Prevalence

The prevalence of vesicular adenitis (vesiculitis) is highest in yearling bulls, but the incidence may vary greatly and depends partly on the criteria used for making a diagnosis. Reported incidences may be higher if enlargement and increased firmness of the vesicular glands without pus in the semen is sufficient for a positive diagnosis. In addition, abattoir findings and histological examination of tissues may elevate the incidence above clinical diagnosis made on transrectal palpation and semen sampling. In general, clinical vesiculitis, with enlarged glands and pus in the semen, has an incidence of 1–5% in populations of yearling bulls;^1–3 however, much higher incidences might be found in individual groups of bulls.⁴

Cause

A large variety of organisms has been implicated in the cause of vesicular adenitis, including numerous types of bacteria, viruses, mycoplasma, ureaplasma, and chlamydia.^5,6 Where brucellosis has not been controlled, Brucella abortus is the primary cause of vesicular adenitis.⁷ Trueperella pyogenes (formerly Arcanobacterium pyogenes) is one of the most frequent isolates in North America.^8,9 Histophilus somni is also a common isolate from bulls with vesicular adenitis during BSE.⁴

Pathogenesis

A definitive pathogenesis for vesiculitis has not been determined, although proposed routes of infection include infectious agents ascending the genitourinary tract, agents descending from the upper urinary or reproductive tracts, hematogenous invasion, or direct invasion from local sources.⁸ Ascending infections, perhaps acquired from bulls riding each other, seem unlikely since repeated infusion of a culture of T. pyogenes into the distal penile urethra of a bull failed to produce vesiculitis.⁵ A hematogenous source of infection has often been favored as an explanation, since vesiculitis has been associated with high-energy diets.⁶ High-energy diets predispose to the development of rumenal acidosis, leading to rumenitis followed by bacteremia. Trueperella pyogenes and Gram-negative anaerobic bacteria, the most common isolates from liver abscesses of feedlot animals, are also commonly isolated from vesicular gland infections.^6,8 However, in Brazil and Argentina where bulls are raised primarily at pasture, incidences of vesiculitis as high as 17.7 and 18.6% have been reported.^10,11 In a report from Argentina, of 489 young bulls on five farms, 18.6% had vesiculitis diagnosed by rectal palpation; 6% also had epididymitis, orchitis or erosions on the penile mucosa. This suggests a relationship between vesiculitis and infections in other parts of the reproductive tract (descending infection). Bacterial and viral cultures of inflamed vesicular glands were often negative,¹² suggesting the possibility of chemical irritation. Congenital abnormalities of the ducts and vessels opening into the urethra at the colliculus seminalis¹³ or a lack of synchrony in the ejaculatory process¹² may lead to reflux of semen and urine into the vesicular glands, causing inflammation but not necessarily bacterial infection. Vesiculitis has not been reported in feedlot steers that commonly suffer from rumenal acidosis and liver abscesses. Rapid development of the duct system of vesicular glands during puberty may allow reflux of semen and urine to occur in young bulls; conversely, lack of development of the vesicular glands may spare steers from vesiculitis.

Effect on fertility

The effect of vesiculitis on sperm viability is variable and is likely influenced by changes in pH and in the components of seminal plasma. Cytokines produced by white blood cells can adversely affect sperm motility and have been shown to reduce fertilizing ability of human sperm in the hamster ovum penetration test.¹⁴ Activated granulocytes can produce large amounts of reactive oxygen species that are damaging to sperm, although seminal plasma contains antioxidant substances that protect sperm.¹⁵ Usually, sperm motility is reduced in the presence of purulent material; however, in some cases sperm motility and morphology are good despite the presence of large numbers of leukocytes and flocculi of pus. This may explain why there are reports of both poor and good fertility when affected bulls have been used in natural service.^3,7

Diagnosis

The great majority of bulls with vesiculitis show no outward symptoms of disease. Usually vesiculitis is discovered during transrectal palpation of the internal reproductive tract during breeding soundness evaluations. Most commonly, one or both vesicular glands feel enlarged and indurated with loss of lobulation. In a small proportion of cases abscessation may occur and rarely there may be adhesions between the glands and the surrounding tissues; even more rarely, an abscessed gland may fistulate to the rectum. Ultrasonography is the best way to establish whether abscessation has occurred and this information is valuable in formulating a prognosis for recovery after treatment. Inflammation in other parts of the reproductive tract may be associated with vesiculitis (e.g., ampullitis, urethritis); however, inflammation in these sites is not easily clinically detected. The finding of enlarged indurated glands may or may not be associated with the presence of pus in semen samples. Many bulls recover spontaneously from vesiculitis and may retain enlarged indurated glands without excreting purulent material. The presence of leukocytes in semen also does not necessarily indicate the presence of vesiculitis since leukocytes might originate from other sites of inflammation in the reproductive tract or the urinary bladder. A common source of leukocytes in semen samples is the surface of the penis and prepuce that may be irritated from riding of pen mates or breeding females.

Special techniques are required to obtain useful samples for culture of causative agents. Collection of jets of semen into sterile culture tubes after disinfection of the glans penis nearly always results in the growth of many environmental contaminants, including staphylococci, streptococci, Escherichia coli, Pseudomonas, Histophilus, and many others. A method for collection of vesicular gland secretions for bacterial culture has been described as follows.¹⁶ The bull may be blindfolded and tranquilized for restraint and for ease of penile protrusion. The preputial hair is clipped and the penis is extended by transrectal massage of the urethralis. The glans penis is held with sterile gloves and surgical sponges. The end of the penis is washed and disinfected and the urethra is irrigated with sterile saline administered through a sterile teat cannula. Then a 25–30 cm sterile Silastic tube is passed up the urethra leaving 2.5–5 cm protruding from the penis. The vesicular glands are then massaged to propel secretions into the urethra to be collected into a sterile vial.