- Open Access
Current global status, subtype distribution and zoonotic significance of Blastocystis in dogs and cats: a systematic review and meta-analysis
Parasites & Vectors volume 15, Article number: 225 (2022)
Blastocystis is a common intestinal protozoa found in animal and human fecal samples, with over 1 billion individuals infected worldwide. Since domestication, dogs and cats have had a close bond with humans. However, their close proximity poses a potential health risk since they may harbor several zoonotic agents. A global estimate of Blastocystis infection and subtype (ST) distribution in dogs and cats would therefore be of great health importance to humans.
We performed a comprehensive systematic search of four English-language databases (PubMed, Scopus, Google Scholar, Web of Science) for relevant articles up to 8 November 2021. The random-effects model was used to make pooled estimates with confidence intervals (CIs).
In total, we identified 49 publications that met our inclusion criteria and subsequently analyzed the 65 datasets in these articles, of which 23 and 42 datasets were on cats and dogs, respectively. Among the 2934 cats included in the 23 datasets, which involved 16 countries, the prevalence rate of Blastocystis infection was 9.3% (95% CI 5.3–15.9%). The prevalence of Blastocystis infection was slightly lower [7%, 95% CI 4.7–10.4%) among the 7946 dogs included in the 42 datasets, involving 23 countries. The sensitivity analysis showed that no remarkable variation in the estimates upon the stepwise removal of each dataset. Higher ST diversity was found among the examined dogs (ST1-8, ST10, ST23, ST24) than among cats (ST1-4, ST10, ST14). Among dogs, ST3 was the most frequent ST (41.3%), followed by ST2 (39.3%), ST1 (30.9%), ST4 (13.4%), ST8 (12.7%), ST10 (11%) and ST5 (8.1%). Also among dogs, each of ST6, ST7, ST23 and ST24 was observed in only one study. Of the ST found in the cats examined, ST4 (29.5%), followed by ST10 (22.5%), ST1 (19.8%) and ST3 (17.6%) were the most common. A single study also reported the presence of both ST2 and ST14 in cats. With respect to zoonotic Blastocystis STs (ST1–ST9 and ST12), eight were reported from dogs (ST1-ST8) and four were isolated from cats (ST1–ST4), showing the implication of dog and cats in zoonotic transmission.
Taken together, our results show that elucidation of the true epidemiology and ST distribution of Blastocystis in dogs and cats demands more comprehensive studies, particularly in the negelected regions of the world.
Blastocystis is a common enteric protozoa found in fecal samples of humans and animals. Over 1 billion people are infected globally [1, 2]. Four major life stages have been described in this polymorphic parasite, comprising vacuolar, granular, amoeboid and cyst stages; among these, the avacuolar and multivacuolar forms are less common during encystation or excystation [3, 4]. General consensus on the transmission of Blastocystis and is that infection occurs through the fecal–oral route with the ingestion of cyst-contaminated water or food . Zoonotic transmission may also be possible through close animal-human contact, but the extent and frequency of such events remain largely unknown, requiring more in-depth investigation [6, 7]. Symptomatic human infections may manifest as diarrhea, abdominal pain, flatulence, inflammatory bowel disease, irritable bowel syndrome (IBS) and cutaneous lesions (urticaria) [8, 9]. Nevertheless, it is not fully known whether Blastocystis possesses pathogenic potential since carriage state is highly frequent .
Microscopy, culturing and molecular assays are the primarily methods used to detect Blastocystis infection in hosts. However, the discrimination of subtypes (STs) is only possible using DNA-based methods and sequence analysis of the small subunit ribosomal RNA (SSU rRNA) gene [2, 11]. A total of 32 phylogenetically distinct Blastocystis subtypes have been proposed based on SSU rRNA analysis, including zoonotic STs (ST1–9, ST12) and STs isolated only from animals (ST10, ST11, ST13–17, ST21, ST23–32). Some experts have noted that ST18-20 and ST22 are invalid due to ambiguities in the 5′ and 3′ ends of the SSU rRNA sequences. Nevertheless, according to the criteria currently in place to qualify as a unique subtype, a total of 28 subtypes (ST1–17, ST21 and ST23–32) are generally widely recognized as being valid subtypes [12,13,14].
The One-Health concept is an integrated approach to human healthcare that considers human health to be closely connected to animal health and the environment, proposing that each constituent (e.g. animals) may play a principal role in transmission dynamics of Blastocystis . Dogs and cats, as important pet animals, may harbor zoonotic agents and be considered potential reservoirs for Blastocystis. Hence, detection of Blastocystis infection in these animals is important for improving human health levels. We performed the present systematic review and meta-analysis to clarify the global epidemiology, subtype distribution and zoonotic importance of this parasitic protozoan in dogs and cats.
Study design and reporting protocol
A systematic review and meta-analysis of the worldwide epidemiology, subtype distribution and zoonotic importance of Blastocystis was designed and implemented in 2021, with dogs and cats as the target population. The reporting protocol was designed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guideline .
Databases and search strategies
A comprehensive search of four electronic databases (PubMed, Scopus, Google Scholar, and Web of Science) was conducted by two of the authors (AA and MSH) for relevant articles published up to 8 November 2021, using the keywords: “Blastocystis,” “Blastocystis sp.,” “Subtypes,” “Prevalence,” “Epidemiology,” “Frequency,” “Occurrence,” “Dog,” “Cat,” “Canine” and “Feline,” with “OR” and/or “AND” operators. To expand the search for relevant publications, additional keywords were also used and the reference lists of identified papers were explored. The titles and abstracts of the identified publications were reviewed, duplicated papers were removed and the full-text of each article identified as being relevant was obtained. The eligibility of the papers was evaluated independently by six of the authors (GH, BM, LSH, AY, AS, SSH); any disagreement was resolved through consultation with the leading reviewer (AA).
Observational cross-sectional studies reporting the prevalence and/or subtypes of Blastocystis in dogs and cats utilizing microscopy of stool samples and/or molecular techniques up to 8 November 2021 were included in present systematic review. Excluded from this systematic review and meta-analysis were case reports, reviews, letters, studies on humans or other animals, studies involving experimentally infected animals, studies without Blastocystis prevalence rates and studies containing unclear/confusing information.
Quality assessment and data extraction
The Joanna Briggs Institute (JBI) critical appraisal checklist for studies reporting prevalence data was used for qualitative evaluation of the articles . Articles were included in this systematic review and meta-analysis if they were assessed to have checklist scores of 4–6 points (moderate quality) or 7–9 points (high quality); papers with a checklist score of ≤ 3 points were excluded. The following items were extracted using a pre-piloted checklist for each study: the first author’s last name, quality assessment score, publication year, implementation year, country, continents, WHO regions, related STs, total sample size and infected sample size. In the current review, information regarding WHO regions was obtained from the relevant WHO URL (https://www.who.int/standards/classifications).
The extracted data were exported to the Comprehensive Meta-Analysis (CMA) version 3 software for meta-analysis, with P < 0.05 considered to be a statistically significant value . A Forest plot diagram was designed using a random-effects model to represent the weighted frequencies with 95% confidence intervals (CIs). The I2 index was used to assess heterogeneity between included studies, ranging from < 25% (low variation) and 25–50% (moderate variation), to > 50% (high variation) . The subgroup analysis of the pooled prevalence of the parasitic infection among dogs and cats was performed based on publication year, WHO region, country, continent and sample size. Additionally, variations in the final weighted prevalence of Blastocystis infection upon stepwise removal individual studies were assessed by sensitivity analysis. Meta-regression was performed to evaluate the likely association between some variables (publication year and sample size) and Blastocystis frequency among examined animals. The funnel plot was used to check the probability of publication bias during the analysis.
Description of the systematic search and article selection
The strategy for the systematic search and study selection is shown in Fig. 1. In brief, 12,321 articles were identified during the primary systematic search; of these 4300 were duplicate papers and discarded, leaving 8021 articles for review of the title and abstract. Of these 8021 articles, 63 met the inclusion criteria and were fully reviewed. Qualitative evaluation using the JBI checklist resulted in the exclusion of an additional 14 articles. Ultimately, 49 studies (65 datasets) [13, 20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67] were assessed as eligible to be included in the meta-analysis (Table 1). Reasons for removing studies from the meta-analysis included animals other than dogs and cats (4 papers), intestinal parasites other than Blastocystis (7 articles), repetitive results (1 study) and ambiguous findings (2 papers).
The quality assessment output
All of the included studies were critically appraised using the JBI quality assessment checklist adapted for cross-sectional studies. Based on the JBI score, 15 studies were of high quality (≥ 7 points) and the remaining 34 studies were of moderate quality (4–6 points) (Additional file 1: Table S1).
Global epidemiology of Blastocystis infection in dogs
The estimated pooled prevalence of Blastocystis derived from the 42 datasets on 7946 examined dogs was 7% (95% CI 4.7–10.4%) (Fig. 2). A significantly high heterogeneity was also identified among assessed studies (Cochran’s Q = 730.2, I2 = 94.4%, P ≤ 0.001). The global prevalence of Blastocystis in dogs by country is shown in Fig. 3.
Worldwide prevalence of Blastocystis infection in cats
The estimated weighted frequency of Blastocystis obtained from the 23 datasets on 2934 examined cats was 9.3% (95% CI 5.3–15.9%) (Fig. 2). A substantially high heterogeneity was reported among the assessed studies (Cochran’s Q = 350.4, I2 = 93.7%, P ≤ 0.001). The worldwide frequency of Blastocystis in cats by country is shown in Fig. 4.
The sensitivity analysis showed that the stepwise removal of individual studies (i.e., each dataset) did not result in any significant variation in the final calculated prevalence (Additional file 2: Figure S1; Additional file 3: Figure S2). However, considering the omission of the studies, the prevalence of Blastocystis infection in dogs and cats was estimated to be between 6.3–7.7% and 8.1–10.7%, respectively.
Overall prevalence of Blastocystis in dogs and cats based on investigated subgroups
Prevalence of each Blastocystis subtype in dogs
Among the 11 genetically diverse STs identified in dogs (ST1–8, ST10, ST23, ST24), ST3 (5 datasets; 41.3%, 95% CI 16.2–71.8%) showed the highest frequency, followed by ST2 (4 datasets; 39.3%, 95% CI 24.9–55.9%), ST1 (8 datasets; 30.9%, 95% CI 19.8–44.7%), ST4 (5 datasets; 13.4%, 95% CI 7.8–22.3%), ST8 (2 datasets; 12.7%, 95% CI 4.6–30.7%), ST10 (5 datasets; 11%, 95% CI 3.8–28%) and ST5 (3 datasets; 8.1%, 95% CI 2.6–22.4%) (Fig. 5). Each of ST6, ST7, ST23 and ST24 was observed in only one study (Table 3). Unlike cats, ST5–8, ST23 and ST24 were only reported in dogs.
Prevalence of each Blastocystis subtype in cats
Relative to dogs, fewer genetically diverse STs were identified in the cats (ST1-4, ST10, ST14). The highest prevalence was observed for ST4 (2 datasets; 29.5%, 95% CI 12.5–54.9%), followed by ST10 (2 datasets; 22.5%, 95% CI 9–46.1%), ST1 (3 datasets; 19.8%, 95% CI 9.1–37.8%) and ST3 (3 datasets; 17.6%, 95% CI 5.6–43.6%) (Fig. 6). Only a single study reported ST2 and ST14, as shown in Table 3. Interestingly, ST14 has only been reported in cats, and there were no reports of dogs being infected with this subtype.
Uncharacterized Blastocystis isolates and zoonotic potential of Blastocystis STs in dogs and cats
As shown in Table 3, not all positive samples were characterized in the included studies, possibly leading to underreporting of the true subtype population in both dogs and cats. Of the 10 recognized zoonotic STs of Blastocystis (ST1–9, ST12), eight were reported indogs (ST1–8) and four were isolated from cats (ST1–4), suggesting the importance of these animals, particularly dogs, in zoonotic transmission of Blastocystis (Table 3).
No significant association was found between Blastocystis prevalence and sample size in cats (regression coefficient (Reg Coef) = − 0.0033, P = 0.101), and publication year in dogs (Reg Coef = − 0.0315, P = 0.364). A statistically substantial association was reported between the frequency of Blastocystis infection in cats and the year of publication (Reg Coef = − 0.0931, P = 0.028), and the sample size in dogs (Reg Coef = − 0.0017, P = 0.046) (Additional files 14, 15, 16 and 17: Figures. S13, S14, S15 and S16).
There was a significant publication bias in the present systematic review and meta-analysis (Egger's regression: intercept = − 3.126, 95% lower limit = − 4.412, 95% upper limit = − 1.841, t-value = 4.86, P < 0.001) (Fig. 7).
The domestication of dogs and cats may be considered as a double-edged sword for humans; these animals are considered to be part of human families on the one hand, but they may carry several zoonotic agents, which can threat human health on the other hand . Blastocystis is a zoonotic protozoa that infects a broad range of animals as well as humans . Consequently, prediction of the global prevalence and subtype distribution of Blastocystis infection in dogs and cats is of great importance for humans. In the present study, we investigated this subject at a global scale.
Information was extracted from a total of 65 datasets (49 papers) on Blastocystis spp. infection in dogs and cats, and pooled frequencies of 9.3% (95% CI 5.3–15.9%) and 7% (95% CI 4.7–10.4%) were estimated for the cat and dog populations included in these datasets, respectively. A true comparison of both groups could not be conducted since a much lower number of studies examined Blastocystis spp. infection in cats. Individual studies had no substantial impact on the total prevalence of Blastocystis infection, as evidenced by the sensitivity analysis results. An obvious gap exists in terms of comprehensive epidemiological studies on Blastocystis infection in animal taxa, and only recently have meta-analyses reported a calculated prevalence rate of 52.4% (95% CI 43.9–60.7%), 31.2% (95% CI 11.2–62%) and 24.4% (95% CI 16.9–33.9%) in domestic pigs, wild boars  and cattle , respectively. Comparison of findings shows that the global frequency of Blastocystis infection is much lower in dogs and cats than in cattle, pigs and wild boars. Possible reasons for such differences may be animal type, number of examined animals, geographical location, among others. Of note, due to the limited number of studies conducted to date, of samples for testing and geographical areas investigated, no accurate comparison can be made and the prevalence rates reported in the present study should be interpreted with caution.
Our findings showed a higher trend of Blastocystis prevalence in studies documented up to and including 2000, with a reported prevalence of 23.2% (95% CI 0.3–96.4%)] and 26.1% (95% CI 0.7–94.6%)] for dogs and cats, respectively. Curiously, South America was reported to the most important area for Blastocystis in both dogs (6 datasets; 16%, 95% CI 7.7–30.4%) and cats (1 dataset; 37.4%, 95% CI 31.4–43.8%), while the infection was most common among dogs of the AMR region (WHO Region of the Americas; 9 datasets; 14.6%, 95% CI 7.5–26.3%) and among cats of SEAR region (WHO South-East Asian Region; 2 datasets; 23.4%, 95% CI 1.3–87.6%). Although derived from single studies, the highest prevalence was recorded in examined dogs in Chile (36.1%, 95% CI 33.1–39.2%) and India (23.8%, 95% CI 15.7–34.3%), as well as examined cats in Algeria (63.2%, 95% CI 40.3–81.3%). These high prevalences emphasize the importance of this parasitic infection in these countries. Nevertheless, the limited geographical areas studied and the lack of a sufficient number of studies in each country make it impossible for us to make an accurate assessment of the epidemiology of this parasitic infection. Inevitably, the sample size has a large effect on the estimated prevalence of an infection, as reflected in our results: sample sizes of ≤ 50 and 51–100 animals demonstrated the highest prevalence rates for Blastocystis infection, a prevalence of 18.6% (95% CI 8.6–35.8%) in dogs and 67.3% (95% CI 5.3.6–78.6%) in cats. It would appear that the results obtained from dogs are more reliable because they have been inferred from several studies (10 datasets), in comparison to the results from cats (1 paper). Taken together, when considering the evaluated subgroups, we found that the confidence intervals of reported frequencies were very wide, which is directly related to the limited number of studies and the large differences in reported prevalence rates. This is obviously a major limitation in our study, which can be eliminated by more comprehensive, nation-wide studies.
Another prominent finding of the present study was that dogs are a crucial source of zoonotic Blastocystis subtypes (ST1–ST8) and, therefore, possibly having the potential to transmit such subtypes to humans. However, the number of isolated STs from dogs and cats may increase in the future as not all positive samples in the studies included in this meta-analysis were subtyped. Mixed infections with multiple subtypes are frequently seen in association with Blastocystis infection . Mixed cases were reported in some of the studies, but due to various limitations, we could not estimate their pooled prevalence.
Meta-regression results revealed that in contrast to the sample size in cats and publication year in dogs, the year of publication in cats and the sample size in dogs were considered as a cause of variability in Blastocystis prevalence. Accordingly, there was a direct association between a reduction in Blastocystis infection rate with recently published studies in cats and with an increase in sample size in dogs. A high rate of heterogeneity was reported as publication bias in the present study, which could substantially skew the outcomes . This may originate from differences in geographical region, publication year, number of studies in each area and sample size, as mentioned in Table 2. Other parameters not mentioned in this current review may also represent publication bias, such as the status of animal health, sampling procedures, sample preservation, method of raising owned animals, sensitivity of diagnostic methods, age and sex of the examined hosts and the quality of studies entered. Hence, the results obtained from the present study must be interpreted with caution. In general, despite the valuable epidemiological information we collected in the current study, future studies could, therefore, shed more light on the ST distribution and epidemiological patterns of Blastocystis infection in dogs and cats across the globe.
Currently, many dogs and cats live in the (close) proximity of humans and have the potential to be a threat human health, particularly through zoonotic infections. To the best of our knowledge, we present here the first comprehensive insights into the worldwide epidemiology, subtype distribution and zoonotic potential of Blastocystis infection in dogs and cats. The prevalence of this infection was relatively low among dogs (7%) and cats (9.3%), albeit higher higher in cats. Notably, of the 28 reported Blastocystis STs, 11 were isolated from dogs and six were isolated from cats, with most of these considered to be zoonotic. Consequently, these animals could play a significant role in the transmission of zoonotic subtypes to humans. The present review was designed and conducted solely on the basis of current published literature (up to 8 November 2021), and more extensive studies are needed to elucidate the epidemiology and distribution of dog and cat STs.
Availability of data and materials
The datasets supporting the conclusions of this article are included in the article (and its additional files).
Asghari A, Zare M, Hatam G, Shahabi S, Gholizadeh F, Motazedian M. Molecular identification and subtypes distribution of Blastocystis sp. isolated from children and adolescents with cancer in Iran: evaluation of possible risk factors and clinical features. Acta Parasitol. 2020;65:462–73.
Maloney JG, da Cunha MJR, Molokin A, Cury MC, Santin M. Next-generation sequencing reveals wide genetic diversity of Blastocystis subtypes in chickens including potentially zoonotic subtypes. Parasitol Res. 2021;120:2219–31.
Asghari A, Sadraei J, Pirestani M, Mohammadpour I. First molecular identification and subtype distribution of Blastocystis sp. isolated from hooded crows (Corvus cornix) and pigeons (Columba livia) in Tehran Province Iran. Comp Immunol Microbiol Infect Dis. 2019;62:25–30.
Liu X, Ni F, Wang R, Li J, Ge Y, Yang X, et al. Occurrence and subtyping of Blastocystis in coypus (Myocastor coypus) in China. Parasit Vectors. 2022;15:14.
Asghari A, Hassanipour S, Hatam G. Comparative molecular prevalence and subtypes distribution of Blastocystis sp. a potentially zoonotic infection isolated from symptomatic and asymptomatic patients in Iran: a systematic review and meta-analysis. Acta Parasitol. 2021;66:745–59.
Shams M, Shamsi L, Sadrebazzaz A, Asghari A, Badali R, Omidian M, et al. A systematic review and meta-analysis on the global prevalence and subtypes distribution of Blastocystis sp. infection in cattle: a zoonotic concern. Comp Immunol Microbiol Infect Dis. 2021;76:101650.
Su C, Mei X, Wei L, Wang J, Feng X, Wang P, et al. Prevalence and molecular subtyping of Blastocystis in domestic pigeons in Henan Province Central China. J Eukaryot Microbiol. 2022;69:e12888.
Sheikh S, Asghari A, Sadraei J, Pirestani M, Zare M. Blastocystis sp. Subtype 9: as the first reported subtype in patients with schizophrenia in Iran. SN Compr Clin Med. 2020;2:633–9.
Asghari A, Sadrebazzaz A, Shamsi L, Shams M. Global prevalence, subtypes distribution, zoonotic potential, and associated risk factors of Blastocystis sp. in domestic pigs (Sus domesticus) and wild boars (Sus scrofa): a systematic review and meta-analysis. Microb Pathog. 2021;160:105183.
Asghari A, Sadeghipour Z, Hassanipour S, Abbasali Z, Ebrahimzadeh-Parikhani H, Hashemzaei M, et al. Association between Blastocystis sp. infection and immunocompromised patients: a systematic review and meta-analysis. Environ Sci Pollut Res. 2021;28:60308–28.
Kim M-J, Lee YJ, Kim T-J, Won EJ. Gut microbiome profiles in colonizations with the enteric protozoa Blastocystis in Korean populations. Microorganisms. 2022;10:34.
Stensvold CR, Clark CG. Pre-empting Pandora’s box: Blastocystis subtypes revisited. Trends Parasitol. 2020;36:229–32.
Higuera A, Herrera G, Jimenez P, García-Corredor D, Pulido-Medellín M, Bulla-Castañeda DM, et al. Identification of multiple Blastocystis subtypes in domestic animals from Colombia using amplicon-based next generation sequencing. Front Vet Sci. 2021;8:932.
Ma L, Qiao H, Wang H, Li S, Zhai P, Huang J, et al. Molecular prevalence and subtypes of Blastocystis sp. in primates in northern China. Transbound Emerg Dis. 2020;67:2789–96.
Shah SSA, Khan A. One Health and parasites. In: Yasobant S, Saxena D, editors. Global applications of One Health practice and care. Hershey: IGI Global; 2019. p. 82–112.
Moher D, Shamseer L, Clarke M, Ghersi D, Liberati A, Petticrew M, et al. Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) 2015 statement. Syst Rev. 2015;4:1–9.
Joanna Briggs Institute (JBI). The Joanna Briggs Institute critical appraisal tools for use in JBI systematic reviews. Checklist for qualitative research. Adelaide: Joanna Briggs Institute. 2017.
Mahdavi F, Sadrebazzaz A, Chahardehi AM, Badali R, Omidian M, Hassanipour S, et al. Global epidemiology of Giardia duodenalis infection in cancer patients: a systematic review and meta-analysis. Int Health. 2022;14:5–17.
Mahdavi F, Shams M, Sadrebazzaz A, Shamsi L, Omidian M, Asghari A, et al. Global prevalence and associated risk factors of diarrheagenic Giardia duodenalis in HIV/AIDS patients: a systematic review and meta-analysis. Microb Pathog. 2021;160:105202.
Abe N, Nagoshi M, Takami K, Sawano Y, Yoshikawa H. A survey of Blastocystis sp. in livestock, pets, and zoo animals in Japan. Vet Parasitol. 2002;106:203–12.
Albakri HS, Al-ani A-AJ. Detection of Blastocystis in cats in Nineveh province-Iraq. AL-Qadisiyah J Vet Med Sci. 2016;15:41–4.
Dalimiasl AAH, Mojarad KS, Jamshidi S. Intestinal parasites of pet dogs in Tehran and evaluation of knowledge of dog owners about zoonotic risk of parasites of dog. J Vet Res. 2001;56:13–6.
Duda A, Stenzel DJ, Boreham PFL. Detection of Blastocystis sp. in domestic dogs and cats. Vet Parasitol. 1998;76:9–17.
Gazzonis AL, Marangi M, Zanzani SA, Villa L, Giangaspero A, Manfredi MT. Molecular epidemiology of Blastocystis sp. in dogs housed in Italian rescue shelters. Parasitol Res. 2019;118:3011–7.
Gillespie S, Bradbury RS. A survey of intestinal parasites of domestic dogs in Central Queensland. Trop Med Infect Dis. 2017;2:60.
González AC, Giraldo JC. Prevalencia de parásitos intestinales zoonóticos en caninos (Canis lupus familiaris) del área urbana del municipio de Coyaima (Tolima). Rev Med. 2015;23:24–34.
Hemalatha C, Chandrawathani P, Suresh Kumar G, Premaalatha B, Geethamalar S, Lily Rozita MH, et al. The diagnosis of Blastocystis sp. from animals—an emerging zoonosis. Malaysian J Vet Res. 2014;5:15–21.
Hurtado HAM, Forero JCG. Zoonotic parasitism in dogs from the department of Vaupés Colombia. Braz J Health Rev. 2019;2:3408–20.
Karakavuk M, Selim N, Yeşilsiraz B, Evren A, Nuray A, Yalçin M, et al. Prevalence of gastrointestinal parasites in stray cats of İzmir. Anim Health Prod Hyg. 2021;10:6–11.
Khademvatan S, Abdizadeh R, Rahim F, Hashemitabar M, Ghasemi M, Tavalla M. Stray cats gastrointestinal parasites and its association with public health in Ahvaz City, South Western of Iran. Jundishapur J Microbiol. 2014;7:e11079.
Mokhtar A, Youssef A. Subtype analysis of Blastocystis spp. isolated from domestic mammals and poultry and its relation to transmission to their in-contact humans in Ismailia governorate, Egypt. Parasitol United J. 2018;11:90–8.
Konig G, Müller HE. Blastocystis hominis in animals: incidence of four serogroups. Zentralbl Bakteriol. 1997;286:435–40.
Kwak D, Seo M-G. Genetic analysis of zoonotic gastrointestinal protozoa and microsporidia in shelter cats in South Korea. Pathogens. 2020;9:894.
La Sala LF, Leiboff A, Burgos JM, Costamagna SR. Spatial distribution of canine zoonotic enteroparasites in Bahía Blanca Argentina. Rev Argent Microbiol. 2015;47:17–24.
Leelayoova S, Siripattanapipong S, Naaglor T, Taamasri P, Mungthin M. Prevalence of intestinal parasitic infections in military personnel and military dogs Thailand. J Med Assoc Thailand. 2009;92:S53–9.
Li WC, Wang K, Qin M, Liu ZH, Yuan G, Liu DY, et al. Blastocystis infection in pet dogs in selected areas of Anhui and Zhejiang Provinces China. J Parasitol Parasit Dis. 2016;34:272–6.
Li W, Liu X, Gu Y, Liu J, Luo J. Prevalence of Cryptosporidium, Giardia, Blastocystis, and trichomonads in domestic cats in East China. J Vet Med Sci. 2019;81:19–111.
Liao S, Lin X, Sun Y, Qi N, Lv M, Wu C, et al. Occurrence and genotypes of Cryptosporidium spp., Giardia duodenalis, and Blastocystis sp. in household, shelter, breeding, and pet market dogs in Guangzhou, southern China. Sci Rep. 2020;10:17736.
López J, Abarca K, Paredes P, Inzunza E. Intestinal parasites in dogs and cats with gastrointestinal symptoms in Santiago Chile. Rev Med Chil. 2006;134:193–200.
Mohaghegh MA, Vafaei MR, Ghomashlooyan M, Azami M, Falahati M, Azadi Y, et al. A wide diversity of zoonotic intestinal parasites in domestic and stray dogs in rural areas of Kermanshah province Iran. Trop Biomed. 2018;35:82–90.
Mohammadpour I, Bozorg-Ghalati F, Gazzonis AL, Manfredi MT, Motazedian MH, Mohammadpour N. First molecular subtyping and phylogeny of Blastocystis sp. isolated from domestic and synanthropic animals (dogs, cats and brown rats) in southern Iran. Parasit Vectors. 2020;13:365.
Arbabi M, Hooshyar H. Gastrointestinal parasites of stray cats in Kashan Iran. Trop Biomed. 2009;26:16–22.
Noradilah SA, Anuar TS, Moktar N, Lee IL, Salleh FM, Manap SNAA, et al. Molecular epidemiology of Blastocystis sp in animals reared by the aborigines during wet and dry seasons in rural communities, Pahang, Malaysia. Southeast Asian J Trop Med Public Health. 2017;48:1151–60.
Okoye IC, Obiezue NR, Okoh FN, Amadi EC. Descriptive epidemiology and seasonality of intestinal parasites of cats in Southeast Nigeria. Comp Clin Path. 2014;23:999–1005.
Onder Z, Yildirim A, Pekmezci D, Duzlu O, Pekmezci GZ, Ciloglu A, et al. Molecular identification and subtype distribution of Blastocystis sp. in farm and pet animals in Turkey. Acta Trop. 2021;220:105939.
Osman M, Bories J, El Safadi D, Poirel M-T, Gantois N, Benamrouz-Vanneste S, et al. Prevalence and genetic diversity of the intestinal parasites Blastocystis sp. and Cryptosporidium spp. in household dogs in France and evaluation of zoonotic transmission risk. Vet Parasitol. 2015;214:167–70.
Pagati AL, Suwanti LT, Anwar C, Yuniarti WM, Suprihati E. Prevalance of gastrointestinal protozoa of cats in animal hospital and animal clinic in Surabaya. J Parasite Sci. 2018;2:61–6.
Parkar U, Traub RJ, Kumar S, Mungthin M, Vitali S, Leelayoova S, et al. Direct characterization of Blastocystis from faeces by PCR and evidence of zoonotic potential. Parasitology. 2007;134:359–67.
Paulos S, Köster PC, de Lucio A, Hernández-de-Mingo M, Cardona GA, Fernández-Crespo JC, et al. Occurrence and subtype distribution of Blastocystis sp. in humans, dogs and cats sharing household in northern Spain and assessment of zoonotic transmission risk. Zoonoses Public Health. 2018;65:993–1002.
Perera PK, Rajapakse R, Rajakaruna RS. Gastrointestinal parasites of dogs in Hantana area in the Kandy District. Natl Sci FNDN Sri Lanka. 2013;41:81–91.
Puebla LEJ, Nunez FA, Rivero LR, Hernandez YR, Garcia IS, Millan IA. Prevalence of intestinal parasites in dogs from municipality La Lisa, Havana Cuba. J Vet Sci Technol. 2015;6:25–30.
Ramírez JD, Sánchez LV, Bautista DC, Corredor AF, Flórez AC, Stensvold CR. Blastocystis subtypes detected in humans and animals from Colombia. Infect Genet Evol. 2014;22:223–8.
Awadallah MAI, Salem LMA. Zoonotic enteric parasites transmitted from dogs in Egypt with special concern to Toxocara canis infection. Vet World. 2015;8:946.
Roberts T, Stark D, Harkness J, Ellis J. Subtype distribution of Blastocystis isolates from a variety of animals from New South Wales Australia. Vet Parasitol. 2013;196:85–9.
Ruaux CG, Stang BV. Prevalence of Blastocystis in shelter-resident and client-owned companion animals in the US Pacific Northwest. PLoS ONE. 2014;9:e107496.
Sanchez-Thevenet P, Carmena D, Adell-Aledón M, Dacal E, Arias E, Saugar JM, et al. High prevalence and diversity of zoonotic and other intestinal parasites in dogs from eastern Spain. Vector-Borne Zoonotic Dis. 2019;19:915–22.
Sardarian K, Maghsood AH, Ghiasian SA, Zahirnia AH. Prevalence of zoonotic intestinal parasites in household and stray dogs in rural areas of Hamadan Western Iran. Trop Biomed. 2015;32:240–6.
Spanakos G, Papadogiannakis E, Kontos V, Menounos P, Velonakis E, Koutis C, et al. Molecular screening for Blastocystis sp. in canine faecal samples in Greece. J Hell Vet Med Soc. 2011;62:216–20.
Udonsom R, Prasertbun R, Mahittikorn A, Mori H, Changbunjong T, Komalamisra C, et al. Blastocystis infection and subtype distribution in humans, cattle, goats, and pigs in central and western Thailand. Infect Genet Evol. 2018;65:107–11.
Villamizar X, Higuera A, Herrera G, Vasquez-A LR, Buitron L, Muñoz LM, et al. Molecular and descriptive epidemiology of intestinal protozoan parasites of children and their pets in Cauca, Colombia: a cross-sectional study. BMC Infect Dis. 2019;19:190.
Wang W, Cuttell L, Bielefeldt-Ohmann H, Inpankaew T, Owen H, Traub RJ. Diversity of Blastocystis subtypes in dogs in different geographical settings. Parasit Vectors. 2013;6:215.
Wang J, Gong B, Liu X, Zhao W, Bu T, Zhang W, et al. Distribution and genetic diversity of Blastocystis subtypes in various mammal and bird species in northeastern China. Parasit Vectors. 2018;11:522.
Badparva E, Kheirandish F. Non-infection to Blastocystis in cats of Lorestan Province Iran. Entomol Appl Sci Lett. 2020;7:49–53.
Bandaranayaka KO, Rajapakse R, Rajakaruna RS. Potentially zoonotic gastrointestinal parasites of dogs in Lunugala Tea estate community in Central Sri Lanka Ceylon. J Sci. 2019;48:43–50.
Belleza MLB, Reyes JCB, Tongol-Rivera PN, Rivera WL. Subtype analysis of Blastocystis sp. isolates from human and canine hosts in an urban community in the Philippines. Parasitol Int. 2016;65:291–4.
Boutellis A, Aissi M, Harhoura K, Drali R, Kernif T, Tazerouti F. First molecular characterization of Blastocystis subtypes from animals and animal-keepers stool in Algeria. Comp Immunol Microbiol Infect Dis. 2021;78:101695.
Can H, Köseoğlu AE, Erkunt Alak S, Güvendi M, Ün C, Karakavuk M, et al. Molecular prevalence and subtyping of Blastocystis sp. isolates in stray cats of İzmir, Turkey: First report of “ST4 allele 42” in cats. Pol J Vet Sci. 2021;24:217.
Miklósi Á, Topál J. What does it take to become ‘best friends’? Evolutionary changes in canine social competence. Trends Cogn Sci. 2013;17:287–94.
Betts EL, Gentekaki E, Tsaousis AD. Exploring micro-eukaryotic diversity in the gut: co-occurrence of Blastocystis subtypes and other protists in zoo animals. Front Microbiol. 2020;11:288.
Oliveira-Arbex AP, David ÉB, da Silva TM, Cicchi PJP, Patti M, Coradi ST, et al. Diversity of Blastocystis subtypes in wild mammals from a zoo and two conservation units in southeastern Brazil. Infect Genet Evol. 2020;78:104053.
Thornton A, Lee P. Publication bias in meta-analysis: its causes and consequences. J Clin Epidemiol. 2000;53:207–16.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Ethics approval and consent to participate
Consent for publication
The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
JBI critical appraisal checklist applied for included studies
Sensitivity analysis on the pooled Blastocystis prevalence in dogs.
Sensitivity analysis on the pooled Blastocystis prevalence in cats.
Pooled Blastocystis prevalence based on publication year in dogs.
Pooled Blastocystis prevalence based on publication year in cats.
Pooled Blastocystis prevalence based on continents in dogs.
Pooled Blastocystis prevalence based on continents in cats.
Pooled Blastocystis prevalence based on WHO regions in dogs.
Pooled Blastocystis prevalence based on WHO regions in cats.
Pooled Blastocystis prevalence based on countries in dogs.
Pooled Blastocystis prevalence based on countries in cats.
Pooled Blastocystis prevalence based on sample size in dogs.
Pooled Blastocystis prevalence based on sample size in cats.
Association between Blastocystis prevalence and publication year in dogs using meta-regression.
Association between Blastocystis prevalence and sample size in dogs using meta-regression.
Association between Blastocystis prevalence and publication year in cats using meta-regression.
Association between Blastocystis prevalence and sample size in cats using meta-regression.
About this article
Cite this article
Shams, M., Shamsi, L., Yousefi, A. et al. Current global status, subtype distribution and zoonotic significance of Blastocystis in dogs and cats: a systematic review and meta-analysis. Parasites Vectors 15, 225 (2022). https://doi.org/10.1186/s13071-022-05351-2
- Systematic review