An investigation of the prevalence of equine filariosis in North and Northeast of Iran

Abstract

Worldwide, equines are affected by equine filariosis, an endemic vector-borne disease caused by heterogenous parasitic nematodes. The main objective of this study was to determine the prevalence of filarial infection among horses in the North and Northeast of Iran. Between October 2021 and July 2022, 145 equine blood samples were investigated, of which 49 cases were from the northeast and 96 were from the north of Iran. Blood samples were taken for microfilariae using Knott's method. Out of 145 blood samples, only 2 cases (1.37%) from northern Iran were positive for microfilaria of Setaria equina, and no positive samples were found from northeast Iran. The first positive sample was a 3-year-old male Iranian horse displaying clinical symptoms of weakness, while the second, an 8-month-old Arabian breed colt, exhibited no clinical signs. According to the results of the current study, the prevalence of equine filariosis is low, contrary to nearby countries. To prevent and control filarial infections among horses and improve their management system, it is therefore important to emphasize filarial infection prevention, control, and management.

Graphical abstract

Introduction

A neglected vector-borne disease known as equine filariasis affects equines worldwide (Khamesipour et al. 2021). This disease is caused by nematodes from Onchocercidae and Setariidae (Nabie et al. 2017; Perumal et al. 2016). Blood or skin residence microfilariae are produced by adult nematodes in the body cavities and tissues (Cambra-Pellejà et al. 2020). During larva development, blood-feeding arthropods ingest the larvae and go through two stages before being transported to a new host (Mäser 2022). Among the many filarioid species identified as contaminating equids, the most prevalent belong to the genera Setaria spp., Dirofilaria spp., and Onchocerca spp. (Bouchery et al. 2013). Several problems can be caused by these parasites, ranging from peritonitis and fibrinous myocarditis to tendinitis when they enter the muscles and ligaments (El Namaky et al. 2019). There have been many cases in which a parasitic infection has been responsible for noticeably limited movement and lameness (Peng et al. 2019; Radwan et al. 2016). Microfilaria may also cause neurological disorders and blindness due to its unusual migration in the central nervous system and the eye (Ratnu et al. 2021; Yu et al. 2021). Furthermore, since filaria is deep inside the tissues and body cavities, as well as their microfilariae being distributed heterogeneously, they must be treated aggressively, which entails surgical removal of the parasite or skin biopsies, which pose a major obstacle to the routine diagnosis of these infections (Bhalla et al. 2013; Grácio et al. 2015; Hassona et al. 2015). As a result of this lack of knowledge of their biology and epidemiology, managing and controlling them is very challenging. In Iran, equids play an important role in abundant parts, including police facilities, agriculture, tourism, transportation, pharmaceutical parts, and recreational activities (i.e., gaming, sport, and entertainment) (Ghadiri Ma'soum et al. 2020). Accordingly, understanding the influence of nematodes on horses must be recognized as a dynamic portion of Iran’s culture and economy. Studies reported Setaria equina, Parafilaria multipapillosa, Onchocerca reticulata, and Onchocerca cervicalis infections from several Iranian provinces (Sazmand et al. 2020). Therefore, this study aimed to have an update on the prevalence of equine filarial and their impact on the host performance of horses from the North and Northeast of Iran.

Methods and materials

Ethical approval

The study procedure has been approved by the ethical committee of the Animal Welfare Committee at the Ferdowsi University of Mashhad (ID: IR.UM.REC.1400.12656860).

Study area

Two different climatic areas in Iran were studied between October 2021 and July 2022. Firstly, Mashhad, the capital city of Khorasan Razavi in northeast Iran, was chosen as the first region to be selected. As an important city in the Iranian economy, Mashhad lies northeast of the country where 36 208° north latitude meets 59 358° east longitude. The city of Mashhad is located 995 m above sea level. It has a cold climate, covers an area of 328 km², and lies in an alternative altitude range of 995 m. It is important to note that Mashhad has a semi-arid climate with hot summers and cold winters. The average amount of precipitation in the city is approximately 250 mm per year, with a few occasionally falling in the form of snow.

Babol, the second region, is located between the northern slopes of the Alborz Mountains and the southern Caspian Sea. It is considered one of Iran's most important cities in the north. The city lies on the west bank of the Babolrud River, approximately 20 km south of the Caspian Sea, and receives abundant rain every year. The climate in Babol is humid subtropical, resembling that in the Mediterranean (Fig. 1).

Fig. 1.

Represents the geographical locations of the sampling, which were conducted in two areas, the Northern and Northeastern regions

Blood samples analysis

Based on previous studies, a total of 145 horses were enrolled in the current study, including 49 from the northeast and 96 from the north of Iran, were randomly allocated to the survey (Faghihzadeh Gorji et al. 2023; Gorji et al. 2023). EDTA blood samples were collected from the jugular vein of horses. The collected blood samples were stored at − 20 °C until examination. Knott’s test using 2% formalin was used to quantify the level of microfilaremia in horse blood fillers (Nehra et al. 2023). One cc of blood was mixed with 9 cc of 2% formalin (freshly prepared) and placed in a centrifuge at 2000 rpm for 2 min, and then the supernatant was discarded. A drop of methylene blue was added to the sediment at the bottom of the tube, then placed on a slide and examined under a microscope with a 10 and 40 lens.

Results

Out of 145 blood samples, only 2 cases (1.37%) from northern Iran were investigated and tested positive for microfilaria of S. equina, and no positive samples were found from northeast Iran. Among the positive samples, the first came from a 3-year-old male Iranian breed horse with clinical signs of weakness. In this case, S. equina measured 289.87 μm in diameter, which is considered a large size for this equine. In the second positive sample, which was from an eight-month-old Arabian colt, there were no specific clinical signs or symptoms apparent in this young colt. S. equina measured 272.14 μm in diameter in this case (Fig. 2).

Fig. 2.

Two positive samples were observed (Methylene blue × 40)

Discussion

Equine filariosis, which triggers a decrease in the working capacity of equids, is a neglected vector-borne disease (Utzinger et al. 2010). Subsequently, in endemic areas, economic losses and health risks are the principal observed complications (Ghasemi et al. 2020). Hence, their accurate detection of equine filariosis and a better understanding of disease epidemiology should be overlooked for disease control and management (Abo-Aziza et al. 2022).

The current study offers new insight into the prevalence of equine filariasis in North and Northeast Iran. Equine filariasis prevalence in horses in the present study was 1.37%, and only one distinct filaroid species, S. equina, was found in equines. These cases highlight the diversity in symptom presentation within equine populations. The first sample, an adult Iranian breed horse, demonstrated typical clinical signs associated with S. equina infection, such as weakness. The observed size of S. equina in this horse was 289.87 μm, which can provide insights into the severity of the infection. Conversely, the second sample, a young Arabian colt, appeared asymptomatic. This raises questions about the potential variability in the clinical manifestations of S. equina across different age groups and breeds of horses. It could suggest that some horses may carry the parasite without showing obvious signs of infection, which has implications for disease monitoring and control.

The filarial disease setariosis, caused by different species of Setaria spp., can affect all bovines. Still, it can also infect unusual hosts such as sheep, goats, donkeys, horses, and camels by accident (Abdullah et al. 2013). Equids are infected by the S. equina, which lives inside their abdominal cavity for free. There are usually no pathogenic consequences associated with equine setariosis. However, they may cause pathogenic effects when found in unusual habitats such as the spinal medulla, brain, eyes, and testicles of horses (Fuehrer et al. 2020; Kingsley et al. 2022; Lee et al. 2021).

In Iran, S. equine microfilariae were found in peripheral blood (Enami 2009), and adults were isolated from the abdominal cavities of donkeys and horses (Hosseini et al. 2009), as well as the cecum and colons of horses. The subconjunctival setariosis due to S. equina has also been reported to have occurred in a 15-year-old girl in Tabriz, a city located in the northwest of the country, who has been diagnosed with this disease (Otranto and Traversa 2005). Furthermore, a 32.1% infection rate was reported in Urmia, which is different from the current study, which may be due to the presence of intermediate hosts (Enami 2009).

A recent study in Hungary reported 9.2% contamination of Setaria spp. (Hornok et al. 2007). In 2003, 4% of S. equina contamination was reported in Turkey. In Baghdad, Iraq, S. equina pollution was declared to be 11.11% (Hadi and Atiyah 2014). In 1997, 2.2% of S. equina infections were reported in Greece (Sotiraki et al. 1997). In 2007, 2.2% of S. equina contamination was announced in Saudi Arabia. Knott's method has been used in all these studies to identify microfilaria.

Conclusion

According to the results of the current study, the prevalence of equine filariosis is low, contrary to nearby countries. There is a need for more research on the biology and transmission mechanisms of these nematodes to advance our understanding of filarial infection in equids in Iran. To prevent and control filarial infections among horses and improve their management system, it is therefore important to emphasize filarial infection prevention, control, and management.

Author contribution

Conceptualization: [HB], …; Methodology: [All Authors], …; Formal analysis and investigation: [All Authors], …; Writing—original draft preparation: [SS]; Writing—review and editing: [HB], …; Funding acquisition: [Ferdowsi University of Mashhad], …; Supervision: [HB]. All authors checked and approved the final version of the manuscript for publication in the present journal.

Funding

Ferdowsi University of Mashhad.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Conflict of interest

The authors declare no conflict of interest.

Ethical approval

All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. (ID: IR.UM.REC.1400.12656860).

Consent to participate

Not applicable.

Consent for publication

Not applicable.