Advancements, challenges, and future perspectives in developing feline herpesvirus 1 as a vaccine vector.

As the most prevalent companion animal, cats are threatened by numerous infectious diseases and carry zoonotic pathogens such as Toxoplasma gondii and Bartonella henselae, which are the primary causes of human toxoplasmosis and cat-scratch disease. Vaccines play a crucial role in preventing and controlling the spread of diseases in both humans and animals. Currently, there are only three core vaccines available to prevent feline panleukopenia, feline herpesvirus, and feline calicivirus infections, with few vaccines available for other significant feline infectious and zoonotic diseases. Feline herpesvirus, a major component of the core vaccine, offers several advantages and a stable genetic manipulation platform, making it an ideal model for vaccine vector development to prevent and control feline infectious diseases. This paper reviews the technologies involved in the research and development of the feline herpesvirus vaccine vector, including homologous recombination, CRISPR/Cas9, and bacterial artificial chromosomes. It also examines the design and effectiveness of expressing antigens of other pathogens using the feline herpesvirus as a vaccine vector. Additionally, the paper analyzes existing technical bottlenecks and challenges, providing an outlook on its application prospects. The aim of this review is to provide a scientific basis for the research and development of feline herpesvirus as a vaccine vector and to offer new ideas for the prevention and control of significant feline infectious and zoonotic diseases.

Development of genogroup-specific ELISAs based on the VP1 protein to detect antibodies to GIV and GVI feline norovirus.

Feline norovirus (FNoV) is a potential pathogen of feline gastroenteritis and has two genogroups (GIV and GVI). Few epidemiological studies have been conducted on FNoV. We designed two enzyme-linked immunosorbent assays (ELISAs) to identify genogroup-specific FNoV antibodies for serological surveillance. Analysis of sera from cats experimentally infected with FNoV GIV or GVI and from specific-pathogen-free (SPF) cats confirmed that the two recombinant proteins used in the assay react in a genogroup-specific manner. Of the 183 samples tested, 6.6% were positive for GIV and 26.2% were positive for GVI. Antibodies to both FNoV genogroups were detected in sera collected in 2005, seven years before FNoV was first reported.

Antibody response after feline panleukopenia virus vaccination in kittens with and without intestinal parasites.

OBJECTIVES: Vaccinations should only be given to healthy cats, and deworming before vaccination is generally recommended; however, so far, no study has investigated the influence of intestinal parasitic infection on the immune response in kittens. The aim of this prospective study was to compare the antibody response to feline panleukopenia virus (FPV) vaccination in kittens with and without intestinal parasites. METHODS: Overall, 74 healthy kittens were included. Of these, 17 had intestinal parasites (12/17 Toxocara cati, 6/17 Cystoisospora felis, 1/17 Capillaria species). Both kittens with and without (n = 57) parasites received two primary kitten vaccinations with modified live FPV vaccines in a 4-week interval starting at the age of 8-12 weeks. Anti-FPV antibodies were determined at the beginning of the study (week 0) and at week 8 (4 weeks after the second vaccination) by haemagglutination inhibition. A ⩾four-fold titre increase (week 8 vs week 0) was defined as a response to vaccination. Comparison of the immune response in the kittens with and without intestinal parasites was performed using Pearson's χ2 test. RESULTS: Pre-vaccination antibodies were present in 4/17 (23.5%) kittens with intestinal parasites and in 24/57 (42.1%) without parasites. A ⩾four-fold titre increase was seen in 13/17 (76.5%) kittens with parasites compared with 32/57 (56.1%) kittens without parasites. There was neither a significant difference in pre-vaccination antibodies (P = 0.17), nor in vaccination response (P = 0.13) between kittens with and without parasites. CONCLUSIONS AND RELEVANCE: The results indicate that asymptomatic intestinal infections with endoparasites do not interfere with the immune response to kitten vaccination series. Parasitic infection (at least with T cati, C felis and Capillaria species) is therefore not a reason to postpone important vaccinations.

Factors affecting the outcome of primary rabies vaccination in young cats.

Limited data exist on the factors affecting feline rabies vaccination outcomes during primary immunization. This study aimed to assess if specific factors (signalment, vaccination count, vaccine brand, and time since last vaccination) correlated with meeting global antibody titer standards and absolute titers in young cats given monovalent inactivated rabies vaccines. Analyzing a dataset from cats tested before their first annual booster using the FAVN test, logistic and linear regression models were applied. Among 379 cats, 94.2 % achieved titers meeting or exceeding the standard threshold (≥0.5 IU/ml). Time since last vaccination proved to be the primary predictor of vaccination success. Cats receiving two vaccinations tended toward higher titers. Age, sex, breed, and vaccine type showed no impact on outcomes. The present study indicates that vaccination failure in young cats is uncommon, and that the time interval from the latest vaccination is the single most important predictor of successful rabies vaccination.

Detection of Antibodies against Feline Morbillivirus by Recombinant Matrix Enzyme-Linked Immunosorbent Assay.

Feline morbillivirus (FeMV) has been associated with feline health, although its exact role in pathogenesis is still debated. In this study, an indirect enzyme-linked immunosorbent assay (i-ELISA) targeting a recombinant matrix protein of FeMV (rFeMV-M) was developed and assessed in comparison to a Western blotting (WB) assay. The i-ELISA was evaluated using blood samples from 136 cats that were additionally tested with real-time reverse-transcription PCR (RT-qPCR). The i-ELISA exhibited a sensitivity of 90.1%, specificity of 75.6%, positive predictive value of 88.2%, and negative predictive value of 79.1%. The agreement between i-ELISA and WB analyses was substantial (a κ coefficient of 0.664 with a 95% confidence interval of 0.529 to 0.799). Within the study group, 68.4% (93/136) of the cats were serologically positive in the i-ELISA and 66.9% (91/136) in the WB assay, with 11.8% (11/93) of false positivity with the i-ELISA. However, only 8.1% (11/136) of the cats tested positive for FeMV using RT-qPCR (p < 0.001). The developed i-ELISA proved effective in identifying FeMV-infected cats and indicated the prevalence of FeMV exposure. Combining FeMV antibody detection through i-ELISA with FeMV RT-qPCR could offer a comprehensive method to determine and monitor FeMV infection status. Nevertheless, this assay still requires refinement due to a significant number of false positive results, which can lead to the misdiagnosis of cats without antibodies as having antibodies. This study also provided the first evidence of seroprevalence against FeMV among cat populations in Thailand, contributing valuable insights into the geographic distribution and prevalence of this virus.

Current status of immunodeficient mouse models as substitutes to reduce cat and dog use in heartworm preclinical research.

Chemoprophylactic prevention of veterinary heartworm disease in companion animals, caused by the vector-borne nematode parasite Dirofilaria immitis, is a multi-billion-dollar global market. Experimental use of cats and dogs in preclinical heartworm drug testing is increasing due to evolving drug-resistance to frontline macrocyclic lactones and renewed investment in alternative preventative drug research. We and others recently published data demonstrating proof-of-concept of utilising lymphopenic severe-combined immunodeficient (SCID) or Recombination Activating Gene (RAG)2 deficient mice with additional knockout of the IL-2/7 receptor gamma chain (γc) as alternative preventative drug screening research models of dirofilariasis. Here we summarise the current knowledge of candidate immunodeficient mouse models tested, including a comparison of susceptibility using different background strains of mice, different D. immitis isolates, following use of anti-inflammatory treatments to further suppress residual innate immunity, and efficacies achieved against different reference anthelmintics. We supplement this precis with new data on treatment response to the veterinary anthelmintic, oxfendazole, and initial evaluation of D. immitis susceptibility in CB.17 SCID and C57BL/6 RAG2 -/-γc -/- mice. We conclude that in addition to NSG and NXG mice, RAG2 -/-γc -/- mice on either a BALB/c or C57BL/6 background offer an alternative screening model option, widening access to academic and commercial laboratories wishing to pursue initial rapid in vivo drug screening whilst avoiding potentially unnecessary cat or dog testing.

Comparison of polyclonal and monoclonal antibody assays for serum amyloid A in cats: a study based on an automated turbidimetric immunoassay in a primary care veterinary hospital.

OBJECTIVE: Comparing the utility of the anti-human serum amyloid A (SAA)-specific monoclonal and polyclonal antibodies assays (LZ-SAA) with the pure monoclonal anti-human antibody assays (VET-SAA) during clinical practice in primary care hospital populations by measuring SAA measurement in healthy and diseased domestic cats. ANIMALS: 52 healthy and 185 diseased client-owned cats. METHODS: SAA concentration was measured using different LZ-SAA and VET-SAA measurements for healthy and various diseased cats. Sensitivity, specificity, and accuracy were calculated for each disease. RESULTS: VET-SAA has higher sensitivity than LZ-SAA for the most common diseases presenting to primary care veterinary hospitals, including chronic kidney disease, tumors, and gingivostomatitis. Our results reveal the capability of detecting low SAA concentrations in healthy and diseased cats using VET-SAA in contrast to LZ-SAA, which found elevations of SAA concentrations only in diseased cats. CLINICAL RELEVANCE: Our findings indicate that switching to the new VET-SAA instead of the conventional LZ-SAA will likely enhance the diagnostic performance in primary care veterinary hospitals.

Preparation of a novel type I feline coronavirus virus-like particle vaccine and its immunogenicity in mice and cats.

Feline coronavirus (FCoV) infection is a leading cause of death in cats. In this study, we produced FCoV-I virus-like particles (VLPs) containing E, M, N, and S proteins using a baculovirus expression system and mixed VLPs with the adjuvants MF59 and CpG 55.2 to prepare an VLP/MF59/CpG vaccine. After immunization of mice with the vaccine, IgG specific antibodies titers against S and N proteins increased to 1:12,800, and IFN-γ+ and IL-4+ splenocytes were significantly increased. Following immunization of FCoV-negative cats, the S protein antibodies in immunized cats (5/5) increased significantly, with a peak of 1:12,800. Notably, after booster vaccination in FCoV-positive cats, a significant reduction in viral load was observed in the feces of partial cats (4/5), and the FCoV-I negative conversion was found in two immunized cats (2/5). Therefore, the VLP/MF59/CpG vaccine is a promising candidate vaccine to prevent the FCoV infection.

The erythrocyte sedimentation rate and other markers of inflammation in cats tested for Leishmania infantum and feline immunodeficiency virus antibodies.

BACKGROUND: In endemic areas, Leishmania infantum and feline immunodeficiency virus (FIV) co-infection occurs in cats, and may favour a progressive course of feline leishmaniosis. Abnormalities in serum protein fractions have been reported, but inflammation markers have scarcely been studied. Erythrocyte sediment rate (ESR) is a marker of inflammation that is poorly used in veterinary medicine, but it has been evaluated in EDTA blood using a recently introduced automatic device. We studied ESR and a pool of feline markers of inflammation (MoI) in cats L. infantum (Li+) and/or FIV antibody-positive (Li+FIV+/FIV+) with the aims (a) to evaluate ESR as MoI in cats with the infectious and clinical conditions considered and (b) to provide data about a pool of MoI never investigated in the feline infections studied and in other cat diseases before. METHODS: This prospective controlled study included 35 study group cats (Li+, n = 20; FIV +, n = 8; Li+FIV+, n = 7) and ten healthy antibody-negative control cats. Clinical findings at physical examination and selected clinical pathological abnormalities related to inflammation were statistically analysed in relation to the infectious status and ESR values. RESULTS: ESR values were higher in Li+, FIV+, and Li+FIV+ cats compared with control cats, and 40% of the study group cats had ESR values above the reference interval (RI). ESR positively correlated with some positive MoI and negatively with some negative MoI studied. Additionally, a higher prevalence of ESR values above the RI has been detected in cats with hypoalbuminemia or hypergammaglobulinemia and higher ESR values were measured in cats with serum protein electrophoresis (SPE) fraction abnormalities. Correlations were also found with erythrocytes, hemoglobin, hematocrit and some erythrocyte indices. FIV+ and Li+FIV+ cats had a higher prevalence of increased ESR values, and almost all had SPE abnormalities and more severe clinical presentations compared with Li+ cats. CONCLUSIONS: Abnormal levels of MoI were found in almost all parameters studied, particularly in FIV+ and Li+FIV+ cats. Also, ESR can be used as a marker of inflammation in cats with L. infantum and/or FIV infection.

Immunophenotype investigation in feline intestinal non-B-cell lymphoma.

Lymphoma is the most common tumour of domestic cats, developing most frequently in the small intestine. Feline small intestinal lymphoma predominantly demonstrates a T-cell immunophenotype identified by standard immunopositivity for T cells with CD3 or immunopositivity for B cells with CD20. In contrast, a wide spectrum of immunohistochemical antibodies are applied in humans to diagnose the various specific lymphoma subtypes according to the WHO classification. Our aim was to augment our knowledge of immunophenotypes in feline non-B-cell lymphomas forming macroscopic masses in the intestinal tract. We evaluated the combined immunohistochemistry and flow cytometry findings from 15 cases. Neoplastic lymphoid cells were immunopositive for CD3 in 93% (14/15), granzyme B in 87% (13/15), CD5 in 20% (3/15), CD8 in 13% (2/15), CD4 in 7% (1/15) and CD56 in 7% (1/15) of cases. Cytotoxic granules indicating a cytotoxic origin of the neoplastic cells were identified by histopathology only in 13% (2/15) and by cytology in 47% (7/15) of the cases. Without immunohistochemical labelling of the cytotoxic protein granzyme B, the cytotoxic status would have been missed in 46% (6/13) of the cytological and in 85% (11/13) of the histopathological slides. These findings suggest that more complex immunophenotyping may advance our understanding and help prognosticate small intestinal T-cell lymphoma in cats.

Multistrain probiotics fail to modulate the asthmatic phenotype, respiratory microbiota, and immune responses in cats.

OBJECTIVE: To determine if multistrain probiotics administered to asthmatic cats treated with anti-inflammatory glucocorticoids would attenuate the asthmatic phenotype and beneficially alter respiratory, blood, and oropharyngeal (OP) microbial communities and immune parameters versus placebo. ANIMALS: 13 client-owned asthmatic cats. METHODS: A randomized, blinded, placebo-controlled clinical trial of asthmatic cats receiving anti-inflammatory glucocorticoids with oral multistrain probiotics or placebo assessed owner-perceived improvement and airway eosinophilia at baseline and after 2 weeks of treatment. Bronchoalveolar lavage fluid (BALF), blood, OP, and rectal microbial communities were compared using 16S rRNA amplicon sequencing. Real-time PCR for transcription factors, activation markers and cytokines, and IgA ELISAs were evaluated. Statistical analyses used 2-way repeated-measures ANOVA or permutational ANOVA (significance, P < .05). RESULTS: After treatment, there were no significant differences in owner-perceived clinical signs or mean ± SEM BALF eosinophils between groups. There was a significant decrease in rectal α-diversity but not in α- or ß-diversity in BALF, blood, or OP between groups or over time. There were no significant differences in CD25, FoxP3, GATA, Helios, IL-4, IL-5, IL-10, IL-13, IL-17, IFN-γ mRNA, or serum or BALF IgA between groups or over time. CLINICAL RELEVANCE: In asthmatic cats, oral multistrain probiotics failed to improve owner-perceived signs, reduce airway eosinophilia, modify microbial community composition, or alter assessed immune responses versus placebo or over time. Longer treatment, different probiotic composition or delivery (eg, aerosolized), or larger number of cats would represent the next stages of study.

Spatial and temporal clustering of anti-SARS-CoV-2 antibodies in Illinois household cats, 2021-2023.

This study aimed to evaluate the seroprevalence and spatial and temporal clustering of SARS-CoV-2 antibodies in household cats within 63 counties in Illinois from October 2021 to May 2023. The analysis followed a stepwise approach. First, in a choropleth point map, we illustrated the distribution of county-level seroprevalence of SARS-CoV-2 antibodies. Next, spatial interpolation was used to predict the seroprevalence in counties without recorded data. Global and local clustering methods were used to identify the extent of clustering and the counties with high or low seroprevalence, respectively. Next, temporal, spatial, and space-time scan statistic was used to identify periods and counties with higher-than-expected seroprevalence. In the last step, to identify more distinct areas in counties with high seroprevalence, city-level analysis was conducted to identify temporal and space-time clusters. Among 1,715 samples tested by serological assays, 244 samples (14%) tested positive. Young cats had higher seropositivity than older cats, and the third quarter of the year had the highest odds of seropositivity. Three county-level space-time clusters with higher-than-expected seroprevalence were identified in the northeastern, central-east, and southwest regions of Illinois, occurring between June and October 2022. In the city-level analysis, 2 space-time clusters were identified in Chicago's downtown and the southwestern suburbs of Chicago between June and September 2022. Our results suggest that the high density of humans and cats in large cities such as Chicago, might play a role in the transmission and clustering of SARS-CoV-2. Our study provides an in-depth analysis of SARS-CoV-2 epidemiology in Illinois household cats, which will aid in COVID-19 control and prevention.

Identification of risk factors on rabies vaccine efficacy from censored data: Pre-travel tests for dogs and cats from Yaoundé (2005-2015).

Little research is available on acquired immunity to rabies in dogs and cats from Central Africa, particularly regarding the legal movements of pets. Movement of domestic animals from rabies-endemic countries like Cameroon to rabies free areas poses one of the main risks for rabies introduction into rabies-free areas. Thus, the aim of this study was to assess the effect of various risk factors on rabies vaccine efficacy in Cameroonian. Since the dependent variable, rabies neutralizing titres, were censored from above (right-censoring), Generalized Additive Model for Location, Scale and Shape (GAMLSS) was used in the analysis. Overall, 85.7% of dogs and 100% of cats had titres greater than or equal to 0.5 IU/mL, which is considered protective. Additionally, compared to cats, the value of the rabies-neutralizing serum titres in dogs was on average smaller by 2.3 IU/mL. For each additional year of age, the value of the rabies-neutralizing serum titre, on average, increased by approximately 0.14 IU/mL. Finally, for each 30 additional days between the date of the last rabies vaccination and the date of the sampling, the value the rabies neutralizing titre, on average, decreased by approximately 0.10 IU/mL, given the species and age at sampling were equivalent. These results are useful for assessing risk and improving surveillance to prevent the introduction of rabies into a country via the international movement of animals.

Evaluation of a Revised Point-of-Care Test for the Detection of Feline Leukaemia p27 Antigen and Anti-p15E Antibodies in Cats.

The first point-of-care (PoC) test (v-RetroFel®; modified version 2021) determining the presence of FeLV p27 antigen and FeLV anti-p15E antibodies has become recently commercially available to identify different feline leukaemia virus (FeLV) infection outcomes. This study aimed to assess this PoC test's performance concerning FeLV p27 antigen and FeLV anti-p15E antibody detection. Sensitivity, specificity, positive and negative predictive values (PPV, NPV) were assessed after ten minutes (recommended) and 20 min (prolonged) incubation times. The test results were evaluated as either positive or negative. Serum samples from 934 cats were included, originating from Italy (n = 269), Portugal (n = 240), Germany (n = 318), and France (n = 107). FeLV p27 antigen and anti-p15E antibodies were measured by reference standard ELISAs and compared to the PoC test results. The PoC test was easy to perform and the results easy to interpret. Sensitivity and specificity for FeLV p27 antigen were 82.8% (PPV: 57.8%) and 96.0% (NPV: 98.8%) after both, ten and 20 minues of incubation time. Sensitivity and specificity for anti-p15E antibodies were 31.4% (PPV: 71.6%) and 96.9% (NPV: 85.1%) after ten minutes incubation time; sensitivity was improved by a prolonged incubation time (20 min) to 40.0% (PPV: 76.3%), while specificity remained the same (96.9%, NPV: 86.7%). Despite the improved sensitivity using the prolonged incubation time, lower than ideal sensitivities for both p27 antigen and especially anti-p15E antibodies were found, indicating that the PoC test in its current version needs further improvement prior to application in the field.

Comparison of intradermal and serum testing for environmental allergen-specific immunoglobulin E determination in a laboratory colony of cats with naturally acquired atopic syndrome.

BACKGROUND: Allergen testing is used to select antigens included in the desensitisation vaccine. Intradermal skin test (IDT) is the gold standard in cats, yet allergen-specific immunoglobulin (Ig)E serological testing (ASIS) is often used. Feline data are lacking regarding the agreement between IDT and ASIS results. HYPOTHESIS/OBJECTIVES: The first objective of the study was to establish a colony of cats with naturally acquired feline atopic syndrome (FAS). Further objectives were to define their hypersensitivity disorder to detail the allergen tests results, and to assess similarity between the allergen tests. ANIMALS: Thirty-five cats with FAS and 10 control cats. MATERIALS AND METHODS: Enrolled cats went through a five phase-screening and quarantine process before joining the colony. An elimination diet trial was performed on all FAS cats. ASIS and IDT were consecutively performed on all cats under sedation. RESULTS: Reactions to 34 allergens were compiled for the 45 cats. Global sensitivity and specificity of ASIS were 34.7% and 78.9%, respectively. Only flea (ICC = 0.26, p = 0.040) and Dermatophagoides pteronyssinus (ICC = 0.48, p < 0.001) allergens had a significant intraclass correlation (weak agreement). Two FAS cats had negative tests including one cat with a concomitant food allergy. CONCLUSIONS AND CLINICAL RELEVANCE: This study depicts the first reported colony of cats with naturally acquired FAS. This is the first feline study to compare and show the poor agreement between allergen tests with a panel of 34 allergens. This colony also harbours two cats with FAS with negative allergen tests. These may represent the first described cats with an intrinsic form of atopic syndrome.

Tumor-infiltrating lymphocytes (TILs) in feline melanocytic tumors: A preliminary investigation.

The presence and the role of tumor-infiltrating lymphocytes (TILs) in different types of tumors, but particularly in melanoma, has become more and more investigated during the last decade, both in human and veterinary medicine. Melanocytic tumors are quite rare in cats, with diffuse iris melanoma being the most commonly diagnosed in this species. The aim of this study was to characterize the lymphocytic infiltration in feline melanocytic tumors and to analyze their association with the histological features of malignancy recognized in these tumors, as well as with the expression of the most commonly used immunohistochemical markers. Thirty-eight feline melanocytic tumors were retrospectively selected; histological and immunohistochemical characterization of the tumors (histologic criteria of malignancy; S100, Melan A, and PNL2 expression) and of TILs (presence/absence, density, distribution, and grade; CD3, CD20 expression) were performed and associations between them tested. Results showed that TILs grade increased with cellular pleomorphism (P < 0.05) and, within the group of cutaneous melanocytic tumors, also with the mitotic count (P < 0.05). On the other hand, TILs grade was inversely associated with the percentage of neoplastic cells positive for Melan A (P < 0.05) and PNL2 (P < 0.05). Both CD3+ and CD20+ lymphocytes increased significantly with TILs grade and in association with mitotic count, when stratified in low/high quantity. This preliminary study suggests that TILs in feline melanoma may be associated with histologic features of malignancy and loss of melanocytic-specific markers, such as Melan A and PNL2. Further studies, with a larger cohort and follow-up information, are recommended.

Use of feline herpesvirus as a vaccine vector offers alternative applications for feline health.

Herpesviruses are attractive vaccine vector candidates due to their large double stranded DNA genome and latency characteristics. Within the scope of veterinary vaccines, herpesvirus-vectored vaccines have been well studied and commercially available vectored vaccines are used to help prevent diseases in different animal species. Felid alphaherpesvirus 1 (FHV-1) has been characterised as a vector candidate to protect against a range of feline pathogens. In this review we highlight the methods used to construct FHV-1 based vaccines and their outcomes, while also proposing alternative uses for FHV-1 as a viral vector.

Modified-Live Feline Calicivirus Vaccination Reduces Viral RNA Loads, Duration of RNAemia, and the Severity of Clinical Signs after Heterologous Feline Calicivirus Challenge.

Feline calicivirus (FCV) is a common cat virus causing clinical signs such as oral ulcerations, fever, reduced general condition, pneumonia, limping and occasionally virulent-systemic disease. Efficacious FCV vaccines protect against severe disease but not against infection. FCV is a highly mutagenic RNA virus whose high genetic diversity poses a challenge in vaccine design. The use of only one modified-live FCV strain over several decades might have driven the viral evolution towards more vaccine-resistant variants. The present study investigated the clinical signs, duration, and amount of FCV shedding, RNAemia, haematological changes and acute phase protein reaction in SPF cats after subcutaneous modified-live single strain FCV vaccination or placebo injection and two subsequent oronasal heterologous FCV challenge infections with two different field strains. Neither clinical signs nor FCV shedding from the oropharynx and FCV RNAemia were detected after vaccination. After the first experimental infection, vaccinated cats had significantly lower clinical scores, less increased body temperature and lower acute phase protein levels than control cats. The viral RNA loads from the oropharynx and duration and amount of RNAemia were significantly lower in the vaccinated animals. No clinical signs were observed in any of the cats after the second experimental infection. In conclusion, FCV vaccination was beneficial for protecting cats from severe clinical signs, reducing viral loads and inflammation after FCV challenge.

Antibodies to SARS-CoV-2 in dogs and cats, USA.

To provide more complete data on SARS-CoV-2 infections in dogs and cats in the U.S., we conducted a serosurvey on convenience serum samples from dogs (n=1336) and cats (n=956) collected from 48 states of the USA in 2020. An ELISA targeting the antibody against nucleocapsid identified eleven positive and two doubtful samples in cats, and five positive and five doubtful samples in dogs. A surrogate neutralization assay detecting antibodies blocking the attachment of the spike protein to ACE2 was positive with three of the ELISA positive and doubtful samples, and one of 463 randomly selected ELISA negative samples. These four positive samples were confirmed by SARS-CoV-2 virus neutralization testing. All were from cats, in New York, Florida, and New Jersey (n=2). The serosurvey results, one of the largest yet completed on dogs and cats globally, support the OIE and CDC positions that currently there is no evidence that pets play a role in the spread of SARS CoV-2 in humans.

Serological Screening for Antibodies against SARS-CoV-2 in Dutch Shelter Cats.

The COVID-19 pandemic raised concerns that companion animals might be infected with, and could become a reservoir of, SARS-CoV-2. As cats are popular pets and susceptible to Coronavirus, we investigated the seroprevalence of SARS-CoV-2 antibodies in shelter cats housed in Dutch animal shelters during the COVID-19 pandemic. In this large-scale cross-sectional study, serum samples of shelter cats were collected during the second wave of human COVID-19 infections in The Netherlands. Seroprevalence was determined by using an indirect protein-based ELISA validated for cats, and a Virus Neutralization Test (VNT) as confirmation. To screen for feline SARS-CoV-2 shedding, oropharyngeal and rectal swabs of cats positive for ELISA and/or VNT were analyzed using PCR tests. In 28 Dutch animal shelters, 240 shelter cats were convenience sampled. Two of these cats (0.8%; CI 95%: 0.1-3.0%) were seropositive, as evidenced by the presence of SARS-CoV-2 neutralizing antibodies. The seropositive animals tested PCR negative for SARS-CoV-2. Based on the results of this study, it is unlikely that shelter cats could be a reservoir of SARS-CoV-2 or pose a (significant) risk to public health.