5 Necropsy Techniques

       Patricia A. Pesavento

       Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, UC Davis, Davis, CA, USA

5.1 Introduction

      The loss of an animal is always discouraging, but it is a valuable and accurate way to establish a cause of death; so, it is especially useful if other animals are at risk. In this chapter, the focus is on the necropsy techniques that help to identify sample collection in the case of infectious or toxic problems. How to collect excellent and useful tissue samples that accurately identify problem pathogens is the goal and can be very time efficient compared to the performance of a full or forensic‐type necropsy. Consider an outbreak of respiratory disease in a kennel run where one affected dog either dies or is euthanized: Extensive testing, whether by culture or polymerase chain reaction (PCR) on oral swabs of in‐contact animals can be expensive and nonetheless confounding, since potentially causative bacteria or viruses will circulate in the population due to either recent vaccination or simply because pathogens can be present but not clinically important. It would require a small, time‐ and money‐consuming epidemiologic study to be confident of the cause in this way. Yet a single sample of lung tissue, taken from the affected dead animal, in a measured combination of culture, histologic review, and/or viral testing, will reveal the problem—and any pathogen in that sample should not be present, and IS significant. It is respectful to both the individual and the population to obtain as much useful information as possible from any animal that dies.

      Necropsy can provide an opportunity to gain valuable insight into diseases, treatment, and husbandry practices in a single shelter. In the bigger picture, well‐performed diagnostics provide the power to understand whether, and when, shelter animals are more susceptible to disease. They can also help identify new, or unexpected pathogens.

      Consider, for example, the situation faced by this shelter:

      Linda is a technician at Metro City All‐Paws Rescue. She has noticed that, over the last few months, the mortality rate in the feral cat room seems high. She checks the records and confirms that, in the past month, 8/40 cats have died and in the previous month, 5 cats died. Averaging over the year prior, the monthly mortality was 1 death/~40 cats total. After consulting with the team, they recognized that many of the recent deaths have been associated with both upper respiratory (URI) signs and skin abscesses. Limited diagnostics had been performed on affected cats and both herpesvirus and calicivirus were found by oropharyngeal swab samples.

In the case of contagious disease, toxins, or husbandry problems, a necropsy performed on affected or sentinel cases could potentially save the lives of many more cats. In the example above, pre‐mortem diagnostic tests had been performed on some of the cats with upper respiratory tract problems that had died, but the agents detected were common in the shelter environment and were therefore not convincingly the cause of death. Moreover, it was unclear to the shelter staff whether the URI or the abscesses were related to the animals' deaths, to each other, or just coincidental findings. An unexplained increase in mortality is one of the most compelling reasons for a shelter to perform a necropsy. See Table 5.1 for a partial list of reasons to perform a necropsy, with specific attention to those significant to a shelter.

      An estimated 6.5 million companion animals entered US animal shelters in 2016 according to the American Society for the Prevention of Cruelty to Animals (ASPCA 2017). Shelters are intensive housing situations where transmission, exposure, and susceptibility to infectious disease are heightened. If compared to the dairy industry, with 9 million cows in the United States in 2017 (https://www.ers.usda.gov/data‐products/dairy‐data), necropsy is not just warranted but state and federally mandated (and funded) for large animal herd health clinicians to track infectious disease. There are hundreds of clinicians and pathologists employed to perform large animal diagnostics in the US and Canada. In contrast, and despite the real and intimate interface with the human population, few states provide funding for necropsy or diagnostics of shelter animals. There is a need for more methodical scrutiny for emerging diseases, infectious diseases, and zoonoses, and necropsy is the most accurate method to collect effective diagnostic samples, assess diagnostic accuracy, and to predict disease emergence. The purpose of this chapter is to provide practical guidelines for necropsy and for collecting, storing, and shipping samples for diagnostic testing.

Table 5.1 Reasons to perform a necropsy in a shelter.