The Therapeutic Monoclonal Antibody Bamlanivimab Does Not Enhance SARS-CoV-2 Infection by FcR-Mediated Mechanisms.

As part of the non-clinical safety package characterizing bamlanivimab (SARS-CoV-2 neutralizing monoclonal antibody), the risk profile for antibody-dependent enhancement of infection (ADE) was evaluated in vitro and in an African green monkey (AGM) model of COVID-19. In vitro ADE assays in primary human macrophage, Raji, or THP-1 cells were used to evaluate enhancement of viral infection. Bamlanivimab binding to C1q, FcR, and cell-based effector activity was also assessed. In AGMs, the impact of bamlanivimab pretreatment on viral loads and clinical and histological pathology was assessed to evaluate enhanced SARS-CoV-2 replication or pathology. Bamlanivimab did not increase viral replication in vitro, despite a demonstrated effector function. In vivo, no significant differences were found among the AGM groups for weight, temperature, or food intake. Treatment with bamlanivimab reduced viral loads in nasal and oral swabs and BAL fluid relative to control groups. Viral antigen was not detected in lung tissue from animals treated with the highest dose of bamlanivimab. Bamlanivimab did not induce ADE of SARS-CoV-2 infection in vitro or in an AGM model of infection at any dose evaluated. The findings suggest that high-affinity monoclonal antibodies pose a low risk of mediating ADE in patients and support their safety profile as a treatment of COVID-19 disease.

Pseudoreticulocytosis by the ADVIA 2120 Hematology Analyzer and Other Hematologic Changes in a Cynomolgus Macaque (Macaca fascicularis) With Malaria.

Important hematologic changes can be observed in nonhuman primates with malaria, including inaccurate reticulocyte counts by the ADVIA 2120 hematology analyzer. A 5-year-old male purpose-bred cynomolgus macaque (Macaca fascicularis) imported from a commercial source in Cambodia was enrolled in a nonclinical toxicity study investigating the effects of an immunomodulatory pharmaceutical agent. On study day 22, an increase in large unstained cells (LUCs), due to increased monocytes (2.20 × 103/µl, reference interval: 0.17-0.76 × 103/µl), was reported by the analyzer during a scheduled hematologic evaluation, which prompted blood smear review and revealed that the macaque had a high burden of Plasmodium spp.. The macaque did not have clinical signs for the infection at this time point. Progressively higher parasite burdens and persistently increased monocytes (markedly increased by study day 56, 10.38 × 103/µl) were observed at subsequent hematologic evaluations. New Methylene Blue stain manual reticulocyte counts were performed on study day 43 and at later time points, and showed that the analyzer reported erroneous higher reticulocyte counts (study day 43: +6.7%, +266.2 × 109/L; study day 50: +18.9%, +409.8 × 109/L) compared with the manual reticulocyte counts (pseudoreticulocytosis). The magnitude of regenerative response was considered inadequate for the severity of anemia at these time points. Atypical reticulocyte scatter plot distributions from the analyzer were also observed at time points with high parasite burdens, and combined with increased LUCs, may suggest high burden parasitemia. Verification of automated reticulocyte counts is important in cases with high malarial parasite burdens and the recognition of pseudoreticulocytosis is prudent in assessing appropriateness of the regenerative response. Increases in monocytes correlated with higher parasite burdens and marked increases may be an indicator of advanced disease.

Screening For Bone Marrow Cellularity Changes in Cynomolgus Macaques in Toxicology Safety Studies Using Artificial Intelligence Models.

Many compounds affect the cellularity of hematolymphoid organs including bone marrow. Toxicologic pathologists are tasked with their evaluation as part of safety studies. An artificial intelligence (AI) tool could provide diagnostic support for the pathologist. We looked at the ability of a deep-learning AI model to evaluate whole slide images of macaque sternebrae to identify and enumerate bone marrow hematopoietic cells. The AI model was trained and able to differentiate the hematopoietic cells from the other sternebrae tissues. We compared the model to severity scores in a study with decreased hematopoietic cellularity. The mean cells/mm2 from the model was lower for each increase in severity score. The AI model was trained by 1 pathologist, providing proof of concept that AI model generation can be fast and agile, without the need of a cross disciplinary team and significant effort. We see great potential for the role of AI-based bone marrow screening.

Talaromycosis (Penicilliosis) in a Cynomolgus Macaque.

A sexually mature Chinese-origin female Macaca fascicularis assigned to the high-dose group in a 26-week toxicology study with an experimental immunomodulatory therapeutic antibody (a CD40 L antagonist fusion protein) was euthanized at the scheduled terminal sacrifice on study day 192. The animal was healthy at study initiation and remained clinically normal throughout the study. On study day 141, abnormal clinical pathology changes were found during a scheduled evaluation; splenomegaly was detected on study day 149 and supported by ultrasound examination. At the scheduled necropsy, there was marked splenomegaly with a nodular and discolored appearance. Cytologic examination of a splenic impression smear revealed yeast-like organisms within macrophages. Histologically, there was disseminated systemic granulomatous inflammation with 2- to 3-µm oval, intracytoplasmic yeast-like organisms in multiple organs identified as Talaromyces (Penicillium) marneffei. This organism, not previously reported as a pathogen in macaques, causes an important opportunistic infection in immunosuppressed humans in specific global geographic locations.

Transvenous heartworm extraction in a ferret with caval syndrome.

A 10-month-old ferret was diagnosed with heartworm disease and caval syndrome. Associated clinical signs included weakness and a green-colored urine, identified as biliverdinuria. Despite the animal's small size, removal of three heartworms via transvenous heartworm extraction was successfully performed. Although at least one female worm remained in the right ventricle, the majority of clinical signs related to the presence of the heartworms resolved. The ferret was subsequently managed medically with corticosteroids and monthly heartworm prevention. This case documents the presence of biliverdinuria associated with caval syndrome and successful transvenous heartworm extraction in a ferret.

Detection of a large unnamed Babesia piroplasm originally identified in dogs in North Carolina in a dog with no history of travel to that state.

CASE DESCRIPTION: A 12-year-old 46-kg (101.2-lb) sexually intact male Labrador Retriever was evaluated because of lymphadenomegaly. The dog resided in Texas, and its travel history included many southeastern and eastern shore states but not North Carolina. CLINICAL FINDINGS: Following evaluation of the dog, a diagnosis of stage IVa intermediate- to large-cell lymphoma was made. A cyclophosphamide-hydroxydaunorubicin (doxorubicin)-vincristine-prednisone chemotherapy protocol was initiated. One week after the first chemotherapeutic treatment, a routine blood smear evaluation revealed single and paired intraerythrocytic large piroplasms that resembled Babesia canis. Via molecular testing, the organism was identified as a Babesia sp that had been detected previously in dogs in North Carolina. TREATMENT AND OUTCOME: The dog was administered imidocarb diproprionate (7 mg/kg [3.2 mg/lb], IM) on 2 occasions (3-week interval). At 1, 4, 15, and 50 weeks after the second treatment, blood samples were analyzed specifically for the North Carolina Babesia sp via PCR assay; the result of each assay was positive. CLINICAL RELEVANCE: Because of the morphologic similarity of the large piroplasm detected in dogs in North Carolina to B canis, molecular testing of large piroplasms detected in dogs is needed to definitively identify the infective Babesia sp. In the dog of this report, the infection was not eliminated following treatment with imidocarb diproprionate, which may have been a result of the immunocompromised state of the dog or the drug's ineffectiveness against this parasite. If imidocarb diproprionate is ineffective against the North Carolina Babesia sp, treated dogs may act as reservoirs of infection.

What is your diagnosis? Rectal scraping from a dog with diarrhea.

A 3-year-old, spayed female, mixed-breed dog was evaluated for chronic diarrhea, vomiting, and weight loss. A marked inflammatory leukogram, mild regenerative anemia, and marked hypoalbuminemia were noted. Cytologic evaluation of a rectal scraping revealed numerous round to ovoid protozoal cysts, 5-25 microm in diameter, with small to moderate amounts of pale blue cytoplasm and round eosinophilic nuclei. A distinct, variably sized, round to oval vacuole was often seen within the cytoplasm and frequently displaced the nucleus. The cysts were morphologically similar to Blastocystis sp., an amoeba-like protozoal parasite found in both diseased and asymptomatic humans and animals. Histologic findings in endoscopic biopsies from the stomach, duodenum, ileum, and colon were unremarkable and protozoal organisms were not observed. The dog was diagnosed with exocrine pancreatic insufficiency based on markedly decreased serum levels of trypsin-like immunoreactivity. Alteration of gastrointestinal flora secondary to the underlying pancreatic disease likely allowed overgrowth of the protozoa, which were considered an incidental finding. Their identification was important in avoiding an incorrect diagnosis and unwarranted treatment.

Hematologic changes associated with Adderall toxicity in a dog.

A 1-year-old intact male Boxer was presented to the Texas Veterinary Medical Center for emergency treatment following suspected ingestion of a large number of tablets of Adderall, a pharmaceutical amphetamine. The dog had a temperature of 41.7 degrees C, heart rate of 192 beats per minute, and a respiratory rate of 100 breaths per minute. The dog was anxious and agitated with bilaterally dilated pupils, and shortly thereafter became recumbent and incontinent. Initial CBC results included mild leukopenia and mild thrombocytopenia. The dog was not anemic (HCT 39.9%) and had only slight polychromasia, but had 48 nucleated RBCs/100 WBC (7500/microL). Moderate numbers of neutrophils had hypersegmented nuclei and several pyknotic cells were noted. The metarubricytosis persisted for approximately 56 hours while hypersegmentation and pyknotic cells were no longer found at 8 hours after presentation. The dog received supportive care and recovered uneventfully. We hypothesized that hyperpyrexia associated with Adderall toxicity resulted in inappropriate metarubricytosis due to damaged bone marrow endothelium, and resulted in hypersegmentation and pyknosis due to damaged or accelerated aging of neutrophils in peripheral blood. Metarubricytosis has been reported previously in dogs with heat-induced illness, such as heat stroke.