PUBLICATION DATE:  15/06/2007

RATING

AUTHOR:  MELISSA NEWMAN - University of Kentucky (Courtesy of Alltech Inc.)

On September 11, 2001 all eyes turned to New York City, Washington, DC and a rural field in Pennsylvania as we experienced a tragedy that will live in memory and nightmare for the rest of our lives. From these terrible events we witnessed unselfish acts of courage, commitment and bravery that were beyond our imagination. Among the heroes, the American public was surprised to see ‘Man’s Best Friend’, the dog. Thousands of people around the country like me, who work dogs in Search and Rescue, already knew what these incredible animals could do for man, not just as a family friend or companion, but as a partner in saving lives or helping victims. Over 300 dogs responded to the events of 9-11. The use of dogs for scent detection may be a new concept for some people, but dogs have truly been a partner since the days of the cave man.


The difference is the nose

Dogs have been used to find explosives, drugs, cancer, rabbits, accelerants, felons, snakes, pipeline leaks, mold, moth larvae, oranges and victims of disaster. The reason these versatile animals are so effective is as plain as the nose on their faces. The sensitivity of the canine nose is dependent upon the substance in question. Dogs can detect some odors, such as a nitroglycerin-based smokeless powder, in levels as low as parts per trillion (Johnston, 1997).

In fact, dogs have been shown to be more sensitive than sophisticated detection equipment to some odors. The added advantage is that vapor collection, processing, and detection are instantaneous in the dog, but may require several hours in the laboratory.

Unfortunately the research to accurately define the effectiveness of the canine nose has been confined to only a few matrices and lacks a comprehensive understanding. To date the majority of research has focused on explosive detection.

Several characteristics of dogs make them better at scent detection than humans. The structure of the canine nose is designed to optimize scent detection (Figure 1).



Figure 1. The canine nose.


The nostrils, which are the entryway to the olfactory system, actually widen when the dog sniffs, thus allowing larger quantities of air to enter the nasal cavity. In this cavity, thin bony ridges called turbinates direct the incoming air and are covered with olfactory receptor cells and mucus.

In humans there are approximately 5 million of these olfactory detection cells. The dog may have up to 125 million cells in the Dachshund, and 220 million in the German Shepherd (Droscher, 1971). These cells report to the olfactory portion of the dog’s brain, which is four times larger than the olfactory portion of a human brain.

Olfactory acuteness varies according to the breed of the dog, and can be interrupted by a disorder in conduction of the olfactory system or the brain (Vadural and Cogny, 1997). During normal breathing, incoming air will rise in the nose to contact the olfactory receptor cells via diffusion or eddy around the turbinates. If a dog is interested in a scent, it will often inhale sharply or sniff. This will increase the volume of air in the nose and force the air deeper into the sensory receptors for analysis.

Often a dog will run with its head high against the wind searching for scent. Upon exhalation from the trachea to the mouth cavity the pressure in the nose will lower, causing an increase in inward air moving through the nose during expiration (Steen et al., 1996). This is an effective means of increasing the volume of air sampled through the nose while running. As a result, dogs have the ability to follow small concentrations of scent to larger concentrations and ultimately the source of the scent.

Another characteristic that makes dogs better at scent detection than humans is that dogs do not suffer from what is known as ‘scent fatigue’ or ‘odor lock’. This is the condition where humans placed in a room filled with flowers will notice the scent upon entering the room, but become less aware of the scent over time. After 10-15 minutes we no longer detect the flower scent because the human sense of smell will become accustomed to the odor.

The dog has demonstrated by following the track of an escaped felon for miles without any signs of decreased perception that it does not experience scent fatigue (Pearsall and Verbruggen, 1982). In addition, dogs have the unique ability to discriminate among similar scents, exceeding that of most laboratory equipment.

One theory that describes this sensitivity of the canine nose is often referred to as the ‘lock and key’ effect. In this theory, each molecule of scent has a specific shape and for each shape there is a correspondingly-shaped olfactory cell that is responsible for detection of the scent.

Perhaps a better way to visualize the ability of the canine nose is that when a human enters an Italian restaurant the individual might just smell ‘pizza’. In contrast, the dog smells the dough, tomato paste, pepperoni, cheese, onions, salt, pepper, garlic and mushrooms on the pizza. This is exactly why a dog has the ability to detect the presence of gasoline in a fire even in the presence of many other burnt materials.


Detection dogs and partners

SEARCH DOGS

Search and Rescue (SAR) dogs are used to detect persons lost in the wilderness or in an urban environment. Dead skin cells or ‘rafts,’ are constantly shed from the body, in combination with skin secretions and perfumed toiletries that make up an individual’s scent profile.

Rafts are approximately 14 microns in size with an average weight of 0.07 micrograms. The human body is covered with approximately two billion skin cells, of which approximately 3% is shed daily. This results in almost 40,000 cells shed per minute from the body (Syrotuck, 1972).

The human body is the source of scent and the rafts provide the substrate for degradation by bacterial metabolism resulting in the unique volatile ‘fingerprint’ that can be recognized by the dog (Marples, 1969; Settle et al., 1994). The rafts, and therefore the scent, can move through the air in response to thermal currents, wind, and humidity and ultimately reach the nose of the Air Scent search dog.

An Air Scent dog travels with its nose in the wind searching for airborne rafts (Figure 2). Once detected, the Air Scent dog will work back and forth in a cone-like pattern to reach the highest concentration of scent emanating from the victim.

Since bacterial metabolism is a necessary component of the development of human scent, environmental factors that influence microbial growth will also influence the development of scent.

Extremely hot and dry weather conditions will inhibit the growth of bacteria and make scent detection very difficult for the search dog. A light rain coupled with moderate temperatures will provide optimal conditions for the bacteria resulting in increased bacterial metabolism and the production of large volumes of volatile compounds.

Search and Rescue dogs can also be Trailing dogs.

These animals will not only follow the volatile fingerprint of the individual but also will follow the route of scent deposited on the ground as a person moves through an area. These dogs tend to work with their noses closer to the ground as is seen with the Bloodhound trailing a felon from a crime scene.

Walking across the ground disturbs the soil and vegetation; and as a result moisture and volatile compounds will be released that can contribute to the ground scent. This ‘vegetative scent’ can act to enhance the overall scent picture and aid the Trailing canine in locating the victim.

Early research demonstrated the ability of a Bloodhound to follow the trail of one twin in an area that had been contaminated with the scent of the second twin (Kalmus, 1955). The Bloodhound is the supreme example of a dog bred to excel in trailing (Sommerville et al., 1993). Problems can occur when the dog focuses only on following the vegetative scent and ignores the raft scent. In these instances footprints or tracks from sources other than the victim can easily confuse the dog.



Figure 2. Air Scent Dog checking the air currents for the presence of human scent.


CADAVER DETECTION

Human detection dogs can further specialize as cadaver dogs. These dogs are used for the detection of drowned, buried, or concealed human remains and are commonly used by law enforcement (Owsley, 1995).

Recent investigations in Canada demonstrated that cadaver dogs can be effective in detecting scattered partial human remains (Komar, 1999). This ability may be used in the detection of human remains following disasters as witnessed in the days and weeks following the tragedy of September 11, 2001.

Within 15 minutes following death, protein synthesis stops in the body and the microorganisms of the gut and skin begin to degrade the body. As a result of this, degradation odors such as putrescine and cadaverine are released. The concentration of these noxious smells will vary depending on the time of death and environmental conditions to which the body is exposed.

Dogs are generally trained to be cadaver dogs using human tissue or soil obtained from beneath a decomposing body. It is essential that dogs are trained to specifically respond to human remains and to not respond to animal remains.

The detection of drowned victims is possible because the skin cells and body oils of the victim will float to the water surface. The canines are generally worked from boats in a grid pattern across the water’s surface. When the dog passes through an area that contains human scent, the dog will alert the handler to that location. The handler will then move the dog back and forth across the scent until the highest concentration of scent is detected.

After taking into account areas of interest and the effect of the environmental and water conditions on the scent movement, efforts to recover the body can begin. In one search in Kentucky, a body was recovered in over 300 ft of water. The canine alerted handlers within 15 ft of where the body was located.


CANCER DETECTION

Williams and Pembroke (1989) reported that malignant tumors emit unique odors that could be detected by dogs. This observation was based on a female patient who sought medical attention after her dog became obsessed with a mole on her leg and eventually tried to bite the mole off. Following biopsy the mole was identified as cancerous.

Since that time chemical markers of melanoma have been reported in the blood and urine (Wakamatsu and Ito, 1990). Researchers at the University of Florida’s Department of Dermatology have subsequently evaluated two dogs trained in the detection of melanoma cells. These dogs demonstrated the ability to detect and accurately locate the presence of the cancerous cells in seven subjects (Pickell et al., 2001).

The potential application of dogs in the diagnosis of cancer is still in debate, particularly since confirmation and treatment would still require surgical procedures. One advantage might be if canine detection provided earlier diagnosis than traditional clinical procedures.


ACCELERANT DETECTION

The first trained accelerant detection dog was reportedly placed into service in 1986 by the Connecticut State Police. These animals are trained to search a fire scene for the presence of common flammable liquids used to start fires. In 1995 over 200 accelerant detection canines were located throughout the US (Tindall and Lothridge, 1995).

The dogs were able to improve evidence selection and arson detection by over 40% in some areas.

The dogs work by moving through the fire scene and alerting the handler to areas with residual flammable materials. Samples of the debris are then collected and sent to a forensic laboratory for confirmation. Problems occur when the detection limits of the analytical equipment are not as sensitive as the dog (Katz and Midkiff, 1997).


EXPLOSIVE DETECTION

Since World War II dogs have been utilized by the military to locate explosives. Unfortunately much of the data describing the detection ability of these dogs is not published in referred journals, but is found in trade publications and government reports.

A field study was conducted in 1975-1976 where dogs averaged over 90% accuracy in the detection of land mines (Nolan and Gravitte, 1977). The Department of Defense has approximately 500 explosive detection canines worldwide with a proficiency requirement of at least 95% (Hannum and Parmeter, 1998).

Currently analytical technologies are being developed to enhance or replace our dependence on explosive detection canines, but at the moment, these instruments still suffer from selectivity problems and the lack of an efficient sampling system. So the detector dogs still represent the fastest, most versatile, reliable, and cost effective real-time explosive detection system available (Furton and Myers, 2001).


Nutrition of the working detection dog

Feeding the working detection dog to optimize health and scent performance is a difficult task. To date, very little research has been performed to define the role of nutrition in the working detection dog. Dog handlers must rely on studies conducted with sled dogs and greyhounds.

Although there are commonalities in feeding these canine athletes, the kind of work accomplished by the sprinting greyhound and endurance sled dog represents extremes rarely experienced by the working detection dog.

Detection dogs, particularly Search and Rescue dogs, must have the endurance to work long hours in rugged terrain. Estimates of 4-8 times the normal amount of metabolizable energy are required for an acclimated dog to search in mountainous terrain while 10 times the normal dietary metabolizable energy is required in racing sled dogs (Hinchcliff et al., 1994).

Energy metabolism in dogs differs from human metabolism in the ability to utilize fat. Canine muscle contains primarily oxidative fibers and a highly active oxidative enzyme, succinate dehydrogenase (Armstrong et al., 1982; Snow, 1987; Guy and Snow, 1981). In addition, dogs can also metabolize free fatty acids two times faster than humans (de Bruijne, 1981).

Diets containing >50% fat and high protein have been associated with increased stamina, maximized energy production, and the prevention of training-induced anemia in sled dogs (Hill, 1998). Fats are highly digestible, energy-dense feedstuffs that provide 8.5 kcal energy/g. Fats play an essential role in the absorption of fat soluble vitamins (A, D, K, and E) and provide a critical source of metabolic water, resulting in 107 g of water for every 100 g of fat metabolized.

Working dogs requiring endurance may benefit from a higher percentage of fat in the diet. When the body is utilizing dietary fat as an energy source, muscle glycogen stores are spared, postponing the deleterious effects of fatigue (Reynolds et al., 1995). In addition, the metabolism of fat has been shown to be metabolically ‘cooler’ than the metabolism of protein. The difference would result in a minimal increase in body temperature in animals utilizing fat as an energy source. This characteristic would be a tremendous advantage for search dogs working in warm environments.

The type of fat in the diet affects scenting ability of dogs. In an unpublished report comparing the effect of 12% fat, 16% highly saturated fat and 16% unsaturated fat diets fed to bird dogs, the researchers reported that the animal’s physical condition was the most significant indicator of scenting ability. Unconditioned dogs demonstrated a 69% reduction in scenting ability following exercise. In addition, the scenting ability of conditioned dogs was significantly reduced following exercise when fed diets containing highly saturated fat (Smith, 2002).

The (ω-6) polyunsaturated acids (PUFA) including linoleic and arachidonic acids are essential fatty acids and play a critical role in cell membrane integrity and health. Dogs are unable to synthesize linoleic acid, and may require dietary supplementation of PUFA when stressed (Bauer, 1997).

Dietary deficiencies are rare but may be seen in animals receiving poor quality, low-fat dry dog foods or poorly prepared homemade diets. A response to dietary supplementation in deficient animals can be seen in 3-8 weeks (Scott et al., 1995). The balance between ω-6 and ω-3 fatty acids is essential in controlling inflammation in the skin, gastrointestinal system and joints (Vaughn et al., 1994). Pro-inflammatory eicosanoids are reduced in animals consuming ω-6:ω-3 fatty acids ratios between 5:1 and 10:1. This reduction in inflammatory compounds may play an important role in maintaining the health and performance of scenting dogs.

Search and rescue dog teams are often subjected to conditions that result in high levels of metabolic stress such as smoke, acute physical exercise, and exposure to altitude or inflammation. This metabolic stress will generate reactive oxygen species such as superoxide anions and hydroxyl radicals, which harm cells by inducing membrane lipid peroxidation and damaging proteins and nucleic acids.

Reactive oxygen species can be counteracted by many self defense mechanisms that are found within the cell or supplied by the diet in the form of vitamins E and C, selenium or as flavonoids. Grandjean and coworkers (1998) compared the effect of high altitude on two groups of search and rescue dogs.

One group was fed a standard diet of dry dog food and the second group was fed the same diet supplemented with fish oil and vitamin E (α- tocopherol). Both groups of animals normally lived at sea level and traveled to altitudes of 5980 meters to perform training exercises. Reactive oxygen species generated by work during the short-term exposure to high altitude induced biological and physiological modifications, which were partly prevented in dogs fed the diet supplemented with fish oil and vitamin E.


WATER A CRITICAL NUTRIENT

A working scent dog must be kept hydrated to optimize scenting ability. Dogs lose water through urine, feces, saliva, exhalation and to a lesser extent sweat. Unlike humans, the only place dogs sweat is through their foot pads. The losses associated with the other sources are dependent on a variety of items including the dog’s health, workload, diet and the environment.

An increase in food intake to compensate for an increased workload will increase urinary and fecal excretion of water. These two waste products are composed of approximately 80- 90% water. Increased intake of protein will also result in an increase in nitrogenous waste excreted in the urine (Kohn and DiBartola, 1993).

Panting is the primary manner in which a dog regulates temperature, and it therefore accounts for the most dramatic increase in water loss from the mouth and respiratory tract. Evaporative loss from the respiratory tract may account for a 10-20-fold increase in water loss depending on the exercise intensity and environmental conditions. Working scent detection dogs must maintain adequate hydration to maintain effective olfactory performance.

Water is a necessary component of all cellular metabolism. Dogs unable to consume sufficient quantities of water to meet metabolic and temperature regulation requirements may experience diminished performance or even death.


Search dog health

The World Trade Center tragedy and the resulting recovery efforts led to the release of hundreds of potentially toxic chemicals into the air and ground (McKinney, 2001). The human workers were able to take precautions in the form of masks, goggles, gloves and protective clothing. The dogs working the site unfortunately did not have protective equipment and worked closer to the ground where the toxic material tended to accumulate.

This is not an unusual condition for the search dogs, since these dogs often work in areas deemed unsafe for, or inaccessible to, human rescuers. The magnitude of the events of 9-11 and the resulting recovery activities drew the attention of the public to the role of dogs in response to large-scale disasters.

The American Kennel Club Canine Health Foundation has awarded grants totaling $400,000 to study the medical consequences of exposure of the search dogs to these environmental toxins. Medical and behavior information will be collected on 300 dogs who responded to the World Trade Center and the Pentagon disaster sites for the next three years.

Because search dogs rely on the sense of smell to do their jobs, they are particularly at risk for exposure to respiratory toxicants. A recent study was designed to compare the olfactory and respiratory characteristics of dogs living in an urban region with high air pollution to dogs living in a region with cleaner air (Rewcastle, 2002).

Significant degradation in the brain-blood barrier and degeneration of the cortical endothelial cells were observed in the animals exposed to high levels of respiratory toxins. The author concluded that persistent pulmonary inflammation leading to deterioration of olfactory and respiratory barriers may result in neuropathological effects.

The longterm effects of this type of exposure may not be observed for several months or years and could significantly affect the future health and effectiveness of the dog. Research is needed to determine if nutritional factors such as ω-3 fatty acids and vitamin E supplementation could modulate the inflammatory process resulting in a reduction in the incidence of gastrointestinal, respiratory and skin disease associated with exposure to airborne toxins.

Toxins found at the site of a disaster may be in the form of solids, particulates, liquids, or gases (Gwaltney-Brant et al., 2003). The particulates result from the explosive and compressive forces associated with urban disasters. These particulate materials, which include fiberglass and asbestos fibers, are especially hazardous to the lungs and eyes (McKinney, 2001). Inhalation of concrete, lime, and fiberglass were reported as the primary respiratory irritants in the dogs that worked the bombing of the Murrah Federal Building in Oklahoma City in 1995 (Duhalme et al., 1998).

The hazardous solids and liquids represent a large number of compounds such as hydrocarbons, polychlorinated biphenyls, acids, alkalis, glycols alcohols, and solvents (Murphy et al., 2003). The toxicological targets of these compounds range from the respiratory system to the gastrointestinal system or to the skin. The effects may be toxicologically acute, as seen with ethylene glycol, or carcinogenic such as in the nonlymphocytic leukemia associated with exposure to benzene.

Perhaps the most significant hazards to the search dog are those that occur in the gaseous form since they can generally reach the alveoli where they can be readily absorbed into the bloodstream or initiate a localized inflammation in the lung (Austin et al., 2001). These compounds are generally present in higher concentrations when fires are still burning at the search scene and may significantly hinder the effectiveness and safety of dogs working at the disaster site.

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PUBLICATION DATE:  15/06/2007

RATING

AUTHOR:  MELISSA NEWMAN - University of Kentucky (Courtesy of Alltech Inc.)

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