A Lecture Notes on Brucellosis in Animals

Lecture Notes on Brucellosis

1. Lecture Notes on B rucellosis Dr Vidya Singh Senior Scientist Division of Pathology, ICAR-Indian Veterinary Research Institute Izatnagar, Bareilly, UP, India- 243122

2. Brucellosis A chronic infectious disease caused by Gram-negative, facultative intracellular coccobacill i of the genus Brucella , affecting a wide range of domestic and wild animals, including humans (zoonosis ). It primarily targets the reproductive tract, leading to abortion, infertility, epididymitis, and placentitis , and causes significant economic losses in livestock production. Etiology Species Natural Host(s) Zoonotic Potential Pathogenicity Order Brucella abortus Cattle, buffalo Yes Moderate Brucella melitensis Goat, sheep Highest Very high Brucella suis Pigs Yes High Brucella canis Dogs Yes (less severe) Moderate Brucella ovis Sheep No Low Brucella neotomae Rodents No Very low Morphology : Small (0.5–0.7 µm), non-motile, non-capsulated coccobacilli . Biochemical properties : Catalase + ve , oxidase + ve , urease + ve (rapid ). Growth requirements : Some strains require 5–10% CO₂ . Brucella agar or Castaneda biphasic media .

3. Epidemiology and Transmission Geographic Distribution : Endemic in India, Africa, Middle East, Mediterranean region , Latin America Controlled or eradicated in Scandinavia, Canada, Australia, Japan Transmission Horizontal Direct contact with infected aborted materials, vaginal discharge, placenta, semen Ingestion of contaminated feed, water, milk Venereal transmission: Bulls, bucks, boars, dogs Aerosol (in confined animal houses, abattoirs, laboratories) Vertical Transplacental infection Congenital (rare) Via milk suckling Risk Factors : Pregnancy (due to erythritol stimulation) Natural mating with infected males Retention of carrier animals Poor farm sanitation Overcrowding

4. Pathogenesis Portal of entry : Oral, conjunctival, genital mucosa Initial replication : Tonsils, local lymphoid tissues Survival inside macrophages : Brucella uses Type IV secretion system ( VirB ) to avoid phagolysosome fusion Produces superoxide dismutase , lipid A , LPS with low endotoxicity Hematogenous dissemination : Local lymph nodes → bloodstream → uterus, placenta, epididymis, joints, bones Target organ colonization : Erythritol -rich tissues (placenta, fetal fluids, mammary gland) Trophoblast necrosis , placental inflammation, and fetal death Immune response : Cell-mediated immunity dominates Humoral antibodies also produced (IgM → IgG) Chronic infection established in intracellular niches

5. Clinical Signs A. Cattle – B. abortus Abortion (typically during 5–9 months gestation ) Retained placenta → Metritis, delayed conception Infertility , reduced conception rate Orchitis , epididymitis in bulls Decreased milk production B. Goats & Sheep – B. melitensis Late-term abortions (main sign) Weak/stillborn kids/lambs Mastitis Arthritis, lameness in bucks C. Pigs – B. suis Irregular oestrus, infertility Orchitis , arthritis, spondylitis Abortion and fetal mummification D. Dogs – B. canis Late abortion (45–55 days of gestation ) Testicular swelling, scrotal dermatitis Enlarged lymph nodes, discospondylitis Persistent bacteremia

6. Organ/Tissue Observations Uterus Congested, edematous, endometrial necrosis Placenta Thickened, leathery, necrosuppurative cotyledons Fetus Autolysis , hepatosplenomegaly , fibrinous peritonitis Testes/Epididymis Enlarged, fibrotic, purulent discharge Joints (chronic) Effusion, synovial hyperplasia Lymph Nodes Enlarged, hemorrhagic , necrotic areas Tissue Changes Placenta Trophoblastic necrosis, mononuclear cell infiltration , vasculitis Uterus Chronic endometritis , fibrosis Testes Lymphoplasmacytic orchitis , seminiferous tubule degeneration Lymph nodes Granulomatous lymphadenitis Joints Fibrinopurulent synovitis , pannus formation Gross Pathology Histopathology

7. Diagnosis Presumptive Diagnosis Reproductive failure history Abortion storm in herd Laboratory confirmation Laboratory Confirmation Direct Methods Isolation from: Placenta, fetal stomach, vaginal swab, milk, semen Media: Brucella agar , Farrell’s medium , Castaneda’s biphasic media Colonies: Small, glistening, convex Gram-negative coccobacilli Molecular Tests PCR (16S rRNA gene) Real-time PCR for species differentiation Serological Tests Test Principle Remarks RBPT Rose Bengal stained antigen agglutination Rapid screening SAT Tube agglutination Quantitative ELISA IgG/IgM detection High sensitivity & specificity CFT Complement consumption Confirmatory Milk Ring Test Lipid-antibody complex in milk Dairy herds only

8. Differential Diagnosis Leptospira spp. – Hemoglobinuria , jaundice Listeria monocytogenes – Encephalitis + abortion Campylobacter fetus – Early embryonic death IBR (BoHV-1) – Respiratory signs + abortion Salmonella spp. – Diarrhea, fever + abortion Treatment Not recommended in food animals due to public health concerns In dogs ( B. canis ): Combination therapy (at least 4–6 weeks): Doxycycline + Streptomycin Rifampicin + Enrofloxacin Relapse is common even after prolonged therapy

9. Control & Prevention A. Biosecurity Test and remove positive animals Segregation of parturient animals Use of disinfectants (Phenol, formalin) Proper disposal of aborted materials Vaccination Vaccine Animal Remarks S19 Calves (3–8 months) Live attenuated; may cause abortion if given to pregnant cows RB51 Cattle Rough mutant, less interference with serological tests Rev.1 Sheep/goats Live attenuated; given by conjunctival route

10. Zoonotic Importance Transmitted to humans by: Raw milk/cheese consumption Contact with aborted materials Inhalation (lab, abattoirs) Human Disease: Undulant Fever Intermittent fever, chills, sweating Arthralgia, fatigue, hepatomegaly and splenomegaly Chronic: spondylitis, endocarditis Occupational disease: farmers, veterinarians, lab workers Public Health Programs (India) NADCP – National Animal Disease Control Programme (2019–2030) Targets: 100% vaccination of eligible cattle Testing and removal of infected animals Awareness and surveillance