23-08-2012, 02:37 PM
Infrared Thermography: Its Use and Application for Detecting Infectious Diseases in Wildlife and Domestic Animals
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Abstract
Remarkable advances and recent research indicate that infrared
thermography (IRT) can be used to remote detect infectious diseases in
wildlife and domestic animals. Research has shown that IRT can be used to
detect some diseases before the development of clinical signs and shedding
of the pathogen, which may reduce transmission of diseases such as footand-
mouth. Recent research has also indicated IRT can detect rabies in
captive wildlife and we have expanded on that research to determine IRT’s
application in the field. Other research includes assessing IRT’s application
potential for detecting classical swine fever, bovine tuberculosis, avian
influenza, and other infectious diseases. This research often focuses
on identifying a thermal pattern that may be unique for the disease, but
many times the first sign of an infectious disease is an increase in body
temperature. Research on infected ponies and mule deer has indicated a
correlation between IRT eye temperature and body temperature. Although
there are obstacles that persist with use of infrared thermography to
accurately detect diseases in animals, its potential in disease detection
applications is promising. Continued research is providing a better
understanding of the utility of such a technique, especially in the field.
Introduction
“Zoo weighs further testing: TB procedure on animals runs risk of causing
harm.” This headline appeared in the Topeka Capital-Journal after the
Topeka Zoo lost a chevrotain during tuberculosis testing (Carlson 2010).
Capture myopathy, caused by stress due to handling and restraint, was one
cause sited as contributing to the death. Injury or death to the animal, and
occasionally to people restraining the animal, is always a concern when an
animal must be restrained either physically or chemically.
Disease transmission is another concern in handling animals. If biosecurity
measures for handling animals are inadequately followed, indirect
transmission of diseases to other animals, or direct transmission of
zoonotic diseases to humans could occur. Biosecurity measures also help
prevent direct transmission between animals and are necessary to prevent
outbreaks. Wide scale screening for diseased animals before they have
contact with other animals is a much-needed biosecurity measure. Such a
screening method needs to be rapid, remote, and noninvasive for practical
implementation. In the 2001 foot-and-mouth disease outbreak in the United
Kingdom, veterinarians had to inspect thousands of individual animals for
clinical signs of the disease (Davies 2002). This inspection often required
each animal to be handled to look for the most common sign, lesions.
Camera and General Methods
Data collection was performed with the E65 and the EX350 cameras. The
resolution of these cameras is 160 x 120 and 320 x 240, respectively.
The white-hot grey palette and area max measurement mode were most
commonly used. The grey palette facilitated focusing and the area max
mode assisted in acquiring the temperature of the target area in the least
amount of time, critical when imaging a moving animal. Additionally, the
area max mode provided the most information from the thermograms
when evaluated with the basic software, ThermCam Quickview 1.3. This
software was used in all the examples. Reporter 8.3 was also used to add
measurement modes to the thermographic image and to facilitate data
entry into EXCEL and ACCESS for statistical analysis. Thermograms were
corrected for distance, humidity, and ambient temperature. Emissivity
was set at 0.95 or above, since the focus was often on skin temperature
changes. When possible, thermograms were collected at least daily.
However, this did not always occur for the opportunistic IRT evaluations.
Case Examples
Foot-and-Mouth Disease
Surface changes associated with foot-and-mouth disease (FMD) include
lesions that occur in the mouth, on the teats, and on the feet. These areas
of lesion development are the probable areas associated with temperature
changes allowing the use of IRT for disease detection. Thermograms of
the mouths and feet of mule deer exposed to the FMD virus revealed
that only the thermograms of the feet provided information useful in
disease screening; foot temperatures significantly increased as lesions
developed (Figure 1; Dunbar et al. 2009). This increase started forty-eight
hours before any lesions were observed indicating that disease detection
before lesion development may be possible. Similar results in cattle were
documented by Rainwater-Lovett et al. (2009). In an opportunist evaluation
of swine exposed to the FMD virus, temperature differences in the feet
could easily be observed (Figure 2). Increased foot temperature is not
expected to be a thermogram unique to FMD. Injury and other diseases
affecting the feet may result in a similar response. Due to the highly
infectious nature of FMD, effective control requires rapid detection and
containment. Instead of handling individual animals to examine for lesions,
IRT could be used to screen a herd or other collection of animals for
perhaps individuals with elevated foot temperatures and then isolating that
animal or animals for further testing and identification of the cause of the
elevated foot temperature.
Summary
As the public becomes less tolerant of some methods used to control
disease outbreaks (e.g. culling) and as awareness of the disease risk
associated with events resulting in the congregation of animals (e.g.
livestock auctions, horse races, fairs, etc.) grows, rapid noninvasive
methods for disease detection are needed.