Scientific Article for Students

Abstract Can you imagine a rat sniffing out a disease? The African giant pouched rat can! Scientists trained these rats to identify if a person has tuberculosis (TB). TB is a bacterial disease that most commonly affects the lungs. It spreads easily and can be dangerous if untreated. When rats smell samples of mucus a person coughs up, they can smell if it has TB bacteria. We wanted to know if rats are better at identifying cases of TB compared to a standard microscope test. We also wanted to know if rats can better identify TB in children than in adults. We found that rats can identify TB in samples that the microscope test said were negative. We also learned that the rats are more likely to identify TB in children – even when they have low levels of bacteria. Using rats can help more people receive treatment for TB and reduce the spread. Introduction There are many bacterial diseases that are very dangerous if left untreated. An important example is tuberculosis (TB). Pulmonary TB is a lung disease caused by bacteria. A person with TB typically experiences coughing, fever, weight loss, and night sweating. The cough can bring up phlegm, sometimes mixed with blood. Phlegm is mucus that the respiratory system uses to protect itself from bacteria and viruses. Because bacteria cause TB, it is usually curable with antibiotics. Even though TB is a treatable and preventable disease, it remains the deadliest infectious disease in the world. Diagnosing TB is important. If people are not treated, they could die. For example, about 10.8 million people fell ill to TB in 2023. Many of these cases are in Africa. In 2023, 1.25 million people died from TB. Diagnosing TB can also prevent people from spreading the infection to others. The most common ways to identify TB are using a smear test or a molecular test. During a smear test, a person analyzes a sample of phlegm using a microscope. During a molecular test, a sample of phlegm is tested for the DNA of the TB bacteria. But another way to identify cases of TB is using trained African giant pouched rats. These rats can detect TB by smelling people’s phlegm. How? Well, you recognize when you smell coffee because it’s composed of chemicals specific to coffee. Similarly, the rats can identify the smell of TB because of several chemicals specifically produced by the TB bacteria. We wanted to answer three questions about rat detection of TB. How does rat identification compare to the smear test? How well do rats identify TB in children and adults? How does the amount of bacteria affect the ability of rats to identify TB? Methods We analyzed phlegm samples from children, men, and women in Tanzania from January to December 2022. We selected 35,766 patients who went to a health facility and who had one of the four TB symptoms. The health facility tested samples from these patients using a smear test or a molecular test. We used samples from patients who tested negative on that first test. We used trained rats to test each sample. We placed the rats on a floor with 10 holes. Each hole had a phlegm sample. The rats sniffed each sample. If they gave the signal (pausing for at least three seconds), we considered the sample TB positive. If they did not, we identified the sample as TB negative. We then confirmed any rat-identified positive samples using a more sensitive smear test. All patients with a positive result received treatment (Fig. 1). *For the curious* If the more sensitive smear test is better at identifying TB, why don’t doctors just use that one all the time? Why go to the trouble of training rats? Well, unfortunately these tests and the molecular tests are also much more expensive. Countries with very limited healthcare budgets rely on the smear test because it is so much cheaper – even if it doesn’t catch all TB cases. We also determined the level of bacteria in all samples. Based on the number of bacteria observed, we classified samples as having very low, low, medium, or high levels of bacteria. Results 1. How does rat identification compare to the standard smear test? The smear test identified 1900 (about 5.3%) of the patients as positive. Our rats identified an additional 2029 cases of TB, so an additional 5.7% of the patients. They were also much better than the smear test at detecting low or very low levels of bacteria (Fig. 2). In fact, our rats were six times more likely than the smear test to detect TB in patients with those lower levels. 2. How well do rats identify TB in children and adults? The rats identified 71% of the total number of children with TB. They identified 51% of the total number of adults with TB. Our rats were twice as likely to identify cases of TB in children than adults. 3. How does the bacteria level affect the ability of rats to identify TB? When the samples had very low or low levels of bacteria, two or three rats out of five identified TB in the samples. For samples with medium and high levels of bacteria, more than three rats out of five identified TB. Discussion We found that rats offer an effective method of identifying TB in adults and children. The rats identified TB in patients that had a negative result from the first test at a health facility. That means we can identify and treat more cases of TB. This treatment will reduce the spread of the disease. It will also reduce the number of people who die from TB each year. Rats are more likely to identify TB in children than in adults. That means rats can help improve the diagnosis and treatment of children with TB. This will also prevent the spread of the disease and save lives. Getting treatment when there are still low levels of the bacteria also means less suffering for children with TB. The ability of rats to identify TB depends on bacteria level. As the bacteria level increased, more rats identified TB cases. This is similar to the smear test. But the data suggests that rats are better than the smear test at identifying cases when levels are very low or low. That is why using rats to identify TB can improve people’s ability to receive treatment. Conclusion There’s a lot we can do to limit the spread of bacterial diseases like TB. Make sure to wash your hands and cover your mouth and nose when you cough and sneeze. Whenever you do not feel well, stay home and rest. This will reduce the likelihood that you will pass on bacteria to other people. You should also visit a doctor when you have symptoms of a bacterial infection. If you need medication, make sure that you follow the instructions. When people don’t take their antibiotics as instructed, it can lead to stronger bacteria that are harder to treat with antibiotics. Our individual actions can help protect people in our communities from infection.