Brucella Brucellosis was first described by British physician David Bruce, who in 1886 - PowerPoint Presentation

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Brucella

Brucellosis was first described by British physician David Bruce, who in 1886 isolated a bacterium from the spleen of patient with a fatal disease known as Malta or Mediterranean fever.

Benhard Bang, a Danish veterinarian recovered what we now known as

Brucella abortus

from a bovine fetus in 1895.

Recognition of brucellosis as a zoonosis in the early twentieth century contributed to establishment of requirements for pasteurization of milk. Brucella species are G-, strictly aerobic, non-motile, coccobacilli or small rods, they are facultative intracellular parasite belong to the family Brucellaceae. They produce oxidase, catalase, nitrate reductase, & urease (Except

Brucella ovis

), indol -, non-hemolytic, MR-VP are negative, Most (except

B. ovis

) utilize glucose as a source of energy.

Six classical species;

B.abortus, B. melitensis, B. suis, B. ovis, B. canis, B. neotomae.

Each species has a preferred host that serve as a main reservoir for infection

.

Brucella species, their host range and the clinical significance of infection

Brucella

species

Usual host/clinical significance

Species occasionally infected/clinical significance

B.abortus

Cattle/ abortion,

orchitis

Sheep, goats, pigs / sporadic abortion

Horses/

brusitis

Human

/ intermittent fever, systemic disease

B.melitensis

Goats,

sheep/abortion,

orchitis

, arthritis

Cattle/sporadic abortion,

brucellae

in milk.

Humans/

Malta fever, severe systemic disease

B.suis

Pigs / abortion,

orchitis

, arthritis,

spondylitis

, infertility

Humans/ intermittent fever, systemic disease

B.ovis

Sheep/

epididymitis

in rams, sporadic abortion

in ewes

B.canis

Dogs/ abortion,

epididymitis

,

discosponydylitis

, sterility in male dogs

Humans/ mild

systemic disease

B.

neotomae

Desert wood rat/ Not isolated from domestic animals

B.Ceti

and

B.pinnipedialis

Sea

animals

Humans / little evidence of disease

Main characteristics of Brucillae

Small

Gram negative

coccobacilli

Stain red using the modified

Zeil-Neelsin

stain

Aerobic and

need CO2

Non-motile

Catalase

-positive

Most isolates

are

oxidase

positive

nitrate

reductase

, &

urease

+

ve

(Except

Brucella

ovis

),

indol

-,

non-hemolytic,

MR-VP are negative,

Most (except

B.

ovis

) utilize glucose as a source of energy.

Intracellular pathogens

Target reproductive organs of certain species of animals

Some species cause undulant fever in humans

Disease

& Epidemiology

Genus Brucella are the agents of Brucellosis, a worldwide zoonotic disease. The disease is highly endemic in Mediterranean countries, Africa, the Middle East, India, Central Asia, Central & South America. The host range include humans, ruminants, swine, rodents & marine mammals. Cats appear to be resistant to infection. Infection occurs through inhalation or ingestion of organisms. Animals are the reservoirs & can be the source of infection. Organisms reside inside cells of the retioculoendothelial system & reproductive tract & cause lifelong chronic infection. They are the leading cause of abortion & sterility in domestic animals. High members of bacteria are shed in urine, milk, vaginal discharge, semen & the products of birth.

Brucellae may remain viable in carcasses & tissue for up to 6 months at approximately 0 C. They survive up to 125 days in dust or soil, & for as long as 1 year in feces.

Disease

& Epidemiology

Brucellae are susceptible to many disinfectants, including 1% sodium hypochlorite, 70% ethanol, iodophors, glutaraldehyde & formaldehyde. The organisms are physically inactivated by moist heat (121 C, 15 minutes) & dry heat (160 C , 1 hour).

Brucella abortus

:

Is the etiological agent of bovine brucellosis (Bang’s disease). The organism preferentially infect bovine, but sometimes transmitted to other animals, including camels, dogs, horses, sheep, goats & pigs.

In cattle, brucellosis is primarily a disease of the cow. Bulls can be infected but they do not readily transmit the organism venereally .

B. abortus

localize in the testicles, resulting in unilateral orchitis, epididymitis & inflammation of accessory reproductive organs with decreased libido & impaired infertility. In cow there is predilection for udder, endometrium & associated LNs.

Disease

& Epidemiology

Clinical signs:

In infected cows include abortion during & after the fifth month of gestation, birth of weak calves, or retained placenta. Although the infected cows typically abort only once, the placenta become colonized by brucellae during each pregnancy. The subsequent offspring may be born weak or apparently health. Because of in utero infection or ingestion of contaminated milk in the neonatal period, apparently healthy calves may become carriers & pose a significant risk to herd & human health.

B. abortus

is shed in large numbers in the afterbirth placental fluids, aborted fetus & vaginal discharge. Cattle become infected when they ingest contaminated forage or lick calves or aborted fetuses.

Horse may be naturally infected with

B. abortus

& the organism has a tendency to localize in joints, bursae, or tendon sheaths.

Disease

& Epidemiology

Sporadic infection with

B. abortus

have been reported in dogs ingested reproductive materials from infected cows. Abortion, epididymitis & joint lesions occur in infected animals.

Brucella melitensis:

Most commonly infects sheep & goats. The organism is regarded as the most virulent of the brucella species & accounts for most cases of human brucellosis. Disease is endemic in Middle East, China, Russia, part of Africa & Latin America. The epidemiology & pathogenesis is similar to that of

B. abortus

. The main risk factor are contact with contaminated genital discharge & ingestion of raw milk. Sexual transmission is more frequent than in bovine brucellosis. Breed susceptibility is variable in sheep, but goat breeds are highly susceptible. Clinical signs include abortion, mastitis, lameness & orchitis.

Disease

& Epidemiology

Brucella ovis

:

Has long been recognized as a pathogen of sheep & display a high degree of host specificity. Although it occasionally associated with abortion, it primarily affects rams. Infectious epididymitis, orchitis, & infertility are common disease manifestations. Persistent nephritis can develop in rams & is the most serious complication. Ewes are often infected with vaginitis, stillbirths, or birth of weak lambs. Ovine brucellosis is most commonly spread directly from ram to ram by sexual contact, or indirectly, from sexual contact with ewes that have been inseminated by infected ram.

Brucella canis:

Is isolated from dogs, although natural disease has also reported in foxes. Infection usually results from ingestion or inhalation of organisms aerosolized from aborted fetuses, vaginal discharge, milk, semen or urine.

Disease

& Epidemiology

Dogs become infected after 4-6 months of cohabitation with an infected dogs.

Only the uterine epithelial cells of the gravid bitch are colonized, result in early embryonic death or abortion. Infected pups are rarely survive. Non-pregnant bitch show no overt clinical signs, but may shed organisms in saliva, nasal or vaginal discharge. In males, brucellosis manifests as infertility with epididymitis rather than orchitis.

Geographical distribution of B.abortus &

B.melitensis

Brucellosis

in humans

Brucellosis in humans is known as undulant fever or Malta fever because of fluctuations in body temperature that are characteristic of the disease. It is an occupational disease of veterinarians, abattoir workers, laboratorians & farmers. All brucellae are potentially pathogenic for humans, but

B.abortus, B.melitensis, B. canis & B.suis

are responsible for most cases. Ruminants are the primarily reservoirs of human infection & the most common mode of transmission is consumption of unpasteurized dairy products. Other routes of infection are contamination of abraded or wounded skin, inhalation of infectious aerosols, & contamination of conjunctiva or other mucous membranes. The infectious dose by inhalation has been estimated at 10-100 organisms. The incubation period is variable (5 days- 2 months). Human brucellosis is a systematic disease with an acute or insidious onset. Symptoms include intermittent fever, chills, sweating, headache, arthralgia, & weakness. Subclinical infection are frequent. The mortality rate in untreated cases is < 5%. Relapses rate is high. Person-to-person transmission is very rare.

Pathogenesis

The pathogenesis caused by most species is much the same. Brucellae are shed near the time of abortion or parturition, as well as in milk of chronic infection of supramammary LNs & from other body sites. Susceptible animals ingest bacteria that invade the oral mucosa reaching the regional LNs either in free state or within the macrophages. Localization & proliferation in the LNs during an incubation period (2weeks- 7 months). After bacteremic period, brucellae localized in the RES (spleen, liver, supramammary LNs or bone marrow), mammary glands & reproductive organs. During midgestation,

B.abortus

proliferate in & around placenta cotyledons due to the growth-stimulatory effects of erythritol, which is present in high concentration in cotyledons & fetal fluids. Necrotic placentitis results & abortion is attributed to fetal anoxia & ebdotoxemia.

The true virulence of brucella species appear to be in their ability to invade & survive within host cell, by mechanism that avoid or inhibit the fusion of phagosome with the lysosome. Inhibition of the TNF-a production, because it is involved in intracellular killing.

Diagnosis

Direct examination of tissues with fluroscent antibody (DFAT).

Isolation & identification of bacteria by culture: the most valuable specimen are aborted fetal tissues, placenta, LNs, uterus, vaginal discharge, semen, urine, & bone marrow. Blood culture the single best diagnostic test. Growth can be enhanced by addition of blood or serum & incubation at 5-10% CO2. Tryptose or Trypticase soy agar containing 5% serum is recommended for a non-selective media. Plates are incubated upto 14 days before being discarded as negative. Brucella agar also can be used.

Biochemical reactions & Modified acid-fast stain.

Serological agglutination test for detection of brucella antibodies in serum specimens (Rose Bengal test). It can be used as screening test.

Direct fluorescent antibody technique

Diagnosis

5. ELISA test for detection of brucella antibodies (IgG or IgM), it is more sensitive & specific than agglutination test.

6. Molecular detection of brucella antigens by PCR. It can discriminate brucella classical species.

7. 2 mercaptaethanol test: The addition of 2ME destroy IgM & leaves IgG for agglutination reaction.

8. Intradermal skin test.

Tests used for diagnosis of bovine brucellosis using milk or serum

test

comments

Brucella

milk ring

Conducted on bulk

milk samples for monitoring infections in dairy herds. Sensitive but may not be reliable in large herds

Rose-Bengal test

Useful screening test. Antigen suspension is adjusted to pH 3.6, allowing

agglutination by IgG1 antibodies. Quantitative test only, positive results require confirmation by CFT or ELISA

Complement-fixation test

Widely accepted confirmatory test for individual animals

Indirect ELISA

Reliable screening and confirmatory test

Competitive ELISA (using monoclonal

antibodies)

Recently

developed test with high

specifity

; capable of detecting all immunoglobulin classes and can be used to differentiate infected animals from S19-vaccinated cattle.

Serum agglutination test (SAT)

A tube agglutination test which lacks

specifity

and sensitivity; IgG1 antibodies may not be detected, leading to false-negative results.

Antiglobulin

test

Sensitive

test for detecting non-agglutinating antibodies not detected by the SAT.

Characteristics of Brucella species of veterinary importance

Brucellae

No. of biotypes

Requirement for CO2

H2S

Prod.

Urease

Growth in

media containing

Thionin

20µg/ml

Basic

fuchsin

20µg/ml

B.abortus

7

V

V

+

V

V

B.meltensis

3

_

_

V

+

+

B.suis

5

_

V

+

+

V

B .

ovis

1

+

_

_

+

_

B.canis

1

_

_

+

+

_

V= variable reactions related to different biotypes