In many developing economies, including Egypt, they rely more heavily on working equines including horses, donkeys, and mules in rural areas. Regardless of the fact that these equines play significant role in sustaining the daily lives of people by providing support in industries such as agriculture, construction, tourism, and public transportation. However, the health and welfare of domesticated equines is frequently overlooked [1].
Gastrointestinal nematodes (GINs) are one of the parasite groups that cause a variety of clinical and economical health problems among equines [2]. Infection with GINs commonly produces broad-based clinical signs. For instance; anorexia, reduced feed intake, and diarrhea [3, 4] elicit a diminished weight gain and degradation of traction power. Gastrointestinal nematodes infecting equines include; (A) strongylid nematodes, which make up about 75% of the total parasite population infecting equines [5, 6], and (B) Non-strongylid nematodes which include Parascaris equorum, Habronema spp., Draschia megastoma, Oxyuris equi, Trichostrongylus axei and Strongyloides westeri [5].
Strongylid nematodes (Family: Strongylidae) are classified into two sub-families; (A) Large Strongyles or Strongylins (Subfamily: Strongylinae) which are characterized by having a globular buccal capsule, and (B) Small Strongyles or Cyathostomes (Subfamily: Cyathostominae) which characterized by having a cylindrical buccal capsule [3,4,5, 7,8,9].
The key difference between large and small strongyles is the existence of extraintestinal migration in the case of large strongyles where L3 of Strongylus vulgaris migrates from GIT toward anterior mesenteric artery, L3 of Strongylus edentatus migrates toward liver and peritoneum, and L3 of S. equinus migrate toward pancreas and liver [3, 4]. Migratory stages of large strongyles contribute to serious health hazards for equines where larvae of S. vulgaris set up fatal thrombi that can block major arteries (i.e., cranial mesenteric artery) causing gangrenous enteritis, intestinal stasis, and colic. Thrombi may also detach and block other arteries (i.e., iliac artery) resulting in lameness. Larvae of S. equinus create hemorrhagic tracts in the liver and pancreas, while larvae of S. edentatus produce hemorrhagic nodules in the peritoneum’s wall, caecum, and colon [3].
Although L3 of small strongyles don’t migrate outside the alimentary tract, they encyst inside the mucosal lining of the cecum and colon where they continue their development then released into the lumen of the cecum and colon giving rise to mature stages [3, 9, 10]. Massive emergence of larval stages of small strongyles from mucosal cysts into the lumen of cecum and colon especially in warm weather (late winter to early spring) triggers a clinical case called “Cyathostominosis” where infected animal suffers from emaciation, colic, diarrhea, subcutaneous edema, pyrexia, and fatality in uncontrolled cases [5, 9, 10].
Strongyloides westeri (Family: Strongyloididae) is a common parasite with a direct life cycle where adult worms inhabiting the small intestine of young equines (up to 4 months of age) who get infected either during suckling or through percutaneous invasion that’s followed by pulmonary migration. Pathological lesions due to S. westeri infestation like enteritis characterized by erosions, catarrhal lesions, and mucosal edema are only executed by female worms of S. westeri that are mirrored clinically by impaired digestion, malabsorption, and diarrhea [5].
Trichostrongylus axei (Family: Trichostrongylidae) is a parasite inhabiting the fundus area of the equine stomach [11]. Infective larvae after being ingested by equines will develop in the lumen of mucosal crypts or deeply in the gastric mucosa. Light infection is usually less pathogenic while heavy infection frequently produces a hyperplastic reaction in glandular tissue of the fundus with the formation of raised plaques that ranged from a half-centimeter to several centimeters which later will erode in their centers [11, 12].
Diagnosis of GINs normally relies on discussing the health status of the animal in former times, clinical signs, and microscopical examination of fecal samples [3]. Although microscopical examination of fecal samples has the advantage of being cheap and requires neither expensive reagents nor equipment [13], it is hard to differentiate GINs to species level. Therefore, as a rule, the microscopical examination comes along with fecal culture to identify GINs to species level based on morphological features of infective 3rd larval stages [3].
In Egypt, there is a paucity of data discussing morphometric characters of 3rd larval stages of GINs infecting equine. Therefore, the present work aims to identify and differentiate L3 of common strongylid and non-strongylid nematodes to species level based on their morphometric features.