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German Journal of Microbiology
eISSN: 2749-0149
Review article
Brucellosis: Why is it eradicated from domestic livestock in the United States
but not in the Nile River Basin countries?
Ahmed F. Hikal1,Gamal Wareth2,3and Ashraf Khan1∗
1Division of Microbiology, National Center for Toxicological Research (NCTR), Food and Drug Administration (FDA),
Jefferson, Arkansas, USA
2Institute of Bacterial Infections and Zoonoses, Fredrich-Loeffler-Institut, 07743 Jena, Germany
3Institute of Infectious Diseases and Infection Control, Jena University Hospital, 07747, Jena, Germany
Article History:
Received: 01-Oct-2023
Accepted: 21-Nov-2023
*Corresponding author:
Ashraf Khan
ashraf.khan@fda.hhs.gov
Abstract
Brucellosis is one of the most highly infectious zoonotic diseases worldwide and has substantial
health and economic impact. Strenuous efforts are essential to combat and prevent this disease
from the one-health perspective. Brucellosis is successfully eradicated from domestic animals in the
United States, but control strategies continue to eradicate it from wildlife in the Greater Yellowstone
Area (GYA). Brucellosis in the Nile River Basin countries (Egypt, Sudan, Ethiopia, and Tanzania) is
highly prevalent and endemic. There are several factors behind the failure of eradication of Brucella
in these countries. The lack of cooperation between policymakers, health officials, veterinary sectors,
and farmers is the key reason that impedes the control and prevention strategies in brucellosis-
endemic countries. This review will focus on the epidemiology, prevention, and control strategies of
Brucella abortus and Brucella melitensis in the United States and the Nile Basin countries (Egypt,
Sudan, Ethiopia, and Tanzania).
Keywords: Brucellosis, USA, Nile Basin, Eradication, Livestock
Citation: Hikal, A. F., Wareth, G. and Khan, A. (2023). Brucellosis: Why is it eradicated from
domestic livestock in the United States but not in the Nile River Basin countries?. Ger. J. Microbiol.
3(2): 19-25. https://doi.org/10.51585/gjm.2023.2.0026
Background
Brucella was first isolated by Sir David Bruce in 1887 from
soldiers who died from Malta fever, and the organism was
first named Micrococcus melitensis but was renamed later
to Brucella (Tan and Davis,2011). Brucellosis is among
the most common zoonotic diseases worldwide that cause
substantial economic losses in livestock. The main disease
manifestations of brucellosis in animals are abortion and
placental retention in females, whereas it causes orchitis
and epididymitis in males (Khan and Zahoor,2018). Bru-
cellosis in humans is mainly an occupational disease affect-
ing people in close contact with infected animals, such as
farmers, veterinarians, slaughterhouse workers, and labo-
ratorians. In humans, brucellosis is mainly a febrile dis-
ease that usually progresses to chronicity and persistence
(Franco et al.,2007). The disease in humans can lead to
abortion, splenic abscess, endocarditis, encephalitis, orchi-
tis, and arthritis (Dagli et al.,2011;Zhong et al.,2013).
The major concern of Brucella is that it can be eas-
ily transmitted via aerosol and used as a possible biolog-
ical (B-) weapon (Neubauer,2010). In the past, Brucella
used to be merged with the free-living Ochrobactrum; how-
ever, after the consensus agreement among researchers to
reclassify them into separate genera, Brucella ended up con-
taining thirteen species, including the most recently dis-
covered Brucella nosferati (Roop et al.,2021;Hern´andez-
Mora et al.,2023;Moreno et al.,2023); among these, B.
melitensis, B. abortus, B. suis (except bv 2), and infre-
quently, B. canis, can infect humans. Interestingly, Bru-
cella species that infect wild animals, such as B. ceti, B.
neotomae, and B. inopinata, have been isolated from hu-
mans with unknown modes of transmission (Roop et al.,
2021). Brucella is transmitted from animals to humans
through direct contact with animal secretions, aborted ma-
terials, or by consumption of contaminated unpasteurized
dairy products (Wareth et al.,2014b). This review focuses
on the epidemiology and control measures of brucellosis in
the United States and the Nile Basin countries (Egypt, Su-
dan, Ethiopia, and Tanzania).
Brucellosis in the United States
B. abortus is the main cause of brucellosis and infects var-
ious domestic and wild animals, such as cattle, buffaloes,
camels, horses, bison, and elk. The Federal-State Cooper-
ative Brucellosis Eradication program in the United States
started in 1934, when brucellosis was highly prevalent, with
antigen reactor rates of 11.5% in the tested cattle (Ragan
et al.,2002). In 1965, the number of infected cattle with
Brucella was around 150,000 cases, then declined dramat-
ically until it reached zero infected cattle in 2000 (Ragan
19
et al.,2002). Why was the brucellosis eradication program
successful? Implementing very effective surveillance and
preventive strategies were the main factors behind the suc-
cess of eradicating B. abortus in the United States. The
brucellosis eradication program started with herd testing
as an initial step to identify infected cattle. For example,
in Vermont, testing for brucellosis started in 1934 and iden-
tified approximately 23,000 infected cattle by 1945; all the
reactor cattle were culled (Wise,1980). To ensure that
there were no undetected infected animals, further testing
was performed every 30-180 days and continued until there
were no reactors (Ragan et al.,2002).
Vaccination was another important element that rein-
forced the brucellosis eradication program. The live attenu-
ated B. abortus strain 19 vaccine has been extensively used
to vaccinate female calves (4 months- 1 year of age) since
the beginning of the eradication program (USDA,2003).
Because the strain 19 vaccine has some disadvantages, such
as induction of abortion in pregnant cows and a persis-
tent titer, which made it difficult to distinguish between
the infected and vaccinated animals, it was discontinued in
some states and replaced with the B. abortus strain RB51
(rough rifampicin-resistant strain) (Dorneles et al.,2015).
The RB51 vaccine was approved to be administered to non-
pregnant heifers (4-12 months of age) only, as it can also
induce abortion in pregnant animals (USDA,2003;Pinn-
Woodcock et al.,2023). As of August 2023, all 50 states
reported brucellosis free-class status (USDA,2023b). How-
ever, wildlife has been an impediment to the brucellosis
eradication program in the United States.
Brucellosis in The Greater Yellowstone Area (GYA),
which encompasses the states of Idaho, Montana, and
Wyoming and harbors more than 5,500 bison and 125,000
elk, is still endemic and poses a threat to cattle herds (NAS,
2017). Elk, more than bison, are the main source of poten-
tial transmission of brucellosis to cattle, and migration of
elk herds outside of Yellowstone National Park, due in part
to the introduction of wolves, has contributed to the in-
crease of brucellosis cases in cattle in the GYA area (NAS,
2017). Nonetheless, a recent study indicated that bison
could also transmit B. abortus to cattle (O’Brien et al.,
2017). Therefore, there are ongoing efforts by The U.S. De-
partment of Agriculture (USDA) and its Animal and Plant
Health Inspection Service (APHIS), in collaboration with
other federal and state agencies, to eradicate brucellosis
from the GYA through blood testing and elimination of
infected animals (NAS,2017).
B. melitensis is the main cause of brucellosis in sheep
and goats. It also infects humans and causes brucellosis
(Malta fever), with an estimated 2.1 million cases globally
yearly (Laine et al.,2023). B. melitensis was eradicated
from sheep and goats in the United States in 1972; since
then, it has been considered an exotic disease. Because
it is not endemic in the United States, there is no strate-
gic plan or program for controlling B. melitensis (USDA,
2023a). The success of the brucellosis eradication program
in the United States is reflected in the number of infected
humans, where only forty-eight cases of human brucellosis
were reported to the Center for Disease Control (CDC) in
2022 (USDA,2023a).
Preview of brucellosis in the Nile Basin countries
The Nile River is the chief river of Africa. The river drains
from Tanzania northward to Egypt around 4,130 miles
(with an estimated length of over 6650 km). The Nile Basin
is shared by eleven countries: four are among the world’s
poorest populations, which undergo severe environmental
degradation. Seven countries suffer from internal or bor-
der conflicts. The estimated total area of the Nile Basin
is around 10.3% of the area of Africa. In Nile Basin coun-
tries, brucellosis is a major infectious bacterial disease that
impacts livestock development, productivity, and human
health (Sanogo et al.,2013). Human brucellosis is a highly
debilitating infection and clinically may be confused with
malaria or typhoid fever. Thus, diagnosing brucellosis in
underdeveloped and low-income countries is problematic,
where diagnostic services are inadequate or non-existent.
The economic burden of brucellosis and its control is more
significant in low-income countries. To set up and imple-
ment efficient control measures against brucellosis in a geo-
graphical area from the perspective of ”One-Health”, there
needs to be sufficient knowledge of the epidemiology of the
disease, particularly the species and biotypes involved at
the national and regional scale. In addition to its zoonoses
significance, brucellosis in livestock is a major concern for
the economy and food security in the Nile Basin countries.
In Africa, camel brucellosis, which can be contracted
from other infected animals, has not received proper atten-
tion from the public health sector or researchers. It is clear
that fighting against brucellosis in the Nile Basin is a mul-
tidimensional process. Collaboration between veterinari-
ans, physicians, and environmental specialists is required
to combat the unique brucellosis situation in the Nile Basin
countries. Studies on potential Brucel la reservoirs, exposed
populations, and interspecies transmission pathways are the
top priorities to eliminate this disease. Cooperative devel-
opment between the Nile Basin countries will offer a great
opportunity to promote regional integration, realize stabil-
ity, and improve health.
Brucellosis in Egypt
From a historical perspective, brucellosis has likely been an
endemic disease for thousands of years in Egypt. There is
evidence of spondylitis and osteoarticular lesions, a com-
mon complication of brucellosis in bone remnants from
ancient Egyptians (750 BC) (Pappas and Papadimitriou,
2007). Brucellosis was reported in a scientific report for
the first time in Egypt in 1939 (Refai,2003). Since then,
the disease has become more prevalent nationwide in farm
animals, the environment, and rats, which act as carrier
hosts for Brucella. Animal brucellosis in Egypt was re-
viewed in detail by (Refai,2003) and updated by (Wareth
et al.,2014a). Serologic testing is a well-established pro-
cedure in Egypt that indirectly proves animal brucellosis
in all governorates. Cross-species transmission of Brucella
is proven to occur. For example, B. melitensis clones can
cross species barriers and establish a permanent reservoir
in cattle and buffaloes (Wareth et al.,2014a). Cultivation
and biotyping of Brucella isolates are unavailable for all
governorates due to a lack of resources. B. abortus and
B. melitensis are the predominant isolates in Egypt. B.
abortus was isolated from cattle, buffaloes, camels, dogs,
and cats (Wareth et al.,2017). Although the main host
for B. melitensis is sheep and goats, it was also isolated
from cattle, buffaloes, camels, dogs, cats, and Nile catfish
(Wareth et al.,2014a). B. suis bv 1 (Ibrahim,1996) and
bv 2 (Wareth et al.,2023) were isolated from domestic pigs.
The inappropriate disposal of infected animal carcasses and
viscera resulted in contamination of the environment with
Brucella. Hot spots of brucellosis are located in the Delta
region and upper Egypt around the Nile River (Hegazy
et al.,2011a,b). Testing and slaughter (T&S) programs
20
and vaccination are the main programs aiming to control
brucellosis in Egypt.
Vaccination has been used on a limited scale in all gover-
norates as another tool to prevent animals from developing
the disease; calves are vaccinated with B. abortus S19 and
adults with BR51 vaccines, whereas B. melitensis Rev 1
vaccine is used for small ruminants (Refai,2002). Despite
the money and efforts spent to eradicate brucellosis, it is
still endemic among livestock in Egypt; this is due to the
lack of awareness among farmers in feeding young calves
with contaminated colostrum and milk from infected ani-
mals. Also, the unhygienic disposal of aborted materials
either in rivers and canals or near feed sources contributed
to the persistence of brucellosis. Additionally, inadequate
government compensation for positive cases hinders the no-
tification process, and eventually, farmers resort to selling
their infected animals illegally. This, of course, is reflected
in the rate of infection with the disease in humans.
The prevalence of human brucellosis in Egypt is greatly
affected by the prevalence of the disease in animals. Acute
febrile illness (AFI) is the common syndrome of human bru-
cellosis reported in many hospitals in Egypt (Afifi et al.,
2005). For instance, of 4,490 patients admitted to hospi-
tals in Fayoum governorate who experienced AFI, 321 (7%)
were confirmed as brucellosis (during 2002-2003) (Jennings
et al.,2007). Although the rate of AFI due to brucellosis
has increased in recent decades, no fatalities have been
reported in Egypt (Refai,2002). The infection rate was
higher in males than females; all cases were in close contact
with animals and had a history of consuming unpasteurized
milk products (Jennings et al.,2007). Human brucellosis
was reported in 59 women admitted to the Al-Zahraa Uni-
versity Hospital and other hospitals in Cairo with osteoar-
ticular lesions, fever, headache, and abortion (Mohammad
et al.,2011). B. melitensis bv 1 and B. abortus bv 1 strains
were recovered from the blood culture of the positive human
reactors who had AFI (El-Olemy et al.,1984). B. meliten-
sis was also cultured from cerebrospinal fluid (CSF) for the
first time in a male suffering from nervous manifestation in
Abbassia Fever Hospital in Cairo (Mansour et al.,2009).
In Assiut University Hospital, patients with neuro-
brucellosis showed highly significant cognitive impairment,
such as loss of logical memory, mental control, and visual
reproduction (Shehata et al.,2010). Despite the high bur-
den of brucellosis in Egypt and frequent empirical treat-
ment, isolates have remained susceptible to most tested an-
tibiotics. The disease is not only confined to occupational
people who have close contact with animals, as people can
contract the infection from drinking raw milk and prod-
ucts made from it, which can be contaminated with Bru-
cella. The widespread home slaughter, raw milk consump-
tion, and milk products perpetuate human brucellosis. For
instance, B. melitensis DNA was detected in milk samples
from apparently healthy animals (Wareth et al.,2014b). In
Egypt, human brucellosis has not received appropriate at-
tention and is often initially diagnosed as typhoid fever and
fever of unknown origin (El-Metwally et al.,2011). Care-
lessness and unhygienic handling of infected animals, either
in slaughterhouses or on farms, along with the existence of
contaminated milk and meat products in the markets, are
still the main factors for maintaining brucellosis among hu-
mans in Egypt.
Brucellosis in Sudan
Brucellosis was first reported in the Sudan in 1908 (Osman
et al.,2015). Since then, the disease remains one of the
major zoonotic diseases among livestock. Studies have pro-
vided indirect proof of the disease in cattle, goats, sheep,
and camels in different governorates by serological assays
(Osman et al.,2015). Infection in cattle, sheep, goats, and
camels is widespread throughout Sudan and in human con-
tact (Mokhtar et al.,2007;Omer et al.,2010). B. abor-
tus and B. melitensis are the predominant species in Su-
dan. B. melitensis bv 3 was isolated from sheep and goats
(Musa and Jahans,1990), while B. abortus bv 6 was iso-
lated from cattle. In the Darfur Province of western Sudan,
the disease is highly prevalent among cattle in nomadic and
semi-nomadic areas (Musa et al.,1990). Mixed grazing of
different animal species induces interspecies transmission
of brucellosis from classical to non-classical hosts. Infec-
tion of camels with brucellosis mainly depends on the Bru-
cella species prevalent in other animals sharing their habi-
tat. Infection of camels with B. abortus bv 3 was reported
in Sudan (Agab et al.,1994). B. abortus bv 6 (the most
prevalent strain in cattle) was isolated for the first time
from camel and the pyometra of a seropositive ewe in Dar-
fur (Western Sudan) and Kassala State (Eastern Sudan),
respectively(Musa et al.,2008;Gumaa et al.,2014).
Human brucellosis in Sudan is prevalent nationwide
among peoples in nomadic, semi-nomadic, and sedentary
populations. Some peculiar habits, such as eating raw
meat, raw liver, or other offal with spices and consuming
raw milk, are significant epidemiological factors in contract-
ing brucellosis, especially in central Sudan (Mohd,1989).
B. melitensis bv 1 and B. abortus S19 vaccine strains were
isolated from the blood of four seropositive, apparently
healthy milkers who work in dairy cattle farms (Osman
et al.,2015). In the Melut district, South Sudan, B. abor-
tus and B. melitensis were serologically detected in cattle,
green long-tailed monkeys, sheep, goats, and school chil-
dren (Sixl et al.,1988). Unfortunately, because Sudan has
been at war for the last century, there is no data about the
bovine brucellosis surveillance and control program in this
country.
Brucellosis in Ethiopia
Ethiopia has the largest livestock population in Africa and
is also the 10th largest livestock producer in the world.
Ethiopia’s agriculture is based on livestock, either for use
in farming-related activities or livelihood. Livestock is a
source of meat, milk, cheese, butter, manure, and export
goods (live animals, hides, and skins). Livestock produc-
tivity in Ethiopia is affected by various infectious diseases.
Among these diseases, brucellosis has been shown to af-
fect animals and humans (Gumi et al.,2013;Asmare et al.,
2014). Brucellosis was first reported in Ethiopia in 1977
in dromedaries (Domenech,1977). Although cattle are the
primary hosts of B. abortus, the infection can spread to
goats and camels co-grazing with cattle (Megersa et al.,
2012). A meta-analysis of Brucella seroprevalence in dairy
cattle reported that the disease is widely distributed in the
country.
The highest prevalence rate was reported among cattle
(Haileselassie et al.,2011), small-ruminant (Gumi et al.,
2013;Teklue et al.,2013), and camels (Teshome et al.,
2003). Camel brucellosis is prevalent in northeastern
Ethiopia (Bekele et al.,2013). In rural communities of
Ethiopia, cattle and camel brucellosis have significant eco-
nomic and zoonotic implications due to feeding habits, tra-
ditional lifestyles, and disease patterns (Megersa et al.,
2011;Bekele et al.,2013). All diagnostic protocols used to
study brucellosis in Ethiopia have relied on serological tests.
21
A recent study showed that the brucellosis seroprevalence
rate, which was confirmed by PCR, among domestic ani-
mals in Southern and central Ethiopia was 3.95% (Wakjira
et al.,2022).
Because of the limited resources, molecular biotyping of
the circulating Brucella spp. is not commonly conducted
in Ethiopia. The first human brucellosis cases in Ethiopia
were documented in 1981 (Alemayehu,1981) as a disease of
acute and chronic febrile illness (Seboxa,1982). The preva-
lence rate among occupationally exposed people was around
4.8% (16/336) in Addis Ababa (Kassahun et al.,2006),
while the prevalence was higher in pastoral communities:
Borana (34.9% (30/88)) and in Hamer (29.4% (5/17)),
who are constantly exposed to animals and consume raw
milk and unprocessed cheese (Regassa et al.,2009). High
seropositivity of Brucella in all pastoral livestock species
tested in Southeast Ethiopia implies human infection risks,
meriting the necessity of further studies of the disease in
animals and humans (Gumi et al.,2013). In addition to
the negligence of policymakers regarding brucellosis, illegal
animal trade with neighboring countries has also compli-
cated the efforts to eradicate brucellosis in Ethiopia. More
than 95% of cross-border trade in East Africa is through
illegal channels. The illegal trade of domestic animals from
Ethiopia to Somalia, Djibouti, and Kenya generates rev-
enue of 250-300 million dollars annually (100 times more
than the official figure) (Pavanello,2010). This trade leads
to the spreading of animal diseases among the neighboring
countries (Pavanello,2010). However, no studies have been
conducted on the relationship between cross-border animal
movement and brucellosis occurrences. Intervention pro-
grams on brucellosis should be formulated based on a com-
prehensive understanding of disease occurrence and spatial
distribution across the country.
Brucellosis in Tanzania
In Tanzania, brucellosis is prevalent and widely distributed
in animals and occupational groups (Swai and Schoonman,
2009,2010). The disease is associated with abortion in hu-
mans and domestic ruminants (Ntirandekura et al.,2020).
Investigation of brucellosis among 635 pregnant women in
urban settings of Mwanza showed a high level of seroposi-
tivity of B. melitensis (Nyawale et al.,2023). B. melitensis
and B. abortus were also isolated from patients who suf-
fered from bloodstream infection (Bodenham et al.,2020).
Another cross-sectional study that was conducted in Kilosa
and Chalinze districts of Tanzania between 2019 and 2020
among healthcare workers and community health workers
revealed that the majority of participants were not aware
of human brucellosis, and they had inadequate knowledge
about the burden and impacts of the disease (Mligo et al.,
2022).
In humans, both B. abortus and B. melitensis were de-
fined as causes of brucellosis with seroprevalences 7.7% and
1.9%, respectively, and mainly associated with assisting in
parturition without wearing personal protective equipment
(PPE) (Ntirandekura et al.,2021). Using the Rose Bengal
Test (RBT) and ELISA, cross-sectional studies on bovine
brucellosis in agropastoral areas in Tanzania have shown
that brucellosis is highly prevalent in those areas (Swai
and Schoonman,2012;Asakura et al.,2018;Shirima and
Kunda,2016). In the last decades, few studies have been
conducted on small ruminants and showed a prevalence be-
tween 0% and 2.0% in goats and between 0% and 5.7%
in sheep (Assenga et al.,2015;Shirima and Kunda,2016).
Circulation of Brucella species, particularly B. abortus, and
B. melitensis, in wildlife species such as lions, wildebeest,
impala, zebra, and hyenas was proved by PCR, emphasiz-
ing the role of wild animals as reservoirs for infections in
domestic animals and humans in Tanzania (Sambu et al.,
2021). Despite the high prevalence of brucellosis in Tan-
zania, the lack of brucellosis awareness among laypeople
and health professionals, limited diagnostic tests and re-
sources, as well as the paucity of skilled laboratorians have
contributed to the absence of brucellosis control programs
(Mengele et al.,2023).
Conclusion
Brucellosis is a major zoonotic disease that causes livestock,
milk, and fertility losses. Implementing efficient control
strategies has eradicated brucellosis from domestic animals
in the United States. In contrast, due to inefficient surveil-
lance and control programs, brucellosis is still endemic in
the Nile Basin countries. Several factors contribute to the
failure of brucellosis eradication in the Nile River Basin
countries: I) Inappropriate disposal of aborted materials in
rivers and canals plays an important role in transmitting
diseases to healthy animals and humans. This occurs due
to a lack of knowledge and awareness toward the burden
of brucellosis and the method of its transmission; II) Lack
of cooperation between policymakers, health professionals,
and stockholders. Health professionals and policymakers
should provide medical professionals and veterinary sectors
with more information about the epidemiology and risk fac-
tors of brucellosis and educate animal owners about the
zoonotic risk of this disease. Raising awareness about Bru-
cella occurrence in traditional livestock husbandry practice
will tremendously impact controlling the disease in animals
and humans; III) Insufficient government compensation for
infected animals due to economic depression impedes farm-
ers’ cooperation with veterinary services. Many farmers re-
sort to illegal selling or hiding sick animals because they do
not receive adequate compensation from the government.
Moreover, due to a lack of guidance, farmers feed young
calves colostrum and milk from infected animals owing to
the high prices of substitutes; IV) Public vaccination reluc-
tance. All the available vaccines are live-attenuated, and
farmers refuse to introduce strains in their farms to avoid
the risk of infection; V) Open borders and uncontrolled an-
imal movements between countries and within each coun-
try contribute to spreading and disseminating brucellosis
across borders; VI) Lack of proper diagnostics and bio-
typing methods and tools. A comprehensive knowledge
of the epidemiology of brucellosis and standard diagnostic
capabilities are prerequisites for valid, accurate diagnosis,
surveillance, and control.
Finally, the ’test-and-slaughter’ strategy and the pas-
teurization of milk, which have been implemented success-
fully in the more economically developed countries, might
not be the optimal control tools in most African countries
due to scarcity of resources. Control strategies should suit
the needs and perceptions of each country. Advanced inter-
sectoral and international collaboration regarding surveil-
lance, diagnosis, control, and medical and veterinary per-
sonnel education are essential in brucellosis eradication pro-
grams.
Article Information
Funding. The authors did not receive support from any organization
Conflict of Interest. The authors have no conflicts of interest to
declare relevant to the article’s content.
Authors contributions. All authors contributed equally to this re-
view.
22
Acknowledgments. We thank Drs. Jing Han and M. S. Nawaz for
critical review of the manuscript.
Disclaimer. This manuscript reflects the views of the authors and
does not necessarily reflect those of the Food and Drug Administra-
tion and Friedrich-Loeffler-Institut.
Publisher’s Note. The claims and data contained in this manuscript
are solely those of the author(s) and do not represent those of the
GMPC publisher, editors, or reviewers. GMPC publisher and the
editors disclaim the responsibility for any injury to people or prop-
erty resulting from the contents of this article.
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