Comparison of diagnostic performances of different serological tests for SARS-CoV-2 antibody detection in cats and dogs.

Serosurveillance among animals, including pets, plays an important role in the current coronavirus disease 2019 (COVID-19) pandemic, because severe acute respiratory coronavirus 2 (SARS-CoV-2) infections in animal populations could result in the establishment of new virus reservoirs. Serological assays that offer the required sensitivity and specificity are essential. In this study, we evaluated the diagnostic performance of three different commercially available immunoassays for the detection of SARS-CoV-2 antibodies in pets, namely two ELISA tests for the detection of antibodies against SARS-CoV-2 nucleocapsid [ID Screen SARS CoV-2 double antigen multispecies (Double antigen) and ID Screen® SARS-CoV-2-N IgG indirect ELISA (Indirect)] and one test for the detection of neutralizing antibodies against SARS-CoV-2 receptor-binding-domain [surrogate virus neutralization test (sVNT)]. The obtained results were compared with those of conventional virus neutralization test (VNT), which was regarded as reference method. A total of 191 serum samples were analysed. Thirteen (6.8%) samples showed VNT-positive results. The overall sensitivity was higher for sVNT (100%) compared to nucleocapsid-based ELISA assays (23% for Double antigen and 60% for Indirect). The specificity was 100% for Indirect ELISA and sVNT, when a higher cut-off (>30%) was used compared to the one previously defined by the manufacturer (>20%), whereas the other test showed lower value (99%). The sVNT test showed the highest accuracy and agreement with VNT, with a perfect agreement when the higher cut-off was applied. The agreement between each nucleocapsid-based ELISA test and VNT was 96% for Indirect and 94% for Double antigen. Our findings showed that some commercially available serological tests may lead to a high rate of false-negative results, highlighting the importance of assays validation for the detection of SARS-CoV-2 antibodies in domestic animals.

Utility of the Ratio between Lactate Dehydrogenase (LDH) Activity and Total Nucleated Cell Counts in Effusions (LDH/TNCC Ratio) for the Diagnosis of Feline Infectious Peritonitis (FIP).

BACKGROUND: We tested the hypothesis that the ratio between lactate dehydrogenase activity (LDH) and total nucleated cell counts (TNCC) in effusions may be useful to diagnose feline infectious peritonitis (FIP). METHODS: LDH/TNCC ratio was retrospectively evaluated in 648 effusions grouped based on cytology and physicochemical analysis (step 1), on the probability of FIP estimated by additional tests on fluids (step 2) or on other biological samples (step 3, n = 471). Results of different steps were statistically compared. Receiver Operating Characteristic (ROC) curves were designed to assess whether the ratio identify the samples with FIP "probable/almost confirmed". The cut-offs with the highest positive likelihood ratio (LR+) or Youden Index (YI) or with equal sensitivity and specificity were determined. RESULTS: A high median LDH/TNCC ratio was found in FIP effusions (step1: 2.01) and with probable or almost confirmed FIP (step 2: 1.99; 2.20 respectively; step 3: 1.26; 2.30 respectively). The optimal cut-offs were 7.54 (LR+ 6.58), 0.62 (IY 0.67, sensitivity: 89.1%; specificity 77.7%), 0.72 (sensitivity and specificity: 79.2%) in step 2 and 2.27 (LR+ 10.39), 0.62 (IY 0.65, sensitivity: 82.1%; specificity 83.0%), 0.54 (sensitivity: 82.1%; specificity 81.9%) in step 3. CONCLUSIONS: a high LDH/TNCC ratio support a FIP diagnosis.

Molecular Detection of Feline Coronavirus in Captive Non-Domestic Felids from Zoological Facilities.

Cases of feline infectious peritonitis (FIP), a disease with a high mortality rate caused by the feline coronavirus (FCoV), have been reported in non-domestic felids, highlighting the need for surveys of FCoV in these endangered species. With the aim of adding information on FCoV prevalence in captive non-domestic felids, samples (feces or rectal swabs and, when available, oral swabs, blood, and abdominal effusion) collected between 2019 and 2021 from 38 non-domestic felids from three different zoological facilities of Northern Italy were tested for evidence of FCoV infection via RT-qPCR. Three animals were found to be FCoV positive, showing an overall 7.9% FCoV prevalence ranging from 0% to 60%, according to the zoological facility. FCoV infection was detected in tiger cubs of the same litter, and all of them showed FCoV-positive oral swabs, with low viral loads, whereas in one animal, FCoV presence was also detected in rectal swabs at low FCoV copy numbers. Future studies should be carried out, including samplings from a higher number of captive non-domestic felids, in order to gain a deeper knowledge of FCoV epidemiology within these populations.

Long-term persistence of neutralizing SARS-CoV-2 antibodies in pets.

We monitored the severe acute respiratory syndrome coronavirus 2 antibody response in seven dogs and two cats by using two multispecies ELISA tests, plaque reduction neutralisation test and virus neutralization. SARS-CoV-2 neutralizing antibodies in pets persisted up to 10 months since the first positive testing, thus replicating observations in COVID-19 human patients.

Do Dogs and Cats Passively Carry SARS-CoV-2 on Hair and Pads?

The epidemiological role of domestic animals in the spread and transmission of SARS-CoV-2 to humans has been investigated in recent reports, but some aspects need to be further clarified. To date, only in rare cases have dogs and cats living with COVID-19 patients been found to harbour SARS-CoV-2, with no evidence of pet-to-human transmission. The aim of the present study was to verify whether dogs and cats act as passive mechanical carriers of SARS-CoV-2 when they live in close contact with COVID-19 patients. Cutaneous and interdigital swabs collected from 48 dogs and 15 cats owned by COVID-19 patients were tested for SARS-CoV-2 by qRT-PCR. The time elapsed between owner swab positivity and sample collection from pets ranged from 1 to 72 days, with a median time of 23 days for dogs and 39 days for cats. All samples tested negative, suggesting that pets do not passively carry SARS-CoV-2 on their hair and pads, and thus they likely do not play an important role in the virus transmission to humans. This data may contribute to confirming that the direct contact with the hair and pads of pets does not represent a route for the transmission of SARS-CoV-2.

Absence of SARS-CoV-2 RNA and anti-SARS-CoV-2 antibodies in stray cats.

SARS-CoV-2 positive or seropositive owned cats have been reported worldwide. The detection of seropositive stray cats in the proximity of farms of infected minks, coupled with the demonstration of cat-to-cat transmission in experimental settings, raise the question whether stray cats may have an epidemiological role in the COVID-19 pandemic and may act as sentinel for the circulation of SARS-CoV-2. The aim of this study was to evaluate the presence of SARS-CoV-2 RNA and anti-SARS-CoV-2 antibodies in free roaming cats belonging to colonies located in an area highly affected by the COVID-19 pandemic and to correlate the results with the positivity rate in people sharing the same area. Interdigital, cutaneous, oropharyngeal, nasal and rectal swabs, as well as blood samples, were collected from 99 cats living in colonies and admitted to our hospital for neutering. This caseload corresponds to the 24.2% of the feline population living in the 25 sampled colonies and to the 5.6% of all the free-roaming registered cats. The presence of SARS-CoV-2 RNA in swabs was assessed using real time RT-PCR. Anti-SARS-CoV-2 serum antibodies were assessed using commercially available ELISA kits and confirmed by serum virus neutralization. In people, the SARS-CoV-2 positivity rate ranged from 3.0% to 5.1% (mean rate: 4.1%) and the seropositive rate from 12.1% to 16.3% (mean rate: 14.2%). Most of the colonies were in urban areas and resident cats had frequent contacts with external cats or people. A COVID-19 positive caretaker was found, whereas all the cats were negative for SARS-CoV-2 RNA and seronegative. Although the negative results cannot exclude previous infections followed by decrease of antibodies, this study suggests that colony cats do not have an important epidemiological role in SARS-CoV-2 transmission dynamics. Further studies on larger caseloads are warranted, also in the light of the emerging new viral variants, on a One Health perspective.

Cross-Sectional Serosurvey of Companion Animals Housed with SARS-CoV-2-Infected Owners, Italy.

We conducted a serologic survey among dogs and cats in Italy to detect antibodies against severe acute respiratory syndrome virus 2 (SARS-CoV-2). We found that SARS-CoV-2 seroprevalence was higher among cats (16.2%) than dogs (2.3%). In addition, seroprevalence was higher among animals living in close contact with SARS-CoV-2-positive owners.

Human-to-Cat SARS-CoV-2 Transmission: Case Report and Full-Genome Sequencing from an Infected Pet and Its Owner in Northern Italy.

There have been previous reports of the human-to-cat transmission of SARS-CoV-2, but there are only a few molecular studies that have compared the whole genome of the virus in cats and their owners. We here describe a case of domestic SARS-CoV-2 transmission from a healthcare worker to his cat for which nasopharyngeal swabs of both the cat and its owner were used for full-genome analysis. The results indicate that quarantine measures should be extended to pets living in SARS-CoV-2-infected households.

Concordance between Histology, Immunohistochemistry, and RT-PCR in the Diagnosis of Feline Infectious Peritonitis.

Histology, immunohistochemistry (IHC), and reverse transcription polymerase chain reaction (RT-PCR) have been used to diagnose feline infectious peritonitis (FIP), but no information regarding the comparison of their diagnostic performances on the same organ is available. The aims of this study were to determine the concordance among these tests and to evaluate which combination of tests and organs can be used in vivo. Histology, IHC, and nested RT-PCR (RT-nPCR) for feline coronavirus (FCoV) were performed on spleen, liver, mesenteric lymph node, kidney, large and small intestine, and lung from 14 FIP and 12 non-FIP cats. Sensitivity, specificity, predictive values, likelihood ratios, and concordance were calculated. IHC and RT-nPCR had the highest concordance in lung and liver, histology and IHC in the other organs. The sensitivity of histology, IHC, and RT-nPCR on the different organs ranged from 41.7 to 76.9%, 46.2 to 76.9%, and 64.3 to 85.7%, respectively, and their specificity ranged from 83.3 to 100.0%, 100% and 83.3 to 100.0%. Therefore, IHC is recommended when histology is consistent with FIP. If RT-nPCR is performed as the first diagnostic approach, results should always be confirmed with IHC. Lung or liver provide accurate information regardless of the method, while IHC is preferred to RT-nPCR to confirm FIP in the kidney or intestine.

Feline infectious peritonitis (FIP) and coronavirus disease 19 (COVID-19): Are they similar?

SARS-CoV-2 has radically changed our lives causing hundreds of thousands of victims worldwide and influencing our lifestyle and habits. Feline infectious peritonitis (FIP) is a disease of felids caused by the feline coronaviruses (FCoV). FIP has been considered irremediably deadly until the last few years. Being one of the numerous coronaviruses that are well known in veterinary medicine, information on FCoV could be of interest and might give suggestions on pathogenic aspects of SARS-CoV-2 that are still unclear. The authors of this paper describe the most important aspects of FIP and COVID-19 and the similarities and differences between these important diseases. SARS-CoV-2 and FCoV are taxonomically distant viruses, and recombination events with other coronaviruses have been reported for FCoV and have been suggested for SARS-CoV-2. SARS-CoV-2 and FCoV differ in terms of some pathogenic, clinical and pathological features. However, some of the pathogenic and immunopathogenic events that are well known in cats FIP seem to be present also in people with COVID-19. Moreover, preventive measures currently recommended to prevent SARS-CoV-2 spreading have been shown to allow eradication of FIP in feline households. Finally, one of the most promising therapeutic compounds against FIP, GS-441524, is the active form of Remdesivir, which is being used as one therapeutic option for COVID-19.

Preliminary investigation on feline coronavirus presence in the reproductive tract of the tom cat as a potential route of viral transmission.

OBJECTIVES: Feline infectious peritonitis (FIP) is an immune-mediated disease initiated by feline coronavirus (FCoV) infection. To date, the only proven route of transmission is the faecal-oral route, but a possible localisation of FCoV in the reproductive tract of tom cats is of concern, owing to the involvement of the male reproductive tract during FIP and to the presence of reproduction disorders in FCoV-endemic feline catteries. The aim of the study was to investigate the presence and localisation of FCoV in semen and/or in the reproductive tract of tom cats, and its possible association with seroconversion and viraemic phase. METHODS: Blood, serum, semen and/or testicle samples were obtained from 46 tom cats. Serology was performed on 38 serum samples, nested reverse transcriptase PCR (nRT-PCR) and reverse transcriptase quantitative PCR (RT-qPCR) were performed on 39 blood samples and on 17 semen samples, and histology, immunohistochemistry and nRT-PCR were performed on 39 testicles. RESULTS: Twenty-four of 38 serum samples were positive on serology. Semen samples were negative on RT-PCR and RT-qPCR for FCoV, while all blood samples were negative at both molecular methods, except for one sample positive at RT-qPCR with a very low viral load. All testicles were negative at immunohistochemistry, while six were positive at nRT-PCR for FCoV. Serology and blood PCR results suggest that the virus was present in the environment, stimulating transient seroconversion. FCoV seems not to localise in the semen of tom cats, making the venereal route as a way of transmission unlikely. Although viral RNA was found in some testicles, it could not be correlated with the viraemic phase. CONCLUSIONS AND RELEVANCE: In the light of these preliminary results, artificial insemination appears safer than natural mating as it eliminates the direct contact between animals, thus diminishing the probability of faecal-oral FCoV transmission.