Abstract:
Brucellosis is one of the most economically important bacterial zoonoses worldwide,
affecting livestock, wild animals and humans. In Tanzania, brucellosis is in the list of six
top priority zoonoses that the government is focusing to control although diagnostics
remain to be a major constraint. An experimental study was carried out at an antipersoonsmijnen
ontmijnende product ontwikkeling abreviateted as APOPO which in
English means anti-personnel landmines removal product development between may
2018 and august 2019 to train nine sniffer rats (Cricetomys ansorgei) to detect Brucella
abortus. The study used the principle of operant conditioning in which sniffer rats were
rewarded on sniffing Brucella abortus positive samples within two seconds. Cattle milk
and aborted materials were the source of Brucella used in the study Brucella was grown
on selective media and confirmed using morphological, biochemical and molecular
methods. The isolated Brucella abortus strain was heat inactivated at 560C for 45 minutes
before being presented to the sniffer rats. To ascertain the status of the sniffer rats
regarding Brucella infection, the sniffer rats were screened for the presence of Brucella
antibodies using Rose Bengal Test before and after the experiment. All sniffer rats were
negative for Brucella antibodies before and after the experiment. Five days prior to the
start of experimental testing, the baseline performance (sensitivity (se) and specificity
(sp)) of the sniffer rats was assessed. On average, baseline sensitivity and specificity for
the nine sniffer rats were 92% (range 82-98%) and 98% (range 95-99%) respectively.
After finding the baseline performances, the sniffer rats were trained and subjected to
three experimental tests to evaluate their ability to accurately detect positive samples
(sensitivity) and discriminate against negative samples (specificity) using 10 positive and
90 negative samples. The average sensitivity for tests one, two and three were 93% (range
60-100%), 97% (range 90-100%) and 76% (range 60-90%) respectively, while average
specificity were 96% (range 88-98%), 93% (range 86-94%) and 98% (range 93-100%)
respectively. Results from this study showed reasonably high sensitivity and specificity
that suggests potential of sniffer rats to be used for diagnosis of Brucella infection.
However, since this experiment used laboratory manipulated samples, further studies are
needed: firstly, to explore its applicability in the clinical samples such as milk, blood and
other tissues secondly, to evaluate components of Brucella abortus that the sniffer rats
were sniffing and thirdly to evaluate their ability to detect other Brucella species.
