Innovative approaches to brucellosis diagnosis
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Date
2022
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Publisher
Sokoine University of Agriculture
Abstract
Brucellosis is an endemic zoonotic disease of public health importance in many low- and
middle-income countries. The main zoonotic species implicated in human infection
however are Brucella melitensis, B. abortus and B. suis infecting over 500,000 humans
annually worldwide. Brucellosis also causes production and reproductive losses in
livestock globally estimated at about two billion USD annually. Brucellosis is listed as
one of six priority zoonoses in Tanzania, where the national One Health strategic plan
highlights gaps in current surveillance data needed for the burden estimation of human
brucellosis and robust tools for the identification of the species of Brucella infecting
animals.
This study evaluated the current practices for diagnosing brucellosis based on a
retrospective survey of records at health facilities in Arusha Region, northern Tanzania.
Patterns of brucellosis testing, brucellosis positivity and test reagent management were
evaluated using generalized, linear mixed-effects, regression models, with two main
outcomes of interest: brucellosis testing practice and brucellosis test positivity variation
compared to the facility type, ownership, ownership, month and year of data collection as
explanatory variables. Brucella species exposure was estimated using real-time,
quantitative polymerase chain reaction assays for the detection and speciation of Brucella
in blood clots from cattle, goats and sheep in northern Tanzania. The association between
animal level characteristics and the results of performance of the Rose Bengal test in this
livestock population was evaluated by logistic regression modeling and cross-tabulation.
Finally, the performance and costs of serological assays used for human brucellosis in
northern Tanzania were evaluated and compared to internationally recommended
reference tests. Significant associations were observed between the probability of brucellosis testing and
the year and ownership of the facility where testing was done. The probability of
brucellosis testing per month was significantly associated with an interaction between
privately owned facilities and the year in which testing was done. The proportion of
individuals classified as positive was significantly associated with the type of health
facility and the district. Four commercial Febrile Brucella agglutination tests (FBATs),
sourced from private distributors, were used with variable protocols to test for brucellosis
in all the study health facilities. In the detection of Brucella spp. from blood clots, fifty-
eight (11.6%) of the livestock samples were positive for Brucella spp. Brucella abortus
(31.0%) and B. melitensis (38.0%) were detected in samples originating from all three
livestock species sampled. However, there was poor agreement (K = 0.102) between the
results of the qPCR and the RBT in the livestock population tested. The performance and
cost evaluation of frontline serological tests for human brucellosis identified the RBT as
the test with highest accuracy (97.7%, CI; 94.7–99.3) and the lowest per-sample cost
($0.69 – $0.79 USD). Comparatively, the often-used FBAT kits had low diagnostic
accuracy and higher per-test costs than the RBT.
In addition to the variable protocols for testing, the widespread use of poorly performing
FBATs limits the inferences that can be made about the epidemiology of human
brucellosis in northern Tanzania. The qPCR assays applied to blood clots detected
Brucella spp. in cattle, goats and sheep on the ranch in Kagera Region. Brucella abortus
and B. melitensis were each detected in all the samples from cattle, goat and sheep that
were positive by the Brucella spp. and species-specific qPCR assays. The widely used
commercial FBATs performed poorly and cost more than the RBT. The findings from this
study highlight areas of focus to achieve improved quality of testing and surveillance of
brucellosis at health facilities in Tanzania. Applied to scale, the uniform application of the
RBT in health facilities, with quick and accurate reporting of test results and the exploitation of blood clots for Brucella genus detection are approaches that, applied
complementarily to brucellosis diagnosis, could ultimately facilitate the formulation of
strategies for prevention and control of this priority disease in many-resource limited
settings in sub-Saharan Africa.
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Thesis
Keywords
Innovative approaches, Brucellosis, Diagnosis