viral dose and virulence, and/or the animal's age, breed, and clinical presentation.
1 Concurrent disease(s):
Parvoviral disease, even when suspected or confirmed clinically, may be exacerbated by concurrent infections with bacteria, Giardia, hookworms, or other enteric viruses such as coronavirus. Samples should be gathered that can potentially rule concurrent disease either in or out.
5.5.2.2.1 Gross Findings of Parvoviral Disease
The gross findings of parvoviral disease, although caused by a similar virus, manifest somewhat differently in the dog and cat. It would be unlikely that a puppy or adult dog would die suddenly of parvovirus in the absence of dehydration, diarrhea, and other well‐documented clinical signs. On the other hand, kittens can die per‐acutely of panleukopenia, with no preceding signs noted. On necropsy, dogs commonly have segmental to diffuse sub‐serosal hemorrhage (reddening) that predominantly affects the small intestine (See Figure 5.8).
The small intestine can be flaccid and/or dilated. There will be scant ingesta within the intestinal system and no formed feces within the colon. On section of the small intestine, the mucosa is segmentally to multifocally discolored tan to dark red (necrosis, congestion, hemorrhage). Peyer's patches, which are more concentrated in the distal small intestine and ileum, can be dark red (lympholysis).
In cats, the findings can be similar but are usually subtle. The small intestine is flaccid or dilated, but not always reddened, and the GI contents, although typically watery or scarce, do not always contain blood. In both dogs and cats, the mesenteric lymph nodes are enlarged, congested and wet (edematous). Because the effect of panleukopenia on bone marrow and primary lymphoid tissues is quite predictable in the feline form of the disease, it is a good idea to include these tissues when performing a necropsy on either a dog or a cat.
Figure 5.8 Canine parvovirus (CPV). The intestines are segmentally thick, edematous, and hemorrhagic, and the mucosal surface (pictured here) is dull and felt‐like.
5.5.3 Respiratory Disease, General
The following collection would be a good starting point for sampling any respiratory disease of unknown origin in dogs or cats. While causes for respiratory distress can be remote from the respiratory system, most cases of infectious pneumonia or upper respiratory infections (URI) result from a direct attack on the respiratory tissues. Gross lesions of the lung are difficult to interpret. This is, in no small part, because there are often peri‐mortem lung changes, and such variability makes a baseline interpretation of “normal” very difficult. Histologic samples are of paramount importance when trying to discern factors contributing to lung disease. In cats, in particular, analyzing the upper respiratory tract as well as the lung is important; many common infections of the upper respiratory tract can contribute to fulminant respiratory disease, and severe URI is often interpreted as pneumonia (infection of the lower respiratory system).
1 Microbiology:In respiratory disease, depending on the lesions and clinical course, bacterial cultures can be taken from the nasal cavity, frontal sinus (swab immediately after opening) and/or lung. In general, because URI is so common in kittens and cats in a shelter, cultures should be taken from both the nasal cavity/sinus and the lungs. In dogs or cats with a clinical course clearly associated with the lower respiratory tract (pneumonia), lung tissue should be submitted. Accurate culture results require using sterile techniques. During a necropsy, these should be the first specimens taken, and the tissue should be minimally or not manipulated. This can be achieved by using sterile instruments and/or a swab stick, or by placing a piece of tissue directly into a sterile container. It is important to alert the microbiology laboratory that the specimen was taken at the time of necropsy. Antibiotic therapy can skew or prevent the culture of many bacteria. Any pre‐mortem therapy should be noted in the submission form and on the necropsy report.
2 Molecular diagnostics:Fresh or fresh/frozen lung or upper respiratory tissue samples are necessary to diagnose agents contributing to pneumonia (former) or URI. These samples need to be taken early in the postmortem stage, using sterile technique, and from tissue minimally manipulated. DNA or RNA from the infectious agent will degrade at rates dependent on time, environmental factors (temperature, pH) and the organism itself. Ideally, samples from affected organs are fresh or fresh/frozen for molecular analysis. Most diagnostic laboratories or veterinary schools can offer guidance and a list of possible tests, the preferred or potentially useful tissue samples, and the preferred method of shipment.
Formalin‐fixed tissues
Histological samples should be taken in ALL CASES no matter what supplementary diagnostic tests are performed. Histology can provide a definitive diagnosis, identify possible causes, or confirm or refute the results of other diagnostic tests. The following is a general list for sampling an animal with respiratory disease. In nearly all cases, these samples would be sufficient to diagnose or exclude common shelter respiratory pathogens.
5.5.3.1 Tissue Checklist for Respiratory 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 Nasal conchae, sinus
2 Trachea, 1‐2 cartilage rings
3 Lung, multiple samples, including cranioventral portions of the cranial lobe(s), the caudal and dorsal regions of the caudal lobes and hilar region including major bronchus
4 Hilar lymph nodes, and/or lymph nodes from the thoracic inlet
5 Heart‐longitudinal sections including atrium, ventricle and valves from both left and right sides.
5.5.3.2 Common Respiratory Diseases in the Shelter
5.5.3.2.1 Canine Distemper Virus (CDV)
Clinical impressions are rarely sufficient to differentiate canine distemper from other causes of infectious canine respiratory disease. Pre‐mortem testing options are limited; serological tests are limited by viral immunosuppression and interference due to maternal or vaccine‐induced antibodies and fluorescent antibody (FA) testing (cells from the conjunctiva, blood, respiratory tract epithelium, or urinary bladder) is very specific but has low sensitivity. Another pre‐mortem test is PCR (on urine sediment, epithelial swabs, bronchoalveolar lavage, buffy coat preps, or CSF); however, PCR may also detect vaccine virus in recently vaccinated animals and for this reason the use quantitative reverse transcriptase PCR (RT‐PCR) is recommended. If an animal dies of suspected distemper, or if the presentation of the disease is unusual and confirmation is necessary, distemper can be identified reliably on necropsy samples and histopathology by a qualified pathologist.
Gross findings: If the lungs are involved, canine distemper virus will be disseminated and affect all lobes. In most cases, oculo‐nasal discharges are thick and mucopurulent. The lungs are generally edematous or consolidated (interstitial pneumonia). Thick, foamy to mucopurulent hemorrhagic exudates may be found in the airways. Secondary (bacterial) infection is common, both because of viral damage to the airways and because of lymphoid depletion. Therefore, a cranioventral distribution of lung consolidation (bronchopneumonia) does NOT rule out distemper. Lymphoreticular tissues are characteristically involved and are the primary site for viral replication. There can be enlargement of the tonsils and/or atrophy of the thymus. Hyperkeratosis (“hardpad disease”) of the nose and/or footpads is sporadically present. There are no gross lesions of the central nervous system even when nervous signs are uniquely present. The heart should always be examined, opened, and sampled