Review of implementation of animal model for diagnosis of past and present with special reference to Canis familiaris

Introduction

We have more to learn from animals than animals have to learn from us, it is rightly said as throughout civilization various animals have been a part of human day-to-day activities. Proof of animal use can be dated as far back as the stone age when animals such as dogs were utilized in hunting and eventually in herding. Animals were used as a mode of transport and gradually as a tool in agriculture. Throughout all these developments one common outcome is that animals have always had keen perceptive sense organs. Hence, even though human beings are exceptional in the animal kingdom, every animal has advanced senses that it needs for its environment and way of life. Among all other animals, humans have taken benefit of canine’s superior sense of smell in various fields including domestic and scientific research.

Ayurveda classic has explained the role of animals as a diagnostic tool in the context of direct observations, where the nature of blood is resolved by feeding the collected blood to dogs and crows. The inference is drawn accordingly to the reception of the given sample of blood by the animals. This art of diagnosis by the means of animals was lost in the quick development of science.  

Over time this application is lost by the advancement of modern equipment. Until recently, a sudden surge of the pandemic has given rise to implementing canine models to distinguish the whiff of COVID-19 infections. Dog trainers have been claiming extraordinary results and in some cases, can identify the virus with almost perfect accuracy. The present review article explains the application of animals for diagnosis, especially familiaris models, in the area of medicine past and present.

This review attempted to critically analyze the implementation of animal models for diagnosis in the past and present with special reference to the Canis familiaris model. This includes the description explained in classics on the use of dogs in pratyaksha pareeksha that is, direct observation in gustatory perception.

This conceptual study was done by analyzing the information available in classical texts of Ayurveda along with commentaries and by incorporating relevant data from articles, journals, and studies on the use of the Canis familiaris model in medical expansions. The collected details were critically analyzed and discussed and conclusions were presented systematically.

Pratyaksha pareeksha

Specific features of diseases can be determined by a threefold approach, that is, methods of aptopadesha (authoritative instruction), pratyaksha (direct observation), and anumana (inference).¹ Prathyaksha is the conception that is directly perceived by the self and the sense organs. Self-perceived are pleasure, pain, desire, and aversion. While sound, etc. are appreciated with the help of the sense organs.²

Acharya Charaka explains that a physician who wants to examine the patient and diagnose the disease through the direct observation method of examination should examine the body of the patient with his senses, except gustatory examination.

The following senses can be examined:

By auditory perceptions:

● Antrakoojanam: Movement of the intestine indicated by a gurgling sound

● Sandhisphutanam: Crackling sound in the joints of the body

● Swara visheshana: Various voice patterns of the patient

● Shabda: Includes sounds in the body of the individual like respiratory and cardiovascular sounds along with the sounds which are produced through percussion and auscultation methods of examination.

By tactile perceptions:

The physician can touch various parts of the patient’s body, and examine varied signs of abnormality in terms of :

● Body temperature

● Skin texture: unevenness, roughness, and presence of moisture

● Eruptions, pitting, tenderness, etc.

By visual examination:

● Variations in color, shape, measurement, and complexion

● Natural features in a healthy individual and in contrast to it, abnormalities or unnatural features as seen in diseased

● Few other changes which can be commonly examined visually like

By gustatory perception:

● The taste of the various tissues in the body of the patient is the object of the gustatory sensory receptors and can be ascertained by conjecture and not by direct observation.

By olfactory examinations:

● Normal and abnormal smells of the entire body of the patient can be examined by the olfactory sensory receptors.³

Animals mentioned in the classics:

Acharya Charaka while explaining pratyaksha pareeksha i.e. direct observation gives a specific exclusion that gustatory examination is an exception to the physician among all the sense organ examinations. Therefore, the taste in the mouth of the patient should be discerned by interrogation. Here the examination is carried out with the help of animals. For example, the sweet taste of the body can be inferred when flies are attracted to the body. In the case of bleeding from the body, if there is a doubt about the nature of the blood, it should be settled by feeding the blood to a dog and crow. Ingestion of the blood by the dog and crow is suggestive of its chastity and rejection by these animals indicates that the blood is vitiated by pitta i.e. the patient is suffering from bleeding disorders. Similarly, other tastes in the patient’s body can also be inferred.⁴

Another instance of mentioning of the crow can be witnessed in Indriya sthana of Charaka Samhitha, where Acharya describes that when an individual offers a piece of daily meal to a crow and it does not accept it, this indicates death within a year for the offering person.⁵

The recent development of the use of species familiaris models:

Dogs have a remarkably larger surface area of the olfactory epithelium, which is approximately 30% more olfactory receptors. These receptors can recognize a much wider spectrum of odorants in contrast to humans. They even have the potential for excellent odor localization, even in the existence of significant background odor, presumably due to the larger nasal cavity size as compared to other species and the unique airflow patterns created by sniffing. This ability of familiaris species to localize each source of scent even in the presence of multiple odors makes the detection dog a crucial associate in many militaries, law enforcement, and search and rescue operations. With this as a foresight, an approach towards the utilization of canines in the detection of various disease conditions is being slowly developed into a full-fledged science.⁶

In 2011, the Department of General Thoracic Surgery proposed a new research approach by involving specially trained sniffer dogs in research strategies to make use of their ability to identify lung carcinoma in the breath sample of patients. Similarly, many types of research were conducted in utilizing canine models in the detection of carcinoma employing their unique olfactory perception.⁷

The surge of the COVID-19 pandemic gave a new outlook on the value of the olfactory system of dogs. The screening of a COVID-infected individual is a game of dice, tricky and time-consuming. Hence, in a large public mass, the detection facility created a lot of havoc and confusion. This gave fodder to the thinking brains to access such a method of screening which will apply to a huge mass. Thus in 2021, a research concluded that the waiting time for COVID-19 scent dog detection results is in seconds as opposed to hours or days for the RT-PCR tests.⁸ Further research is being carried out to explore more on this concept.

A study on the classification and etiology of diabetes in dogs and cats concludes that dogs do not have an amyloidogenic amino acid structure of islet amyloid polypeptide (IAPP) and do not develop islet amyloidosis during periods of sustained insulin resistance. This explains why type 2 diabetes is not recognized in dogs, even when they are morbidly obese. However, immune-mediated diseases are very common in dogs, hence it is not surprising that type 1 diabetes predominates in them.⁹

Correspondingly, studies have also concluded that experimentally-induced and transplantable tumors of rodents provide valuable models for analyzing the biological and physiological mechanisms underlying a varied response of tumors to multiple forms of cancer therapy. However, it is difficult to translate these “sterile” experimental results directly to humans. Dogs with naturally occurring cancer render an important resource for the study of the pathogenic mechanisms of human disease and provide significant information regarding the treatment efficacy, particularly when analyzing normal tissue toxicities.¹⁰

Another canine model following the features of X-linked Alport′s disease (AD) was reported by Lees and colleagues (Lees et al., 1999). Analysis of the collagen α5 chain gene in these dogs resulted in the identification of a 10-bp deletion in exon 9, which causes a frameshift mutation and premature stop codon. Kidney disease described in these dogs follows essentially the same course as described in the Samoyed model.¹¹

Discussion

Modern studies are more oriented toward using the canine’s olfactory system. But Acharya has explained the application of the gustatory system which is the ability of the canine to differentiate in the perception of taste. Dogs have about 1700 taste buds, whereas humans have about 9000. The canine tongue has a unique distribution of taste buds for the basic flavors (meat, salt, sweet, sour, bitter). In a further study, it was explained that dogs have highly sensitive sweet receptors and contrasting salt receptors since wild ancestors of dogs, as carnivores, obtain sufficient salt from their diet.¹² Acharya Sushruta when explaining the features of blood tissue mentioned sweetness as a characteristic and the opposite is seen in the case of bleeding disorder where the vitiated blood is predominant with salt and bitter taste.¹³ Thus, it can be correlated as to why dogs acknowledge the given sample of blood, the priorly explained way.

Conclusion

Knowledge gained by the proximity of the soul, sense organs, and mind to the object of study or observation is known as perception or direct observation.¹⁴ Even though we carry forward many principles of direct perception, the art of including animals is lost in the tangle of time. By indulging ourselves more in this we will be able to finally solve the lack of medical diagnostic approaches. Because the available diagnostic methods are a slave of a very tiring time frame and expensive that is far from reach of a common person. Acharya has already given us the information required in the classical texts, we just have to put a little more effort into conducting research and clinical trials on the already available data.

Conflicts of Interest

None