Potential of sniffer rats in detection of brucella species in Cattle

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Sokoine University of Agriculture


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.



Brucella species, Sniffer rats, Cattle, Morogoro, Tanzania