A standardized algorithm was developed (Figure 1) and applied to each case. All animals reported met the United States Department of Agriculture’s (USDA) SARS-CoV-2 confirmed positive case definition for animals (12). Cycle threshold (Ct) values are from real-time (RT) PCR using CDC’s N target assay (13).
On April 28, an owner sought veterinary care for a 7-year-old male German Shepherd dog showing lethargy, labored breathing, decreased appetite, and weight loss of 30 pounds since mid-April. A chest radiograph suggested an enlarged heart, but an electrocardiogram was unremarkable. The dog’s owner had been diagnosed with COVID-19 on April 21.
On May 15 and with no improvement, the dog presented to a second veterinarian with tachypnea and severe pallor of the mucus membranes. Bloodwork revealed severe non-regenerative anemia (red blood cell [RBC] 1.67 M/μL, reference range [RR]: 5.39 - 8.70 M/μL) and thrombocytopenia (54 K/μL, RR: 143 - 448 K/μL). White blood cell (WBC) count was within normal limits (9.92 G/l) but had a predominance of monocytes (54.5%). A screening test for heartworm disease and tick-borne pathogens was negative. Nasal swabs collected on May 15 and 20 were positive for SARS-CoV-2 RNA (RT-PCR; Ct 31) and negative, respectively. Serum collected on May 15 and 20 detected virus neutralizing antibodies (1:512). Prednisone and doxycycline were administered. The owner reported immediate improvement, with increased appetite and energy.
Over the next several weeks, the dog developed urinary incontinence, hematuria, hematemesis, and worsening dyspnea. Bloodwork on June 21 showed continued severe non-regenerative anemia, an increasing WBC count (72 G/l) with a predominance of monocytes (80%). Large, immature blastic cells, suggestive of a hemic neoplasia, were found on manual differentiation. The dog was euthanized on July 11. A necropsy was not performed. Based on laboratory results and clinical course, the cause of death was consistent with a hemic neoplasia such as acute lymphoid leukemia or lymphoma. This animal had clinical signs attributed to other disease processes (Figure 1, 1.i.), and had severe co-morbidities (Figure 1. 2a.i.). Therefore, SARS-CoV-2 infection was concluded to have been an incidental finding (Table 1).
On June 19, a 6-year-old male, neutered Boxer mix dog acutely developed seizures and hypersalivation. Both owners had developed symptoms (June 11 and 13) and tested positive for SARS-CoV-2 (June 12 and 15).
The dog was presented to a veterinary clinic on June 20 and was euthanized on June 21 after failing to improve with medical therapy. Upon learning that owners had been diagnosed with COVID-19, a nasal swab for SARS-CoV-2 testing was collected post-mortem and confirmed positive by RT-PCR (Ct 27). A necropsy performed on June 24 revealed an intracranial Schwannoma with regionally extensive encephalomalacia and neovascularization involving the optic nerve and overlying brain. Minimal rhinitis and palatitis were also noted; however, the dog did not show respiratory signs. The cause of death was attributed to intracranial Schwannoma and acute secondary hemorrhage. This animal had clinical signs attributed to other disease processes (Figure 1, 1.i.), and had severe co-morbidities (Figure 1. 2a.i.). SARS-CoV-2 was determined to be an incidental finding (Table 1).
On June 22, an 11-year-old male neutered domestic short-hair (DSH) cat developed dyspnea. On June 24, the cat was presented to a veterinary clinic. No diagnostics were performed, no treatments were attempted, and the owner was instructed to return if the clinical signs did not resolve. Between June 7 and June 14, all four persons in the household had developed febrile illness and tested positive for COVID-19.
On June 24, the cat’s dyspnea worsened, and it was taken to an emergency clinic where clinicians noted tachypnea, hypothermia, and a heart murmur. Thoracic radiographs revealed no pneumonia or other abnormalities. Cardiac ultrasound showed bilateral markedly thickened myocardium and left atrial enlargement, consistent with hypertrophic cardiomyopathy (HCM). While hospitalized on June 25, the cat remained laterally recumbent with poor mentation. The cat died later that day; necropsy was not performed. After veterinary staff were informed that the animal came from a household that had people with COVID-19, nasal swabs were collected post-mortem and were positive for SARS-CoV-2 by RT-PCR (Ct 34). A standard respiratory panel was positive for Mycoplasma felis. Since clinical signs and cause of death were attributed to HCM, SARS-CoV-2 was concluded to be an incidental finding (Figure 1, 1.i. and 2a.i.; Table 1).
On July 13, a 9-year-old female spayed Boxer-mix dog developed rear leg paresis. Radiographs were consistent with spinal disc disease or spinal neoplasia. At the request of the owner, who had tested positive for SARS-CoV-2 on July 20, a nasal swab was collected by the veterinarian on July 22 and tested positive for SARS-CoV-2 by RT-PCR (Ct 30). The dog was euthanized on August 5 due to hind limb plegia, with a presumptive diagnosis of intervertebral disc disease. Necropsy was not performed. A second nasal sample collected by the veterinarian post-mortem tested positive by RT-PCR (Ct ≥ 37), and serum was positive for virus neutralizing antibodies. SARS-CoV-2 infection was determined to be an incidental finding, as the dog showed no clinical signs consistent with SARS-CoV-2 (Figure 1, 1.i.,) and was euthanized for unrelated reasons (Figure 1, 2a.i.; Table 1).
On August 3, an 8-year-old Newfoundland dog developed acute respiratory distress and pyrexia (temperature:105.2oF) and presented to a veterinary clinic. Owners reported that the dog was normal that morning. The dog’s condition deteriorated over 12 hours, resulting in referral to an emergency hospital, where clinicians noted respiratory distress, weakness, tachypnea, tachycardia, and pyrexia (temperature: 104.8oF). Thoracic radiographs showed a severe alveolar pattern in the right caudal lung fields. Oxygen saturation was 70% while receiving supplemental oxygen. Bloodwork was consistent with metabolic acidosis. The dog arrested that evening and could not be resuscitated. One of the dog’s owners had become symptomatic for COVID-19 on July 6 and tested positive on July 13.
Initial gross and histological post-mortem examination identified acute pneumonia, necrotizing rhinitis, mild hemothorax, mild to moderate right atrial and ventricular chamber dilatation, and chronic focal mural ulceration in the urinary bladder. Due to a COVID-19 positive household member, a respiratory panel and SARS-CoV-2 RT-PCR were run on nasal swabs collected post-mortem and were negative for all targets except for SARS-CoV-2 (Ct 31-36). Formalin-fixed paraffin-embedded (FFPE) sections of lung and nasal turbinates were negative for SARS-CoV-2 by RT-PCR and immunohistochemistry (IHC) at CDC’s Infectious Diseases Pathology Branch (IDPB). Escherichia coli was isolated by culture from lung and spleen, and neutrophilic alveolar infiltrate was appreciated histologically. Gram-negative rods were seen within inflammation in the lungs, and IHC stains for E. coli were positive on lung tissue. These histopathology results were consistent with pneumonia without evidence of a viral component.
This dog had clinical signs consistent with SARS-CoV-2 infection (Figure 1, 1.ii.), but the primary cause of death was attributed to bacterial bronchopneumonia (Figure 1, 2b.i.) and there was no evidence of virus in critical organs (Figure 1, 3a.i.). SARS-CoV-2 was determined to be an incidental finding (Table 1).
On September 24, a 5-year-old male neutered DSH cat with a recent history of upper respiratory signs developed neurologic abnormalities (head pressing and seizures) and weakness. The cat received one dose of clindamycin but became unresponsive and died at home on September 25. A household member had tested positive for SARS-CoV-2 on September 18.
A necropsy revealed nasal discharge, pulmonary congestion and edema. Nasal and oral swabs were positive for SARS-CoV-2 (Ct 25-29) and a virus neutralization assay was positive (1:128). Fresh lung tissue was positive by RT-PCR (Ct 37). FFPE lung and tracheal tissues were positive by RT-PCR for SARS-CoV-2 at CDC IDPB. All tissues were negative by SARS-CoV-2 IHC. Histopathology showed suppurative meningoencephalitis, lymphoplasmacytic tracheitis, and mild myocardial disarray. In situ hybridization (ISH) for SARS-CoV-2 was performed, which showed sparse staining in the tracheal submucosal glands, and no staining in other tissues (lung, brain, spleen, liver, muscle). Histopathological changes suggestive of a viral infection were not observed in lung tissue. Broad-range 16S rRNA gene PCR assays for bacterial detection in brain were indeterminate. Assays aimed at identifying another infectious cause of the meningoencephalitis were negative.
This cat had respiratory signs consistent with SARS-CoV-2 infection (Figure 1, 1.ii.), a significant co-morbidity (suppurative meningoencephalitis) (Figure 1, 2b.i.), and evidence of SARS-CoV-2 in lung tissue (Figure 1, 3a.ii.) but without associated histopathologic lesions (Figure 1, 4a.i.). SARS-CoV-2 was considered the cause of tracheitis but incidental to the cause of death, which was attributed to suppurative meningoencephalitis (Table 1).
On October 2, a 16-year-old male neutered DSH cat presented for evaluation of increased respiratory effort beginning in late September. The cat was treated with cefovecin and methylprednisolone. A respiratory panel was negative, and an oropharyngeal swab was positive for SARS-CoV-2 (Ct 28). On October 4, the owner reported improvement, but respiratory signs returned October 10. On October 13, the cat presented at a veterinary hospital with respiratory distress and paradoxical breathing and was euthanized. Additional nasal, oropharyngeal, and rectal swabs, as well as heart, lung, and liver tissue samples were collected. The owner had tested positive for SARS-CoV-2 on September 18.
A post-mortem oropharyngeal swab and frozen nasal passage and lung tissue were positive for SARS-CoV-2 by RT-PCR (Ct 30-36); heart and liver specimens were negative. Molecular evidence of SARS-CoV-2 was not appreciated in five blocks of FFPE lung tissue evaluated at CDC IDPB. Histologically, moderate multifocal cardiomyocyte hypertrophy and disarray with degeneration, necrosis, and severe mineralization and fibrosis was seen in the heart. In the lungs, mild to moderate multifocal alveolar histiocytosis and interstitial fibrosis with edema, congestion, and hemorrhage was evident. Gross and histologic findings in the heart were consistent with HCM, and lung lesions were consistent with heart failure. The cat had clinical signs consistent with SARS-CoV-2 infection (Figure 1, 1.ii.), a severe co-morbidity (Figure 1, 2b.i.), and presence of virus in critical tissues (Figure 1, 3a.ii.) but without associated histopathologic lesions (Figure 1, 4a.i.). The cause of death was attributed to HCM with subsequent heart failure; SARS-CoV-2 was determined to be an incidental finding (Table 1).
On January 1, a 3-year-old male neutered DSH cat began vomiting and vocalizing in the litterbox. No respiratory signs were reported, and the animal was previously healthy. The owner did not take the animal for veterinary evaluation and elected to monitor overnight at home. The cat became weaker and died at home the next morning. The cat was brought to the veterinary hospital on January 2 for necropsy and cremation. Gross necropsy showed a urinary obstruction.
Two household members were symptomatic and recently confirmed positive for SARS-CoV-2. A nasal swab collected from the cat at necropsy was presumptive positive for SARS-CoV-2 via RT-PCR (Ct 29) on January 4 and confirmed positive via RT-PCR at USDA National Veterinary Services Laboratories (NVSL) (Ct 30) on January 11. Lung tissue was RT-PCR negative for SARS-CoV-2 on January 11 at NVSL.
SARS-CoV-2 infection was determined to be an incidental finding, as the cat showed no clinical signs consistent with SARS-CoV-2 infection (Figure 1, 1.i.), and necropsy findings suggested morbidity and mortality could be explained by urinary blockage (Figure 1, 2a.i.). Additionally, lung tissue was negative for SARS-CoV-2 by RT-PCR.
Beginning in March 2020, an eight-year-old male neutered Shepherd mix dog developed increased respiratory rate and effort. These signs initially resolved without treatment but reappeared on approximately June 12. One owner became symptomatic on June 21 and tested positive for SARS-CoV-2 on a sample collected on June 24.
The dog was presented to a veterinarian on June 21. Thoracic radiographs showed a bronchointerstitial to alveolar pattern. The dog’s condition later deteriorated, and he was presented to an emergency hospital for dyspnea and cyanosis on June 23. Bronchoalveolar lavage (BAL) culture was positive for Corynebacterium, computed tomography showed chronic, diffuse pulmonary interstitial infiltrates with resultant cylindrical bronchiectasis, initial bloodwork was unremarkable (only mild neutrophilia noted), and bronchoscopy showed diffusely vascular and hyperemic airways and multiple, small blood clots in small airways. Antibiotics (ampicillin/sulbactam and enrofloxacin), corticosteroids, and supplemental oxygen were administered.
On June 26, veterinarians learned that the dog’s owner had been diagnosed with COVID-19, and pursued SARS-CoV-2 testing. Based on the clinical picture, diagnostics, imaging, BAL culture, and the lack of response to therapy, the clinicians suspected end-stage lung disease (interstitial fibrosis or a poorly exfoliative neoplasia) that had been exacerbated by an acute infection. The dog failed to improve with treatment and was euthanized on July 2.
A respiratory PCR panel performed on the nasal swab collected on June 26 was negative for common causes of respiratory illness and positive for SARS-CoV-2 by RT-PCR (Ct 21). Histologic examination of formalin-fixed lung tissues revealed severe, chronic lymphoplasmacytic bronchointerstital pneumonia with marked interstitial fibrosis and bronchiolar squamous metaplasia consistent with chronic, severe lung disease. One section showed features of proliferative and organizing diffuse alveolar damage, with patchy type II pneumocyte hyperplasia and occasional fibroblastic proliferations; these finding suggest repair from a recent infection on the background of severe chronic lung disease. SARS-CoV-2 was detected in RNA extracted from FFPE tissue in one of three sections of lung by RT-PCR. However, viral antigen was not detected by IHC or ISH in the respiratory tissues.
This animal had clinical signs consistent with SARS-CoV-2 infection (Figure 1, 1.ii), significant comorbidities (Figure 1, 2b.i.), presence of SARS-CoV-2 in critical tissues (Figure 1, 3a.ii.), and associated histopathologic changes (Figure 1, 4a.ii.); therefore, the final determination was that acute SARS-CoV-2 infection contributed to this animal’s death, but the primary cause was chronic interstitial lung disease.
On December 10, a 4-year-old male neutered domestic medium hair cat became lethargic and inappetant. On December 13, the cat began to show signs of respiratory distress, and was seen at three veterinary clinics. On December 15, the owner elected euthanasia due to the cat’s rapid, progressive clinical deterioration. Both household members tested positive for COVID-19 on December 5 and 21.
A necropsy was performed. Nasal, tracheal, oropharyngeal, and rectal swabs collected on December 18 were positive for SARS-CoV-2 by RT-PCR (Ct 14-16). On histopathologic examination, bronchointerstitial pneumonia, acute myocardial degeneration and necrosis, and mild HCM were appreciated (14). A necropsy was performed. Nasal, tracheal, oropharyngeal, and rectal swabs collected on December 18 were positive for SARS-CoV-2 by RT-PCR (Ct 14-16). On histopathologic examination, bronchointerstitial pneumonia, acute myocardial degeneration and necrosis, and mild HCM were appreciated (14). Live virus was isolated from nasal, tracheal, oropharyngeal, and rectal swabs, as well as heart and lung tissue. Both ISH and IHC were positive. A feline respiratory panel was positive for Mycoplasma felis. This cat had clinical signs consistent with COVID-19 (Figure 1, 1.ii.), sub-clinical co-morbidities (mild HCM) (2b.ii.), evidence of SARS-CoV-2 in critical tissues (Figure 1, 3b.ii.), and histopathological changes attributed to SARS-CoV-2 in critical tissues (Figure 1, 4b.ii) (14). Therefore, infection with SARS-CoV-2 was determined to be primary reason for the animal’s euthanasia.