https://www.theguardian.com/technology/2018/nov/04/five-diseases-that-dogs-can-detect

Scientists are investigating canines’ extraordinary sense of smell, hoping that it will prove a more reliable predictor of illnesses than conventional testing

Last week, researchers presented evidence that dogs could tell from sniffing someone’s socks whether they had malaria. After several months of training, a labrador and a labrador-retriever could tell if a child had the disease even if they were not showing symptoms.