The life cycle, pathogenisis and epidemiology of S. vulgaris in the horse.

This research article discusses the lifecycle, pathogenesis, and epidemiology of the Strongylus vulgaris parasite in horses. The researchers present their findings from several years of study in Glasgow to contribute to the understanding of this parasite, which has been little studied due to the complexities involved in using horses as experimental animals.

Study Background

• The research focused on the parasitic disease Strongylus vulgaris in horses, a topic that has been underresearched due to the challenges and expenses associated with utilizing horses for experimental studies.
• The researchers aimed to present their cumulative findings, gathered over several years, on the lifecycle, pathogenesis, and epidemiology of this parasite in hopes of contributing to the overall understanding of the subject.

Life Cycle of S. Vulgaris

• The researchers noted that there have been an assortment of opinions over the past 40 years on the life cycle of S. vulgaris, leading to a diversity of theories.
• Among the theories discussed were those presented by Olt (1932), Wetzel and Enigk (1938, 1950, 1951), Ershov (1949, 1956), and Farelly (1954), each proposing different migration routes for the S. vulgaris larvae inside the horses’ bodies.

Various Theories on Larvae Migration

• Olt (1932) proposed that the S. vulgaris larvae found in the anterior mesenteric artery and its branches were “off course”, and that normally the larvae would migrate from the gut via the portal system to the liver, and then to the lungs via the circulation. From the lungs, the larvae would be coughed up and swallowed, eventually reaching their final destination within the large intestine.
• Wetzel and Enigk (1938 and 1950, 1951) based on their experimental infections, proposed that fourth stage larvae penetrated the sub-mucous arterioles in the intestine and migrated in the intima of these vessels to the anterior mesenteric site. Here, they developed for two to three months before returning to the intestine via the arteries.
• Ershov (1949) also proposed that S. vulgaris larvae reached the anterior mesenteric site by migrating between the mesentery layers and then penetrating the arterial wall. Later, in 1956, he favoured Enigk’s hypothesis but suggested that larvae migrated in the arterial lumina rather than the intima.
• Farelly’s (1954) theory was that the larvae migrated through the bloodstream to the lungs and left heart, and then moved on via the aorta and intestinal arteries to reach the final destination in the large intestine.