Infectious Disease Management in Animal Shelters. Группа авторов
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5 Trachea
6 Nasal turbinates
7 Thyroid/parathyroids – leave intact
8 Urinary bladder, ureters, urethra‐ cross‐section of the bladder and 2 cm sections of ureter and urethra
9 Eye – intact
10 Spinal cord (if neurologic disease)‐ sections from cervical, thoracic and lumbar cord
11 Skeletal muscle – diaphragm, cross‐section of thigh muscles
12 Bone marrow – Opened rib or longitudinally sectioned ½ femur; marrow must be exposed for proper fixation
5.5 The Diagnostic Shelter Necropsy
Consider the following case history:
There is an outbreak of diarrhea, with a concurrent increase in mortality, in cats and kittens in a large, municipal shelter. Several cats and kittens have been found dead within the past few weeks. The bodies were disposed of and the cages cleaned thoroughly but even with isolation procedures in place, the number of affected animals appears to be increasing. The shelter manager and part‐time veterinarian at the shelter both suspect that the feline panleukopenia virus is the culprit. Animals are vaccinated at intake and every two weeks during their stay, but the disease presentation seems more aggressive than they have seen in the past, and several older cats have been affected. A fecal antigen test was performed on two affected animals, but the result was negative for viral antigen on the first and weakly positive on the second animal. Although apparently well yesterday, a cat and a three‐month old kitten were found dead at morning rounds. They believe both animals are part of this outbreak, although diarrhea was seen in the cat's cage but not in the kitten's cage. What is the best way for staff to establish the cause of gastrointestinal disease in their feline population?
This scenario is not at all uncommon in shelters. If accurate (sensitive and specific) pre‐mortem tests are available and results are consistent in affected animals, a cause for increased morbidity and mortality is comfortably determined. However, there are many reasons (e.g. less sensitive test, unusual presentation for a disease, unusual behavior of the disease in a population, non‐responsive to treatment for that disease) a shelter might seek additional information about a disease. In this case, although feces from one cat was positive for the presence of feline panleukopenia virus, the disease seemed to be occurring in the face of vaccination and isolation and was occurring in animals less commonly associated with the suspected disease (older animals).
What should they do? Staff are understandably very busy and need to efficiently diagnose the problem. The tests have been somewhat equivocal and doing full necropsies on each of these animals would likely be very time‐consuming; moreover, they are not sure the gross exam will be helpful since they are not exactly sure what they are seeing.
In a shelter (herd) situation, it is sometimes practical, sufficient, and time‐efficient to ask a more specific (limited) question about disease or death of an animal. Gastrointestinal and respiratory diseases, in particular, are frequent problems in shelters. To ask a more limited question of a necropsy means that the necropsy itself can be simplified. Necropsy samples can be the best samples to definitively diagnose a cause of disease, and proper necropsy sampling in a sentinel case or an infectious outbreak will save other animals.
5.5.1 Sampling a Carcass, General Considerations
The success of infectious disease diagnosis depends largely on the quality of the specimen and the conditions under which the specimen is transported and stored before it is processed in the laboratory. It would be naive to generalize; depending on the suspected agent and the test, the optimum sample and optimum conditions for stabilization during transport are variable. For example, if a bacterial agent is suspected, freezing the specimen could compromise future culture; however, DNA would remain intact and a PCR test relying on extracted bacterial DNA would be unaffected. Some viruses, on the other hand, can withstand freezing, especially if samples are stored in the proper media. There are specific transport media that stabilize viruses and prevent bacterial overgrowth. What this means, of course, is that if the cause of the disease is completely open and multiple tests are going to be performed, multiple types of samples are necessary. Collection is simpler if a certain agent is highly suspect, or if a single agent needs to be ruled in or out.
Because gastrointestinal disease and respiratory disease are the most common infectious diseases associated with morbidity and mortality in the shelter environment, the following section is devoted to the sampling of a cadaver in these types of outbreaks.
5.5.2 Necropsy and Sampling for Gastrointestinal Disease
The following sample collection would be a good starting point for sampling any enteric disease (diarrhea and/or vomiting) of unknown origin in both dogs and cats. While causes of diarrhea can be remote from the gastrointestinal system (heat shock, for example), MOST contagious or toxin‐associated GI disease results from a direct attack on the gastrointestinal system. Moreover, the distribution of lesions (grossly) is very helpful in determining the cause of disease. See Table 5.4
1 Feces:If abundant, feces collection can be made from the distal colon. Even if scant, feces can be scraped from the colonic mucosa or obtained by a swab. Postmortem feces are useful samples for multiple tests, including fecal antigen test (parvoviruses, see below). Pooling feces from the small intestine and colon has been noted to increase the sensitivity of the parvo antigen tests, which is sensible for a viral infection with a segmental distribution and episodic shedding. Also, the feces can be used for direct smear/fecal flotation/parasite analysis, or viral analyses. If collecting formalin‐fixed tissue for histologic correlate analysis, tissue should be collected from an undisturbed (unsampled) region of the colon (mucosa is fragile and will slough easily with handling).
2 Formalin‐fixed tissues:Histological samples should be taken in ALL CASES, no matter what supplementary diagnostic tests are chosen. Histology can provide a definitive diagnosis, it can direct to possible causes, or it will confirm or refute the results of other diagnostic tests. A general list for sampling an animal with enteric disease is found below. In nearly all cases, these samples would be sufficient to diagnose or exclude common shelter enteric pathogens. In cases where the agent or cause is unexpected, these samples would establish whether an enteric disease is inflammatory, infectious, toxic, or neoplastic.
Table 5.4 Necropsy and sampling for GI disease.
| Feces |
| Formalin‐fixed tissues |
| Microbiology |
| Molecular diagnostics |
| Toxicology |
| Serology |
5.5.2.1 Tissue Checklist forGastrointestinal Disease
Tissues should be no thicker than 1 cm. Tissues should be placed immediately in 10% buffered formalin at a ratio of 1 part tissue to 10 parts formalin.
1 Duodenum, two (up to 5 cm long) segments
2 Pancreas (1 cm section, can be left attached to the duodenum)
3 Jejunum (proximal, mid, distal), at least three (up to 5 cm long) segments
4 Ileo‐ceco‐colic junction (these regions can be sampled individually, or this region can be sampled in its entirety. If the latter is chosen, the sample should be opened enough so that formalin can perfuse the mucosa throughout the section, but do not scrape or touch the mucosa while handling.) See