Brucellosis
Author: Prof Jacques Godfroid
Adapted from: Godfroid J., Bishop G.C., Bosman P.P. & Herr S. 2004. Bovine brucellosis, in Infectious diseases of
livestock, edited by J.A.W. Coetzer & R.C. Tustin. Oxford University Press, Cape Town, 3: 1510-1527.
Licensed under a Creative Commons Attribution license.
Introduction
healthy, infected cows continue to harbour and
Brucellosis is a contagious, costly disease of ruminant
discharge infectious organisms and should be
animals that also affects humans. Although brucellosis
regarded as dangerous sources of the disease. Other
can attack other animals, its main threat is to cattle,
signs of brucellosis include an apparent lowering of
sheep and goats, and swine. It can also affect wildlife.
fertility with poor conception rates, retained afterbirths
Considering the damage done by the infection in
with resulting uterine infections, and (occasionally)
animals such as decreased milk production, weight
enlarged, arthritic joints.
loss in animals, loss of young, infertility, and lameness,
it is a serious disease of livestock. The rapidity with
Where does brucellosis occur?
which it spreads and the fact that it is transmissible to
Information related to the epidemiology of brucellosis
humans emphasizes the serious nature of the disease.
per country or continent, can be found at the World
Animal
Health
Information
Database
(WAHID)
The disease is caused by a group of bacteria known
Interface:
scientifically as the genus Brucella. Three species of
http://web.oie.int/wahis/public.php?page=home
Brucella
abortus,
The WAHID Interface provides access to all data held
principally affecting cattle; B. suis, principally affecting
within OIE's new World Animal Health Information
swine; and B. melitensis, affecting sheep and goats.
System (WAHIS). Disease timelines (2005-2012) can
Bacteria are shed in milk or via the aborted fetus,
be retrieved from the database. The information
afterbirth, or other reproductive tract discharges.
reported for South Africa can be summarized as
cause
the
most
concern:
B.
follows: the presence of B. abortus is confirmed but
Salient features of brucellosis
limited to certain zones, both in cattle and wildlife.
There is no effective way to detect infected animals by
Confirmed clinical infection has also been reported.
their appearance. The most obvious signs in pregnant
Brucella melitensis has been confirmed on 2 occasions
animals are abortion or birth of weak calves. Milk
in 2007 and 2010, whereas the disease has not been
production may be reduced from changes in the normal
reported at other times during the period 2005-2011.
lactation period caused by abortions and delayed
Brucella suis has never been reported. Brucella ovis
conceptions. Not all infected cows abort, but those that
clinical infection has been seen in rams (epididymitis)
do usually abort between the fifth and seventh month
during the whole period.
of pregnancy. Infected cows usually abort once, but a
percentage will abort during additional pregnancies,
and calves born from later pregnancies may be weak
and unhealthy. Even though their calves may appear
What triggers an outbreak of brucellosis?
ingesting
interface it is critical to reduce opportunities for Brucella
contaminated feed or water or licking an infected
to jump host species as has already occurred in
placenta, calf or fetus, or the genitalia of an infected
livestock, wildlife and humans.
Cattle
usually
become
infected
after
cow soon after it has aborted or calved at which time
very large numbers of B. abortus are present,
particularly in the placental lochia. Animals may also
become infected by inhaling organisms or through the
conjunctiva. Calves may acquire infections in utero or
they may become infected after ingesting infected
colostrum or milk. Although some will rid themselves of
the infection within a few months, others may remain
infected for life and may spread the disease at their
first and subsequent parturitions.
In a study done in Kampala, urban residents who had
no contact with livestock were at risk of being Brucella
infected, an exposure attributed to consumption of raw
milk products purchased from rural and peri-urban
area. Since consumption of raw milk continues to be a
major mode of exposure as demonstrated in several
studies, pasteurization or boiling of milk and milk
products is likely to reduce human infections.
Prevention and control
Vaccination is the cornerstone of control programmes
in livestock and although the S19, RB51 (both in cattle)
and Rev 1 (in sheep and goats) vaccines have been
successfully used worldwide, they have drawbacks and
the ideal brucellosis vaccine is still awaited. There is no
vaccine
available
for
pigs
and
wildlife.
Animal
brucellosis control strategies differ in the developed
and the developing world. Most emphasis is put on
eradication and on risk analysis to avoid the reintroduction of Brucella in the developed world.
Information related to the prevalence of brucellosis is
still scarce in the developing world and control
programmes are rarely implemented.
Since there is no vaccine available for humans,
prevention of human brucellosis relies on its control in
the animal reservoir. At the animal/ecosystem/human