Prevalence of endo‐ and ecto‐parasites of equines in Iran: A systematic review

Abstract Equines are subject to infection with many parasites, which threaten their health. In the present study, we systematically reviewed existing literature on the prevalence of endo‐ and ectoparasites of equines in Iran. Major electronic databases, including PubMed, PubMed Central, Google Scholar, Science Direct and Scientific Information Database (SID), were searched (Last updated 11/05/2018) for relevant literature of parasites that have been identified from equines in Iran. Of the 1809 titles produced by bibliographic search, 38 were included in the review. Twenty‐seven of the studies were on horses, six on donkeys, three on both horses and donkeys, and one study was on both horses and mules. Furthermore, 24 of the studies reported infections caused by protozoa, thirteen by helminths, two by ectoparasites, and one by both protozoa and helminths. The overall pooled prevalence of parasitic infection was 28.8% (95%CI: 22.9–35.7, I 2 = 93.4%). Helminths were the most prevalent parasites 46.7% (95% CI: 24.1–70.7, I 2 = 96.0%). Furthermore, donkeys were the most affected equine, with a prevalence of 70.7% (95% CI: 53.2–83.7, I 2 = 92.5%). The protozoa frequently reported included nine species belonging to the genera: Neospora, Toxoplasma, Theileria, Babesia and Eimeria. Also, the helminths frequently reported included 21 species belonging to the genera: Strongylus, Dicrocoelium, Oxyuris, Habronema, Echinococcus, Dictyocaulus, Cyathostomum, Probstmayria, Anoplocephala, Setaria and Fasciola. Ticks were the only ectoparasites frequently reported. Parasitic fly species of the genera Gasterophilus were also reported. The study‐level risk of bias was likely to be high because of differences in study design. Parasitic infections of equines in Iran are frequent and caused by a diversity of parasites, which threatens the health and well‐being of these animals. Further research is needed in the area to identify the risk factors of infection for effective control of the parasites.

More than 90% of the estimated 44 million donkeys in the world are in developing countries (Matthee, Krecek, & Milne, 2000). In developing countries, equines contribute greatly to the development of the agricultural economy, being used as a means of transportation due to economic and/or topographical constraints (Ali & Yagoob, 2015;Pritchard, Lindberg, Main, & Whay, 2005), and also are used in recreational activities such as sport, gaming and entertainment.
The consequences of parasitic infection in equine may range from diarrhea, anemia, fever, colic, weight loss, weak growth, emaciation, impaired growth, increased susceptibility to other infectious diseases and sudden death (Arfaei et al., 2013;Taylor, Coop, & Wall, 2007).
In Iran, there are over two million equids, of which about 75% are donkeys (Hosseini et al., 2009). Like in other parts of the world, equines contribute to the agricultural economy of Iran and are a valuable means of transportation in some areas of the country.
Parasites are also a menace to the health and welfare of equines, but a systematic review of the parasite status of equine in Iran is not readily available. The objective of the present study was to systematically review the existing literature on the prevalence and aetiology of parasitic diseases affecting equines in Iran to inform control policies.

| MATERIAL S AND ME THODS
A literature review was carried out between 1st of April and 11th of May 2018, to identify scientific articles reporting parasitic infections of equines in Iran. The current study conforms to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines (Moher et al. 2009) (File S1).

| Search strategy and selection criteria
Relevant studies were searched in electronic databases, including PubMed, PubMed Central, Google Scholar, ScienceDirect and Scientific Information Database (SID) using the keywords: Parasites OR Infection OR Equine OR Horse OR Donkey OR Mule OR Iran.
No time limits were defined, and articles reporting parasitic infections of equine irrespective of the methods used for identification (i.e. serology, coprology or molecular methods) were selected.
Subsequently, the titles and abstracts of the selected articles were examined by two reviewers independently (parallel method), to identify articles reporting parasitic infections in equines in Iran. Where there was any discrepancy in their report, a third reviewer was brought in to resolve it. Relevant papers were also manually crosschecked to identify further references. In the articles selected, the following data were extracted by one reviewer and crosschecked by a second: Type of parasitic infection, the prevalence of infection, species of parasites identified and their frequencies, host type involved (horses, donkeys, mules, etc.), the geographical location of study, association with host factors (age, sex or season) and the method used to identify the parasite. Articles were excluded when they did not report any parasite species. The selection process is detailed in Figure 1.

| Statistical analysis
Pooled prevalence was determined using Comprehensive Meta-Analysis V3.3.070 software (Biostat, USA). Data were pooled using a Fixed and random-effect model. The heterogeneity between these studies was assessed with the I 2 test. An I 2 value of >50% indicated substantial heterogeneity. For the pooling of the results, a more conservative random-effect model was used as heterogeneity was substantial.

| RE SULTS
The

TA B L E 1 (Continued)
PubMed, 1213 on Google Scholar, 30 on ScienceDirect and 172 on SID), 1699 of which were discarded as they were found to be duplicated using a reference manager software (EndNoteTM) and confirmed manually (Figure 1). During the review of the remaining 110 works, 70 abstracts were discarded because they did not contain information on the parasites detected. The remaining 40 studies were analysed, rejecting two articles that were not written in English and did not contain an abstract in English (Figure 1).
A total of 38 articles were selected, all written in English. in the western region of the country (Figure 2). Generally, the helminth parasite species reported were very diverse compared to protozoa parasites (21 species versus nine species). known to be acquired passively (i.e., through the ingestion of infective larvae on pasture). However, in some species, larvae burrow through the skin or are transmitted by invertebrate intermediate hosts (Anderson, 2000).  (Abedi, Razmi, Seifi, & Naghibi, 2015;Arfaei et al., 2013;Davoodi, Rauli, & Jafari, 2010;Habibi et al., 2016;Hassanpour & Nematollahi, 2014;Malekifard, Tavassoli, Yakhchali, & Darvishzadeh, 2014;Sakha, 2007). Control of ticks and tick-borne diseases of equine is therefore vital for the protection of the health of the animals and an increase in their productivity in the area.

Control of parasites of animals is equally important in protecting
human health as some of these parasites are zoonotic. At least one of the studies reviewed showed a higher rate of Cryptosporidium infection in persons who were in contact with infected animals (Naghibi & Vahedi, 2002). Another study in France reports of three cases of acquired toxoplasmosis in humans caused by the consumption of raw horse meat (Pomares et al., 2011). Although this does not fit in the traditional classification of parasites (as either ectoparasite or endoparasite), the larvae of parasitic flies, Gasterophilus intestinalis, G. nasalis, G. inermis, have also been reported to cause serious health problems to equines in Iran (Davari et al., 2017;Hosseini et al., 2009;Tavassoli & Bakht, 2012).
The parasitic infections frequently reported from this review included neosporosis, equine piroplasmosis, and strongylosis.
Neosporosis is caused by Neospora caninum, an Apicomplexan protozoan parasite with a worldwide distribution .
The parasites can infect a wide range of animal species, including cattle, sheep, goats, horses, dogs, and cats, and have been associated with abortion, protozoal myeloencephalitis, and neuromuscular disorder signs in equine (Finno, Aleman, & Pusterla, 2007). Equine piroplasmosis is a haemolytic disease caused by two intra-erythrocytic hemo-protozoan, Theileria equi and Babesia caballi (Mahmoud et al., 2016). The disease is characterized by fever, anaemia, red urine, jaundice, oedema, weight loss and even death in equine (Mahmoud et al., 2016). On the other hand, strongylosis is caused by several nematodes, often referred to as the small and large strongyles (Tavassoli, Yamchi, & Hajipour, 2016). They are frequently responsible not only for poor health, but also for gastrointestinal dysfunction, including colic, and infection with some such as acute larval cyathostomosis may be fatal (Love, Murphy, & Mellor, 1999).
Reports of vector-borne parasitic diseases such as filariosis (Lia et al., 2017;Radwan, Ahmed, Elakabawy, Ramadan, & Elmadawy, 2016) and trypanosomosis (Luckins, 1994), known to cause major problems in equines worldwide, have not been reported in Iran. The only filarial species that has been reported in equines in Iran are Setaria equina (Hosseini et al., 2009) and Parafilaria multipapillosa (Maloufi 1995). The under-reporting of filarial parasites in equines in the country may be due to individual study level biases in the design of the different studies, pertaining to the methods used to detect the presence of parasites; serology was used to detect exposure to most of the protozoa parasites meanwhile concentration techniques, culture and molecular methods were not used in all the studies, constituting a major limitation to the study. At least one study has reported a higher detection rate of parasitic infection using molecular methods compared with serological and standard parasitological techniques (Habibi et al., 2016;Mahmoud et al., 2016). The differences in the diagnostic methods may also explain the variability in the observed prevalence of the parasitic infections from one area to another.
This study demonstrates heterogeneity in the distribution of parasitic infection in Iran. The pooled prevalence of protozoa infection was highest in the western region meanwhile, the prevalence of helminth infection was highest in the northwestern region. The discrepancy in the prevalence of parasitic infection in the different areas of Iran could also be attributed to the inter-regional differences in the endemicity of the parasites. Climatic and cultural differences may also be a contributing factor to these inter-regional differences.
As evident from this review, no study has been conducted to determine risk factors for parasitic infections of equines in Iran, which therefore presents a major challenge for the successful implementation of control strategies in the area. There is, therefore, a need for more empirical research to establish risk factors associated with parasitic infections to develop appropriate control strategies for parasites in equines in Iran.

Control of parasitic infections of equines and other livestock
can be achieved using chemical and biological control methods (Kwenti, 2017). Many biological products are available in the markets that have a proven track record to effectively reduce parasite infections in livestock, including the nematopathogenic fungi (Duddingtonia flagrans) (Kwenti, 2017), which make a more suitable alternative to the chemical methods. For example, feeding or field trials in sheep have shown that dosing with a few hundred thousand spores per kilogram of live birth weight of D. flagrans not only reduced the number of infective larvae but also increased the birth weight of lambs compared with controls (Larsen, 2006 (Mcallister, 2014;Sharma, Singh, & Shyma, 2015). Vaccines might present a cheaper and more effective alternative to control parasite infection, thereby improving animal production. However, more research is required to develop and evaluate more effective vaccines against parasites.
In conclusion, our work revealed that parasite infections and infestations of equines in Iran are frequent and caused by a diversity of parasites (ectoparasites, protozoa, helminths and parasitic flies), which threatens the health and welfare of the animals. Further research is needed in the area to identify the risk factors of infection for effective control of the parasites.

CO N FLI C T O F I NTE R E S T
The authors declare that they have no competing interests.

AUTH O R S' CO NTR I B UTI O N S
All authors have read and approved the final version of the paper.

DATA AVA I L A B I L I T Y S TAT E M E N T
The original research articles included in this systematic review are publicly available.

PE E R R E V I E W
The peer review history for this article is available at https://publons.