Ovine Epididymitis (Brucella ovis Infection)

Ovine epididymitis is a contagious, chronic, and economically significant reproductive disease of rams primarily caused by the Gram-negative facultative intracellular bacterium Brucella ovis. The disease is characterized by epididymitis, particularly of the tail of the epididymis, with subsequent impairment of spermatogenesis, semen quality, and fertility. In ewes, infection is usually subclinical but can occasionally cause placentitis and abortion. The disease is distributed worldwide, with high prevalence in intensive sheep-raising regions, and is a major cause of ram infertility and flock reproductive inefficiency. In goats, infection is rare and typically subclinical, but serological cross-reactions can complicate diagnosis. The disease is not a significant zoonosis, but it causes substantial economic losses through reduced lamb crop, increased culling of rams, and costs associated with testing and control programs.

The primary etiological agent is Brucella ovis, a small, non-motile, non-spore-forming, aerobic Gram-negative coccobacillus. It is a member of the genus Brucella, which is characterized by intracellular survival within phagocytes. B. ovis is closely related to B. melitensis but is distinguished by its requirement for serum-enriched media, its rough lipopolysaccharide (LPS) phenotype, and its lack of urease activity. The organism is shed in high concentrations in the semen of infected rams, and to a lesser extent in urine and feces. Transmission occurs primarily through venereal contact during mating, but also through homosexual activity among rams, and less commonly through contaminated bedding, equipment, or fomites. The organism can survive for several weeks in the environment under cool, moist conditions, but is susceptible to desiccation, sunlight, and common disinfectants. Other bacteria that can cause epididymitis in rams include Actinobacillus seminis, Histophilus somni, and Corynebacterium pseudotuberculosis, but B. ovis is the most common and economically important cause.

Ovine epididymitis caused by B. ovis is a disease of sexually mature rams, typically affecting animals over 1 year of age. The prevalence varies widely, from less than 5% in well-managed flocks to over 40% in flocks with poor biosecurity. Breeds with a high incidence of the disease include Merino, Suffolk, and other meat and wool breeds, but all breeds are susceptible. The disease is more common in range flocks where rams are kept in groups and mating is uncontrolled. In intensively managed flocks, the prevalence may be lower due to better hygiene and testing. The disease is transmitted primarily during the breeding season, with a peak incidence of clinical epididymitis occurring 2 to 4 months after initial exposure. Morbidity in affected flocks can be high, with up to 50% of rams becoming infected, but mortality is negligible. The economic impact is significant due to reduced fertility, increased ram replacement costs, and the cost of testing and culling. In goats, B. ovis infection is rare and usually subclinical, but serological cross-reactions with B. melitensis can cause diagnostic confusion in areas where caprine brucellosis is endemic.

Following venereal or oral exposure, B. ovis invades the mucosal surfaces of the prepuce, urethra, or oropharynx, and is taken up by macrophages. The bacteria survive and replicate within the phagolysosome, evading the host immune response. From the initial site of infection, the organism disseminates via the bloodstream and lymphatics to the epididymis, particularly the tail, where it establishes a chronic inflammatory focus. The epididymal epithelium is damaged, leading to obstruction of the epididymal duct, accumulation of spermatozoa and inflammatory exudate, and formation of spermatic granulomas. The inflammatory response is characterized by infiltration of neutrophils, macrophages, and lymphocytes, with subsequent fibrosis and scarring. The obstruction and fibrosis impair sperm transport and maturation, leading to reduced sperm count, motility, and increased morphological abnormalities. In the testes, there may be degeneration of the seminiferous epithelium due to increased intratubular pressure and local immune responses. The infection can also spread to the seminal vesicles and ampullae, further compromising semen quality. In ewes, infection is usually subclinical, but if a ewe is exposed to a heavily infected ram, the bacteria can cross the placenta and cause placentitis and abortion, particularly in the last trimester. The pathogenesis of abortion involves the invasion of the trophoblast and the induction of a necrotizing placentitis, leading to fetal death and expulsion.

Several factors increase the risk of B. ovis infection in a flock. Intrinsic factors include age (sexually mature rams are more susceptible), breed (some breeds may have a genetic predisposition), and individual immune status. Extrinsic factors include management practices such as mixing rams from different sources without quarantine, failure to test new rams before introduction, and allowing rams to run together in groups, which facilitates homosexual transmission. Poor hygiene in pens and breeding areas can increase environmental contamination. The use of contaminated artificial vaginas or other breeding equipment can also transmit the disease. In addition, concurrent infections, such as those caused by Actinobacillus seminis or Histophilus somni, may predispose to more severe disease. Stress, malnutrition, and concurrent diseases can compromise the immune system and increase susceptibility. In goats, the disease is rare, but the presence of B. melitensis in the flock can complicate diagnosis and control.

The clinical signs of ovine epididymitis vary depending on the stage of infection. In the acute phase, which occurs 2 to 4 weeks after exposure, rams may exhibit fever, depression, and a unilateral or bilateral swelling of the scrotum, particularly the tail of the epididymis. The affected epididymis is painful, hot, and edematous. Rams may show lameness or a stiff gait due to pain. The semen quality is markedly reduced, with decreased sperm concentration, motility, and increased numbers of abnormal spermatozoa. In the chronic phase, which develops over several weeks to months, the acute swelling subsides, leaving a firm, fibrotic, and often enlarged epididymis. The testis may become atrophic due to pressure and degeneration. Palpation of the scrotum reveals a characteristic firm, nodular mass at the tail of the epididymis. The ram may be infertile or subfertile, but libido is usually maintained. In some cases, the infection may be subclinical, with no palpable lesions, but the ram can still shed the organism in semen. In ewes, infection is usually asymptomatic, but abortion may occur in the last trimester if the ewe is exposed to a high dose of the organism. The aborted fetus may be autolyzed, and the placenta may show necrotic lesions.

The differential diagnoses for ovine epididymitis include other infectious causes of epididymitis and orchitis, as well as non-infectious conditions. Key differentials include: 1) Actinobacillus seminis infection, which causes epididymitis and orchitis in rams, often in younger animals, and can be differentiated by culture and PCR. 2) Histophilus somni (formerly Haemophilus somnus) infection, which can cause epididymitis and orchitis, and is also associated with respiratory and systemic disease. 3) Corynebacterium pseudotuberculosis (caseous lymphadenitis) can cause abscesses in the scrotum and epididymis, but is usually associated with peripheral lymph node enlargement. 4) Trauma or injury to the scrotum can cause swelling and fibrosis, but is usually unilateral and not associated with systemic signs. 5) Testicular neoplasia is rare in rams but can cause testicular enlargement. 6) Scrotal hernia or hydrocele can cause scrotal swelling, but palpation and ultrasonography can differentiate these. 7) Brucella melitensis infection, which is a zoonotic pathogen, can cause epididymitis in rams and is a major differential in regions where it is endemic. Definitive diagnosis requires culture, PCR, or serology.

The diagnostic approach to ovine epididymitis should be systematic and include flock history, physical examination, and laboratory testing. Step 1: Obtain a thorough flock history, including the source of rams, recent introductions, breeding management, and any history of infertility or abortion. Step 2: Perform a physical examination of all rams, with particular attention to palpation of the scrotum and epididymides. Note any asymmetry, swelling, or firm nodules. Step 3: Collect blood samples for serological testing. The complement fixation test (CFT) is the standard test for B. ovis, but ELISA tests are also available and are more sensitive. Step 4: Collect semen samples from suspect rams for bacteriological culture and PCR. Semen should be collected by electroejaculation or artificial vagina, and cultured on selective media. Step 5: If a ram is positive on serology or culture, it should be culled or isolated. Step 6: In cases of abortion, submit fetal tissues and placenta for culture and PCR. Step 7: Implement a control program, including testing and culling of positive rams, vaccination of replacement rams, and biosecurity measures.

Laboratory findings in ovine epididymitis include: 1) Serology: The complement fixation test (CFT) is the most widely used test, with a titer of 1:4 or higher considered positive. ELISA tests are more sensitive and can detect infected rams earlier. 2) Semen culture: B. ovis can be cultured from semen on selective media, such as Brucella agar with antibiotics. The organism is slow-growing and may take up to 10 days to appear. 3) PCR: Polymerase chain reaction (PCR) assays targeting the IS711 element or the omp25 gene are highly sensitive and specific for B. ovis detection in semen and tissues. 4) Hematology: Complete blood count may show mild leukocytosis with neutrophilia in acute cases. 5) Semen analysis: Semen quality is reduced, with decreased sperm concentration, motility, and increased morphological abnormalities. 6) In aborted ewes, serology may be positive, and the organism can be cultured from the placenta and fetal abomasal contents.

Imaging modalities can aid in the diagnosis and assessment of ovine epididymitis. Ultrasonography of the scrotum is the most useful imaging technique. In acute epididymitis, the epididymis appears enlarged and hypoechoic due to edema and inflammation. In chronic cases, the epididymis is hyperechoic with areas of fibrosis and calcification. The testis may appear atrophic and have a heterogeneous echotexture. Ultrasonography can also detect spermatic granulomas, which appear as well-defined hypoechoic or anechoic areas. Radiography is not commonly used for scrotal imaging, but can be used to detect calcification in chronic cases. Computed tomography (CT) is rarely used in small ruminants due to cost and availability, but can provide detailed images of the scrotal contents if needed.

Cytological and histopathological findings are characteristic. In acute epididymitis, histopathology of the epididymis reveals severe neutrophilic inflammation, edema, and necrosis of the epididymal epithelium. The lumen of the epididymal duct contains neutrophils, cellular debris, and spermatozoa. In chronic cases, there is granulomatous inflammation with macrophages, lymphocytes, and plasma cells, along with fibrosis and obliteration of the epididymal duct. Spermatic granulomas are formed by the extravasation of spermatozoa into the interstitium, eliciting a granulomatous reaction with multinucleated giant cells. The testis may show degeneration of the seminiferous epithelium, with loss of germ cells and Sertoli cells. In the seminal vesicles, there may be similar inflammatory changes. In aborted ewes, the placenta shows necrotizing placentitis with infiltration of neutrophils and macrophages, and the fetal lung and abomasum may contain the organism.

Treatment of ovine epididymitis is generally not recommended because the infection is chronic and the organism is difficult to eliminate. Antibiotic therapy with tetracyclines, such as oxytetracycline, or fluoroquinolones, such as enrofloxacin, may reduce shedding but does not eliminate the infection. The use of antibiotics in food animals is also regulated, and withdrawal times must be observed. Therefore, the primary control strategy is testing and culling of infected rams. In valuable rams, surgical removal of the affected epididymis (epididymectomy) has been attempted, but the ram may still shed the organism in semen. Vaccination with a killed B. ovis vaccine is available in some countries and can reduce the incidence of infection, but it does not prevent infection in all animals. The vaccine is typically given to replacement rams before sexual maturity. In a flock outbreak, all rams should be tested, and positive rams should be culled. Negative rams should be vaccinated and retested after 30 days. Ewes that have aborted due to B. ovis should be culled or isolated, as they may shed the organism in subsequent pregnancies.

The prognosis for individual rams with ovine epididymitis is poor, as the infection is chronic and progressive. Affected rams may become permanently infertile and should be culled. The prognosis for the flock is guarded, but with a rigorous testing and culling program, the disease can be controlled and eventually eradicated. The economic impact can be significant, but early detection and control can minimize losses. In ewes, the prognosis is good, as they usually recover from abortion and can produce normal lambs in subsequent pregnancies, although they may remain seropositive.

After a diagnosis of ovine epididymitis, a comprehensive follow-up plan is essential. All rams in the flock should be tested serologically (CFT or ELISA) at least twice, 30 days apart, to identify all infected animals. Positive rams should be culled immediately. Negative rams should be vaccinated and retested after 30 days. New rams introduced into the flock should be tested and quarantined for at least 30 days before being allowed to mix with the flock. Breeding management should be reviewed to minimize the risk of transmission, such as avoiding group mating and using individual mating pens. The flock should be monitored for any signs of infertility or abortion, and any aborted fetuses should be submitted for diagnostic testing. Annual testing of all rams is recommended to maintain a disease-free status.

Clinical pearls: 1) Palpation of the epididymis is a critical part of the breeding soundness examination in rams; any asymmetry or firm nodule should raise suspicion of epididymitis. 2) Serological testing is essential for detecting subclinical carriers, which can shed the organism without palpable lesions. 3) Vaccination of replacement rams is a cost-effective control measure in high-prevalence flocks. 4) Semen culture and PCR are the gold standard for confirming infection, but serology is more practical for flock screening. Pitfalls: 1) Failure to quarantine and test new rams is a common cause of introducing the disease into a clean flock. 2) Relying solely on clinical examination can miss subclinical infections. 3) Antibiotic treatment is ineffective and can lead to a false sense of security; culling is the only reliable method of control. 4) Cross-reactions with B. melitensis can cause false-positive serological results in areas where caprine brucellosis is endemic, so confirmatory testing with culture or PCR is necessary.

There is no effective drug protocol for the treatment of ovine epididymitis. Antibiotics such as oxytetracycline (10 mg/kg IV or IM, q24h) or enrofloxacin (2.5-5 mg/kg IM, q24h) may reduce shedding but do not eliminate the infection. Their use is not recommended for treatment, but may be considered in valuable animals to reduce shedding during the breeding season, with strict adherence to withdrawal times (e.g., oxytetracycline: meat 28 days, milk 72 hours; enrofloxacin: meat 14 days, milk 72 hours). Vaccination with a killed B. ovis vaccine is the primary preventive measure. The vaccine is administered subcutaneously at a dose of 1 mL per ram, given at 3-6 months of age, with a booster 4 weeks later. Annual revaccination may be recommended in high-risk flocks. There are no specific drug protocols for ewes, as infection is usually subclinical.

The literature on ovine epididymitis is extensive. Key studies include: 1) A study by Ridler et al. (2006) evaluated the performance of the complement fixation test and an ELISA for the diagnosis of B. ovis infection in rams, finding that the ELISA had higher sensitivity. 2) A study by West et al. (1999) demonstrated that vaccination with a killed B. ovis vaccine reduced the incidence of epididymitis in rams in a field trial. 3) A study by Bulgin (1990) reviewed the economic impact of ovine epididymitis and emphasized the importance of biosecurity and testing. 4) A study by Ficapal et al. (1998) used PCR to detect B. ovis in semen samples, showing high sensitivity and specificity. 5) A consensus statement from the American Association of Small Ruminant Practitioners (AASRP) recommends a testing and culling program for control, with vaccination as an adjunct. Overall, the evidence supports the use of serological testing and culling as the most effective control strategy, with vaccination being beneficial in high-prevalence flocks.