CHAPTER 35Penile Infections
Infectious disease of the equine penis is relatively uncommon. Sexually transmitted infectious disease is a concern for active stallions and can disrupt breeding use for extended periods of time. Other local infectious issues often are predisposed by parasitism, neoplasia, or trauma. Careful physical examination and appropriate laboratory-supported diagnostic efforts can lead to timely treatment and successful outcome. Delay in recognition and treatment can result in the need for aggressive surgical treatment, which can further interfere with or prevent a breeding career.
BACTERIAL INFECTION
Simple infection of the penis and/or prepuce by bacteria is not common.1,2 Bacteria contaminants typically invade these tissues secondary to another cause. Typical bacterial infection complications are preceded by injury that opens the skin, neoplasia, or parasitism. Excessive washing with soap has resulted in coliform colonization, and excessive disinfection of the stallion’s penis has been associated with removal of normal bacteria and colonization of potentially pathogenic bacteria such as Pseudomonas.3 The microorganisms that are commonly identified are the bacteria that would be expected as local flora opportunists. Streptococcus spp., Klebsiella spp., and Pseudomonas spp. have been routinely implicated in penile and preputial infections.2 It should be noted that these organisms have also been cultured from the equine penis and prepuce in routine screening of the skin when no lesions have been present.2 Therefore culture results should be interpreted with strict attention to the clinical situation.
Treatment of bacterial infections should be directed at resolving the primary disease. In the unusual case of simple bacterial balanitis or balanoposthitis, topical treatment is usually successful in resolving the infection.1,2 Close attention to hygiene with daily cleansing of the penis and prepuce is important. This can be accomplished with water alone or with a mild disinfecting soap. Care should be taken to ensure that all soap residues are removed after cleaning. Large volumes of water should be encouraged. If skin erosions are present or the infectious process appears advanced, application of local antibiotic ointments can help sterilize the tissues.2 Ideally antibiotic selection should be based on culture and sensitivity results; however, systemic antibiotic administration is not commonly indicated. Sexual rest during treatment is necessary.
Prevention of bacterial infections may be possible through routine maintenance of hygiene practices. Monthly cleansing of the penis and prepuce with large volumes of water, water-based lubricants, or a mild soap can reduce smegma accumulation and associated skin irritation. Harsh soaps and antibiotic ointments should be avoided because the use of these agents can result in skin irritation/inflammation and potentially alter the normal skin flora such that infection may be more likely.2
VIRAL INFECTION
Viral infection of the penis and prepuce is also not very common in horses. Equine herpes virus 3 is the most common viral infection in male horses.1,2 This virus is the cause of coital exanthema and is typically acquired through sexual transmission.1–3 Vesicles and ulcers on the penile skin are common clinical signs, and the lesion sites are frequently invaded and infected secondarily by bacteria. Another name for this disease is genital horse pox due to the long-lasting, often depigmented healed ulcer sites.1,2
Coital exanthema is highly contagious, and sexual rest should be enforced during treatment. The lesions are painful, and affected stallions may avoid intromission during the acute phases of infection, although this may depend on an individual stallion’s libido.1,2 Treatment is typically directed at local hygiene and topical antibiotic application if bacterial contamination is considered a problem. Immune-competent horses will develop a successful immune response to help resolve the viral infection, yet the immunity is considered to be short-lived and perhaps only protective through the current breeding season.2 This is typical for most herpes viruses.2
PROTOZOAL INFECTION
Dourine is a protozoal disease associated with Trypanosoma equiperdum.1,2 This is a reportable disease considered to be currently eradicated in the United States.2 Dourine is most commonly diagnosed in Africa, South America, and the Mediterranean regions.1,2 This is a highly contagious, sexually transmitted disease apparently only affecting members of the horse family. Affected horses, weeks to months after exposure, develop swelling in the penis and prepuce as well as systemic signs of disease (i.e., fever, lethargy, anorexia).2 Skin lesions are common at the penis, prepuce, and along the neck and shoulders. Lesions are erosive and often result in depigmented plaques. Mucopurulent exudate is often observed from the urethra and penile lesions.2 Dourine is usually diagnosed by observation of the typical lesions and confirmation of trypanosomes in the discharge or by complement fixation examination.2 Treatment is considered impractical, and isolation of infected individuals is highly recommended while disease confirmation efforts are conducted.1,2
PARASITISM
The most frequent parasitic considerations for lesions on the penis and prepuce of horses are Habronema muscae, Habronema microstoma, and Draschia megastoma.2,4 These large stomach worms are most commonly found in warm, moist climates like the southeastern United States. Lesions of habronemiasis have been noted in many locations on the body. The penis and prepuce are common locations for infection as are wound sites on the limbs.2
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