The effect of Strongylus vulgaris larvae on equine intestinal myoelectrical activity

Abstract

Summary The myoelectrical activity of the ileum, caecum and large colon was monitored from Ag‐AgCl bipolar recording electrodes in four conscious ‘parasite‐naive’ weanling foals. All foals were inoculated with 1000 infective 3rd‐stage Strongylus vulgaris larvae and alterations to the myoelectrical activity observed. The frequencies of caecal and colonic spike bursts increased significantly in all post infection periods coinciding with assumed larval penetration into the intestinal mucosa and migration through the vasculature. Peaks in caecal and colonic activity occurred at Days 1 to 5 post infection. In the caecum, peaks occurred again at Days 15 and 31 post infection, preceding similar rises in colonic spike burst frequency at Days 19 and 35. Longer term changes indicated a return towards pre‐infection levels of activity suggesting smooth muscle adaptation to decreased blood flow. The analysis of caecal and colonic spike burst propagation indicated that the increases in burst frequency were not attributable to an increase in the propagation of spike bursts in any particular direction, but rather to proportional increases in all directions of activity. There was a slight decrease in the simple ileal spike burst frequency immediately post‐infection. None of the experimental animals exhibited signs of abdominal pain during the trial, and there was no evidence of bowel infarction at post mortem examination despite the presence of severe parasite‐induced arterial lesions. The results suggest that increased caecal and colonic motility is an important host response in susceptible foals exposed to S. vulgaris larvae.

Systematic review of gastrointestinal nematodes of horses from Australia

“…Thrombi (and emboli) within mesenteric arteries can obstruct blood flow resulting in infarction of intestinal walls and colic [48]. Increased colonic and caecal motility have also been observed in S. vulgaris infections in horses [50].…”

Equine gastrointestinal motility research: Where we are and where we need to go

“…As for S. vulgaris, Berry et al (1986) saw a distinct disruption of the ileal MMC following nasogastric instillation of infective larvae. In a different study, increased caecal and colonic spike activity was seen, suggesting an increase in motility (Lester et al 1989). Electrophysiology, therefore, can definitely offer a window into the clinical setting.…”

The role of parasites in equine colic

“…A second phase of pathogenesis takes place from 3 weeks to 4 months post infection (Duncan and Pirie 1975;Lester et al 1989). This is characterised by the development of fourth stage larvae within small arterioles of the intestine and at their predilection site at the origin of the cranial mesenteric artery.…”

“…Two variations on the theme of thromboembolic ischaemia were vulgaris-infected ponies when compared to noninfected controls. The differences reported are complex, but of particular significance are the decrease in ileocaeco-colic motility in chronically infected animals (Bueno et al 1979), disruption of normal electrical complexes and hypermotility associated with larval migration through the intestinal wall (Berry et al 1986;Lester et al 1989). Interestingly, when killed third stage larvae were administered to ponies, the same changes in intestinal physiology were observed (Berry et al 1986).…”