A systematic literature review and meta-analysis of characterization of canine parvoviruses 2 prevalent in mainland China

The study search was planned and performed according to the Meta-analysis of Observational Studies in Epidemiology guidelines [19]. To identify the epidemiological studies on CPV-2 in China, the literature published either in English or Chinese was searched up to December 2019. English databases (PubMed, Google Scholar, Cochrane library, and Clinical Trials) and Chinese databases (CNKI, Cqvip, WANFANG data, and Baidu scholar) were searched using “Canine parvovirus or CPV”, “epidemiology or incidence or prevalence”, “dog or canine”, and “China or Chinese”, or variants and combinations of these words, as keywords. Studies included in this systematic review had to contain any epidemiological data related to CPV-2 among dog populations from mainland China.

The following studies were excluded from this systematic review and meta-analysis: (1) data from countries and regions outside mainland China; (2) literature that had review studies, case reports, press releases, newsletters, forums, and questionnaire surveys; (3) non-epidemiological studies (e.g., basic research); (4) no clear sampling time, sample size, infection rate, and prevalence rate in the study; and (5) insufficient information and duplicated findings.

The corresponding data were extracted from studies that met inclusion criteria and extracted into a Microsoft Excel datasheet. Recorded bibliographic data contained the following information: province, study design, background information, sample size, detection method, publication year, author, detection method, and sampling season.

The selected publications were independently evaluated by two reviewers based on the established inclusion criteria. These publications were selected based on the information provided in the title and/or abstract as well as their full-text availability in Chinese or English. Furthermore, these publications had to contain prevalence data related to CPV-2 in mainland China. The quality of selected publications was assessed using the Newcastle–Ottawa scale (NOS). Studies with scores of 5 or above (out of 10) were included in the meta-analysis.

This study was planned and performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) [20]. In the eligible studies, a random effects model was utilised to calculate the pooled prevalence of CPV-2 infection among domestic dogs. Meta-analysis was performed using Review Manager 5.3 (Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014). The pooled estimates were the outcome of the meta-analysis and visualised the heterogeneity among the included studies using Forest plots. Forest plots were used to summarise estimates with 95% confidence intervals (CIs). The heterogeneity index among the included studies was determined using the Cochrane’s Q test (chi-squared) and Higgins I² statistics. An I² > 50% represents substantial heterogeneity [21]. Potential publication bias was assessed using a funnel plot. It was considered significant when the P value was less than 0.05.

Based on search strategies of databases, a total of 5008 Chinese or English articles were identified. After the preliminary screen, 76 full-text articles were selected, and papers, duplicate citations, and studies not relevant to the current meta-analysis were removed. After excluding 37 articles with incomplete data, 39 articles met the inclusion criteria and were included in the systematic review (Fig. 1). The articles were published between 2006 and 2019, and covered 20 provinces in China. A cross-sectional study of all articles was performed, and period prevalence was calculated (Table 1).

A total of 137,844 domestic dogs and 27,464 CPV-2-positive cases were included in the meta-analysis. The total prevalence of CPV-2 in mainland China was 36% at 95% CI (0.31, 0.41), and demonstrated a strong heterogeneity (Chi² = 29,260.2, I² = 100%, P < 0.00001) (Fig. 2). Data from 39 studies were collected from 20 provinces, with the eastern and northern provinces being the majority. Among those provinces, the prevalence in Liaoning and Hunan provinces were higher than 70%, while that in most provinces of northern China reached above 30% (Fig. 3). The prevalence of CPV-2 in administrative districts of China (from highest to lowest) was as follows: 63% in Northeast China, 48% in Southwest China, 43% in North China, 38% in Central China, 29% in Northwest China, and 18% in East China. The prevalence of CPV-2 in Northeast China was higher than that in other administrative districts of China (Table 2).

As shown in Table 2, we analysed the risk factors related to the prevalence of CPV-2 infection in dogs. Among these risk factors, the occurrence of CPV-2 infection was significantly associated with age, sampling season, immunisation status, and breed: (1) the prevalence of infection in young dogs under 6 months of age was 68%, while that in dogs 6 months of age or above was 20%, which is a significant difference (P < 0.05); (2) the prevalence in unimmunised dogs (68%) was higher than that in immunised dogs (20%), and shows a significant difference (P < 0.05); (3) the prevalence of CPV-2 was the highest in spring (34%) and the lowest in summer (15%), which was significantly different (P < 0.05). The infection was more frequent in spring than in other seasons; (4) the prevalence of infection in purebred dogs was 66%, while in mutts it was 24% (P < 0.05), indicating that CPV-2 was more susceptible in purebred dogs than in mutts. However, the prevalence of CPV-2 in male dogs was 45%, and in female it was 38%; The prevalence based on the antigen Rapid CPV Ag Test kit was 43%, and based on the PCR it was 39%; The prevalence relying to publication year of included studies was as follows: Before 2016 35% and 2016 or later 40%. These results all shows no significant difference (P > 0.05), indicating that CPV-2 prevalence was less affected by gender, diagnostic methods and published time.