Authored by: Venkat Rao
A team of British scientists working with the Medical Research Council in Gambia went to a local school and handed children aged 5 to 14 beige-colored nylon socks to wear overnight. Socks were collected from children returning to school the next day, safely packed, and sent to train dogs to recognize scents—the molecular signature of malaria—imperceptible to the human nose. Results were stunning: two trained dogs were able to correctly pick out the scent of children infected with the malaria parasite 70 percent of the time. Out of a total of 175 sock samples tested, 30 belonged to malaria-positive children and 145 were uninfected. Dogs were able to positively detect the disease in 70% of the cases and accurately identify 90 percent of the samples without malaria. Subsequent tests onsite at school indicated that while all children appeared healthy, 30 children were carrying the parasite without showing the disease symptoms. Asymptomatic carriers of the deadly disease who will go undetected using current test methods at airports, ports of entry, or other border crossings.
Asymptomatic malaria is the most challenging problem for malaria health eradication programs.
A highly trained dog can detect COVID-19 in humans faster than a PCR test! How cool is that. Numerous publications report trained dogs can scent-identify unique odors of volatile organic chemicals generated during COVID-19 infection. Trained dogs detect body odors directly from the body of a patient, or through sniffing samples collected from patients. A meta-analysis of 27 studies published last month in the Journal of Epidemiology conclude that trained dogs can detect COVID-19 disease with greater than 80% of the cases presented and with 90% accuracy in sweat samples, saliva, masks, and urine. Data from more than 70 studies performed in 60 countries during the COVID-19 pandemic before diagnostic tests were made widely available worldwide. In six studies with high-quality data, 82% to 97% detection sensitivity, and 83% to 100% accuracy was reported. These results simply put, are astounding. A study on breath analysis report 1,765 volatile organic compounds appear in extremely low concentrations in exhaled breath, skin secretions, urine, saliva, human breast milk, blood, and feces. The levels of these chemicals are extremely low, in parts per billion or trillion, beyond the realm of current disease detection systems and way beyond smelling sense capability of humans. Volatile compounds in exhaled breath and other body secretions denote a record of historical exposure or a pathological condition. To profile and train a machine learning algorithm to undertake breath analysis to detect volatile compounds specific to a virus such as SARIS-CoV-2, or a bacterium such as Streptococcus pneumonia from a complex mixture of 1,765 chemicals in the breath would be a tedious process, to say the least, and rife with inaccuracies. However, trained dogs can quickly sniff out a test sample or an infected individual and accurately detect a disease condition when presented with a plethora of thousands of organic volatile compounds in the test sample or an individual for screening. Successfully combating COVID-19 pandemic requires a timely and accurate method to detect the disease. Note that the detection approach must be timely and accurate. None of the currently available detection and diagnostics techniques satisfy these two critical requirements. Enter man’s best friend, dog, to help out. In a recent study, investigators trained 6 dogs to detect the SARS-CoV-2 viral scent in masks to scent human respiratory secretions unique to COVID-19 patients. Dogs were also trained to directly sniff human subjects to detect COVID-19 infection. In both instances, trained dogs were able to detect SARS-CoV-2 virus in mask samples with 95% accuracy and 95% specificity, indicating scent-detection by trained dogs is a highly accurate and rapid screening technique for detection of COVID-19, with a 99% rate of success in detecting infected individuals. A truly amazing observation is that the detection accuracy was 95% even while screening infected individuals without COVID-19 disease symptoms. Trained dogs were far more accurate and quicker in detecting SARS-CoV-2 virus than prevailing DNA tests currently in use.
Why trained dogs are an attractive alternative to the current nasal swab sampling and rRT-PCR test? Simply put, there is no intrusive sampling required when using trained dogs to detect the virus at a meagre cost yielding highly accurate and specific results. Compare this to the highly intrusive nasal sampling and expensive DNA testing current in play as gold standard for the pathogen detection regime. Second, an ideal goal of any disease detection test is that it should detect the pathogen at early stages of infection when individuals exposed to the virus are yet to present the disease symptoms. Although the DNA test is 100% accurate in detecting the SARS-CoV-2 virus in test samples, it comes with a key shortcoming—the DNA test is not sensitive during the first 5 days post-exposure to the virus—0% on day-1, 33% on day 4 and 62% on day 5 post exposure.
Antigen detection tests are basically useless when it comes to detecting the virus and preventing spread of the disease, as these tests tend to be more accurate at later stages of infection, and after the pandemic washes out of a community. Trained dogs offer a unique alternative to SARS-CoV-2 detection in the general community and surveillance in public places such as schools, baseball games, concerts and other gatherings that might need a rapid, yet highly accurate screening method. Dog’s smell sensing (Olfactory) system is built that way. A dog’s nose has over 300 million receptors, the smell capturing unit, compared to 6 million in humans.
Dogs possess a unique kind of receptors called neophilia, which attracts them to new and interesting odors. With that many smell-sensing receptors, dogs can smell 10,000 to 100,000 times better than humans. The part of the brain that processes smell signals from the nose is 40 times larger in relative size compared to the human brain. Dogs possess a scent-sensing system that is more sensitive than the most advanced electronic sensors with capability to detect scent of a single drop of chemical in an Olympic sized swimming pool. The powerful olfactory capability of dogs has been put into good use by law enforcement agencies, armed forces, customs and border security, and sports arena to detect contraband narcotics, explosive chemicals, and other prohibited items. Public health and health researchers have reported dogs with a high degree of precision detection through scent signatures of diseases such as cancer, diabetes, tuberculosis, malaria, and now COVID-19.
What exactly is neophilia in animals and how is it put to advantageous uses by us, humans?
The term, neophilia, merely means a love of novelty and new things, which is how exploratory behavior in animals driven to seek new sources of food, explore novel environments, familiarize routines for obtaining food, and detect threats.
The large smell-sensing (olfactory) organs in the nose of a dog are large compared to other mammals. Dogs are reported to have 1094 olfactory receptor genes of which 872 genes are unique to the functional acuity of the scent detection. A critical feature of dog’s olfactory organ is the presence of a large number of receptors affording a tremendous capacity to seek, capture and process chemical signals from the environment. Sniffing is extensively studied in dogs. Associated with the smell-sensing feature, dog’s nose has another unique apparatus known as vomeronasal organ, which does not exist in humans. This unique smell-sensing organ is highly complex in dogs that allows conduction specific-chemical signals to the brain.
Human sensing apparatus works differently. When human nose sniffs for a scent the air volume is larger and tiny amounts of scent may go undetected. In contrast, while sniffing, dogs inhale 6 to 7 times faster than humans and each sniff takes in a small amount of air as a result. These rapid sniffs inhaling smaller volumes of air provide more chemical signals for detection. Dogs’ unique way of sniffing air takes advantage of a highly sensitive sensing apparatus. When dog inhales air, it splits into two streams, with the first stream going to the lungs for respiration, and the second stream going to an interior part of the nose for scent analysis. Inhaled air during exhalation takes a different route altogether passing through the nasal slits, which separates new inhaled air from the exhaled air that way less dilution of scent. The sheer anatomy of dog’s nasal cavity is well equipped to allow small amounts of scents in sniffed (inhaled) air and retain it as well without dilution as the act of sniffing continues.
In 1789, King Frederick of Prussia once made a prescient comment that dog is a “man’s best friend”. This is proven once again with this best friend serving as the reliable and rapid biosensor for COVID-19. To you all dog lovers out there, and count me as one, go give your best friend a big hug!