153. Bovine brucellosis, eradication, maintenance of brucella free herds (Zoon.).

Question 1

Occurence, ethiology and epidemiology?

Answer 1

OCCURRENCE, ETIOLOGY AND EPIDEMIOLOGY

• Worldwide, but it is well controlled in most developed countries
• Free: Japan, Canada, some EU countries, Australia, New Zealand, Israel. Majority of EU are free
• Caused by B. abortus & B. melitensis (Abortion), B. suis (localized form udder infection, but shed with milk)
• Infection of a livestock via newly introduced asymptomatic but infected animals, from horse, dog or cat, via milk,
• means of transport or footwear
• Transmission between animals by contact with the placenta, fetus, fetal fluids or vaginal discharge
• In fetal fluid - # of brucella 109-1010 CFU/ml, Infectious dose (ID) of a catlle ʹ 104 bacteria
• Newly infected pregnant cows
• acute abortion outbreak (abortion storm!), usually occur after 5th month of gestation and subsequent pregnancies are usually carried to term
• Closed livestock: calms down, but a new susc. animal (or animal movement)
• new abortions
• The become chronic carriers and shed lifelong

Question 2

Pathogenesis?

Answer 2

PATHOGENESIS

• Infection P.O. (ingestion), or through broken skin/mucous membranes of genital organs (venereal contact)
• Settle down in the regional lymph nodes
• carried in macrophages to blood stream
• septicemia within 2-3 weeks
• settle down in predilection organs (pregnant uterus, placenta, udder)
• necrosis in chorionic villi,
• abortion, fetal membrane retention
• Large number of Brucellae are excreted in uterine discharges for about 2-4 weeks following an abortion
• Brucella eliminated from the uterus after about 3 weeks, but they survive in the udder, lymph nodes, joints, tendon sheaths and bursae
• subsequent pregnancy
• shed at parturition
• Repeated abortions are rare, and usually a result of heavy reinfection
• Males: settle down in epididymis, testicles, accessory genital glands, shed in the semen

Question 3

Clinical signs?

Answer 3

CLINICAL SIGNS

• Incubation period of 2 weeks- 3 months
• Abortion happens around 6-8 month of gestation
• 1-2 days before the abortion: vulvovaginitis and greyish-white or reddish vaginal discharge
• Fetal membrane retention: brown, turbid, smelly uterine discharge
• Udder: no signs, but brucella is shed in huge numbers in the milk (risk for humans!)
• Bulls: mucosa of penis and preputium is flushed, enlarged and painful testicles
• Arthritis, tenosynovitis and bursitis
• In affected herds: fertility, milk production, testicular degen. Of bulls, abortions in susc. repl. animals

Question 4

Pathology?

Answer 4

PATHOLOGY

• Fetal membrane: Placentitis, hyperemia, edema, yellowish paste form a coating material, necrotic lesions,
• edema of umbilical cord
• Fetus: edema, small hemorrhages, small necrotic foci in the liver
• Testicles, epididymis purulent, necrotic foci

Question 5

Diagnosis?

Answer 5

DIAGNOSIS

• Epidemiological situation, clinical and pathological findings (abortions in first-calf heifers & repl. animals)
• Abortion: whole fetus + fetal membranes + blood sample of cow sent to laboratory
• Direct smear: uterine discharge, cotyledon, fetal abomasal contents, milk, semen, synovial fluid
• Clusters of MZN-positive coccobacilli
• Detection of agent: PCR, bacteriological examination
• Serological tests
• Sensitivity and specificity are different Æ more tests at the same time, repeat after several weeks
• Slide agglutination test (Rose-Bengal test), Tube agglutination (above 1:40 titer - +) ʹ early IgM
• Complement fixation test (1:5 dilution +) ʹ later will be + (detect IgG antibodies)
• ELISA, Antiglobulin (Coombs) test ʹ incomplete Abs, ABR test (Brucella milk ring test ʹ Abs in milk)

Question 6

Treatment and prevention?

Answer 6

TREATMENT & PREVENTION

• No practical treatment, aim is eradication and maintain the disease-free status
• Imported susceptible animal in quarantine for at least 30 days,
• 2x serological test (21 days apart)
• Imported pregnant animals: if serology is negative after calving ʹ release from quarantine
• Examination of abortion cases in diagnostic institute, regular serological survey of livestock
• Freshly calved livestock ʹ ELISA from milk
• National eradication schemes
• detection and slaughter of inf. cattle.
• Detection with serological methods

Question 7

Eradication?

Answer 7

ERADICATION

• Selection procedure: removal of seropositive animals from the livestock
• Good hygiene conditions
• Serological test in each 6 weeks
• 3 months: seropositivity must be lower than 10%
• High risk strategy, rarely successful
• Generation change
• Calves originated from a seropositive livestock will grow up separately
• Calves born free of infection, 3 days old calves will be separated from the dam, and rear in brucella free environment
• Serological testing of 4-6 month old calves, and later in each 3-6 months
• Seropositive animals will be separated and slaughtered
• Offspring population is free of brucellosis if all of the cows will be seronegative post-parturition
• Herd replacement
• Slaughter of infected livestock, cleaning and disinfection, introduce new, disease free breeding stock
• Best method : safest, fastest, but most expensive
• Wildlife species (bison, elk, deer) acquired the infection ʹ eradication is extremely difficult!

Question 8

Vaccination?

Answer 8

VACCINATION

• Aim: reduction of losses in infected livestock, young heifers , strategic measure during early years of eradication schemes
• S19 and RB51 ʹ alive, attenuated strains
• 2-4 month of age female calves only,
• protection for 3 gestation periods
• After 18 months of age: seronegativity
• Vaccination of mature animals leads to persistent (lifelong) antibody titers!
• Not in bull calves
• colonize in testicles: impair germinal epithelium + lifelong seropositivity
• 45/20 ʹ inactivated, oil adjuvanted bacterin
• Young and adults ʹ 2x, revaccination in each year
• Protection last 1 year, Abs can be detected with agglutination till 2-3 months, CFT till 6 months
• In free countries
• vaccination is NOT ALLOWED!