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THE guttural pouches (diverticulae of the eustachian tubes) are enigmatic structures in horses whose function remains unclear. Among their proposed functions are: cooling of the blood flowing through the internal carotid artery and thus cooling of the brain; equalising air pressures across the tympanic membrane; and acting as a resonating chamber for vocalisation (Freeman and Hardy 2012). Regardless of their function, guttural pouches contain many vital nerves and blood vessels lying superficially beneath their mucosa that are susceptible to injury in the presence of guttural pouch infections.
Guttural pouches can suffer from a variety of microbial infections and in particular are a predilection site for Streptococcus equi (var equi), ie, strangles, infection. Because the guttural pouch mucosa is part of the common upper airway mucosal system, it can also be affected by all respiratory viral infections and thus guttural pouch mucosal inflammation occurs with all such infections.
The guttural pouch mucosa is also occasionally prone to mycotic infection, including Aspergillus fumigatus, Aspergillus niidulans and Aspergillus niger (Cook and others 1968, Lepage and others 2004). These fungi are commonly found growing on decomposing organic matter especially in rural environments.
Why these commonly occurring, opportunistic fungi that are present in the upper airways of many horses infect the guttural pouches of some horses, but not of others, is unclear. It is also unclear why, when such infections develop, they preferentially affect the guttural pouch mucosa overlying the dorsal aspect of the medial compartment that …