Enzootic Posthitis and Vulvitis
(Sheath rot, Pizzle rot, Enzootic balanoposthitis)
This moderately contagious disease is caused by C renale, a gram-positive, diphtheroid bacterium capable of hydrolyzing urea. When protein intake is high, urinary urea concentration increases. Hydrolysis of urea by C renale results in local production of large quantities of ammonia, which is believed to irritate the penis, lamina interna of the prepuce, and skin surrounding the preputial orifice. The condition is more common in male castrates, probably because of the hypoplastic nature of the penis, exacerbated in some cases by failure of penile-preputial separation that leads to pooling of urine in the prepuce. If preputial hair is cut too short or becomes caked with mud or organic matter, drainage of urine away from the preputial orifice (normally facilitated by this hair) is impaired, and ulcerative lesions may develop.
The incidence of ulcerative posthitis is highest in Merino and Angora wethers, which is attributed to the long hair or wool surrounding the prepuce in these animals, allowing urine to soak the area, which in turn is conducive to bacterial growth and activity. It is also seen in show rams or rams that have been fit for sale; in this case, the condition is more associated with dietary protein levels. The condition can be transmitted experimentally by infective material from a preputial or vulvar ulcer. Ulcerative posthitis or vulvitis has a seasonal occurrence that varies with local animal husbandry methods. Peak incidence corresponds to the time when animals graze lush green pasture (eg, spring and early summer in New Zealand or autumn and winter in southern Brazil) or are fed or have access to high-protein feedstuffs.
In mild cases, signs are limited to swelling of the prepuce. In severe cases, swelling and inflammation interfere with urination and result in straining, which needs to be differentiated from urolithiasis (see Urolithiasis in Large Animals). Histologic characteristics are acanthosis, parakeratosis, and hyperkeratosis, followed by leukocyte invasion and ulceration. Ulcers and scabs may be found around the preputial orifice, on the lamina interna of the prepuce, and on the shaft of the penis. Urine and exudate may accumulate in the prepuce. The condition may cause severe discomfort. If the preputial orifice or urethra is occluded, affected animals may die. Ulcerative vulvitis begins with signs of vulvar inflammation, including swelling and redness, and progresses to development of a yellow exudate with ulceration and scab formation around the vulva, vestibule, and caudal vagina. The glans clitoridis may be swollen, red, and ulcerated.
Lesions of ulcerative posthitis or vulvitis should be distinguished from those of granular posthitis or vulvitis (associated with Mycoplasma spp or Ureaplasma spp, see Vulvitis and Vaginitis in Large Animals), herpesviral balanoposthitis or vulvovaginitis, ulcerative dermatosis (see Ulcerative Dermatosis of Sheep [sheep only]), or contagious ecthyma (orf, see Contagious Ecthyma [goats only]). Removal of the scabs of ulcerative posthitis or vulvitis characteristically results in little or no hemorrhage.
If possible, affected animals should be isolated from the rest of the herd and not fed a high-protein diet. Lesions should be examined to ensure they do not interfere with urethral patency. Clipping and cleaning hair around the prepuce may be beneficial. C renale is usually sensitive to penicillins and cephalosporins, which may be beneficial if practical. Ulcerative posthitis is controlled principally by limiting dietary protein to a level consistent with requirements. If untreated, scarring may be so severe that the penis cannot be extended.