Infectious Disease Management in Animal Shelters. Группа авторов
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For ideal infectious disease surveillance, a board‐certified or accredited pathologist would examine all deaths at a given shelter. If that is an option, animals that die should be turned in immediately, without freezing of the carcass, for the most accurate results. However, state‐subsidized diagnostics are not an option for most shelters. Full necropsy services at state diagnostic laboratories or veterinary schools are available, and although costs vary, they can be quite high for small animals. In contrast, performing a necropsy/sampling at a shelter and testing, or at least storing samples (for possible future examination) is relatively inexpensive and both biopsy services (“necropsy in a bottle”) and microbiology services are readily available. Shelter personnel need to be trained to recognize lesions, and to perform a necropsy as part of the overall healthcare plan for their shelter population.
5.2 Why Sample Tissues at Necropsy?
Expedient pathogen identification can help minimize deaths and maximize successful outcomes from infectious illnesses. Appropriate and adequate sample collection can help with such identification and is one of the most important reasons for a shelter to perform a necropsy. See Figure 5.1.
Figure 5.1 The prosector takes a sample of lung. Samples taken for microbiological analysis (culture or PCR) should be taken first during a necropsy. Use a sterile scalpel blade or scissors to take a section, and/or use a sterile swab to sample.
Necropsy has its limitations, and necropsy findings can be inconclusive as to the actual cause of death. Some conditions are simply not characterized by lesions that can be detected either grossly or microscopically. However, it is a very useful method to rule in (or out) infectious/inflammatory vs. OTHER causes of death. It is the intention of this chapter to put clinicians in a confident position to collect samples correctly so that the best material is available for analysis and diagnosis. Samples collected at necropsy can be used for culture, cytology (impression smears), molecular diagnostics (polymerase chain reaction or PCR), serology (antibodies are generally stable in postmortem blood for serology tests), histological analyses (of target tissues or all tissues collected) or other tests.
5.3 The Necropsy
5.3.1 General Considerations
To complete an effective necropsy, specific and consistent protocols (procedure, sampling, documentation) should be followed. The optimal time to perform a necropsy is as soon as possible after the animal's death. Depending on environmental conditions, changes in tissues occur in minutes after an animal has expired. It is important, for an accurate diagnosis, to take appropriate tissue samples for culture and/or microscopic examination in a timely fashion. If a necropsy cannot be performed immediately, the animal should be placed in a cooler (for up to two days post‐death). Tissue integrity and most pathogens and toxins are stable during that time, although overgrowth of postmortem bacteria becomes a problem. For any longer time window, freezing the carcass is warranted.
Any animal that dies should be examined to the best of one's time and ability; however, a necropsy performed specifically for sample collection can be much shorter (for example, collecting gastrointestinal (GI) samples in a dog with diarrhea to confirm or exclude parvovirus). Here are a few important considerations before performing a necropsy:
1 Zoonoses: It is important to be aware that animals in the shelter may have a disease that is transmissible to humans (zoonosis) and, even more likely, a disease transmissible to other animals. The situation postmortem is no different than when the animal was alive, however, exposure to some agents is higher when a necropsy is performed (e.g. blood‐borne pathogens, anthrax, rabies, and some fecal pathogens). The necropsy should be performed in a quiet, isolated, well‐ventilated space. Precautions should be taken consistently (protective clothing, gloves, mask) during a necropsy, and any unfixed tissues should be placed in leak‐proof containers or disposed of as medical waste according to the protocols specified by the state or institution.
2 Handling cadavers: If the necropsy cannot be carried out immediately, cadavers should be stored in a refrigerator (+2 °C to +4 °C) as soon as possible after death until the necropsy can be performed. A cadaver should be frozen only if necessary; while still present in the tissue, some microbes will not be viable after freezing.
3 Euthanasia: Euthanasia policy and strategy is widely variable among shelters. The method of euthanasia should always be documented. There are both gross and histologic sequelae to any form of euthanasia, and it is important to understand whether a lesion is “real” or simply related to the method of euthanasia. For example, intra‐abdominal administration of pentobarbital can result in puncture trauma, a layer of chemically induced necrosis on the surfaces of abdominal organs, or in peri‐mortem intra‐abdominal hemorrhage (See Figure 5.2).
Also, because euthanasia solution is caustic, intra‐abdominal administration of euthanasia solution is not the best route of administration if an animal has an enteric (gastrointestinal) disease and histopathological analysis is anticipated.
The clinical history (including duration) and knowledge about any therapy are both vital to the appropriate interpretation of findings. In a shelter with the capacity to provide medical resources, necropsy may be limited to animals that have received medical care, such as antibiotics, which can compromise postmortem culture results. It is always beneficial to perform a necropsy on a more recently affected or moribund animal, rather than one that had recovered but might be weakened and subject to a secondary disease process.
Figure 5.2 Euthanasia can cause artifactual changes to tissues. Here the granular, dull texture of the region of lung defined by the arrows is caused by intrathoracic contact with beuthanol during intracardiac euthanasia.
5.3.2 Documentation
5.3.2.1 Written Data
Pre‐mortem information: Historical and clinical information are equally as important in the investigation as transcribing observations at the necropsy. Pre‐mortem information includes clinical signs, date of intake and onset of illness, location held in the shelter, and all treatments received. Especially in a shelter, this information is necessary to identify patterns of susceptibility to disease over time, whether geographical, age‐related, treatment‐associated, time of year, etc. This information is also essential to interpret the necropsy and histological lesions, and/or to compare future or past cases. Pre‐mortem and historical information can be written on a separate form or can be included on the necropsy form itself.
Necropsy results: There are several well‐organized necropsy templates available (see resources below) and a shelter should have copies of one of these on hand. Which directions, forms, and/or templates are used are not important; they are designed to remind the prosector (the person doing the dissection) to be methodical, thorough, and consistent. It is important to try to be as objective as possible in reporting observations; specifically, to describe abnormalities without presuming cause (without adding interpretation). For example, if the liver appears large,