Brucellosis

Author

Alessandro Gerada

Published

September 4, 2023

Brief history of brucellosis

Described in many historical texts, all the way back to Hippocrates in 450 BC:

”Protracted fevers accompanied by ‘tumours’ and joint aches” (Hippocrates, n.d.)

In 1751, Cleghorn describes intermittent tertian fevers in Minorca (Cleghorn 1749).

In 1859, Assistant Surgeon Jeffrey Allen Marston described his own symptoms of “Mediterranean remittent” fever:

There is no fever so irregular as this in its course and symptoms

Sir David Bruce, in 1886, visualised and isolated Micrococcus melitensis from the spleen of a post-mortem patient:

“As it had been found by experiment that the air of the mortuary was peculiarly rich in germs … I removed the spleen to a small room in my quarters, the door and window of which had been keep shut for some time” (Bruce 1887)

Etymology

Malta fever
Rock fever
Undulant fever
Mediterranean fever
Gibraltar fever
Cyprus fever
Neapolitan fever
Italian fever

Crimean fever
Corps disease
Satan’s fever
Scottish delight
Bang’s disease
Goat fever
Fist of mercy
Milk sickness
Jones disease

Other important historical milestones

Development of serum agglutination method by Wright in 1897

Isolation of M. melitensis from goats by Temi Zammit in 1905

Against all odds

Zammit’s first attempt at investigated serostatus of 7 goats (H. V. Wyatt 2005):

all 7 were negative
it is estimated that at the time, 50% of Maltese goats were positive
odds of 7 negatives = 1:128

Repeated experiment in 1905 on 6 goats – 5 positive

Importantly, infected goats remained healthy

Mediterranean fever commission

(The Members of the Mediterranean Fever Commission. n.d.)

Sir Temi Zammit led the excavation of Tarxien temples (image c/o Heritage Malta)

Public health measures

Pasteurisation was not introduced until the late 1930

Public health measure to ban goat milk was put in place in 1906 (replaced with imported canned milk).

A milkman strike in protest of the measures likely contributed to disease control (Vassallo 1992).

(H. P. Wyatt 2013)

Bruce and the microbe

David found a little Germ

Its name, of course, you know;

For everywhere that David goes

That name is sure to go.

He found it in a Spleen one day,

And raised a cultured stock;

“With you,” he said “I’ll demonstrate

The postulates of Koch.. ”

David knew a little Boat

That was for New York bound,

With five-and-sixty little goats

That yielded milk all round.

And in the milk that microbe lurked.

(Hence David would forbid it),

And when the men got sick and ill,

“Twas germs,” he said, “that did it.”

(Vassallo 1992)

Bacteriology of Brucella spp

Gram negative coccobacillus
Evolved from environmental soil organisms
“Triple positive”:
- Oxidase positive
- Catalase positive
- Nitrate positive

Brucella colonies

(Anantha et al. 2019)

Brucella Gram stain

(Anantha et al. 2019)

Pathogenesis and immunity

Intracellular survival protects organism:

therapeutics depend on antimicrobials with high intracellular concentrations
long-term survival causes recurrence and treatment failure

Incomplete immunity

Species

In 2020, the Ochrobactrum genus was controversially assigned to the Brucella genus (Moreno et al. 2022)

Species	Preferred zoonotic host
B. melitensis	goats, camels
B. abortus	cattle
B. suis	pigs
B. canis	dogs
B. ovis	sheep
B. pinnipedialis	sea mammals

Transmission and risk factors

Modality	Mechanism
inhalation	aerosols
ingestion	dairy products
direct contact	inoculation/hypersensitivity
uncommon	human breast milk sexual blood transfusion bone marrow transplant

Worldwide epidemiology

(Pappas et al. 2006)

European epidemiology

(European Centre for Disease Prevention and Control 2022)

Clinical features of brucellosis in humans

Travel history is undoubtedly the most important question

Fever is the most important finding – classically undulating (waves) or remittent (comes and goes), although rarely seen

Musculoskeletal symptoms – differentiate febrile myalgia from localised bone and joint involvement

History may be long

Most patients are not severely unwell (if so, suggests infective endocarditis)

Any organ can be involved

Undulant fever

(Hardy et al. 1930)

Diagnosis – culture

Culture is unequivocal evidence of infection (i.e., Brucellae do not colonise)

Blood culture:

sensitivity probably around 40-50%
requirement for extended incubation times is less important if using automated incubator

Bone marrow has higher sensitivity – 60%

Other sites – joints, abscesses, etc.

Identification – MALDI-TOF is good, but defaults to B. melitensis

Laboratory risk

Significant laboratory risk – probably the most important laboratory pathogen (Traxler et al. 2013)

Largest laboratory outbreak reported in Lanzhou, China (2019) (Pappas 2022)

An inadequacy in sanitizing processes in a biopharmaceutical plant in Lanzhou, China, during July and August 2019, led to the aerosolization of Brucella that was subsequently spread through wind to nearby settlements and academic institutes, resulting in more than 10 000 human brucellosis cases…

…officials responsible for the leak have been identified and punished…

UK guidelines

Guidance on UK management available on BRU website (punishment for responsible microbiologists is not specified)

Castañeda medium

(Castaneda, n.d.)

Diagnosis – serology

Wright’s Serum Tube Agglutination remains the gold standard test – unchanged for over 120 years

Procedure:

Set up serial dilutions of the test serum
Add antigen (heated B. abortus) to tubes
Incubate overnight
Agglutinating serum forms clumps in the bottom of the tube
Non-agglutinating serum remains cloudy, with no clumps

B. canis lacks LPS, therefore needs specific serology

SAT

(Mariam et al. 2017)

Prozone effect

(Jin and Zehnder 2016)

Interpretation of serology tests

Variation between runs and interpreter – quality assurance is critical

Ideally demonstrate 4-fold increase in titre

An absolute cut-off is hard to define – certain titres may be tolerated in endemic areas

1:160 is the most agreed on cut-off

Other agglutination tests, e.g., Rose Bengal, work the same way

Diagnosis – PCR

Around 80% sensitive

Useful, but beware of idiosyncratic prolonged positivity

Case study

Clinical suspicion should be raised by presence of fever and travel to or residence in an endemic area (+/- consumption of high risk food)

Chronic infection and end organ involvement is challenging:

53-year-old man presented (Saudi Arabia) with ankle pain and swelling. No fever, animal contact, raw milk consumption reported. Routine observations and bloods normal. X-ray of ankle normal. Brucella serology 1:160. Treated with oral flucloxacillin. Bone scan showed uptake in ankle and great toe. Blood cultures negative, but synovial fluid culture of ankle joint grew B. melitensis. Repeat serology 1:640

(Adapted from: Madkour (2001))

Treatment

Susceptibility testing is not helpful, although note that B. abortus live vaccine strain is inherently rifampicin resistant

Two agents minimum

Duration:

Uncomplicated/acute – 6 weeks
Chronic/complicated – 12 weeks

Antimicrobial agents

In order of likely efficacy:

doxycycline & streptomycin (or gentamicin)
doxycycline & rifampicin
doxycycline & co-trimoxazole

Children (under 8) and pregnancy – rifampicin & co-trimoxazole

Global Impact

Brucellosis is likely to be the most common worldwide zoonotic disease

Although mortality rare, morbidity and loss of productivity due to illness is high

Brucella canis will continue to be of increasing concern in Europe and US

Lanzhou outbreak shows why Brucella spp continue to be recognised bioterrorism agents