Brucella Flashcards
What is the morphology of Brucella? What respiration does it undergo?
non-motile, single-celled coccbacillus
strict aerobe
(Category B select agent - BLS-3 required to culture nomenspecies and BLS-2 for infected tissues)
What type of pathogen is Brucella? Although most strains are aerobes, what else is required for growth?
facultative intracellular pathogen
increased levels of CO2
Why is Brucella divided into nomenspecies? What 5 things are the differentiated based on?
very similar, >90% DNA homology —> tough to separate into species
- biochemical reactivity
- antigen composition
- bacteriophage susceptibility
- DNA specificity
- sensitivity to aniline dyes
What are the principal nomenspecies of Brucella causing disease in horses, pigs, dogs, cattle, sheep, goats, and humans?
HORSES: B. abortus
PIGS: B. suis
DOGS: B. canis
CATTLE: B. abortus, B. suis
SHEEP: B. melitensis, B. ovis (epididymitis)
GOATS: B. melitensis
HUMANS: B. abortus, B. melitensis, B. suis
(NOT host-specific)
How is Brucella able to survive in macrophages?
(facultative intracellular pathogen)
- inhibits phagosome-lysosome fusion
- suppresses oxidative metabolites
What nomenspecies of Brucella have LPS antigens? How are they differentiated?
smooth nomenspecies - B. abortus, B. melitensis, B. neotomae, B. suis
~100 repeats of 4,6-dideoxy-4-formamido-D-mannose with A or M antigens linked to O antigen
- A antigen = B. abortus
- M antigen = B. melitensis
What is the purpose of the LPS on Brucella’s surface?
- O antigen is involved in the agglutination reaction
- may contribute to intracellular survival, but is NOT a substantial endotoxin
What 3 species of bacteria are closely related antigenically to Brucella?
- Yersinia entercolitica O:9
- Francisella tularensis
- E. coli O157:H7
What 2 species of Brucella have rough LPS? What does this mean?
B. canis and B. ovis
lacks O antigen, making it less virulent, and has a core oligosaccharide of mannose, glucose, etc. (KDO)
What acts as a reservoir for Brucella? What are 4 ways of transmission?
carrier animals or newly infected animals
- ingestion of placenta, uterine fluid, milk, or urine
- exposure of infected mucous membranes
- venereal
- congenital
What is the most common way of zoonotic transmission of Brucella?
(B. abortus, B. melitensis, B. suis, B. canis)
handling of aborted fetus, placenta, uterine fluids, or consuming infected milk or cheese
What is the most common result of venereal transmission and genital Brucella infection?
cleared in 4-6 weeks, but can persist in the udder and reticuloendothelial system indefinitely
In what 3 ways is Brucella abortus most commonly transmitted?
- ingestion*
- venereal
- intramammary/congenital
What is the pathogenesis of Brucella abortus?
- bacteria penetrate mucous membranes
- localizes in regional lymph nodes
- phagocytosis by neutrophils and fixed macrophages
- bacteremia disseminates to udder, uterus, genital tract of males, and reticuloendothelial system
Where does Brucella abortus proliferate best?
within cells with high levels of erythritol, like trophoblasts of the placenta —> gives a genital tract tropism
- placenta with hemorrhagic cotyledons
How does Brucella abortus affect the placenta? What is the end result of most infections after symptoms cease?
- thickened
- cotyledons show local or diffuse areas of necrosis
- retained placenta
most infected animals remain carriers and shed bacteria after calving
In what 2 ways does Brucella abortus infection affect the fetus?
- abortion after 5th month, usually only during first pregnancy
- edematous fetus with blood-tinged fluid in the body cavity (+/- turbid abomasal contents)
Brucella is fastidious and can often get overgrown by other bacteria. How can it be isolated from tissue?
it can be isolated from sterile tissue only, like the fetus and lungs
- NOT the placenta
- send to BSL-3 facility
How is serology used to diagnose Brucella abortus infection? What 2 tests are commonly used?
based on LPS O antigen
- tube agglutination test - IgM, IgG
- Card/Rose Bengal test - slide type agglutination assays performed with a stained B. abortus suspension at pH 3.6-3.7 + serum test of IgM —> acute infection
How are Rivanol and Mercaptoethanol tests used to diagnose Brucella abortus infection?
distinguishes between chronic infection and vaccination where IgM is removed from the serum
- titer decrease = strain 19 (vaccine)
- IgG > IgM = chronic infection
(allows for DIVA)
What aspect of immunity is used to defend against Brucella abortus infection?
cell-mediated immunity where sensitized T cells release cytokines that activate macrophages
- humoral immunity may act as blocking antibodies to prevent complement-mediated lysis or enhance cellular uptake as opsonins
Why are pregnant animals not vaccinated with the attentuate live vaccine (Strain RB51) of Brucella abortus? What is a major benefit to this vaccine?
virulent enough to cause abortion
rough strain (no LPS) allows for DIVA —> O antigen presence in infected animals
Why is there no DIVA in the viable smooth strain (Strain 19) vaccine against Brucella abortus?
smooth strain has O antigen, so there is no way to differentiate between infection and vaccination
How is Brucella abortus infection controlled?
- test and slaughter
- vaccinate all replaceable animals
- enhance hygiene
What is the Brucella antibody milk ring test? How is this test used?
antibodies to Brucella is added to milk and, if the bacteria is present, agglutination will occur
- herd level
- high false-positives, so on a positive test, begin testing individuals
Where is Brucella abortus a major problem?
elk and bison in Yellowstone and Western states in contact with farm animals
(US was declared Brucella-free in 2008)
Why isn’t treatment of Brucella abortus attempted in pigs and ruminants? What treatment is usually done?
therapy needs to be long-term and failures are common
- intracellular infection = difficult to eliminate
cull infected animals and vaccinate new ones
What was the first Brucella species isolated?
B. melitensis —> most virulent to humans; Southwestern US, Mexico, Central America, Southern Europe, Africa
(low infectious dose by aerosol, low mortality)
What is the major way that Brucella melitensis is transmitted? What are 2 major sources?
ingestion
- food and water contaminated by urine and vaginal discharges
- milk and cheese (humans)
In what animals does Brucella melitensis typically cause disease? What are 3 major clinical signs?
goats* and sheep
- late pregnancy abortion
- lameness, hygromas (cysts with serous fluid)
- mastitis, orchitis
How is Brucella melitensis typically diagnosed?
serologic tests (screening, antibody tests)
+ clinical signs and direct culture in BSL-3 labs
What are the main 2 Brucella melitensis strains used for vaccinations?
- Strain Rev 1 - live avirulent strain most effective for preventing abortion and reducing shedding (may localize in placenta and cause abortion in pregnant animals)
- Strain 53H38 - inactivated strain that stimulates a more persistent antibody response (no DIVA)
In what 2 ways is Brucella suis most commonly transmitted? What typically acts as a reservoir? What is unique about this species?
- venereal
- ingestion of feed contaminated by urine or genital excretions
wild hares
able to persist in the environment better than the other species
Why has Brucella suis been difficult to eradicate and a persistent human pathogen? In what animals is infection most common?
high prevalence in feral swine and can transmit it to domestic swine and humans (abattoir workers, farmers, veterinarians, hunters)
adult swine
What are 8 signs of Brucella suis infection?
- bacteremia (death, infected carcasses in immunocompromised)
- abortion
- metritis
- spondylitis
- orchitis
- arthritis
- lameness
- paralysis
How does Brucella suis infection compare in females and males? How long does immunity last?
females recover after several months and males usually do not
immunity in swine is short-lived —> most animals are readily re-infected when re-exposed —> abortions are most common after initial infection
What is considered the best way of diagnosing Brucella suis infection?
Rose Bengal card test (+ other serum agglutination tests)
- not as effected as with B. abortus (different O antigen)
+ clinical signs, direct culture
What is the best means of controlling Brucella suis infection? What is Brucella-Free Herd status simultaneously determined with?
- eradicate infected animals
- Pseudorabies
Why is Brucella canis less virulent to humans?
lacks O antigen (rough)
In what 2 ways is Brucella canis transmitted?
- ingestion - primary mode
- venereal - intermittent shedding in males that recover
How long does bacteremia from Brucella canis typically persist?
2 years after infection
- persistence leads to chronic inflammatory response
What are 4 clinical signs of Brucella canis infection in females?
- abortion - last trimester (~50 days)
- lymphadenitis and splenitis
- infertility
- sick or stillborn puppies
What are 3 clinical signs of Brucella canis infection in males?
- epididymitis
- scrotal dermatitis
- testicular atrophy (unilateral) —> infertility
What immunity is necessary for protection from Brucella canis infection?
cell-mediated immunity
- humoral response is highest during bacteremia, but is not protective
What is the best method of Brucella canis infection diagnosis? Why?
direct culture from blood, bone marrow, or lymph nodes
not as virulent as other nomenspecies
Why are serological tests not as commonly used to diagnose Brucella canis infection? What is the gold standard if it this type of testing is used? When are negative results reliable?
subject to false positives, since assays used for serological diagnosis of B. abortus and others are based on the presence of the O antigen, which B. canis lacks
immunodiffusion
in chronic infections
Why are serological tests not as commonly used to diagnose Brucella canis infection? What is the gold standard if this type of testing is used? When are negative results reliable?
subject to false positives, since assays used for serological diagnosis of B. abortus and others are based on the presence of the O antigen, which B. canis lacks
immunodiffusion
in chronic infections
What is the best means of control of Brucella canis infection? Second best?
euthanasia
neuter and long-term antibiotic therapy (relapse concern, infection lasts a long time)
How is Brucella ovis transmitted?
venereal
(remember, lacks O antigen = rough)
How does Brucella ovis affect rams, ewes, and the entire herd? What goats are most commonly clinically affected?
RAMS: epididymitis
EWES: late abortions
HERD: lowers flock fertility rate
rams > ewes
What is the zoonotic potential of Brucella? What is the relative pathogenicity of the nomenspecies? What 2 antibiotics are recommended?
highly infectious for humans
B. melitensis > B. suis and B. abortus > B. canis
tetracyclines and gentamycin
What are 5 common clinical signs of Brucella infection in humans?
- lethargy
- malaise (discomfort)
- chills
- night sweating
- intermittent fever
What are the most common Brucella nomenspecies causing occupational infections in humans?
- B. abortus
- B. suis
How does Brucella melitensis most commonly transmitted to humans?
ingestion of goat milk, cheese, or dairy product
(importance of pasteurization!)
