brucellosis (Brucella ovis)

Preferred Scientific Name

• brucellosis (Brucella ovis)

International Common Names

• English: Brucella ovis ram epididymitis; brucellosis in sheep; epididymitis of rams; epididymitis, orchitis, in sheep, goats, and pigs; orchitis; ovine contagious epididymitis; ovine epididymitis; ovine epididymitis (Brucella ovis); seminal vesiculitis, adenitis, in large animals

Ovine contagious epididymitis is a chronic disease that affects the reproductive tract of rams, causing reduced fertility (Burgess, 1982). The causative agent was isolated in the early fifties in New Zealand and Australia (McFarlane et al., 1952; Simmons and Hall, 1953), and the organism was named Brucella ovis in 1956 (Buddle, 1956). The micro-organism causes a transmissible disease unique to sheep in which the major symptom is epididymitis in rams and occasionally abortion in ewes. The disease in rams causes economic loss to the sheep industry of many countries mainly due to low fertility rates. Humans are not affected by B. ovis.

Ovine epididymitis (Brucella ovis) is on the list of diseases notifiable to the World Organisation for Animal Health (OIE). For further information on this disease from OIE, see the website: www.oie.int.

Lesions in male animals are largely in the epididymis, tunica vaginalis and testis varying from a slight enlargement of the epididymis, either unilateral or bilateral, to large indurations. Spermatoceles containing partially inspissated spermatic fluid may be found in the epididymis and fibrous atrophy can occur in the testis. The tunica vaginalis is often thickened and fibrous, and can have extensive adhesions. There are generally no clinical signs in the ewe although occasionally infection causes abortion or the birth of weak or stillborn lambs, associated with a placentitis.

Blasco, (1990) extensively reviewed the pathogenesis, pathology and histology of Brucella ovis infection. Briefly: as with other Brucella infections there is a period of generalized infection (Enright, 1990). After infection, the bacteria remain in the lymph nodes close to the entry site for 2-3 weeks. This is followed by a bacteraemic stage that may last up to 2 months. The organism infects the reticuloendothelial system and various organs (Biberstein et al., 1964). Although the bacteria can be isolated from several tissues they usually localize in the epididymis causing an epididymitis. However, not all infected rams develop a palpable epididymitis. Lower fertility and seminal degeneration almost always precede the appearance of lesions. In most cases there is a unilateral epididymitis affecting the tail of the epididymis. Sometimes the body and the head of the epididymis are also affected (Blasco, 1990). Following localization in the epididymis there is perivascular oedema and the infiltration of lymphocytes and monocytes into the peritubular tissue. Eventually the epithelial cells are destroyed, either by bacterial products or by extravasation of spermatozoa. This leads to formation of spermatic granulomas that block the epididymis (Jubb et al., 1985).

Testicular atrophy is characteristic for chronic infection. This affects semen quality, breeding efficiency and capacity. The affected testicle appears firm but on the cut surface granulomas and calcification may be apparent (Blasco, 1990). During the bacteraemic stage B. ovis can cause chronic interstitial nephritis resulting in permanent shedding of B. ovis in the urine (FAO/WHO, 1986).

Only ewes exposed to infection at early or mid-pregnancy develop infection that may lead to abortion. In pregnant sheep, B. ovis may cause placental necrosis and abortion 23-80 days post infection (Enright, 1990). For abortion to occur there has to be a sufficient accumulation of bacteria and exudate to cause necrosis of the placenta and separation from the caruncles. Thus, the primary effect of infection in ewes is a placentitis that interferes with normal foetal nutrition resulting in the death of lambs and abortion, or in birth of lambs with low birth weight (FAO/WHO, 1986). Dead foetuses are usually oedematous. Calcified plaques on the soles of the hooves are characteristic of abortion due to B. ovis infection (Enright 1990).

Brucella ovis is the least pathogenic of all the Brucella species that infect domestic animals. It almost exclusively infects sheep and affects mainly rams, although male goats experimentally inoculated with B. ovis develop lesions similar to those observed in rams (Blasco, 1990). Whereas in practice the source of infection is contaminated semen excreted by infected rams, not every infected ram excretes B. ovis in the semen (Burgess, 1982). Passive venereal transmission is the main route of spread for B. ovis infection (Buddle, 1955; Hartley et al., 1955). However, passive venereal transmission requires both an infected and non-infected ram to mate with the same ewe in one oestrus cycle. Rams may become infected at the post-abortion oestrus, as B. ovis could be found for 10 days in the vaginal discharge following abortion (Hughes, 1972). Although venereal transmission is the most important route of exposure (Jubb et al., 1985), demonstration of infection in 4-month-old rams (Burgess et al., 1982) casts doubt whether age susceptibility to B. ovis infection exists (Blasco, 1990). It has been suggested that sodomy is responsible for the spread of infection amongst young rams (Burgess, 1982). Transmission, however, may also occur when healthy rams are housed in pens where previously infected rams were kept (Clapp et al., 1962). Furthermore, since rams often sniff the genital organs of other rams infection via the nasopharynx is also possible (FAO/WHO, 1986). Under experimental conditions sheep can be infected with B. ovis via several routes (Muhammed et al., 1975; Simmons and Hall, 1953; Blasco, 1990).

Susceptibility to B. ovis may vary between breeds of rams (Cameron et al., 1971; Blasco, 1990). Rams are more susceptible to infection than ewes. Ewes also rarely become actively infected or transmit the disease during abortion to another ewe although they usually develop complement fixation titres. Since only a few infected ewes abort or have dead or weak lambs it would appear that ewes are relatively resistant to infection (Buddle, 1955; Hartley et al., 1955; Clapp et al., 1962; Haughey et al., 1967). It is generally accepted that the role of an infected ewe in congenital transmission of the disease is negligible (Blasco, 1990).

Outbreaks of Brucella ovis infections may cause significant economic loss in countries where the sheep industry plays a role in the national economy. The main economic problems arise from reduced numbers of lambs born, a high percentage (20%) of barren ewes, and a high percentage of lambs born alive that die within six weeks of birth. Furthermore, prolonging of the lambing season due to disease interference with the normal breeding scheme is of significant economic importance. Lamb yield may drop in infected flocks from 100% to 25% (FAO/WHO, 1986).

There are no confirmed reports of human infections with B. ovis and, unlike many Brucella, this species is not considered zoonotic.

Treatment of Brucella ovis ram epididymitis with antibiotics is very expensive and not very effective. The effect of the treatment is of a short duration, with not all the shedders being cured and the fertility of some animals remaining impaired (Dargatz et al., 1990; Hajtós et al., 1994). Thus, antibiotic therapy is not endorsed except when rams with high breeding quality are infected (Blasco, 1990).