The use of African Giant Pouched Rats in Tanzania for the Detection of Mycobacterium Tuberculosis

Subject: Environment
Type: Evaluation Essay
Pages: 8
Word count: 2132
Topics: Africa, Animal Testing, Biology, Disease, Experiment, Medicine


Trained African giant pouched rats (Cricetomys gambianus) are increasingly being used in Tanzania to help in the detection of tuberculosis. First introduced in Tanzania in 2007 by a Belgian charitable organization known as APOPO, the application of rats to sniff out TB has nearly doubled over the past few years with more than 60 clinics currently being served across Tanzania from the initial 29. This is particularly attributed to the successful detection rates. Recent empirical evidence suggest that that African giant pouched rats have the ability of evaluating samples faster and are precise in the process of detecting the disease. This paper critically investigates the use of African giant pouched rats in Tanzania for the detection of mycobacterium tuberculosis.

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Tuberculosis is currently one of the deadliest infectious diseases in the world, claiming nearly 1.7 million people annually[1]. Although the disease is curable and preventable, TB is still a major problem particularly in developing countries in sub-Saharan Africa like Tanzania where it is the main cause of death among people living with HIV/AIDs [2]. In Tanzania, it is estimated that 287 in 100,000 are currently infected with Tuberculosis, putting the country to be among the top 30 nations considered to be TB hotspots by the WHO. However, the detection rates for TB in these countries are relatively poor with only about 1% of individuals with HIV currently being tested for TB. This is particularly attributed to the scarcity and unavailability of cheap, efficient and reliable means of TB testing in developing countries [3]. Additionally, lack of awareness and money has made many people in countries like Tanzania not to undergo screening.

The use of trained African giant pouched rats (Cricetomys gambianus) in Tanzania for detecting mycobacterium tuberculosis (TB) in human sputum samples is a promising development which has a significant potential for improving the detection rates of TB thereby constituting a major step forward when it comes to TB control. The rats are trained detect tuberculosis based on their unique olfactory abilities which enable them to effectively sniff out the volatile organic compounds which are usually produced by the bacteria M. tuberculosis. For example, the rodents are subjected to a vigorous training be able to effectively screen more than sputum 100 samples in under 20 minutes [4]. “When they find a sputum sample from a TB-positive patient, the rats usually begin to rapidly scratch the sample using their front paws with an almost 100% accuracy” [3]. The present study examines the use of African giant pouched rats in Tanzania for the detection of mycobacterium tuberculosis.

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Literature Review

Tuberculosis (TB) is a preventable and curable disease. “African pouched rats which are scientifically termed as the Cricetomys Gambianus have been proved to have the ability of detecting Mycobacterium Tuberculosis”[4]. “According to research that was conducted by World Health Organization, tuberculosis is among the deadliest infectious disease killing more than 1.7 TB patients in the world” [5].The populations most affected by the disease reside in African and Asian countries. A large percentage of tuberculosis patients living in these countries are yet to be detected as a result of poor sensitivities of smear microscopy. “In Tanzania, 287 out of 100000 people are thought to be infected with Tuberculosis” [6]. The pouched rats are taught to sniff out Mycobacterium Tuberculosis with the help of olfactory abilities. The process has been reported to be successful to an extent that they will be servicing more than 60 clinics from the previous 29 clinics [5].

Use of Giant Pouched Rats in TB Detection

Trained African giant pouched rats (Cricetomys gambianus) are increasingly being used in Tanzania to help in the detection of tuberculosis. In 2010, pouched rats were used to analyze sputum samples that were collected from treatment centers across Dar es Salaam. “Since then, the application of rats to sniff out TB has nearly doubled over the past few years with more than 60 clinics currently being served across Tanzania from the initial 29” [6].  The sputum specimens were collected from the target patients found at the treatment centers. And the outcomes were subjected to comparisons with smear microscopy findings at the same center. The samples were then stained and smeared on the slides using Ziehl Nelson Technique. The remaining samples were frozen and then transferred to Belgian Charity Organization called Anti-Persoonsmijhen Ontmijnende Product Ontwikkeling  (APOPO) center for evaluations.  APOPO got approval to carry out research from Institute of Medical Research Studies. “The sputum samples were then sorted by APOPO technicians and heated at 90 degrees to destroy microorganisms. The samples were subjected to high temperatures in order to kill any microorganism” [5]. “A total of 10 sputum samples were then availed to the detection pouched rats by positioning them below the holes which were symmetrically placed across a testing cage” [4].

During the testing process, detection pouched rats would walk across the cage sniffing sputum samples. “A positive response is noted when rat paused on the sample for over five seconds. The specimens were then tested by eight, nine or ten pouched rats” [6]. The specimens that recorded a negative TB by smear microscopy but TB positive by 2 or more pouched rats were then evaluated using Ziehl Neelson Method. Those samples that were identified TB negative through smear microscopy but TB positive with Ziehl Neelson Method were termed as new case detection. New cases were generated on a weekly basis and then reported to the centers for confirmation.

Methods of Identifying Tuberculosis (TB)

The most common technique which identifies Tuberculosis within the east African region is called the Sputum smear microscopy. “In most developing nations, tuberculosis diagnosis is solely based on smear microscopy. Sputum smear technology is a cheaper method of detecting tuberculosis” [6]. However, the method consumes a lot of time and has failed to flag out and identify tuberculosis positive samples especially when huge sputum samples are used. “It is therefore, crucial to come up with a new tuberculosis diagnosis test that will improve the detection of tuberculosis in patients born in low and middle income households.” [3]. That is the reason why Tanzania went ahead to train detection pouched rats as an approved case finding instruments.

According to research that was carried out in 2009, the scent detection pouched rats rose Tuberculosis positive findings by over 30 per cent over smear microscopy [3]. “The sputum samples were subjected to evaluation by ten pouched rats and considered them positive. As such, the current study presents a research finding that was collected in Tanzania back in 2010” [4]. Recent study that involved 10523 patients from Dar es Salaam proved that using pouched rats immediately after smear microscopy raised the case detection by over 45 per cent [3].

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The objective of the research was expanding the number of samples that were previously used when simulating the second line screening. Specifically, pouched rats that were used in the previous study were used in the current research. However, a total of 30 per cent of the total pouched rats used were new under different configurations. The idea behind this process was to find out the ability of those trained pouched rats in detecting M. Tuberculosis under a programmatic surrounding[4]. “According to results, the detection pouched rats increases the detection of Tuberculosis in sputum samples by 44 per cent” [4]. This statistics is based on the research study which was carried out in 2009 and 2010. Similar detection rates were confirmed in two research studies which reported independent data which were collected in various points in time with varying pouched rats which confirmed the current study to be reproducible [5]. “Therefore, it then appears that the trained pouched rats are useful in screening Tuberculosis” [4]. They can evaluate sputum samples in a faster manner compared to the smear microscopy.

Additionally, the evaluation of pouched rats increases the detection rates when one compares it with Ziehl Neelson Method. “The specificity of a single pouched rat was 93 per cent while that of a combined pouched rat was 89 per cent”[4]. These values are considered to be better compared to those obtained from smear microscopy. “This medical intervention which involves tuberculosis testing by pouched rats and the method of flagging out TB patients that cannot be detected through clinical means will enable diagnosis and treatment move by over 70 per cent” [2]. This is a crucial proportion since more patients were proved to be Tuberculosis positive in pouched rats while negative in hospital.

Results and Conclusion

The results of the literature review on the use of African giant pouched rats in Tanzania for the detection of mycobacterium tuberculosis reveal a number of important findings. Firstly, the findings proved that trained pouched rats increased the case detection tuberculosis by more than 40 per cent” [5] “Recently, the rate increase in the Tuberculosis detection was noted because of the trained pouched rats.”[3] “Generally, there existed a total of 22858 smear microscopy negative samples. From this number, 5421 were identified as positive by detection pouched rats but negative by smear microscopy at APOPO” [4]. The detection pouched rats differentiate the M. Tuberculosis from the other microorganisms. “There existed 3807 positive samples from smear microscopy out of which 420 samples were not detected by pouched rats but identified positive by 2nd smear microscopy at APOPO” [3]. They also have the ability of differentiating the clinical sputum which contains M. Tuberculosis from Sputum which contains other pathogens.

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The results above showed that the sensitivity of an individual pouched rat is 73.1 per cent while sensitivity of a combined pouched rat is 86.6% [4]. “When a number of pouched rats evaluated similar sputum samples with positive samples by more than two pouched rats, the general sensitivity relative to the overall outcome of smear microscopy and APOPO, was found to be approximately 89 per cent with a specificity of 76.3 per cent” [3]. The general sensitivity was 95.6 per cent with a specificity of 73.6 per cent. Sensitivities and specificities were then computed for ten pouched rats that were deemed operational for the whole year and were not used in any research. In reference to the smear centers and APOPO combined the mean specificity was 85.7 per cent while the mean sensitivity was 72 per cent as shown in the table [4]

Additionally, according to the results, “the pouched rate confirmed that it takes only 20 minutes for the pouched rats to screen a total of 100 samples” [6]. This is compared to a total of 4 days which takes a laboratory technician to do the same. Therefore, “it places pouched rats to have a higher accuracy of detecting tuberculosis compared to other detection methods like smear microscopy” [6]. However, the pouched rats cannot separate the drug resistant strains from the normal strains. The pouched rats are subjected to a training process that begins when the pouched rats are only a month old after which they are deployed to detect tuberculosis in selected clinics.  “Sniff detection of tuberculosis using the pouched rats were subjected to analysis and evaluation by medical researchers in Tanzania” [5]. The proof of principle shows that the pouched rats have the ability of detecting Tuberculosis positive samples in a faster and accurate manner compared to the smear microscopy.

Nevertheless, one of the limitations that were observed in the research is that there was no reference standard that could be used to compare the yield of both the pouched rats and the smear microscopy. Therefore, it would be important if future research incorporates this attributes in their future research studies. “Additional research studies need to confirm the actual samples that are detected as negative through smear microscopy and APOPO, but positive through rat detection” [4]. “During the study that was conducted in 2010, 4635 negative patients were identified as positive with pouched rats but smear microscopy only confirmed 716 patients”[4]. The lower sensitivities from smear microscopy method show that in reality there are lots of patients who have bacillus in their sputum samples.  It is highly hoped that using pouched rats for initial detection for purposes of confirmation is rise the new detection rates without an increase in cost.

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In conclusion, the application of trained African giant pouched rats (Cricetomys gambianus) in Tanzania in the detection of mycobacterium tuberculosis (TB) in human sputum samples is a novel and promising approach towards improving the detection rates of TB which is critical in controlling the disease. The use of rats in TB detection is relatively effective with almost 100% accuracy. This is particularly important considering the scarcity and unavailability of cheap, efficient and reliable means of TB testing in Tanzania which has contribution to low screening and detection rates for the disease.

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  1. World Health Organization. (2016). Global tuberculosis report 2016. Retrieved on July 1, 2018 from
  2. Ellis, H., Mulder, C., Valverde, E., Poling, A., & Edwards, T. (2017). Reproducibility of African giant pouched pouched rats detecting Mycobacterium tuberculosis. BMC Infectious Diseases17(1). Doi: 10.1186/s12879-017-2347-3.
  3. Mgode, G. F., Cox, C., Mulder, C., Valverde, E., Mwesiga, G., & Maeda, J. (2016). Detection Rats Technology for Diagnosis of Tuberculosis in High-Risk Populations. In Special Issue: Edited Proceedings of the 4th COSTECH Annual National STI Conference and Exhibitions held from From 24th–26th June 2015 at the Julius Nyerere Convention Center in Dar es Salaam, Tanzania (p. 40).
  4. Mgode, G., Cox, C., Mwimanzi, S., & Mulder, C. (2018). Pediatric tuberculosis detection using trained African giant pouched pouched rats. Pediatric Research. Doi: 10.1038/pr.2018.40
  5. Mahoney, A., Weetjens, B., Cox, C., Beyene, N., Mgode, G., & Jubitana, M. et al. (2017). Using giant African pouched pouched rats to detect tuberculosis in human sputum samples: 2010 findings. Pan African Medical Journal9(1). doi: 10.4314/pamj.v9i1.71204
  6. Melo, S. (2017). Giant pouched rats increase their attack on tuberculosis in Tanzania. Reuters2(1), 3.
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