An Overview of Gastrointestinal Nematodes of Equines in Ethiopia

Girma W, Terfa W and Negasa T

Published on: 2024-04-20

Abstract

Nematodes are recognized to affect the health of humans and animals worldwide. Gastrointestinal nematode infections in equines can cause a variety of intestinal, respiratory, and other issues that have a direct impact on the health and productivity of working animals. Equines, which include horses, donkeys, and mules, act as a mode of transportation for the public and materials and offer a living for many rural and semi-urban inhabitants around the world. They play an important role in the agricultural systems of many developing countries. Donkeys may play an important role in the frameworks of food security and social fairness in secure countries. In locations without roads, many people rely on mules and donkeys to bring food and supplies to villages. Although equines provide significant contributions to the national economy, parasitic helminths are one of the most prominent reasons that impede. Equines as a means of transport for men and materials provide livelihood to a number of rural and semi-urban populations in the world. They have a prominent position in the agricultural systems of many developing countries. In areas away from roads, many people use mules and donkeys to transport food and other supplies to villages. Although equines have great contributions to the national economy of the country, parasitic helminths are one of the most common factors that hinder the maximum utilization of these animals to their potential.

Keywords

Equines; Ethiopia; Gastrointestinal helminths

Introduction

The equine population of the world is 122.4 million (40 million donkeys, 15 million mules, 43.3 million horses, 24.1 million zebras, and camels) [1]. The number of equines in Africa is in the range of 38.9 million, comprising 30.6 million donkeys, 0.9 million mules, and 7.4 million horses [2]. Ethiopia retains a total of 21.43 million equines, 10.80, 2.15, 0.38, and 8.1 million donkeys, horses, mules, and camels, respectively [3]. Horses, donkeys, mules, zebras, and camels belong to the equine group. They are found mainly in temperate, semi-arid, or highland areas. Horses and donkeys are herd animals and will happily live in groups with other donkeys or animals of a different species, such as sheep and goats. Donkeys and horses are very friendly animals and enjoy the company of humans. They are easily trained and are suitable for handling by children, especially donkeys [4].

Equids (donkeys, mules, and horses) are important working animals in many parts of the world, including Ethiopia and India, and are used for packing, riding, carting, and plowing. Equine power is essential for both rural and urban transportation systems, as it is inexpensive and provides the best alternatives in areas where the road network is inadequately developed [5]. Donkeys deliver items between the farmhouse, fields, and markets. In distant rural areas of the country where modern transportation is unavailable, donkeys play a critical role in enabling agricultural product marketing. They have reduced the domestic transportation burden on rural residents, particularly women, who play an important role in the economy of the country [6].

The helminths, which include cestodes, nematodes, and trematodes, are important causes of morbidity as well as mortality in humans and animals worldwide [7]. The prevalence and type of internal parasites afflicting equines in general are common, with continuous exposure throughout their lives. Although they are frequently heavily parasitized by helminths, the prevalence and kind of internal parasites affecting equids in Ethiopia have not been well documented [8]. Thus, the objectives of this paper are,

To review available documents on the prevalence and risk factors of gastrointestinal nematodes of equine in some parts.
To show the gap in studies and forward the appropriate recommendations.

General Aspects of Gastrointestinal Nematodes in Horses

In Ethiopia, gastro-intestinal (GI) parasite infection is one of the most important health problems for equines, contributing to poor body condition, reduced power output, poor reproductive performance, and a short lifespan. The major GI parasites of equines are large and small strongyles, ascarids, pinworms, and stomach worms. Strongyles are among the most frequently encountered and highly pathogenic helminths of Equidae, responsible for death when control measures are neglected [9]. Gastrointestinal parasites are one of the greatest limiting factors to successful horse raising throughout the world. They are a worldwide problem for both small and large-scale farmers, with the greatest impact in sub-Saharan Africa due to the availability of a wide range of agro-ecological factors suitable for diversified hosts and parasitic species [10].

Etiology

Strongyles are classified under the kingdom of animalia, phylum Nemathelminthes, class Nematoda, order Strongylida, superfamily Strongyloidae, family Strongylidae, and subfamily Strongylinae. The sex of large strongyles is separating, that is, female and male. Females are oviparous, and eggs are of the strongyle type. They are reproduced sexually, and they do not have a circulatory system (no blood vessels) or respiratory system [11]. Species with globular or funnel-shaped buccal capsules are known as large strongyles or strongylins (subfamily Strongylinae), while species with cylindrical or ring-shaped buccal capsules are called small strongyles, cyathostomines, cyathostomins, or cyathostomes (subfamily Cyathostominae).

Oxyuris equi (the equine pinworm) is classified in the superfamily Oxyuroidea. It has a global distribution and is found on every continent where horses and donkeys are raised. Pinworm infections are reported to be far more common in weanlings, yearlings, and young adults compared to mature or geriatric horses [12]. Parascaris equorem contains two species, Parascaris equorum and Parascaris univalens, which are morphologically identical but can be distinguished by karyotyping, as P. equorum has 2 pairs of chromosomes and P. univalens has 1 pair. Recent studies from North America and Europe have shown that P. univalens is the dominant species infecting horses.

Life Cycle

The majority of GIT nematodes have similar life cycles. The majority of them are oviparous, and their eggs are identical and distinct; thus, infection does not spread quickly from one host to another. The nematode's life cycle can be both direct and indirect. The sexes are typically segregated. However, all commercially relevant horse gastrointestinal parasites have direct life cycles with no intermediate hosts. Strongylid gastrointestinal nematodes have a direct life cycle, with adults found in the caecum and colon of horses. Adult females lay eggs, which are shed in their feces and hatch into first-stage larvae (L1) in the environment at optimal temperature and humidity. After two moults, larvae develop into infectious third-stage larvae [13].

Adult female strongyloides reproduce by parthenogenesis, which means that the females create viable eggs without the need for insemination. Male parasites are therefore not required and are not found in the host. The eggs enter free-living stages after becoming embryonated and emerging from the host's excrement. L1 larvae have an anterior-thick area and a posterior bulb on their rhabditiform esophagus, which they develop into L2 larvae after hatching and molting. After that, the L2 molts into the FL L3, which has a long, filariform esophagus devoid of a posterior bulb. Equines can absorb FL-L3 through their skin or mouth [14].

The life cycle of Parascaris equorum is direct, with eggs being released into the environment together with excrement. According to Paula et al. (2016), eggs are spherical, have roughened shells, and have a sticky surface that makes them stick firmly to other eggs and things in their surroundings. The ideal environment, with temperatures between 25°C and 35°C, allows the infectious third-stage larvae to develop in ten days. The L3 stage has a five-to-ten-year lifespan in its natural habitat. After consuming L3, the larvae travel to the liver and lungs and populate the host's gastrointestinal tract, mostly the small intestine (Hildreth and McKenzie, 2020). Adult O. equi normally lives in the lower part of the colon, near the rectum. The adults stay close to the anus, and it happens that female worms are found hanging out from the anus. Only after a few days will they develop into L3. Eggs stick to the surroundings when the horse rubs its tail. After ingestion of the eggs, L3 is released in the small intestine, where it matures to L4 in the mucosa of the cecum and colon [15].

Epidemiology

Strongylosis is a widespread illness that kills horses and donkeys when preventative measures are not followed. It is found all over the world. Egg deposition peaks in the spring and stays high throughout the summer in regions with cold winters and moderate summers. The temperatures are appropriate for the development of larvae at this time of year, and when young, susceptible donkeys are around in late summer and early fall, large numbers of infectious larvae may hatch (Saeed et al., 2019).

The great persistence of the infectious stage in the environment and the prevalence of infection in young horses are the epidemiologies of parascarosis [16]. Due to the prolific egg-laying nature of female worms, infected foals may excrete millions of eggs per day. Since fertilized eggs can withstand freezing and drying for up to ten years, a single infection may have an impact on the health of multiple foal generations in the future. Hypobiosis, or halted larval development, is a highly significant phenomenon in epidemiology because it permits nematodes to survive difficult times and because the environment becomes more contaminated when these larvae mature [17].

Pathogenesis

The disease processes associated with Strongylus can be divided into those produced by migrating larvae, those provoked by the mass emergency of mucosal larvae, and these associated adult worms. Heavy intestinal infections can alter intestinal motility, intestinal permeability, and carbohydrate absorption [18]. The larvae of S. vulgaris are the most pathogenic, causing arthritis, thrombosis, and thickening of the wall of the cranial mesenteric artery. Emboli may break away and lodge in smaller blood vessels, leading to partial or complete ischemia in part of the intestine, thus producing colic. The result of this depends on the length of the segment of the intestine affected and the ability of the collateral blood supply to become established before necrosis and gangrene occur [15].

Parascaris equorum larval migration through the liver results in hemorrhage and fibrosis appearing as white spots under the capsule. In cases of heavy infection, diffuse fibrosis may occur. The most serious damage occurs in the lungs, where the larvae provoke alveolar injury with edema and consolidation. This damage can exacerbate preexisting lung infections or provide a portal of entry into the body for pyogenic organisms [18].

Severe infection with 3rd to 4th stage Oxyuris equi may produce significant inflammation of the ceacal and colonic mucosa, manifested by vague abdominal signs. The most important effects of O. equi are the perineal irritation and anal pruritis caused by the adult females during egg-laying. The resultant dull hair coat and loss of hair are known as rattails [19].

Diagnosis

The infection with Strongylus spp. is predicated on the presence of eggs in the feces. The majority of oval, thin-shelled eggs laid by Strongylus spp. are seen during standing fecal flotation [20]. The diagnosis of Parascaris equorum is based on clinical manifestations and the detection of rough-shelled, round, thick, brownish eggs during fecal testing. Occasionally, unusual eggs with thick walls and no black outer shell are observed [21]. Ascarid eggs are smooth-surfaced, brown, and have thick walls. These 90–100-millimeter eggs have one or two cells in their cores, and they are easily recoverable using a typical fecal flotation method. At postmortem, migratory larvae are too small to be seen with the neck eye [20].

Treatment

Treatment can target immature and adult large strong worms in the gut lumen, migratory Strongylus spp. larvae, particularly S. vulgaris, and Cyathostomins larvae in the intestinal mucosa. Standard anthelmintic dosages, including ivermectin and moxidectin, are effective against the larval stages of infection (L4 and L5). Anthelmintics, such as bezimidazoles, pyrantel, and ivermectin are effective against adult large Strongylus spp. Oxyuris equi is sensitive to a variety of broad-spectrum anthelmintics and should be treated with regular chemotherapy for the most problematic horse parasites. Treatment consists of applying a moderate disinfectant ointment to the perianal region and administering ivermectin, moxidectin, any of the newer broad-spectrum benzimidazoles, or pyrantel at the normal dose [22].

Control and Prevention

Pasture management can help control nematode infections in equines. The animal must be evacuated from diseased ground, placed on dry grass, and provided with clean drinking water. Draining and resting pasture during the dry summer kills many larvae that can survive harsh winters. Their feces should not be used to fertilize sites where green feeding crops are cultivated, damp grasses should not be fed to animals, and adults should not graze alongside young stock [13]. Therapeutic usage of medicinal plants as an alternative to synthetic medications for treating gastrointestinal nematodes in equines might be envisioned through a targeted feeding regimen during peak seasonal incidence or as part of daily feed supplements or additives [23].

Treatment can be directed at immature and adult large strong worms in the gut lumen, migratory Stronglylus spp. larvae, notably S. vulgaris, or Cyathostomins larvae in the intestine mucosa. Standard dosages of anthelmintics, ivermectin, and moxidectin are effective against the larval stages of infection (L4 and L5). A variety of anthelmintics, including benzimidazoles, pyrantel, and ivermectin, are effective against adult big Strongyle spp. [22]. Oxyuris equi is susceptible to numerous broad-spectrum anthelmintics and should be managed with routine chemotherapy for the most serious horse parasites. Treatment consists of using a moderate disinfectant ointment to the perianal region and administering ivermectin, moxidectin, or any of the newer broad-spectrum benzimidazoles or pyrantel at the standard dose rate for horse piperazine salts, which are also effective [24-27].

Conclusion and Recommendation

Gastrointestinal parasites are one of the most common causes of equine health and performance issues. Strongylus spp., Parascaris equorum, Oxyuris equi, Dictycolous arnifieldi, Fasciola, Strongyloides, and Anoplocephala spp. were the most common internal parasites found in equines. Strongyles are among the most common and extremely harmful helminths in Equidae, causing death when management measures are not implemented. They are a global issue affecting both small and large-scale farmers, having the greatest impact in Sub-Saharan Africa. To minimize the associated repercussions on the economy and production of equines, a regular and strategic deworming program with effective anthelminthics and improved husbandry practice systems should be indicated. Based on the above conclusions, the following recommendations are forwarded:

Control the burden of parasites by sufficient feed supply and minimizing extensive open grazing area.
Further research is required for the identification of each gastrointestinal nematode in equines.
Improved housing and feeding management systems should be implemented to decrease the incidence of parasites in equines.
The government should formulate and implement policies regarding management and health aspect of equines.

Acknowledgments

The authors wish to thank Prof. R.K. Narayan for going through the manuscript for computer help. This paper is dedicated to the Scientists who made outstanding contributions in the field of gastrointestinal nematodes in equines.

Author’s Contributions

All authors have made substantial, direct, and intellectual contributions to the work.

Conflict of Interest

The authors declare that they have no conflict of interest.

Financial Support

No financial support received from any organization.

International Journal of Veterinary Science and Medical Diagnosis