Effects of migrating Gasterophilus intestinalis larvae (Diptera: Gasterophilidae) on the mouth of the horse.

This research article investigates how the larvae of the Gasterophilus intestinalis impact horses, particularly in the mouth area. The larvae burrow through the tongue and embed themselves in the gums, causing various tissue and nerve damage, as well as the formation of microabscesses.

Study Procedure and Findings

• The researchers began by observing how the first and second-stage Gasterophilus intestinalis larvae affected the mouths of horses. The larvae formed lesions by burrowing through the top millimeter of the tongue and embedding themselves in the interdental gingiva, which is the part of the gum between the teeth.
• The appearance of the lesions depended on how actively the larvae were burrowing, as well as how the healing process was progressing. Changes in the lesion’s shape and color indicated the presence of active larvae, with active tunneling happening at the posterior end of the lesion.
• The larvae destroyed almost all tissue in their path while forming a tunnel. This destruction included the tops of the lamina propria mucosae evaginations – tiny projections of the mucous membrane – and the deeper portions of the lamina epithelialis mucosae, a layer of the mucous membrane.

Impact on Nerve and Blood Supply

• One key finding in the study was that the tissue destroyed by the larvae included the nerve and blood supply to the proprial evaginations. This led to bleeding and exocytosis, the process through which cells expel waste and toxins, into the tunnels.
• Erythrocytes or red blood cells were also observed in the tunnels, mixed with immune cells such as macrophages and lymphocytes. Eosinophils, a type of white blood cell, were also found but in smaller numbers.
• The tunnels enabled bacteria to enter, adhere to the larvae, and initiate microabscesses, which are small collections of pus. These were composed of erythrocytes, bacteria, disintegrating epithelial cells, and large numbers of neutrophils, another type of white blood cell.

Tissue Damage and Healing

• The cells surrounding the tunnel showed pyknosis – the condensation of the cell’s nucleus, epithelial hydropic degeneration – a form of cellular swelling, and they also became separated from each other.
• However, healing of tongue lesions was observed. The cells pushed the tunnel upwards and the affected tissue was shed off in a process known as desquamation.

Damage to the Gingiva and Periodontal Pockets

• The gingiva invaded by the larvae showed heightened blood flow (hyperemia) and were stripped of their epithelial cells.
• Recession of the gingiva created pockets around the teeth, also known as periodontal pockets. More extensive damage by the larvae led to the formation of compound periodontal pockets.
• Finally, the researchers found that the larvae’s mouth hooks were embedded in the submucosa of these pockets. These hooks tore at engorged capillaries, or blood vessels filled with blood, exacerbating the damage.

No Damage from Attachment at Tongue Root

• The second-stage larvae were seen to attach near the root of the tongue, causing no visible damage there. Despite this, the overall impact of the Gasterophilus intestinalis larvae on the horse’s mouth was substantial and concerning.