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Diagnosis of portosystemic shunts (PSS) in dogs often requires multiple diagnostic tests, and available clinicopathologic tests have limitations in sensitivity and specificity. The objective of this study was to train and validate a machine learning model (MLM) that can accurately predict the presence of a PSS utilizing routinely collected demographic data and clinicopathologic features. Dogs diagnosed with PSS or control dogs tested for PSS but had the condition ruled out (non-PSS) were identified. Dogs were included if a complete blood count and serum chemistry panel were available from PSS diagnostic testing. Dogs with a PSS were subcategorized as having a single intrahepatic PSS, a single extrahepatic PSS, or multiple extrahepatic PSS. An extreme gradient boosting (XGboost) MLM was trained with data from 70% of the cases, and MLM performance was determined on the test set, comprising the remaining 30% of the case data. Two MLMs were created. The first was designed to predict the presence of any PSS (PSS MLM), and the second to predict the PSS subcategory (PSS SubCat MLM). The trained PSS MLM had a sensitivity of 94.3% (95% CI 90.1–96.8%) and specificity of 90.5% (95% CI 85.32–94.0%) for dogs in the test set. The area under the receiver operator characteristic curve (AUC) was 0.976 (95% CI; 0.964–0.989). The mean corpuscular hemoglobin, lymphocyte count, and serum globulin concentration were most important in prediction classification. The PSS SubCat MLM had an accuracy of 85.7% in determining the subtype of PSS of dogs in the test set, with variable sensitivity and specificity depending on PSS subtype. These MLMs have a high accuracy for diagnosing PSS; however, the prediction of PSS subclassification is less accurate. The MLMs can be used as a screening tool to increase or decrease the index of suspicion for PSS before confirmatory diagnostics such as advanced imaging are pursued.

Abstract Background Awareness of prescribing practices helps identify opportunities to improve antibiotic use (AU). Objectives To estimate AU prevalence in dogs and cats in U.S. veterinary teaching hospitals (VTHs) and identify antibiotic drugs commonly prescribed, indications for use, and evidence of bacterial infection. Animals Medical record data were collected from dogs and cats examined at 14 VTHs. Methods Data were collected from VTH medical records of dogs and cats examined by primary care, urgent care, emergency and critical care, internal medicine, and surgery services on a single day during August 13‐September 3, 2020. Data included signalment; clinical service; inpatient or outpatient status; clinical conditions; diagnostic tests; evidence of bacterial infection; intended reason for AU; name and route of antibiotics prescribed. Results Of 883 dogs and cats, 322 (36.5%) were prescribed at least 1 antibiotic. Among 285 antibiotics administered systemically intended for treatment of infection, 10.9% were prescribed without evidence of infection. The most common class of antibiotics presribed for systemic administration was potentiated penicillin for dogs (115/346, 33.3%) and cats (27/80, 33.8%). For dogs and cats, first‐generation cephalosporins (93/346, 26.9% and 11/80, 13.8%, respectively) and fluoroquinolones (51/346, 14.7% and 19/80, 23.8%, respectively) was second or third most‐prescribed. Common AU indications included skin, respiratory, and urinary conditions, and perioperative use. Conclusions and Clinical Importance Collaborative data collection provides a sustainable methodology to generate national AU prevalence estimates and bring attention to areas requiring additional research and detailed data collection. These efforts can also identify practice improvement opportunities in settings where future veterinarians are trained.

Abstract Background Pyothorax, an accumulation of inflammatory fluid in the pleural space, is often caused by foreign body inhalation in dogs, whereas the etiology in cats can be more difficult to discern. Objective Compare clinical, microbiologic findings, and etiology in cats and dogs with pyothorax. Animals Twenty‐nine cats and 60 dogs. Methods Medical records of cats and dogs diagnosed with pyothorax from 2010 to 2020 were reviewed. Clinical findings, fluid analysis, and microbiologic results were retrieved. Results Antimicrobials had been administered to equal proportions of cats and dogs before fluid sampling (45% and 47%). Groups did not differ in age or total protein concentration or percentage neutrophils in pleural fluid, but effusion cell count was significantly higher in cats than in dogs (P = .01). Neutrophils containing intracellular bacteria were identified in more cats (27/29, 93%) than dogs (44/60, 73%; P = .05). Penetrating damage to the thorax was implicated as the cause of pyothorax in equal percentages of cats (76%) and dogs (75%). Etiology could not be determined in 2 cats and 1 dog. Cats had higher numbers of bacterial isolates per patient (median, 3) than dogs (median, 1; P = .01) and anaerobes were isolated more often in cats (23/29, 73%) than in dogs (27/60, 45%; P = .003). Conclusions and Clinical Importance Pyothorax had similar etiologies in cats and dogs. Cats had higher fluid cell counts, higher numbers of bacterial isolates identified per patient, and intracellular bacteria detected more commonly than did dogs.

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Feline infectious peritonitis (FIP) is a multisystemic, generally lethal immuno-inflammatory disease of domestic cats caused by an infection with a genetic variant of feline coronavirus, referred to as the FIP virus (FIPV). We leveraged data from four different antiviral clinical trials performed at the University of California, Davis. Collectively, a total of 60 client-owned domestic cats, each with a confirmed diagnosis of naturally occurring FIP, were treated with a variety of antiviral compounds. The tested therapies included the antiviral compounds GS-441524, remdesivir, molnupiravir and allogeneic feline mesenchymal stem/stroma cell transfusions. Four client-owned cats with FIP did not meet the inclusion criteria for the trials and were not treated with antiviral therapies; these cats were included in the data set as untreated FIP control cats. ELISA and Western blot assays were performed using feline serum/plasma or ascites effusions obtained from a subset of the FIP cats. Normalized tissue/effusion viral loads were determined in 34 cats by a quantitative RT-PCR of nucleic acids isolated from either effusions or abdominal lymph node tissue. Twenty-one cats were PCR “serotyped” (genotyped) and had the S1/S2 region of the coronaviral spike gene amplified, cloned and sequenced from effusions or abdominal lymph node tissue. In total, 3 untreated control cats and 14 (23.3%) of the 60 antiviral-treated cats died or were euthanized during (13) or after the completion of (1) antiviral treatment. Of these 17 cats, 13 had complete necropsies performed (10 cats treated with antivirals and 3 untreated control cats). We found that anticoronaviral serologic responses were persistent and robust throughout the treatment period, primarily the IgG isotype, and focused on the viral structural Nucleocapsid and Membrane proteins. Coronavirus serologic patterns were similar for the effusions and serum/plasma of cats with FIP and in cats entering remission or that died. Viral RNA was readily detectable in the majority of the cats in either abdominal lymph node tissue or ascites effusions, and all of the viral isolates were determined to be serotype I FIPV. Viral nucleic acids in cats treated with antiviral compounds became undetectable in ascites or abdominal lymph node tissue by 11 days post-treatment using a sensitive quantitative RT-PCR assay. The most common pathologic lesions identified in the necropsied cats were hepatitis, abdominal effusion (ascites), serositis, pancreatitis, lymphadenitis, icterus and perivasculitis. In cats treated with antiviral compounds, gross and histological lesions characteristic of FIP persisted for several weeks, while the viral antigen became progressively less detectable.

Abstract Background Dogs with hypoadrenocorticism (HA) have clinical signs and clinicopathologic abnormalities that can be mistaken as other diseases. In dogs with a differential diagnosis of HA, a machine learning model (MLM) has been validated to discriminate between HA and other diseases. This MLM has not been evaluated as a screening tool for a broader group of dogs. Hypothesis An MLM can accurately screen dogs for HA. Animals Dogs (n = 1025) examined at a veterinary hospital. Methods Dogs that presented to a tertiary referral hospital that had a CBC and serum chemistry panel were enrolled. A trained MLM was applied to clinicopathologic data and in dogs that were MLM positive for HA, diagnosis was confirmed by measurement of serum cortisol. Results Twelve dogs were MLM positive for HA and had further cortisol testing. Five had HA confirmed (true positive), 4 of which were treated for mineralocorticoid and glucocorticoid deficiency, and 1 was treated for glucocorticoid deficiency alone. Three MLM positive dogs had baseline cortisol ≤2 μg/dL but were euthanized or administered glucocorticoid treatment without confirming the diagnosis with an ACTH‐stimulation test (classified as “undetermined”), and in 4, HA was ruled out (false positives). The positive likelihood ratio of the MLM was 145 to 254. All dogs diagnosed with HA by attending clinicians tested positive by the MLM. Conclusions and Clinical Importance This MLM can robustly predict HA status when indiscriminately screening all dogs with blood work. In this group of dogs with a low prevalence of HA, the false positive rates were clinically acceptable.

Abstract Background Clinical findings of glucocorticoid‐deficient hypoadrenocorticism (GDH) can overlap with other diseases, presenting a diagnostic challenge. Objectives Describe clinicopathologic and ultrasonographic features of dogs with GDH and those suspected of having GDH that had the disease ruled out. Animals Six hundred twenty‐three dogs. Methods Records from dogs with suspected GDH between 2003 and 2018 were reviewed. Dogs with hyperkalemia or hyponatremia were excluded. Dogs were categorized as controls when the resting serum cortisol or post‐ACTH cortisol concentration were > 2 μg/dL. Clinicopathologic and ultrasonographic features were compared between groups. The optimal cut‐point, area under the receiver operating characteristic curve (AUC), sensitivity, and specificity were calculated for individual features used to detect GDH. Results Dogs were categorized as GDH (n = 29) or controls (n = 594). Lymphocyte count (>1750 cells/L; sensitivity, 96.6%; 95% confidence interval [CI], 82.8%‐99.8%; specificity, 60.3%; 95% CI, 56.3%‐64.1%; AUC, 0.828; 95% CI, 0.762‐0.894) and albumin/globulin ratio (

Abstract Background Factors associated with outcome in dogs diagnosed with infective endocarditis (IE) are not well characterized. Objectives Evaluate outcome and prognostic factors in dogs with IE. Animals One hundred and thirteen dogs with IE. Methods Medical records for dogs that fulfilled the modified Duke criteria between 2005 and 2020 were retrospectively reviewed. Signalment, preexisting conditions, clinicopathologic findings, treatment regimen, and outcomes were recorded. Univariate logistic regression was performed to identify categorical factors associated with mortality, and then multivariate analysis was performed. Results Dogs were categorized as survivors (n = 47), non‐survivors (n = 57), or lost to follow‐up (n = 9). Survival to discharge and at 1 month was documented in 79 (70%) of 113 and 56 (54%) of 104 dogs, respectively, with median survival time (MST) of 72 days. Risk factors associated with mortality included development of congestive heart failure (odds ratio [OR], 11.8; 95% confidence interval [CI], 1.4‐97.8), thromboembolic events (OR, 5.7; 95% CI, 2.3‐14.4), and acute kidney injury (OR, 6.2; 95% CI, 2.0‐18.8). Administration of antithrombotic medications was associated with survival (OR, 0.35; 95% CI, 0.13‐0.97). Dogs that were not treated with antithrombotics had MST of 92 days, whereas dogs treated with antithrombotics did not reach MST during the study period. The heart valves involved and etiologic agent identified did not correlate with outcome. Conclusion and Clinical Importance Dogs with IE that had thromboembolic events, acute kidney injury, or congestive heart failure had higher risk of mortality. Administration of antithrombotics was associated with prolonged survival time.

Infective endocarditis (IE) is a potentially fatal disease in dogs. Limited information exists regarding the characterization of bacterial isolates from dogs with IE. The objective of this study was to describe bacterial isolates associated with IE and their antimicrobial susceptibility patterns. A retrospective analysis of dogs with IE and bacterial isolates was performed, and antimicrobial susceptibility was interpreted using current veterinary cut points where available. The susceptibility rate was assessed for association with survival and previous antimicrobial administration. Fifty-one bacterial isolates were identified from 45 dogs, and 33 had antimicrobial susceptibility performed. Staphylococcus spp. (14/51; 27.5%) was the most common organism. Antimicrobials with the lowest susceptibility rate were ampicillin (19/26; 73%), doxycycline (16/22; 73%), and enrofloxacin (22/29; 76%) with 12/33 (36%) of isolates exhibiting multidrug resistance (MDR). Individual antimicrobial resistances and the MDR rate were not associated with a difference in survival rate. Bacterial isolates from dogs that had received fluoroquinolone antimicrobials in the month before diagnosis had a higher rate of non-intrinsic fluoroquinolones resistance (5/8;62.5%) compared to those that did not receive fluoroquinolones (2/21; 9.5%) (p = 0.03). Antimicrobial resistance and MDR phenotype were common in this study. Culture and antimicrobial susceptibility testing should be pursued in dogs with IE to help guide antimicrobial therapy.

Nucleoside analogs GS-441524 and remdesivir (GS-5734) are effective in treating cats with feline infectious peritonitis (FIP). However, no studies have compared the efficacy between antiviral medications. The objective of this study was to evaluate the efficacy of orally administered GS-442514 (12.5–15 mg/kg) compared to orally administered remdesivir (25–30 mg/kg) in a double-blinded non-inferiority trial. Eighteen cats with effusive FIP were prospectively enrolled and randomly assigned to receive either GS-442514 or remdesivir. Cats were treated daily for 12 weeks and evaluated at week 0, 12, and 16. Survival and disease remission at week 16 were compared between groups. Five of 9 (55%) cats treated GS-441524 and 7/9 (77%) cats treated with remdesivir survived, with no difference in survival rate (p = 0.2). Remdesivir fulfilled the criteria for non-inferiority with a difference in survival of 22% (90% CI; −13.5–57.5%). Three of the 18 cats died within 48 h of enrollment. Excluding these cats, 5/6 (83%) of the cats treated with GS-441524 and 7/9 (77%) of the cats treated with remdesivir survived. These findings suggest that both orally administered GS-441524 and remdesivir are safe and effective anti-viral medications for the treatment of effusive FIP. Further optimization of the first 48 h of treatment is needed.

Abstract Background Clinical features, treatment, and outcome of opportunistic infections with Rasamsonia spp., a nonpigmented filamentous mold, are not well documented in dogs. Objectives Describe clinical, radiographic, pathologic features, and outcome of dogs with disseminated Rasamsonia species complex infections. Animals Eight client‐owned dogs. Methods Retrospective case series. Medical records were reviewed to describe signalment, history, clinicopathologic and imaging findings, microbiologic and immunologic results, cyto‐ and histopathologic diagnoses, treatment, and outcome. Results Presenting complaints were nonspecific with anorexia (n = 5) and back pain (n = 4) most common. Five dogs were German Shepherd dogs. Six dogs had multifocal discospondylitis and 2 had pleural effusion. Six dogs had Rasamsonia piperina and 2 had Rasamsonia argillacea infections with isolates identified using DNA sequencing. Rasamsonia spp. were isolated by urine culture in 5 of 7 dogs. Five of 6 dogs had positive serum Aspergillus galactomannan antigen enzyme immunoassay (EIA) results. Median survival time was 82 days, and 317 days for dogs that survived to discharge. Four died during initial hospitalization (median survival, 6 days). All isolates had low minimum effective concentrations (MECs) to echinocandins with variable minimum inhibitory concentrations (MICs) for azole antifungal drugs. Conclusions and Clinical Importance Rasamsonia spp. infections in dogs are associated with multisystemic disease involving the vertebral column, central nervous system, kidneys, spleen, lymph nodes, lungs, and heart. The infection shares clinical features with other systemic mold infections and can be misidentified when using phenotypical microbiologic methods. Molecular techniques are required to identify the organism and guide appropriate antifungal treatment.

Abstract Background Point‐of‐care (POC) Coccidioides antibody assays may provide veterinarians with rapid and accurate diagnostic information. Objectives To determine the agreement of a POC lateral flow assay (LFA), sona Coccidioides (IMMY, Norman, Oklahoma) with the current diagnostic standard, the immunodiffusion assay (agar gel immunodiffusion [AGID]; Coccidioidomycosis Serology Laboratory, University of California, Davis, California). Animals Forty‐eight sera specimens from 48 dogs. Methods Sera specimens were collected from client‐owned dogs that had a clinical suspicion for coccidioidomycosis. Animals were classified as Coccidioides antibody‐positive (n = 36) based on a positive AGID or Coccidioides antibody‐negative (n = 12) based on a negative AGID. The performance of the LFA assay was determined by comparing results to AGID results. Results The LFA assay demonstrated agreement in 32 of 36 Coccidioides antibody‐positive specimens and 12 of 12 Coccidioides antibody‐negative specimens, resulting in a positive percentage agreement of 88.9% (95% confidence interval [CI], 74.7‐95.6%) and negative percentage agreement of 100% (95% CI, 75.8‐100%) as compared to AGID. A receiver operator characteristic curve was constructed, and the area under the curve was 0.944 (CI, 0.880‐1.000). Conclusion and Clinical importance This LFA is a rapid alternative to the traditional AGID. The LFA provides excellent predictive value for positive results. Positive agreement was lower in dogs with low AGID titers; therefore, confirmatory testing is recommended if a high index of suspicion exists.

The rising prevalence of extended-spectrum β-lactamase (ESBL)-producing Enterobacterales is a significant threat to animal and human health. This study aims to describe the clinical features, antimicrobial susceptibility patterns, and genotypic features of infections associated with ESBL-producing Enterobacterales in dogs and cats seen at a tertiary referral veterinary teaching hospital. Enterobacterales isolated from dogs and cats that underwent ESBL testing during the study period were identified using a search of the hospital antimicrobial susceptibility test software database. Medical records of confirmed ESBL isolates were reviewed, and the source of infection, clinical findings, and antimicrobial susceptibility were recorded. Genomic DNA from bacterial isolates was evaluated for antimicrobial resistance genes with whole genome sequencing. Thirty ESBL-producing isolates were identified based on phenotypic testing (twenty-nine from dogs, one from a cat); twenty-six were Escherichia coli and the remainder were Klebsiella spp. Bacterial cystitis was the most commonly identified (8/30, 27%) clinical problem associated with infection. Resistance to three or more antimicrobial classes was identified in 90% (27/30) of isolates, and all isolates were susceptible to imipenem. Over 70% of isolates were susceptible to piperacillin-tazobactam, amikacin, and cefoxitin. BlaCTX-M-15 was the most common ESBL gene identified, present in 13/22 (59%) isolate genomes. A wide range of clinical infections were identified. Piperacillin-tazobactam and amikacin may be alternatives to carbapenem therapy. Further, larger-scale studies are needed.

Feline infectious peritonitis (FIP) is a fatal disease of cats that currently lacks licensed and affordable vaccines or antiviral therapeutics. The disease has a spectrum of clinical presentations including an effusive (“wet”) form and non-effusive (“dry”) form, both of which may be complicated by neurologic or ocular involvement. The feline coronavirus (FCoV) biotype, termed feline infectious peritonitis virus (FIPV), is the etiologic agent of FIP. The objective of this study was to determine and compare the in vitro antiviral efficacies of the viral protease inhibitors GC376 and nirmatrelvir and the nucleoside analogs remdesivir (RDV), GS-441524, molnupiravir (MPV; EIDD-2801), and β-D-N4-hydroxycytidine (NHC; EIDD-1931). These antiviral agents were functionally evaluated using an optimized in vitro bioassay system. Antivirals were assessed as monotherapies against FIPV serotypes I and II and as combined anticoronaviral therapies (CACT) against FIPV serotype II, which provided evidence for synergy for selected combinations. We also determined the pharmacokinetic properties of MPV, GS-441524, and RDV after oral administration to cats in vivo as well as after intravenous administration of RDV. We established that orally administered MPV at 10 mg/kg, GS-441524 and RDV at 25 mg/kg, and intravenously administered RDV at 7 mg/kg achieves plasma levels greater than the established corresponding EC50 values, which are sustained over 24 h for GS-441514 and RDV.

Abstract Background Point‐of‐care (POC) Cryptococcus antigen assays may provide veterinarians with a more rapid, patient‐side diagnosis when compared with traditional laboratory‐based latex agglutination tests. Objective To determine the sensitivity and specificity of 2 POC lateral flow cryptococcal serum antigen tests, CrAg LFA (Immy, Norman, OK) and the CryptoPS (Biosynex, Strasbourg, France) for diagnosis of cryptococcosis in dogs and cats, using the cryptococcal antigen latex agglutination system (CALAS) as the reference standard. Animals 102 serum samples from 51 dogs and 40 cats. Methods Specimens were classified as CALAS‐positive (n = 25) or CALAS‐negative (n = 77). The sensitivity and specificity of each POC assay was calculated by comparing the results to the serologic reference standard results. Results The CrAg LFA assay correctly classified 23/25 CALAS‐positive specimens and 69/74 CALAS‐negative specimens resulting in a sensitivity of 92.0% (confidence interval [CI], 75.0%‐98.6%) and specificity of 93.2% (CI, 85.1%‐97.1%). The CryptoPS assay correctly classified 8/10 tested CALAS‐positive specimens and 56/59 tested CALAS‐negative specimens resulting in a sensitivity of 80.0% (CI, 49.0%‐96.5%) and specificity of 94.9% (CI, 86.1%‐98.6%). Conclusion and Clinical Importance The POC assays appear to be a sensitive and specific alternative to the traditional CALAS assay with more rapid turnaround times, which may result in earlier diagnosis and treatment.

Abstract Gastrointestinal (GI) pythiosis is a severe and often fatal disease in dogs that traditionally has been poorly responsive to medical treatment. Although aggressive surgical resection with wide margins is the most consistently effective treatment, lesion location and extent often preclude complete resection. Recently, it has been suggested that the addition of anti‐inflammatory doses of corticosteroids may improve outcome in dogs with nonresectable GI pythiosis. This report describes 3 dogs with colonic pythiosis in which complete resolution of clinical signs, regression of colonic masses, and progressive decreases in serological titers were observed after treatment with itraconazole, terbinafine, and corticosteroids. This treatment protocol represents a promising treatment for dogs with GI pythiosis in which surgical intervention is not feasible.

A One Health approach to the epidemiology, management, surveillance, and control of leptospirosis relies on accessible and accurate diagnostics that can be applied to humans and companion animals and livestock. Diagnosis should be multifaceted and take into account exposure risk, clinical presentation, and multiple direct and/or indirect diagnostic approaches. Methods of direct detection of Leptospira spp. include culture, histopathology and immunostaining of tissues or clinical specimens, and nucleic acid amplification tests (NAATs). Indirect serologic methods to detect leptospiral antibodies include the microscopic agglutination test (MAT), the enzyme-linked immunosorbent assay (ELISA), and lateral flow methods. Rapid diagnostics that can be applied at the point-of-care; NAAT and lateral flow serologic tests are essential for management of acute infection and control of outbreaks. Culture is essential to an understanding of regional knowledge of circulating strains, and we discuss recent improvements in methods for cultivation, genomic sequencing, and serotyping. We review the limitations of NAATs, MAT, and other diagnostic approaches in the context of our expanding understanding of the diversity of pathogenic Leptospira spp. Novel approaches are needed, such as loop mediated isothermal amplification (LAMP) and clustered regularly interspaced short palindromic repeats (CRISPR)-based approaches to leptospiral nucleic acid detection.

Case summary A 9-month-old intact female domestic mediumhair cat presented with a 5-month history of obtundation, lethargy, hypernatremia (181 mmol/l; reference interval [RI] 151–158 mmol/l), hyperchloremia (142 mmol/l; RI 117–126 mmol/l), azotemia (blood urea nitrogen 51 mg/dl; RI 18–33 mg/dl), creatinine 3.0 mg/dl (RI 1.1–2.2 mg/dl), hyperphosphatemia (8.3 mg/dl; RI 3.2–6.3 mg/dl) and total hypercalcemia (11.4 mg/dl; RI 9–10.9 mg/dl), with concurrent polyuria with adipsia. Neurologic evaluation revealed proprioceptive deficits, and this finding paired with a history of focal seizure-like activity despite improving sodium concentrations suggested a cerebrothalamic lesion. For this reason, and historical and biochemical findings consistent with adipsic diabetes insipidus (DI), MRI of the brain was performed, which revealed a lesion of the hypophyseal fossa consistent with a pituitary cyst. Given the patient’s age and the timeline of clinical signs, a congenital pituitary cyst was strongly suspected. The patient was managed initially with intravenous fluids to correct the hypernatremia, then managed for more than 4 years with topical ocular desmopressin acetate administration and free water administered through a feeding tube. This cat’s clinical diagnosis included a congenital pituitary cyst with subsequent central DI and primary adipsia. Relevance and novel information The clinical presentations of primary adipsia or central DI are both rare in cats. This is the first report to describe these conditions occurring in a cat owing to a congenital pituitary cyst and describes successful long-term management of this condition.

Mosquito salivary proteins (MSPs) modulate the host immune response, leading to enhancement of arboviral infections. Identification of proteins in saliva responsible for immunomodulation and counteracting their effects on host immune response is a potential strategy to protect against arboviral disease. We selected a member of the D7 protein family, which are among the most abundant and immunogenic in mosquito saliva, as a vaccine candidate with the aim of neutralizing effects on the mammalian immune response normally elicited by mosquito saliva components during arbovirus transmission.We identified D7 salivary proteins of Culex tarsalis, a West Nile virus (WNV) vector in North America, and expressed 36 kDa recombinant D7 (rD7) protein for use as a vaccine. Vaccinated mice exhibited enhanced interferon-γ and decreased interleukin-10 expression after uninfected mosquito bite; however, we found unexpectedly that rD7 vaccination resulted in enhanced pathogenesis from mosquito-transmitted WNV infection. Passive transfer of vaccinated mice sera to naïve mice also resulted in increased mortality rates from subsequent mosquito-transmitted WNV infection, implicating the humoral immune response to the vaccine in enhancement of viral pathogenesis. Vaccinated mice showed decreases in interferon-γ and increases in splenocytes producing the regulatory cytokine IL-10 after WNV infection by mosquito bite.Vector saliva vaccines have successfully protected against other blood-feeding arthropod-transmitted diseases. Nevertheless, the rD7 salivary protein vaccine was not a good candidate for protection against WNV disease since immunized mice infected via an infected mosquito bite exhibited enhanced mortality. Selection of salivary protein vaccines on the bases of abundance and immunogenicity does not predict efficacy.