2. Brucelloses

What is Brucellosis?

Brucellosis is a contagious disease of livestock caused by various bacteria of the family Brucella.

What type of bacteria are Brucella species?

Brucella species are small, gram-negative, non-encapsulated, acidoresistant coccobacilli.

How do Brucella bacteria function?

Brucella bacteria function as facultative intracellular parasites, causing chronic disease that usually persists for life.

What are the main clinical signs of Brucellosis in animals?

In animals, Brucellosis is characterized by abortions or reproductive failure. Animals may recover, but they can continue to shed the bacteria.

How many species of Brucella are distinguished, and can they affect humans?

There are six species of Brucella distinguished. Some species have zoonotic potential and can affect humans.

Which species does B. abortus affect?

cattle, horses, sheep, goats, dogs, and humans

Which species of Brucella is the most important pathogen and affects cattle, horses, sheep, goats, dogs, and humans?

Brucella abortus is the most important pathogen and affects cattle, horses, sheep, goats, dogs, and humans.

Which species of Brucella is associated with Malta fever and what species does it affect?

Brucella melitensis is associated with Malta fever and affects sheep, goats, cattle, dogs, and humans.

Which species does B. suis affect?

swine, hares, reindeer, rodents, and humans

Which species of Brucella affects swine, hares, reindeer, rodents, and humans?

Brucella suis

Which species does B. canis affect?

dogs and humans

Which species of Brucella primarily affects dogs and humans?

Brucella canis

Which species does B. ovis affect?

sheep (rams)

Which species of Brucella causes infectious epididymitis in rams but is not zoonotic?

Brucella ovis

What does B. neotomae affect?

rodents

Which species of Brucella is associated with rodents?

Brucella neotomae

What causes bovine brucellosis?

*Brucella abortus*

How many biovars of *B. abortus* are there?

8

Where are the biovars of *Brucella abortus* found?

1 🡪 global, most frequently isolated from cattle

3 and 6 🡪 Africa and Asia

2 and 4 🡪 South America

5, 7 and 8 🡪 rarely isolated

How can *Brucella abortus* be cultivated?

blood agar

What is the transmission of *Brucella abortus*?

Transmission –movement of **infected animals, aborted foetus, membranes, uterus discharge, semen, milk**. Oral **sexual contact, damaged skin, conjunctiva**. **Urine and faeces**

The bacteria can survive in the environment for several months and remain infectious to other animals that become infected by ingesting the bacteria. 

* Pasture contamination causing never ending cycle

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**Ingestion/inhalation, (aerosols), vertical/veneral**

What is the pathogenesis for *Brucella abortus*?

After entering the body – phagocytosis, but not killing – persistence in mononuclear cells. Therefore, Brucella spp. invade unnoticed by the innate immune system. Brucella form granulomatous nodules in which intracellular growth is favoured. 

How long is the incubation period for *Brucella abortus*?

14 days - 6 months

What are the clinical signs of *Brucella abortus*?

Very variable 🡪 **Abortion** (5-7 month) up to 30 to 80%, **infertility** (may be only sign)

* Retained placenta, metritis, mucopurulent discharge, orchitis and epididymitis, arthritis (carpal joints), bursitis, hygroma, abscess. 

Human – serious zoonosis 🡪 **undulant (bang) fever,** depression, weakness, headache, joint pains, sweating

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Horses 🡪 **dominant = chronic bursal enlargements in neck and thorax**; also arthritis, sternal abscess, abortion (rare), lameness (navicular bursae)

What is the pathology for *Brucella abortus*?

Cows: mild to severe endometritis, placentitis, necrosis of cotyledons (yellowish-grey, destroyed, no clear structure)

Aborted foetuses: subcutaneous oedema, blood stained fluid in thoracic and abdom cavities, enlarged and discoloured liver, enlarged mammary gland

What are the diagnostic methods for *Brucella abortus*?

Suspicion based on clinical signs (always with abortions) but must do lab


1. Isolate and identify agent (confirmation): Ziehl nelson staining, a modified stamp staining, culture (columbia agar), PCR
2. Serology (blood serum) – ELISA, milk ring test, complement fixation test, tube agglutination

Biological test – not used now

**Serological (OIE)**

* **Complement fixation = gold standard**
* **Serum agglutination**
* **Rose Bengal**
* **ELISA**
* **Milk ring**

Samples: milk, vaginal swabs (can be +ve 8 weeks post), placenta

* Cows at slaughter 🡪 LN, spleen, uterine tissues and fluids
* Aborted foetuses 🡪 stomach contents and spleen
* Suspected bulls 🡪 semen

What is the treatment for *Brucella abortus*?

No therapy in animals. Long antibiotic treatment in humans

What is the prevention for *Brucella abortus*?

Decisive importance 🡪 measures against introduction

Necessary 🡪 surveillance and serological monitoring

Strict **hygiene precautions when handling aborted foetuses or other suspect material**

* Can infect **through skin, ingestion and inhalation**

**Pasteurisation of milk**

Two control methods:

* **Elimination** based on serological exam 🡪 exclude positive animals plus disinfect
* **Radical** where all susceptible animals in outbreak are slaughtered, stables decontaminated and before slaughter do serological exam

**Vaccination only in endemic areas** but can’t then use serological tests

* Live or inactivated

How many biovars does *Brucella melitensis* have?

5

What is the transmission for *Brucella melitensis?*

**Nasopharynx, abraded skin, aborted foetus, placental and foetal fluids, vaginal discharge**

Humans 🡪 ingestion of **contaminated milk**, uncooked meat, handling aborted animals

What are the clinical signs caused by *Brucella melitensis*?

Small ru – abortions, mild mastitis, orchitis, epididymitis, arthritis 

Man - irregular fever, headache, weakness, chills, weight loss, general aching.

What is the diagnosis for *Brucella melitensis*?

Microscopic exam 🡪 **smear from foetal stomach content**, cotyledons, discharge 

* Stamp staining or direct immunofluorescence

Bacteriological, biological test

Serological exam as above

How is *Brucella ovis* transmitted?

**Contact, insemination, mating, milk**

How long is the incubation period of *Brucella ovis*?

6 weeks - 6 months

What are the clinical signs caused by *Brucella ovis*?

**Chronic disease**

Abortion in ewes (rare) and **infectious epididymitits** of rams 🡪 unilateral or bilateral epididymitis, atrophy of testes

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Oedema of scrotal fascia and exudate in tunica vaginalis

What is the diagnosis for *Brucella ovis*?

Semen, vaginal swabs, milk

PM exam of epididymis, lymph nodes, uterus, aborted foetus

Bacteriological, biological test, microscopical, serological

What causes canine brucellosis?

*Brucella canis*

How long is the incubation period of *Brucella canis*?

14-19 days

What are the clinical signs of canine brucellosis?

Veneric disease 🡪 **abortion in pregnant bitches (second half)** or no clinical signs if not pregnant

**epididymitis/ orchitis** in males

Pathology: hyperplasia of LN and splenitis, testicular fibrosis and atrophy, scrotal ulcer, abscess

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Low grade pathogenicity in humans

What is the diagnosis for *Brucella canis*?

Microscopic exam 🡪 smear from foetal stomach content, cotyledons, discharge 

* Stamp staining or direct immunofluorescence

Bacteriological, biological test

Serological exam as above

No vaccine

Which species of *Brucella* affect swine?

*Brucella suis, Brucella abortus*

How is swine brucellosis transmitted?

Contact, insemination, mating, milk

What are the clinical signs of swine brucellosis?

Dominant: Pregnant sow: abortion; Boar: epididymitis and orchitis

Also **subcutaneous abscess and arthritis**

**Serious zoonosis 🡪 biovars 1-3 highly infective** (of 5)