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The
study was designed to evaluate the seroprevalence of brucellosis in Nigerian
breeds of dog in North bank area of Makurdi, Benue State Nigeria. Serum samples
from one hundred and two (102) dogs were used for serum agglutination and Rose
Bengal test. Questioners were used to obtained information on the various
management systems being practiced. The results showed that two of the dogs a
male and a female were positive for brucellosis indicating a prevalence of
1.96%. In conclusion, brucellosis in dogs remains endemic in many parts of the
world and without stronger intervention measures it might remain an
unrecognized threat to human health and animal welfare.
Keywords:
Seroprevalence,
Brucellosis, Serum, Dogs
INTRODUCTION
Brucella canis is a
gram-negative coccobacillary bacterium that primarily causes reproductive
failure in dogs [1]. The genus Brucella comprises of 12 recognized species [2].
Of these, B. melintensis, B. abortus and B. suis are well known causes of undulant fever and influenza like
symptoms in humans. It is worth noting that B.
canis is not widely accepted as being zoonotic [3].
B. canis was first
characterized in 1966 after several outbreaks of abortion and infertility in
dogs in different countries [1]. Since the discovery of B. canis as a cause of abortion, outbreaks in breeding and research
Kennels have been sporadically reported worldwide [4,5]. The primary hosts are
domesticated dogs; however, B. canis
in wild canids and human has also been reported [6,7]. Brucellosis in dogs
occurs worldwide and is endemic to the Americas, Asia and Africa [8]. In the
past two decades, serological studies involving dogs have been published from
countries in Africa, Asia and South America; these have reported moderate to
high seroprevalence, ranging from 6-35% (online Technical Appendix). This
worldwide range of seroprevalence, could be attributed to multiple factors, but
not limited to true disease prevalence in the region or country, sampling
design, study samples and diagnostic test used. B. canis infection in dogs occurs predominantly through ingestion,
inhalation and contact with aborted foetuses, placenta, vaginal secretion and
semen [9,10]. Like the rest of the Brucella
species, B. canis exhibits
tropism for reproductive tissue. Thus, infected dogs intermittently shed low
concentration of bacteria in seminal fluids and estrus vaginal secretion. Post
abortion vaginal fluids contain a high level of bacteria and are a source of
infection for other dogs and humans [9]. Even after castration, male dogs may
still serve as a source of infection as the bacteria can persist in the
prostate and lymphoid tissues [10,11]. In addition to reproductive secretions,
dogs can shed the bacteria in saliva, nasal secretion and urine [12,13].
Studies have suggested that the concentration of B. canis in urine is higher in male than female dogs; this
difference is attributed to urine contamination with seminal fluid [9]. Humans
acquire B. canis infection through
direct contact with infected dogs or their reproductive waste, secretions or blood
products [14,15]. Clinical signs and symptoms include undulant fever, chills,
malaise and splenomegaly [16].
The public
health relevance of B. canis infection in human is unclear
because most of the information available comes from case reports. The perceived
infrequency of human infection with B.
canis and lack of reliable diagnostic
tools of the disease detection has led to few serologic surveys in
MATERIALS AND METHODS
The study was
conducted during the raining season (October, 2018), in the North bank area of
Makurdi Benue State Nigeria. Makurdi lies approximately on Latitude 7° 44’ N
and longitude 8° 4’ E, in the southern Guinea Savannah zone of Nigeria, has a
temperature range of 22.5-40°C and annual rain fall of 1,290 mm [20].
Research animals
A free
anti-rabies vaccination campaign was organized in three strategic locations at
an earlier date to cover the North bank area. The dogs brought were one hundred
and two dogs comprising of 51 females and 51 males all between ages 1 year to
10 years; these were the dogs used for this research.
Samples collection
3 ml of blood
was collected through the jugular vein using a 5 ml syringe with a 21 gauge
needle into plain sample bottle and spun at 300 rpm to harvest serum on the
field. The serum samples were then kept on ice packs and transported to the
laboratory to be stored at -20°C until used. Also, information on the type of
feed and system of management used for each dog was obtained by use of
questioners.
Serological test
Serum samples
were tested for Brucella antibodies using the Rose Bengal Plate Test (RBPT) and
Serum Agglutination Test (SAT) as described by Time and Tor [21]. The antigens
for the two tests were procured from Veterinary Laboratory Agency, United
Kingdom.
Rose Bengal plate test (RBPT)
30 µL of
antigen was placed on a white ceramic tile and same volume (30 µL) of test
serum sample was placed beside the antigen. The sera and the antigen were mixed
with an applicator stick and rocked gently for 4 min after which it was
observed for agglutination. The formation of distinct pink granules
(agglutination) was recorded as positive while the absence of agglutination was
reported as negative. Known positive and negative controls were set up along
with the test sera.
Serum agglutination test (SAT)
The British
method in which five test tubes were required per sample was used. For the
first test tube, 0.8 ml of phenol saline was dispensed while 0.5 ml was applied
to the second, third, fourth and fifth test tube using micro titer pipette
fitted with corresponding tips. Similarly, 0.2 ml of the test sera was added to
the first tube and mixed properly. Serial dilution was then carried out by
pipetting 0.5 ml of mixture into the first; second, third, fourth and fifth
test tubes, respectively. The final 0.5 ml of antigen (diluted 1:10 with phenol
saline) was added to all the tubes. The tubes were covered, shaken and
incubated at 37°C for 20 h. The result was then read and agglutination titer
determined. Titer of 1:40 (50 IU/ml) and above was taken as diagnostic for
brucellosis [22,23]. Known positive and negative control sera were set up along
with the test sera.
RESULTS
The result of
this research showed that out of the 102 dogs screened for brucellosis two dogs
were positive (Table 1) male and
female. The prevalence of brucellosis in both sexes was 1.96% each with total
prevalence of 1.96% (Table 2). Among
the positive dogs, one of them feeds on abattoir waste and left over home food
while the other feeds on only left over home food (Table 3).
DISCUSSION
The prevalence of brucellosis in dogs from
this study was 1.96%, which is below the findings of the serologic studies of
brucellosis in dogs from Africa, Asia and South America which have reported
moderate to high prevalence of 6-25% (online Technical report Appendix). This
wide range of seroprevalence has been reported to be due to multiple factors
such as sampling design, study samples and diagnostic test used but not the
true disease prevalence in the region or country.
The positive
samples were from the dogs that were fed on abattoir waste and home left over
food; both dogs were also allowed to roam about. Flores-Castro and Segura [24]
and Brown et al. [25] reported that when compared with owned dogs stray dogs
are more likely to be intact and have a higher documented level of B. canis seropositivity. A higher burden
of canine brucellosis in stray/roaming dog populations could lead to a spill
over into human population in areas with a large number of stray dogs since
these dogs are usually taken into shelters or placed in foster home pending
adoption [26].
Considering the
nature of the disease, the potential source of B. canis dissemination is breeding kennels where animals are housed
in close contact and constantly moved from one breeding point to the other or
point of sale [25]. Unrestricted movement of reproductively intact dogs or
puppies is also known to be a risk factor for the spread of infectious diseases
and has led to incidences of human infection with B. canis [25,26]. Quarantine periods and pre-movement health test
of dogs vary from region, but no region is known to test dogs for brucellosis
before there are moved. Testing of breeding animals or their offspring before
interstate or international movement would decrease the risk of B. canis transmission between dogs and
humans [27].
CONCLUSION
In conclusion,
brucellosis in dogs remains endemic to many part of the world and without
stronger intervention measures, it will probably remain an unrecognized threat
to human health and animal welfare. Implementation of mandatory testing before
interstate or international movement of dogs will be a step in the right
direction in containing the disease.
ACKNOWLEDGEMENT
We thank the Director of Veterinary Teaching
Hospital Federal University of Agriculture Makurdi for providing a facility for
the storage of the research sample. We are also grateful to the staff of
Brucellosis unit of National Veterinary Research Institute (NVRI) Vom for
analysing the research samples.
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