There are estimated to be more than one billion domestic goats worldwide (1), and the global goat population has more than doubled in the last four decades (2). Despite significant growth in the global goat population, the productivity of the goat industry is challenged by health, management and production constraints (3). Among various health concerns, gastrointestinal diseases (e.g., parasitic gastroenteritis) can lead to significant economic losses for the global goat industry (4).

For instance, coccidiosis, a parasitic disease caused by the intracellular protozoan parasites of the genus Eimeria (Apicomplexa: Eimeriidae) (5), is a significant concern for goat farmers due to its economic impact. Globally, several species of Eimeria (also known as coccidia) infect goats (6–16), leading to significant economic losses due to poor growth and lower productivity. Although the economic impact of coccidiosis is believed to be substantial (17), there is a lack of data to substantiate such a statement regarding small ruminant coccidiosis.

To date, the number of Eimeria spp. that are considered parasites of goats remains variable and controversial (14, 18, 19) and depends on the acceptance of the validity of certain Eimeria spp. (12). For instance, Levine (20) reported 13 species of Eimeria as the true parasites of goats, including Eimeria arloingi, E. ninakohlyakimovae, E. christenseni, E. caprina, E. caprovina, E. alijevi, E. hirci, E. jolchijevi and E. aspheronica, which are distributed globally (6–16). Among these species, E. arloingi, E. ninakohlyakimovae, E. christenseni and E. caprina are considered the most pathogenic and prevalent (21), while others are non-pathogenic.

Goats between 1 and 6 months of age are most susceptible to Eimeria spp. which inhabit the small and large intestines (22, 23). The oocysts are passed in feces, infecting other animals after further development (i.e., sporulation – asexual reproduction) in the environment. When a susceptible host ingests a sporulated oocyst, the sporozoites are released in the gastrointestinal tract and invade intestinal epithelial cells. Following a number of predetermined generations of development (schizogony – asexual reproduction) in intestinal cells, the female and male gametes form a zygote, which develops into an oocyst (24). The damage to the host occurs due to cell disruption during schizogony and later during gametogony (sexual reproduction). The more prevalent form of coccidiosis is a subclinical disease resulting in poor growth while the clinical form of the disease is most commonly characterized by diarrhea (25). The economic losses due to coccidiosis (26) are attributed to reduced productivity, reduced weight gain, mortality (22, 23) and treatment costs (27). The damage done to the kid’s intestines may be permanent in severe cases, resulting in kids that exhibit ill-thrift for life, i.e., they remain “poor doers” as they fail to recover fully after treatment (25). These kids are more susceptible to other diseases, such as respiratory infections, due to their lower immunity (28).

Given that the global prevalence of Eimeria spp. in goats is variable (29–35), with more than 90% prevalence reported in some regions (11, 14, 35–39), effective control measures are essential to minimize losses associated with subclinical and clinical coccidiosis (40). Currently, control of coccidiosis is based on sound management, using preventive medications and treating clinical cases using anticoccidial drugs (23). Although coccidiosis is well-studied in poultry, sheep and cattle, our understanding of goat coccidiosis is limited despite the remarkable growth in the global goat industry in recent decades (14). As a first step to ascertain the current state of play, an exploration of the prevalence and geographical distribution of Eimeria spp. in goats could pave the way for global efforts to control goat coccidiosis. Therefore, we conducted a systematic review and meta-analysis to estimate the global prevalence of Eimeria spp. infecting goats, with an emphasis on temporal and spatial trends, frequency and spatial distribution of species, diagnostic methods, sample size and quality of selected studies. The findings of this study could be used by veterinarians, researchers, goat farmers and policymakers to make informed decisions about the effective control of coccidiosis in goats worldwide.

This is the first study on the global prevalence of Eimeria spp. infection in goats using a substantial number of studies (n = 255) retrieved from five databases. The overall global prevalence of Eimeria spp. in goats is 62.9%. The 95% prediction interval (PI) is estimated at 4–100%. The highest prevalence was found in North America (92.2%), followed by Europe (86.6%), while it was the lowest in Asia (52.0%). Surprisingly, in 42 out of 56 countries, the estimated prevalence (63–100%) was higher than the overall pooled estimate (62.9%).

The subgroup analysis by region and country showed that the highest pooled prevalence of Eimeria spp. was found in North America (92.2%), and the meta-regression showed a positive beta coefficient (b = 0.58). Within this region, the USA had a higher prevalence of Eimeria spp. in goats (92.4%), whereas it was lowest in Mexico (71.2%). In the USA, the higher prevalence of Eimeria spp. in goats was attributed to risk factors such as season, age, farm management, and the use of deep litter straw bedding materials (57). Additionally, the intensive production system and climate conditions contributed to the higher prevalence of Eimeria spp. in the USA (9). However, no studies reported the prevalence of Eimeria spp. in goats in other North American countries with significant goat populations such as Haiti and Cuba (1). The study conducted by Cantú-Martínez et al. (58) from Mexico contributed most to the observed heterogeneity on the continent (Figure 8F). Interestingly, no publication bias was detected in this region (Supplementary Table S7).

The estimated prevalence of Eimeria spp. in goats in Europe was 86.6%. A meta-regression analysis showed a positive beta coefficient (b = 0.27, p < 0.01) (Table 2). In Europe, 80% (12/15) of countries had a prevalence of Eimeria spp. higher than 70%. The lowest estimated prevalence was 57.1% in Serbia, which is still higher than the estimated prevalence of the Asian continent (52.0%). The goat sector in Europe is specialized in milk production and is highly commercially oriented, dominated by an intensive production system, as reviewed by Miller and Lu (59). This may have contributed to the higher prevalence of Eimeria spp. in goats reported in this region, because the intensification of dairy goat production presents challenges in limiting the spread of infectious and parasitic diseases (e.g., coccidiosis), which are facilitated by environmental stressors such as high stocking density (60, 61). A major challenge in commercially oriented dairy goat production systems arises when multiple kidding events occur throughout the year to maintain a consistent milk supply. If the same pens are used repeatedly for successive batches or if newly born kids are introduced to a pen already housing older animals, the later-born kids are immediately exposed to a heavy challenge. They can develop severe coccidiosis in the first few weeks of life (62). Moreover, herd size, age and climatic conditions were associated with varying levels of Eimeria spp. prevalence in Europe (40). The studies conducted by Ruiz et al. (40) in Spain and Corrias et al. (63) in Italy influenced the estimated prevalence and contributed to the observed heterogeneity (Figure 8E). We also detected the probability of publication bias in Europe (b = −5.59; p = 0.02) (Supplementary Table S7; Supplementary Figure S3), which may have further contributed to the heterogeneity.

In Oceania, the estimated prevalence of Eimeria spp. in goats was 66.6%. However, it is worth mentioning that almost all studies were conducted in Australia, with limited prevalence data available from countries such as Fiji, New Zealand, Vanuatu, and French Polynesia, which have a significant goat population (64). The studies conducted by O’Callaghan (13) and Al-Habsi et al. (65), had an impact on the pooled estimate and contributed to the heterogeneity (Figure 8G). The number of studies accessible in Oceania was insufficient (< 10) to perform Egger’s test.

In South America, the estimated prevalence of Eimeria spp. in goats was 65.7%. The apparent prevalence of Eimeria spp. in goats ranged from 4.0 to 91.2%, and almost all studies were conducted in Brazil. This meta-analysis identified the highest prevalence in southern Ecuador and the lowest in Brazil (Supplementary Table S4). The high prevalence of Eimeria spp. in goats from Ecuador is often related to the animals’ exposure to risk factors such as age, presence of cattle, type of pasture and body condition (66). In addition, this may be due to the typical situation in goat pens in Ecuador with moist and dark environments, ideal conditions for oocyst sporulation to occur (66). However, countries with a goat population greater than 1 million, such as Bolivia, Peru and Venezuela (1), do not have data on the prevalence of Eimeria spp. in goats. A study conducted by Cardoso et al. (67) from Brazil influenced the pooled estimate in this region and contributed to heterogeneity (Figure 8D).

The estimated prevalence of Eimeria spp. in goats in Africa was 63.9%. Despite Africa being home to over 40% of the world’s goat population (1), only 72 studies from 17 countries reported the prevalence of Eimeria spp. in goats in Africa. The majority of these studies were conducted in five countries, including Egypt (n = 16), Nigeria (n = 12), Kenya (n = 10), Ethiopia (n = 8) and Tanzania (n = 7) (Figure 5). The highest estimated prevalence of Eimeria were found in Algeria (89.0%) and Botswana (89.0%), while the lowest estimate was recorded in Lesotho (26.0%). However, it is important to note that the estimates for these countries were based solely on one study, which may not accurately reflect the true prevalence of Eimeria spp. The studies conducted in Africa were more heterogeneous than those of other continents. The heterogeneity was influenced by studies from Egypt (68) and Tanzania (69) (Figure 8C). Egger’s test did not identify publication bias in the prevalence estimates in Africa.

Asia has recognized the importance of dairy goat husbandry in the face of climate change, leading to significant investments in dairy goat projects over the past few decades [see the review by (59)]. This explains the large number of studies (n = 128) that report the prevalence of Eimeria spp. of goat in Asia. Interestingly, the estimated prevalence of Eimeria spp. in Asia, which is home to the world’s largest goat population (1), is 52.0%. This result is significantly lower than the global pooled estimate (Table 2). Moreover, the meta-regression analysis showed a negative beta coefficient (b = − 0.02, p < 0.05). The highest estimated prevalence in Asia was found in China (95.1%), a global leader in goat populations (1). This result differs from the previous study reported by Diao et al. (42), who estimated the pooled prevalence of Eimeria spp. in goats in China to be 78.7% (95% CI: 68.2–87.7%). This discrepancy could be due to the differences in the number of studies (70 studies) and (3 studies in present estimate) included in the meta-analysis and the study periods. Conversely, studies from Saudi Arabia, and Kuwait, Asian countries that reported the lowest prevalence of Eimeria spp., were conducted in extensively managed goat flocks and in regions with higher annual average temperatures and lower relative humidity (arid areas) (70, 71). These environmental conditions are known to negatively affect the sporulation and survival of Eimeria oocysts in the environment which could be the reason for the lower prevalence. The lower prevalence of Eimeria spp. in Saudi Arabia was also attributed to sanitation efforts in management programs introduced by goat producers or ecological differences (8). Most studies used to estimate the prevalence of Eimeria spp. in goats in Asia were conducted in India (n = 73), Malaysia (n = 11) and Pakistan (n = 8). However, countries with large goat populations, such as Bangladesh, Indonesia, Mongolia, Nepal and Myanmar (1), had limited or no available data on the prevalence of Eimeria spp. In this region, Egger’s test identified statistically significant publication bias (b = 7.42; p = 0.005) and the greatest contribution to heterogeneity was shared by Rahman et al. (56) (Figure 8B).

It was believed that Eimeria spp. in goats and sheep were the same for a long time because their oocysts have strikingly similar morphologies (12, 72). However, cross-infection studies disproved this assumption in the late 20th century (73, 74). In this meta-analysis, we conducted a subgroup analysis based on the year of publication to investigate any discrepancies between studies conducted before and after the assumption was made. We also aimed to identify any changes in the temporal trend of reported cases over time. The prevalence of Eimeria spp. in goats sampled before 2000 was 74.3%, whereas in the samples collected in 2000 or later, it was 59.6%, which clearly showed a statistically significant decline (p < 0.05). The rationale behind this trend remains uncertain, but it is possible that the previous misconception concerning Eimeria spp. in goats and sheep contributed to these differences. Further comprehensive research and scientific justifications are needed to determine whether the decrease in Eimeria spp. infection in goats is genuine or not.

The antemortem diagnosis of Eimeria spp. infection traditionally relies on the concentration and/or quantification of Eimeria oocysts per gram (OPG) in the feces through microscopic examination using flotation techniques and/or the morphometry of sporulated oocysts (24, 75). Most studies (n = 202) in this review used fecal flotation techniques to detect and/or enumerate Eimeria fecal oocyst count. However, determining a threshold OPG value that indicates clinical coccidiosis is challenging (76). For instance, while some studies suggest that an OPG of 50,000–100,000 could indicate clinical coccidiosis, non-pathogenic Eimeria spp. can also be excreted in large numbers without clinical signs (76). Therefore, it is crucial to differentiate between pathogenic and non-pathogenic species to confirm clinical coccidiosis (24).

Our systematic literature review shows that morphological identification is the primary method used to differentiate Eimeria spp. in goats. Interestingly, only 47% (119/255) of the studies included in the review documented the identifications of Eimeria spp. worldwide. More than 26 Eimeria spp. have been reported in goats, including recognized/valid species such as E. arloingi, E. ninakohlyakimovae, E. christenseni, E. caprina, E. caprovina, E. alijevi, E. hirci, E. jolchijevi and E. aspheronica as well as other less characterized species. The spatial distribution of the recognized/valid Eimeria spp. shows no distinct regional pattern, suggesting their widespread presence (Figure 4). However, there is considerable variation and controversy regarding the number of Eimeria spp. parasitising goats (14, 18, 19), and this variation depends on the acceptance of certain Eimeria spp. as valid (12). Mixed species infections were commonly observed in most studies, with an average of 7.3 and a median of 8 Eimeria spp. reported per study. This review also supports the ongoing controversy that some studies have reported Eimeria spp. typically found in sheep (E. faurei, E. crandallis, and E. intricata) and cattle (E. zuernii), raising concerns about misinterpretation despite evidence of the absence of cross-host species transmission of Eimeria (73, 74). Recent studies in South Korea (77), India (78), and Slovakia (34) described unspecified Eimeria spp. Moreover, species such as E. masseyensis and E. charlestoni (19) from New Zealand, E. hawkin and E. charlestoni (33, 79) from India, E. minasensis (80) from Brazil, E. sundarbanensis (81) from India, E. megaembryonica (82) from Iraq, and E. tunisiensis and E. masseyensis (83) from Nepal have been reported despite these species never been previously recorded or described globally. Eimeria capralis was first reported in New Zealand (19), with subsequent reports in Iraq (84) and Nepal (83). Furthermore, at least 14 studies reused the same data and/or published their findings twice in different journals, raising significant concerns about the validity of the description of new Eimeria spp. or morphological identification of previously described species.

The accurate identification of Eimeria spp. is paramount for understanding their epidemiology and assessing the effectiveness of anticoccidial drugs, as only a few Eimeria spp. are pathogenic to goats (36, 76, 85). This systematic review showed that the pathogenic species of Eimeria (E. arloingi, E. ninakohlyakimovae, E. christenseni and E. caprina) are widely distributed. For goat farmers, the widespread presence of these pathogenic Eimeria spp., along with a 62.9% estimated prevalence of Eimeria spp. poses significant economic losses (42).

Despite the morphological characterization of sporulated oocysts being the primary method for identifying Eimeria spp. in goats, this approach has notable limitations, including low sensitivity, the extended time required (1–2 weeks) for oocysts to sporulate under varying conditions (86), labor intensive requirements, requires experienced microscopists (87) and difficulty in differentiating morphologically similar oocysts in certain species of Eimeria (12). Although more than 26 Eimeria spp. have been documented globally, molecular characterization has only been partially achieved for a few Eimeria spp., including E. arloingi, E. christenseni, E. hirci, E. ninakohlyakimovae, and one unidentified Eimeria spp. Only a limited number of studies (n = 10) across eight countries have used molecular techniques, primarily using PCR amplification of 18S, and/or COX1, and ITS-1 or ITS-2. The lack of combined morphological and molecular methods could lead to the erroneous identification of certain Eimeria spp. in goats. As of June 25th, 2024, at least 78 nucleotide sequences have been deposited in GenBank⁴ along with their accession numbers. Most of these sequences were based on partial amplification of 18S gene. Surprisingly, most of these nucleotide sequences (>50%) are not accompanied by peer-reviewed publications, casting doubts on their reliability and validation. Given these challenges, adopting a combined approach using morphological and molecular methods is imperative to accurately identify Eimeria spp. More nucleotide sequencing is needed, particularly for Eimeria spp. that have yet to be characterized. Furthermore, advanced molecular-based studies that include the genetic characterization of new Eimeria spp. and utilizing next-generation sequencing tools could help address the challenges associated with Eimeria.

In this systematic review and meta-analysis, there were only 27 low-quality studies with a score of 1–2, but 149 with a score of 3–4. The reasons for fewer points in some studies were: (1) they needed to clarify whether the sampling was random or not, and the sampling method needed to be detailed. (2) Furthermore, neither was the sample size calculated in most studies nor Eimeria reported at the species level. When investigating the prevalence of Eimeria spp. in goats, we recommend researchers report and/or identify Eimeria spp., calculate the sample size, apply representative sampling techniques, and collect and present as much information as possible. Detailed data on potential risk factors, such as age, production systems, study period, and climatic conditions is also quite important. Such data would enhance the understanding of the factors driving Eimeria spp. prevalence and allow for more robust risk factor analyses in future meta-analyses.

This meta-analysis has shown high I² and Cochran’s Q statistics, suggesting significant heterogeneity among the studies reporting the prevalence of Eimeria spp. in goats worldwide. The wide range of the 95% PI (4 to 100%) further supports this finding. This variation could be due to several reasons, including geographical factors, differences in production systems, the immune status of the host, differences in the age of goats included in the studies, sample size, diversity of the study populations, breed differences, sampling methods, sex and study periods (88–93). Our meta-regression analyses further showed that region, year of publication, sample size, and the quality level of studies were significant sources of heterogeneity, while the diagnostic methods did not have an impact. Although the improvement in R² was minimal (4.4%) compared to the full and best models, the full model allows for improved balance, fit and parsimony, making it the preferred model that achieves a good fit with fewer predictors. Additionally, the study by Rahman et al. (56) notably influenced the pooled estimate and contributed the most to the overall heterogeneity.

The estimated pooled prevalence reported in this systematic review and meta-analysis should be interpreted with caution due to the following limitations. Firstly, we found high heterogeneity and publication biases (for the Asian and European continents). Although we applied relevant statistical methods, these may not completely eliminate the impact of heterogeneity and publication bias on the interpretation of the pooled results. Secondly, our database search was conducted only in five databases, and the search strategy might have overlooked some research, particularly that published in languages other than English. Thirdly, we excluded a substantial number of studies published in languages other than English, which could introduce potential bias. However, considering the narrow range of the 95% CI, the missed studies are unlikely to significantly affect the present estimate. Furthermore, the wider range of the 95% PI (4–100%) is likely to encompass future primary studies reporting the prevalence of Eimeria spp. in goats. Despite these limitations, the authors strongly believe that this systematic review and meta-analysis provide a reliable reflection of the true global prevalence of Eimeria spp. in goats.

This study presents the global prevalence of Eimeria spp. in goats based on data collected from approximately 30% (n = 56) of countries worldwide. The results of the meta-analysis indicate variations in the prevalence of Eimeria spp. in goats globally, with significant heterogeneity observed between studies. Nevertheless, the narrow range of the 95% CI (58.6–67.2%) suggests a precise and reliable estimate of the pooled prevalence of Eimeria spp. in goats (62.9%). This finding indicates that the included studies reported similar prevalences, instilling high confidence in the accuracy of the current estimate. However, the wide 95% PI (4–100%) reflects substantial heterogeneity and underscores the need for further studies utilizing advanced molecular tools to resolve the ongoing controversy regarding the number of Eimeria spp. parasitising goats. Although a limited number of studies have reported the prevalence of and/or characterized Eimeria spp. using molecular data, this technique is known for its sensitivity and accuracy. More sensitive molecular-based approaches, such as next-generation sequencing and genomic analyses based on single oocyst isolation for mixed infections, could offer more precise insights. Our study provides the first meta-analysis of prevalence data on Eimeria spp. globally, thereby serving as a valuable reference for the prevention and control of Eimeria spp. in goats. Considering the high prevalence and the widespread presence of pathogenic Eimeria spp. in goats globally, it is recommended that integrated parasite management approaches be implemented for the effective control of coccidiosis in goats.