Brucella

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Brucella abortus

Obligate parasite with no life cycle outside the host.

Highly infectious: transmission can be by ingestion, venereal or by skin (vets). Aborted foetuses and foetal membranes are the main contaminants of the environment.

Once introduced by ingestion/mating or skin contact it enters the reticuloendothelial system. If the animal is a bull it then localises in the testes (as they contain erythritol which is required by Brucella for growth), if it is non-pregnant cow it will travel to the mammary glands causing interstitial mastitis and will be shed in the milk (pathway for zoonotic spread), if the cow is pregnant then it will also localize in the placental and foetal fluid containing erythritol and cause abortion around 6 months gestation. The aborted foetus and placenta then contaminate the environment.

CSx: 3rd trimester abortions, retained placentas that have a leathery appearance, endometritis, birth of weak/dead calves, decreased fertility, testicular degeneration in bulls, reduced milk production and hygromas in endemic brucellosis (swollen joints).

Virulence factors:

- invasiveness

-erythritol requirement

-serum resistance (more so in smooth strains that have the long O side chain blocking igG).

-intracellular survival, resistance to lysosomal degradation,

Immunity

- predominantly CMI, but is not always enough to prevent re-infection so there are chronically infected carriers.

Diagnosis

- clinical exam, hypersensitivity reaction

-samples from placenta, fetus, semen, milk, for acid fast stains, culture,

- rose bengal test as initial screen, then test positives by compliment fixation for identification and culling if wanting to eradicate.

-PCR

Control

-test and cull

-vaccination in endemic areas to prevent abortion, but not infection, however stopping abortion does break the cycle of transmission.

Brucella melitensis- Caprine and Ovine brucellosis

In the Middle East, Central Asia, parts of South America.

Late term abortion, retained placentas, orchitis, arthritis, and hygromas. Reduced milk yield/mastitis too.

Brucella canis

Causes abortion in the 7-9th week, prolonged vaginal discharge, orchitis, epididymitis, and prostatitis.

Transmission ingestion.

Lower virulence. Control by desexing. Readily killed by antibiotics.

Brucella ovis

Affects sheep not gaots, causes abortion and fertility problems. Epididymitis, orchitis and sterility in rams.

Transmission is venereal. Diagnosis by palpation of testes, culture of semen and compliment fixation test.

In Australia Brucellosis is a notifiable disease.

B suis

Transmission venereal. In sows is causes abortion and metritis. In boars it causes lameness, orchitis and sterility. In Australia it is rare in commercial piggeries, but relatively common in feral pigs. There are 20-30 humans cases/yr, related to feral pig hunting and much less commonly lab exposure.

CSx in humans include fatigue, and arthralgia but not abortion.

Brucellosis in humans

B melitensis > B suis > B abortus and rarely infected by B canis.

B melitensis the principal cause of human brucellosis, and is usually transmitted by consumption of unpasturised milk.

It is also an occupation risk for veterinarians, farmers and meat workers that may be exposed to aborted foetuses, placentas etc containing large amounts of brucella.

CSx in humans are variable, but do not include abortion as the human placenta does not contain erythritol. Complications may include suppurative pericarditis, mental depression and arthritis. Mortality is low.

Dx by isolation of brucella in blood, bone marrow, or other tissues. Can also do a paired serum agglutination test looking for a 4 fold increased in titer. There is also PCR.

Tx: high dose and long course of antimicrobials. CNS cases should be treated for 6-9 months.