortion, new tests have been developed and validated, and it is timely to review progress to date.

Methods: Bibliometric methods were used to identify major trends and research topics present in the published literature on N. caninum. The tools used were SWIFT-Review, VOSviewer and SciMAT, along with the published papers found in the MEDLINE, Dimensions and Web of Science databases. A systematic review of the published Neospora literature (n = 2933) was also carried out via MEDLINE and systematically appraised for publications relevant to the pathogenesis, pathology and diagnosis of Neospora abortions.

Results: A total of 92 publications were included in the final analysis and grouped into four main time periods. In these four different time periods, the main research themes were "dogs", "abortion", "seroprevalence" and "infection". Diagnostics, including PCR, dominated the first two time periods, with an increased focus on transmission and abortions, and its risk factors in cattle.

Conclusions: Longitudinal analyses indicated that the main themes were consistently investigated over the last 30 years through a wide range of studies, with evolving emphasis initially on dogs and diagnostic test development, followed by application to cattle, the identification of the risk factors leading to abortion, and in the latter time periods, an understanding of the immunity and a search for vaccines.

Keywords: Neospora caninum; abortions; cattle; diagnosis; dogs; pathogenesis; review.

Figure 1

Overview of topic models generated from the MEDLINE dataset using SWIFT-Review.

Figure 2

VOSviewer network with nine colour-coded clusters produced using VOSviewer and the Dimensions dataset containing 2935 unique publications from 1989 to 2019 inclusive (for clarity, links to the terms “Colombia” and “seroprevalencia” have been truncated at the bottom right hand corner).

Figure 3

Main themes in Neospora-related publications from the Web of Science (WoS) over four time periods identified using SciMAT ((a)—1989–1996 (n = 15); (b)—1997–2005 (n = 733); (c)—2006–2012 (n = 1172) and (d)—2013–2019 (n = 1013)). The figure shows the links in terms to the four major themes identified during these time periods.

Figure 4

Frequency histogram of 92 publications derived from a systematic search of the Neospora literature, conducted in March 2020 in the Dimensions database for search terms: Neospora, dogs, abortion, seroprevalence and infection; showing peak publication activity between 1996 and 2006, with the highest number of publications in the search yielding from the year 2002.

Figure 5

Author network from 1107 N. caninum publications from targeted SciMAT process.

Figure 6

Graphical depiction of the systematic literature review process of the WoS database (numbers in the blue boxes represent the number of papers analysed at that step).