Contagious abortion - Bang's disease"
fever, Malta or Mediterranean fever
Nature of the disease
is the contagious disease caused by the genus Brucella,
in which it generally cause reproductive failure; that is,
abortion or birth of unthrifty newborn in the female, and
orchitis and epididymitis with frequent sterility in the male
in a wide range of animal species and can affect man.
Animal brucellosis caused by various Brucella spp. is
widespread, it affects cattle and buffalo (B. aborts),
sheep (B. ovis), sheep and goats (B. melitensis),
and pigs (B. suis). Brucellosis occasionally affects
dogs (B. canis) and horses (B. aborts - B. suis).
In man, infection by B. melitensis and B. aborts
causes Malta, and undulant fever respectively.
Persistent "lifelong" infection is common with this
facultative intracellular organism that is able to survive and
multiply within phagocytic cells and reticuloendothelial
tissues with shedding in reproductive and mammary secretions.
Brucellosis is considered by FAO, WHO, and 0IE as the most
widespread zoonosis in the world. B. melitensis, being
very pathogenic for humane beings and the possibility of
infection occurring by the drinking of infected sheep and goat
milk necessitates the pasteurization of milk.
Animal brucellosis has a major economic impact in the major
cattle-farming regions of the world primarily due to abortions
and calf losses, decreased milk production and infertility
that increases the period between lactations and prolongs the
average of intercalving period. In sheep and goats, the
economic losses stems from decreased breeding efficacy due to
rams infertility and reduced milk production.
0IE classification: list "B."
History and Occurrence
Bruce in Malta identified B. melitensis for the first time in
1887 whereas B. abortus was identified by Bang in Denmark in
1897. The first record of brucellosis in Africa was that of
Gray in 1906 in South Africa. In Egypt, Ahmed was the first to
investigate the problem of brucellosis serologically among
animals in 1939.
Brucellosis is widespread in most undeveloped countries
especially of the Mediterranean region Middle East, Western
Asia, and parts of Africa including Egypt and Latin America.
Many countries have made considerable progress with their
eradication programs and some eradicated the disease.
Brucella spp. are small Gram-negative, non-motile,
non-sporulated, non-encapsulated rods or coccobacilli. They
are partially acid-fast in that they resist decolorization by
weak acids in the modified Ziel-Neelson stain and the retained
carbol fuchsin stains red the coccobacilli against the blue
Brucella are aerobes that require enriched media for primary
isolation, they grow well on 5-10% blood agar but specimens
other than fetal abomasal contents and colostrums requires
selective serum agar media, such as Farrell's medium. B.
abortus biotype-2, B. ovis, and B. canis are fastidious, slow
growing, and require 5-10 % C02 for primary isolation to start
and later ordinary air is sufficient. On specific media, such
as tryptose agar, brucella allbimi agar, liver infusion agar,
blood agar, and serum dextrose agar, at pH 6.6 - 6.8, after
2-4 days incubation brucella colonies are round entirely
smooth, convex, glistening and translucent. Young colonies are
pale honey color, 1-2 mm in diameter. Later, colonies become
larger and slightly darker on continuous incubations.
Brucella spp. and biovars can differentiated on the bases of
C02 requirements, production of hydrogen sulfide (HS),
sensitivity to azo dyes, phage susceptibility, agglutination
in monospecific sera, and other in vitro laboratory
There are six species presently known in the genus Brucella.
They are nearly similar morphologically, culturally,
biochemically and serologically, B. abortus (9
biotypes-cattle), B. melitensis (3 biotypes-sheep and goats),
B. suis (4 biotypes-swine), B. ovis (sheep), B. canis (dogs
and other carnivores), and B. neotama (desert wood rat).
B. abortus will survive for up to 8 months in an aborted fetus
in shade, 1-2 months in dry soil, 2-3 months in wet soil, 3-4
months in feces and for 8 months in manure storage tanks at
15°C. The pathogen will survive for few hours only when
exposed to direct sunlight.
Brucellae are sensitive to pasteurization temperatures, sour
milk or other products with a low pH., and susceptible to
chemical disinfectants such as 2- 5 % carbolic acid solution
Cattle and buffalo are the natural hosts for B. abortus, and
infection occurs in all ages but is most common in sexually
mature animals, particularly dairy cattle. Cattle and buffalo
are liable to catch B. melitensis and B. suis (rarely) in
regions where these spp. are prevalent.
B. melitensis is the important spp. that ordinarily infects
goat flocks, but goats are liable to catch B. abortus and B.
suis. Sheep are naturally infected with B. ovis and B.
melitensis, but are liable to catch B. abortus and B. suis.
Camels are liable to catch B. abortus and B. melitensis.
Horses may occasionally infected with B. abortus and B. suis.
Dogs and cats may occasionally infected with B. canis, but
dogs may also catch B. abortus, B. melitensis and B. suis.
Dogs are important mechanical vectors of brucellosis by
transporting of infected placentas and fetuses.
In human brucellosis: B. melitensis is the most pathogenic
and occurs more frequently, followed, in order by B. suis and
Immature animals often showing little or no clinical disease
but sexually mature animals are the most susceptible
especially in the breeding season.
Guinea pigs are susceptible to all brucellae except B. ovis.
Brucellae are present in the placenta, fetal fluids, fetus,
vaginal discharges, milk, semen and urine. Infectious bacteria
are also found in the bursa of horses with poll evil or
fistulous withers. The major sources of infection are the
contents of the pregnant uterus, the fetus and the fetal
membranes, which contain large number of organisms that
contaminate the vulva, tail, legs of the animal, and the
surrounding environment. Excretion of organisms may occur for
several days before abortion and up to several weeks after.
Some infected cows that aborted previously shed brucellae from
the uterus at subsequent normal parturitions. Most cows and
heifers excrete brucellae in colostrums and milk during the
first month of lactation, but some animals, can shed long-term
or lifelong. In addition, the organism is secreted in urine,
semen, and feces of infected animals.
Infection occurs mainly by ingestion of contaminated feed and
water or after licking an infected placenta, calf, fetus or
the genitalia of infected cow soon after it has been aborted
or calved. Infection can also occur by penetration of skin,
mucous membranes, and conjunctiva, or via inhalation. Venereal
transmission rarely occurs in bovine brucellosis. However,
artificial insemination with infected semen often results in
transmission of the disease.
Calves are infected in utero or by sucking infected dams.
Humans become infected by ingestion (raw milk - unpasteurized
cheese), through the mucous membranes and breaks in the skin,
and probably by aerosols (in abattoirs and laboratories).
Most wild animals, rodents, insects and blood sucking
arthropods (such as ticks) are carriers and reservoirs for
infection, so they play a role in transmission of the disease
Cattle and buffalo are the natural hosts for B. abortus, and other
animals that are liable to catch the infection are considered
"dead-end hosts" as they rarely act as a source of infection to
The course and infection consequences are usually governed by the
age of infected animal and the immune status of the herd. Systemic
signs do not usually occur and abortion rates in full susceptible
herds vary from 30-70%. Calves not yet at puberty are fairly
resistant to infection.
In highly susceptible non-immune herds, there is a high incidence
of abortion (storm of abortions) in pregnant cows last for a year
or more during the second half of gestation especially in the last
3 months of pregnancy. In subsequent pregnancy, the fetus is
usually carried to full term but she will continue, at subsequent
normal calvings, to shed the bacteria from the uterus and in the
milk, although second or even third abortions may occur in the
same cows. In less acute infections, cattle may give stillbirths
and weak calves, or merely show a retained placenta leading to
increased incidence of retained placenta in a herd. After
abortion, metritis will follow in the majority of cases, impairing
the fertility of the animal. Other signs of brucellosis infection
in a herd may be decreased milk yield. In infected bulls, an acute
to chronic orchitis, epididymitis and seminal vesculitis
occasionally occurs. Arthritis and hygromas, especially of the
carpal joints may occur in chronic infections in both males and
females. Septicemia and death may occur in rare cases.
Cattle and buffalo are readily infected with B. melitensis when in
close contact with infected goats and sheep, which sometimes
causes them to abort but often confined to the udder and
supramammary lymph nodes and excretion of the organism in the milk
may prolonged for months or years. B. suis infection in cattle is
rare and self-limiting.
In sheep and goats, B. melitensis can cause abortion, retained
placenta, orchitis and epididymitis. Abortions usually occur late
in gestation in sheep and during the fourth month of gestation in
goats. In goats, mastitis and lameness may be seen. Arthritis is
rare in sheep.
B. ovis affects sheep only that can cause epididymitis, orchitis
and impaired fertility in rams. Initially, only poor quality semen
may be seen; later, lesions may be palpable in the epididymis and
scrotum. The testes may atrophy permanently. Abortions,
placentitis and prenatal mortality can be seen but are uncommon.
Systemic signs are rare.
B. abortus and B. suis occasionally infect sheep and goats if kept
in contact with cattle and pigs.
Brucellosis in pigs
In pigs infected with B.suis, the most common symptom is abortion
at any time during gestation, weak or stillborn piglets, and
temporary or permanent infertility. Temporary or permanent
orchitis can be seen in boars that excrete B. suis
asymptomatically in the semen and sterility may be the only sign
of infection. Swollen joints or lameness can occur in both sexes.
Brucellosis in camels
B. abortus and B. melitensis occasionally can infect camels, which
may leads to abortion or stillbirths, bilateral lacrimation,
slight lameness, and reduced appetite.
Brucellosis in horses
In horses, B. abortus and occasionally B, suis can cause
inflammation of the supraspinous or supra-atlantal bursa known as
fistulous withers or poll evil respectively. The bursal sac
becomes distended by a clear, viscous, straw-colored exudate and
develops a thickened wall. It can rupture, leading to secondary
inflammation. Arthritis, intermittent lameness, and abscesses in
the region of the sternum and fetlock may be evident.
Brucella-associated abortions are rare in mares.
Brucellosis in dogs
Dogs occasionally become infected with B. canis and may catch B.
abortus, B. melitensis and B. suis.
B. canis causes abortions, stillbirths, and infertility in dogs.
Abortions usually occur during the last trimester and are followed
by a prolonged vaginal discharge.
Infected dogs may have lymphadenitis, epididymitis, orchitis and
Asymptomatic infections are common in humans. In symptomatic
cases, the incubation period varies from 1-3 weeks or longer. Some
cases of brucellosis resemble influenza; the symptoms may include
irregular fever, headache, generalized weakness, malaise,
sweating, fatigue and severe limb or back pains. Gastrointestinal
signs especially in adults. Coughing and pleuritic chest pain,
irritability, insomnia, and mental depression are occasionally
In many patients, the symptoms last for 2 to 4 weeks and are
followed by spontaneous recovery. Others develop recurrent bouts
at 2 - 14 day intervals. Most people with this undulant form
recover completely in 3 to 12 months. A few patients become
chronically ill, with symptoms of chronic fatigue, depressive
episodes and arthritis. Relapses can be seen months after the
initial symptoms, even in successfully treated cases.
Hypersensitivity reactions, influenza, and malaria can mimic the
symptoms of brucellosis.
Occasional complications include arthritis, endocarditis,
granulomatous hepatitis, meningitis, uveitis, orchitis,
cholecystitis, osteomyelitis, and rare cases of encephalitis.
adult cattle and buffalo, there is considerable variation in
the lesions that are not pathognomonic. There may be a mild to
severe endometritis that becomes chronic. The chorion may
appear normal or uniformly affected. The cotyledons may be
normal or necrotic covered by a sticky, odorless brown exudate
and are yellow-grey. Parts of the intercotelydonary region are
typically leathery with a wet appearance and focal thickening.
The fetus may be normal, autolyzed, or may have varying
degrees of subcutaneous edema, blood-stained fluid in their
thoracic and abdominal cavities, or have evidence of
bronchopneumonia. Beside the reproductive tract, the
granulomatous inflammatory lesions may be found in the mammary
gland, supramammary lymph nodes and joints.
In bulls, there may be seminal vesiculitis, epididymitis, and
In sheep infected with B. melitensis, the Placentitis, edema,
necrosis of the cotyledons and the thickened and leathery
intercotyledonary region, mimics that seen in cattle whereas
the placenta is usually normal in goats.
Fetal and placental lesions are rare in pigs infected with B.
Brucellosis is generally of no unique set of symptoms and may
even be asymptomatic for long periods, so its diagnosis has
traditionally relied on the detection of circulating
antibodies followed by the bacteriological isolation and other
Samples and specimens:
For culture, aborted fetuses (abomasal contents, lung,
spleen), fetal membranes, vaginal secretions (swabs), milk,
semen, and arthritis or hygroma fluids. Post mortem, mammary
tissues, supramammary or genital lymph nodes, spleen, and
graved uterus. Tissue samples are removed aseptically with a
small amount of sterile phosphate buffered saline.
For serology, serum, milk, whey, and semen samples are used.
Microscopic examination of direct smears made from vaginal
swabs or cultivation of milk and vaginal swabs on specific
media have the advantage of detecting the organism directly
and thus limiting the possibility of false positive results
but culture is an expensive and time-consuming procedure.
Direct examination may not detect the small numbers of
organisms present in milk and dairy products.
Serological tests: There is no single test available that
completely satisfies an accurate diagnosis requirement. Some
serologic tests are not useful in some hosts or for some
species of Brucella. Surveillance testing consists of
conducting a series of tests, each of which has its own
The brucella milk ring test "MRT" is a sensitive, valuable and
inexpensive screening test used in bulk milk samples. The
added stained antigen is agglutinated by the brucella
antibodies/fat-globule complexes and the all rise to form a
colored cream layer at the top.
Serum agglutination tests (rapid plate agglutination test and
standard tube agglutination test) are one of the traditional
standard diagnostic tests. Agglutination tests may also detect
antibodies in milk, whey, plasma, and vaginal mucous. It
detects specific and non-specific antibodies originating from
brucella infection or vaccination and considered the last test
to reach diagnostically significant levels during the
incubation stage of the disease and after calving or abortion
in cows or heifers. In addition, during the chronic stage of
the disease, it often becomes negative due to the low serum
agglutinins when the results of the other tests may be
Rapid plate test has the advantage of speed and in not being
affected by the prozone phenomenon but it is slightly less
sensitive than the tube test.
The slow tube agglutination test "SAT" is sometimes used as
supplementary test and has some value in detecting IgM, the
persistent and predominant immunoglobulin resulting from
strain 19 vaccination.
Buffered brucella antigen tests "BBAT" is the most commonly
used tests and relies on the principles that the ability of
nonspecific IgM antibodies to bind is markedly reduced in a
low pH. They include card test, rose bengal test "RBPT", and
buffered plate agglutination test "BPAT". Rose bengal test
is simple, rapid, spot agglutination test used for large-scale
screening of sera. The buffered antigen inhibits the IgM and
detects IgG and IgA. RBPT may be false negative in cases of
residual antibody from vaccination, colostral antibodies in
calves, and cross-reaction with certain Gram-negative bacteria
such as Yersina enterocolitica, Salmonella urbana, Escherichia
coli or, Pseudomonas maltophilliia, and Vibro species.
Complement fixation test "CFT" is very sensitive and specific
and is regarded as the definitive test of choice but it is
difficult to carry out. The test was better indicator of
infection than the SAT and reactions to the CFT receded sooner
than those to the SAT after S19 calfhood vaccination. It more
accurately detects chronic infections and there is a more
rapid decline of CFT titers following vaccination, than with
infection. The CFT is often the last test to become negative
in calves with colostral antibodies
Recently, an ELISA test is used to detect brucella antibodies
in milk and serum and brucella antigens in vaginal discharge,
it is more sensitive but less specific.
Other, less commonly used, serologic tests include rivanol
precipitation and indirect hemolysis test "IHLT" as a
supplementary to CFT in the latter stages of eradication
schemes. Fluorescence polarization tests are being developed.
Allergic tests: Intradermal brucellin allergic skin test is of
little value due to its minor sensitivity.
Screening tests: The brucella milk ring test " MRT " are commonly
used to screen bulk milk samples for B. abortus for locating
infected dairy herds, whereas rose bengal or tube agglutination
tests are commonly used for testing sera collected from cattle at
markets or abattoirs to screen nondairy herds in an area, and
reactors are traced to the herd of the origin.
Negative animals should be retested 30-60 days later or 14 day
after calving as the first test may be carried out during the
incubation stage of the disease and some infected cows or heifers
may remain serologically negative for up to 21 days or longer
after calving or aborting.
A definitive test must be carried out on animals, which are
positive to a screening test as the screening tests are very
sensitive but not always specific. Non-specific reactions are
caused by strain 19 vaccination and occasionally by infection with
other Gram-negative bacteria as Salmonella and Yersinia. CFT is
the most specific definitive test and commonly used to detect
individual reactors. All sera that test positive to RBPT should
subject to CFT.
CFT and ravinol precipitation are designed to detect primarily
antibodies specifically associated with brucella infection, and
are used to distinguish between residual vaccinal titers and those
due to infection and improves the probability of detecting
All bulls from infected herds should be subjected to clinical
examination including palpation of the seminal vesicles and
ampullae, serological tests, and bacteriological and antibody
examination in semen.
In sheep, B. ovis infection can be diagnosed by several methods,
which include palpation of the external genitalia of rams, the
presence of B. ovis and neutrophils in semen smears with repeated
sampling especially of subclinical cases, and serological tests as
rose bengal test, tube agglutination test, CFT, FAT, and
In sheep and goats, B. melitensis infection can be diagnosed by
the presence of B. melitensis in fetal abomasal content, vaginal
discharge, or epididymis smears, and serological tests as rose
bengal test, CFT, and ELISA. Brucellin allergic skin test can be
used as a screening test in unvaccinated flocks. The bulk milk
ring test is not used in small ruminants.
In pigs, B. suis infection can be diagnosed bacteriologically and
serologically with CFT and ELISA.
In camels, rose bengal test and CFT are the most practical tests.
A wide range of infectious and
non-infectious causes may be implicated in an abortion problem.
Abortion problem investigations should follow a standard pattern
that may include:
Ascertain the age and necropsy of the fetus and examination of the
placenta for evidence of placentitis;
Clinical examination of the cow to exclude conditions such as
acute salmonellosis, summer mastitis or tick borne fever;
In laboratory: Blood samples for serological tests for brucellosis
and leptospirosis. Examination of vaginal discharge and the
contents of the fetal abomasum at the earliest opportunity for
trichomonads, and by culture methods for B. abortus, Campylobacter
fetus, trichomonads, listeria, and fungi. Examination of urine for
Interpretation of results.
Naturally, infected animals and those vaccinated are considered to
have a relative immunity. Sexually immature and sexually mature
but non-pregnant animals become immune to one degree or another
following infection, in that they may never show clinical signs of
disease. Aborted animals are also become immune and do not usually
Naturally infected animals and those vaccinated as adults with
strain 19 remain positive to the serum, and other agglutination
tests, for long periods. The infected cattle sera contain high
levels of IgM, IgG1, IgG2, and IgA isotypes antibodies. After
vaccination of cattle with strain 19, IgM, the persistent and
predominant immunoglobulin begin to appear after 5 days, reaching
peak values after 13 days whereas IgG1 antibodies may appear with
IgM and reach the peak values at 28-42 days, after which they
Most chronically infected animals remain positive to the CFT, but
a significant proportion become negative to SAT as serum
agglutinins tend to wane within a few months.
Calves nursing positive reactor cows are passively immunized via
colostrums, the half-life of colostral antibodies is about 22
Treatment of bovine brucellosis neither effective nor
practical, because of the intracellular sequestration of the
organisms in lymph nodes, the mammary gland and reproductive
organs. The drugs are unable to penetrate the cell membrane
barrier and some antibiotics may cause L-transformations to B.
abortus that may prevent its serological detection leading to
creation of carrier animals. Also there is no practical
treatment for infected pigs.
Antibiotics can eliminate B. ovis infections in valuable rams
but the fertility may remain poor. Long-term antibiotic
treatment is sometimes successful for B. canis infections in
dogs. In horses with fistulous withers or poll evil, the
infected bursa may need to be surgically removed.
Prevention and control measure
Control and eradication of bovine brucellosis strategies and
policies will invariably differ according to the situation in
each instance. The control and ultimately eradication of
bovine brucellosis is broadly based on vaccination,
test-and-slaughter policy, and the prohibition of the sale and
movement of infected cattle.
In countries and areas with a high prevalence of brucellosis,
the major goal of control is the reduction of infected cattle
through vaccination and good hygiene and management. In this
situation, large-scale vaccination is used as the first phase
of control before test-and-slaughter procedures are adapted.
Vaccination greatly reduces the risk of abortion and the
excretion of organisms. It will reduce the number of infected
animals in a herd by over 90% if carried out for about 5
Strain 19 vaccine: Vaccination of heifer calves at 4-8 months
of age with strain 19 B. abortus, a live strain of low
pathogencity and high immunogenicity provides a relative
immunity for about 16-18 months.
A small percentage of vaccinated animals develop antibodies
especially SAT that may persist into adulthood, and thus may
confuse diagnostic test results. To minimize this problem,
calves are vaccinated with a greatly reduced dose.
Vaccination of the adult cattle is usually not permitted but
it may be of value in the event of an outbreak for reducing
the effects of an abortion storm.
Strain 19 vaccine is of low virulence in cows, but systemic
reactions may occur rarely in both calves and adults. Strain
19 vaccine is of no value and may cause orchitis in bulls. In
addition, it has a zoonotic risk for veterinarians and cattle
The cessation of immunization with strain 19 vaccine should be
considered only when the prevalence of infection is reduced to
0.2% or less.
The inactivated strain 45/20 adjuvant vaccine "Abortex" is
safe in all ages but is not as protective as strain 19 vaccine
in animals less than 9 months old. For animals over six
month's, two consecutive inoculations are usually recommended
to with 6-12 weeks apart. It interferes greatly with the
interpretation of the CFT but little with the SAT.
Strain RB-51 vaccine: Strain RB-51 is a live attenuated,
stable rough mutant of B. abortus strain, capable of inducing
protection against infection and abortions as strain 19
vaccine. Unlike strain 19 vaccine, it does not develop
antibodies detectable by the traditional tests of brucellosis,
hence enabling to identify vaccinated animals from those
infected with field strains. It is indicated for active
immunization of heifer calves over 4 months old but it may
induces placentitis that can cause premature birth when given
to pregnant heifers in the six month of gestation. Age limits
for vaccination are the same as strain 19 vaccine, 4-7 months
of age is preferable.
Complete eradication in a region or a country when the
prevalence of infection is reduced to 0.2 % or less, needs
detection and slaughter of infected animals, followed by
proper disinfection of premises with 2.5 % formalin and
continuous screening, possibly combined with vaccination of
calves. Its economic implications should consider.
All calves of infected herds should be regarded as potential
sources of infection as latently infected calves that remain
serologically negative until mid-gestation or later during
their first pregnancy "two-year breakdown syndrome".
Continuous surveillance should maintain through regular blood
testing in infected herds at 2-3 months as well as
bacteriological examination. In MRT, milk from negative
animals should be retested regularly at short intervals. All
animals diagnosed bacteriologically or serologically positive
should be regarded as infected and must be permanently
It is important to prevent spread of the disease especially in
outbreak. Cows prior and after parturition should be isolated.
Aborted cows should isolated immediately with incineration of
aborted fetuses, placenta, and discharges and tested
serologically. Positive animals should be culled and negative
animals should be retested 2-3 weeks later.
The herd is regarded as negative after 2-3 successive tests
The negative herd must be maintained as such. Replacement
animals should be purchased from herds certificated free and
should be tested before introduction into the herd and/or they
should be vaccinated animals only.
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