Brucellosis: Etiology and Hosts

• Brucellosis has other names including Contagious abortion, Bang's disease, Mediterranean fever, Undulant fever, and Malta fever.

Etiology

• Brucella is a gram-negative cocco-bacillus.
• Brucella is a facultative intracellular organism that favors Erythritol.
• Brucella is host preferable but not host specific.
• Brucella is serophillic and requires serum for growth.
• Some Brucella species are microaerophilic and require CO2, such as Br. Abortus.
• Brucella can be stained using a modified Ziehl-Neelsen stain.
• Brucella resists environmental conditions if not exposed to sunlight.

Host Affected

• Cattle and Buffaloes are affected by Brucella abortus and Brucella melitensis.
• Camels are affected by Brucella abortus and Brucella melitensis.
• Equines are affected by Brucella abortus and Brucella melitensis.
• Sheep and Goats are affected by Brucella melitensis and Brucella ovis in rams.
• Pigs are affected by Brucella suis.
• Dogs are affected by Brucella canis, Brucella abortus, and Brucella melitensis.
• Humans are affected by Brucella canis, Brucella abortus, Brucella melitensis, and Brucella suis.

Sources of Infection

• Sources of infection in animals include aborted fetuses, placenta, milk, colostrum, contaminated food and water, and semen.
• Recovered cows that are "carriers" intermittently excrete the bacteria in milk, especially during late lactation.
• Less common sources include infected bulls or horses with fistulous withers.

Transmission to Animals

• Transmission routes include ingestion, mucous membranes, inhalation of aerosols, skin contact, and genital tract (venereal).

Clinical Signs in Cattle

• Brucellosis in cattle can cause abortions in the third trimester, often described as a "storm of abortion".
• Retained placenta is a common clinical sign.
• Infected cattle may give birth to dead or weak calves.
• Chronically infected animals shed organisms in milk.
• Aborted fetuses may have swollen and thickened umbilical cords, along with necrotic foci on the liver.
• The placenta may be swollen with a leathery texture (leather-like necrosis).

Brucellosis in Bulls

• In bulls, Brucellosis can manifest as orchitis, epididymitis, seminal vesiculitis, arthritis, and bursitis.
• Hygroma in the joint can lead to lameness.
• Insidious forms of Brucella may go unnoticed but eventually cause significant harm, often due to inefficient vaccination programs or improper vaccine use.
• There can be reaction with serological test.

Brucellosis in Horses

• Brucella abortus is the most common Brucella species found in horses.
• Fistulous withers or Poll Evil (inflammation of the supraspinous bursa) can be clinical signs.

Diagnosis of Brucellosis

• Isolation of the organism requires specific samples; semen, hygroma lesion or abscess for males, milk, placental or uterine discharge or blood for females, and abomasal content for fetuses.
• Identification of the bacteria involves direct smear, culturing (using 10% CO2 for Brucella Abortus), antigen detection (immunostaining, PCR, or DNA probe), and animal inoculation (guinea pigs, causing strawberry shape spleen).
• Serological examination should be performed 2-3 weeks before and after parturition, as antibody titers may be low, leading to false negatives.

Herd Tests

• Herd tests include the milk ring test (screening test), Rose Bengal test (field test), Rivanol test, BAPA, and Mercapetoethanol test.
• Agglutination tests include slide agglutination test, tube agglutination test, and Seminal plasma agglutination test.
• The complement fixation test (CFT) is specific for IgG detection.
• In cases of latent infection or insidious forms or carriers, an anamnestic test can be used.
• K45/20A (Abortox) vaccine can be used in the Anaminestic test.
• Chronic latent infections or insidious forms produce consistent CFA titers.
• CFA declines rapidly in non-infected animals.
• A bull from an infected herd should not be used for breeding, even if serologically negative.
• The Allergic test (Brucellin test) involves a rough strain of Br. Abortus (Intradermopalberal in one eye).
• A positive allergic test results in severe Panophthalmitis, with the eyelid closing within 24 hours.

Prevention and Control

• Prevention and control are difficult due to the large number of wild, infected, and carrier animals as well as a lack of specific serological tests.
• The disease is zoonotic.
• Controlling the disease involves hygienic measures, test and slaughter, and vaccination.

Hygienic Measures

• Hygienic measures include isolating infected animals, proper disposal of aborted fetuses, and disinfection with 5% formalin or phenol, as Brucella can remain viable for up to 3 months.
• Bulls from infected herds should not be used for breeding even if serologically negative.
• Water and food troughs should be raised to prevent contamination.
• When introducing pregnant or fresh cows, they should originate from Brucellosis-free herds, test negative for agglutination, and be separated for at least 30 days.

Test and Slaughter

• Regular testing should be performed every 2-3 months, including MRT and Serum agglutination tests or Rose Bengal tests.
• The infected herd is tested at intervals until 2 or 3 successive negative tests.

Vaccination

• Common Brucella vaccines include Strain 19 (calf hood), 45/20 (Abortex), H38 (Aborlane), RB51, and Rev 1.

Vaccination Schedule and Effects

• Brucella abortus Strain 19 (Calf hood V) involves a live smooth strain B. abortus, administered at 4-8 months, with 5 ml via subcutaneous injection, immunity lasts 5 years in cattle and buffaloes, and may cause abortion or orchitis in males.
• 45/20 (Abortex) vaccine is a killed rough strain B. abortus, given in two doses of 3 ml via subcutaneous or intramuscular injection, provides 6 months to 1 year of immunity, and can cause skin reactions.
• H38 (Aborlane) vaccine uses a killed smooth strain B. melitensis, administered to non-infected animals at 4-6 months for the first dose, followed by a booster after 2 months and annually with Abortex to protect cattle and sheep against Br. abortus and Br. Melitensis. For infected animals, 2 doses are given with a 2-month interval, followed by an annual booster of Aborlane.
• RB51 vaccine involves a live rough strain B. abortus for non-infected females at 3-12 months of age, which results in immunity in Cattle and Buffaloes for less than a year and may cause placentitis.
• Riv one is a live strain B. melitensis given at 3-6 months to female sheep and goats and information on immunity is abscent.

Control During Storm of Abortion

• During a storm of abortion, testing and disposing of reactors may be unsatisfactory as the spread is faster than eradication.
• Vaccinating all non-reactors and retesting the herd before the second vaccination and culling cows with a rise in agglutination titer are imperative.

Eradication Program

• Use a calfhood vaccination program.
• Eradication on an area basis can be considered when infection is below 4% of the cattle population.
• Infected herds should be quarantined and retested at intervals until tested negative.
• The movement of the cattle between areas is controlled.
• In dairy herds, the milk ring test is conducted.
• In beef herds, the Rose Bengal Test (RBT) and CFT should be performed.

Additional Information

• Brucella is intracellular and intercellular, potentially leading to transient antibody titers.
• Brucella abortus often affects cattle and buffaloes.
• Br. melitensis commonly affects sheep and goats.
• Br. ovis affects sheep and goats like rams.
• Clinical signs in bull include Orchitis and Epididymitis and Arthritis & Hygroma in joint.
• Clinical signs in Calf include Edematous Calf ( dropsical Calf) & Leathery Placenta.
• Clinical findings may be observed using a direct smear, stained with modified Ziehl-Neelsen or Kasloviciki stain.
• When culturing Brucella, 10% CO2 should be used along with a specific antibiotic like Bacitracin.
• When inoculating animals use, 2 female guinea pigs (because male gives Strauss reaction) are injected with suspected material intraperitoneally.
• After 10-15 days, heart blood is taken for antibody titer detection.
• After 15 days - 4 weeks, scarify one G. pig, and during slaughter, blood and spleen swab should be taken (Spleen strawberry appearance).
• After 6 weeks, the second G. pig is taken, and the previous procedures are applied.
• False negatives result from recent infection or recent abortion.
• False positives result from vaccination and cross-reaction with other microorganisms.
• Use killed Vaccine K 45 / 20 A in Anamenstic Test for Chronic or latent infection.
• In the case of high titre of Ab for long time, infection occur and in the case of high titre of Ab then decline, no infection occur.