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ABSTRACT Porcine deltacoronavirus (PDCoV) is an infectious disease that causes diarrhoea in pigs of different ages; however, piglets are more susceptible. PDCoV was first reported in 2012 in China and Hong Kong. Later, it was first reported in the USA in 2014 and in Mexico in 2019. Several studies have shown that M protein is highly conserved and, therefore, suitable for diagnostic systems. In this study, for the first time, an indirect enzyme‐linked immunosorbent assay (iELISA) based on a recombinant M protein (rM‐PDCoV) was developed to evaluate the seroprevalence of PDCoV in four states in Mexico. High sensitivity (83%) and specificity (100%) were observed for the iELISA. The kappa index calculated a nearly perfect agreement (0.8831) compared to the Western blot (gold standard test), suggesting acceptable statistical value support. In this study, 50.38% of the serum samples from backyard pigs were PDCoV‐positive. The serological comparison showed that PDCoV/PEDV coinfections occurred in 31.98% of the analysed sera. These results can enrich our understanding of how this virus spreads and enable the evaluation of PDCoV infections. Moreover, it highlights the importance of continually investigating the seroprevalence of PDCoV in Mexico because there is also no information about the current prevalence of the disease. Developed an iELISA with the PDCoV recombinant protein M to sero‐evaluate 516 samples from 4 different states of Mexico and serologically compare PDCoV/PEDV.

Many rabies endemic-countries have recognized rabies as a public health problem that can be eliminated. As a result, some countries have started implementing small-scale vaccination programs with the aim of scaling them up. Post-vaccination serological monitoring is crucial to assess the efficacy of these programs. The recommended serological tests, the rapid fluorescent focus inhibition test, and the fluorescent antibody virus neutralization (FAVN) are accurate; however, the procedures require considerable expertise and must be carried out in high containment facilities, which are often not available in rabies endemic countries. Given these constraints, enzyme linked immunosorbent assays (ELISAs) have been considered as alternative methods to neutralization tests. This is the first study to evaluate, under field conditions, the performance of the commercial rabies indirect-ELISA (iELISA), the PlateliaTM Rabies II kit ad usum Veterinarium kit, using sera from domestic dogs. Serum samples were collected from two groups of community dogs in northern Tanzania: i) dogs with no history of vaccination against rabies (n = 100) and ii) dogs vaccinated with the Nobivac Canine Rabies® vaccine (n = 101) four weeks previously. When compared to the gold standard FAVN test, the iELISA was found to be 99% specific and 98% sensitive and there was a significant correlation between the two tests (p < 0.001, r = 0.92). Given these findings, we conclude that the PlateliaTM Rabies II kit ad usum Veterinarium can be considered a valuable tool for the rapid assessment of vaccination status of animals in vaccination programs.

Toxoplasmosis caused by Toxoplasma gondii ( T. gondii ) is a zoonotic disease with great medical and veterinary significance. Felines, the definitive hosts of T. gondii , play a crucial role in the transmission of toxoplasmosis. The booming pet industry has led to more cats and cat-owning families, increasing the risk of toxoplasmosis transmission from animals to humans. Monitoring feline T. gondii infection accurately is crucial for reducing transmission risks. However, existing diagnostic methods focus on detecting whether cats are infected with T. gondii but fail to trace whether feline toxoplasmosis infections originate from oocysts or cysts. In this study, we assessed four late-stage development abundant proteins that were highly expressed specifically in sporulated oocysts to evaluate their specificity in binding to cat anti- T. gondii -oocyst serum. The LEA880 protein can only specifically react with cat anti- T. gondii -oocyst positive serum, but not with cat anti- T. gondii -cyst positive serum or negative cat serum. The optimized indirect enzyme-linked immunosorbent assay (iELISA) method based on the LEA880 protein exhibits good specificity and sensitivity in detecting T. gondii oocyst infection in cats.

Background Difficulty in detection of silent carriers of Streptococcus equi is a key reason for its continued spread to immunologically naïve groups of horses. Objective To determine whether clinical examination, markers of inflammation, or serology differentiate silent carriers of S. equi in recovered comingled horses. Animals Ninety‐eight warmblood yearlings and 72 unaffected mares on a large breeding farm (outbreak A), 38 mature Icelandic horses at a riding stable (outbreak B), and 27 mixed breed horses at a boarding stable (outbreak C). Methods Prospective observational study 6 months to 2 years after strangles outbreaks. Carriers were defined as any animal positive on culture or qPCR to S. equi from nasopharyngeal lavage or guttural pouch endoscopy and lavage. Most horses had complete physical exams and 1 group included evaluation of white blood cell counts and serum amyloid A. Sera from all horses was tested for antibodies to antigens A and C of S. equi using an enhanced indirect ELISA. Descriptive statistics were calculated. Data were compared using paired t tests, Wilcoxon ranked test, chi square, or the Fishers exact test. Significance was set at P < .05. Results Apart from weanlings at 6 months in outbreak A, there was no significant association between any clinical markers or serology with carrier state (P = .06‐1). Moreover, 3/12 culture positive carriers were seronegative to S. equi. Conclusions and Clinical Importance Silent carriers of S. equi do not differ clinically or on markers of inflammation to their noncarrier herd‐mates. Moreover, serology alone will not distinguish carriers in comingled horses.

Background Antibiotic treatment of horses with strangles is reported to impair the development of immunity to subsequent exposure to Streptococcus equi ssp equi (S. equi). However, apart from a single clinical report, evidence‐based studies for this hypothesis are lacking. Hypothesis/Objective To determine whether penicillin treatment during clinical strangles influences the development or persistence of seropositivity to S. equi‐specific antibodies. Animals A natural outbreak of strangles with 100% morbidity in 41 unvaccinated mature Icelandic horses. Methods A prospective longitudinal study of acute clinical strangles from onset through full recovery approximately 10 months after the index case. Horses were monitored clinically 6 times for S. equi, as well as serologically for antibodies to antigens A and C of S. equi using an enhanced indirect ELISA. Seven horses received penicillin within 11 days of onset of fever (Group 1), 5 between 16 and 22 days after onset of fever (Group 2), and the remainder (Group 3, n = 29) received no antibiotics during clinical disease. The proportions of seropositive horses in each group were compared using an extension of Fisher's exact test with P < .05 as the level of significance. Results Although all horses were seropositive to S. equi within 2 months of the index case, significantly fewer horses treated early (Group 1) remained seropositive by 4 to 6 months (P = .04 and .02, respectively). Conclusions and Clinical Importance Findings support earlier suggestions that penicillin administered during acute strangles can interfere with persistence of humoral immunity to S. equi.

The tick Rhipicephalus microplus is responsible for the transmission of Anaplasma marginale, which causes hemolytic anemia, abortion, decreased production, and mortality in cattle in Brazil. However, A. marginale can also persist in cattle herds without any clinical signs. This study investigated the relationship between the number of ticks present on each cattle and the circulating number of A. marginale msp1β gene copies in the blood of Brangus and Nellore cattle reared in the Brazilian Cerrado through a year period. Twenty-three animals (11 Brangus and 12 Nellore) were raised for 12 months with ticks counted every 18 days, and blood collected every 36 days. Blood sera was used for total antigen iELISA, genomic DNA was extracted from whole blood by the phenol/chloroform method and then analyzed by PCR to confirm A. marginale presence with the msp5 gene. Positive samples were quantified by qPCR using msp1β gene. Brangus cattle presented 4.5 fold more ticks than Nellore group. Although Brangus cattle carried a higher overall A. marginale msp1β gene presence than Nellore cattle, no relationship of tick count and copy number could be achieved due to high variability in copy number. Moreover, both breeds showed similar weight gain and a similar serological pattern throughout the year. None of the animals showed any clinical signs of anaplasmosis during the experimental period, indicating that a low level of tick infestation may be sufficient to maintain a stable enzootic situation.

Trichinella is a zoonotic nematode traditionally detected worldwide in both domestic and wild animals. In South America, along with the occurrence of this parasite in domestic pigs and wild boars, there are reports of infection in wild carnivores. Brazil is considered free of the domestic cycle of Trichinella, but there is unpublished serological evidence of infection in wild boars, which changed the Brazilian status in OIE regarding the disease after an official communication. We investigated Trichinella spp. infection in wild boars and wild carnivores in the Southeastern region of Brazil. A total of 136 samples were tested, 121 from wild boars and 15 from wild carnivores. Artificial enzymatic digestion (AED) tests were performed on muscle samples from 37 wild boars and 15 wild carnivores, and 115 serum samples from wild boars were tested by iELISA. Seven serum samples from wild boars tested positive (7/115 = 6.1%, 95% CI 3.0–12.0), but no larvae were found in the AED. There was no significant difference between sex, age, and location of the samples. The serological results suggest that a wild cycle of Trichinella spp. may occur in Brazil, but further analyses should be performed to confirm the presence of the parasite.

Porcine deltacoronavirus (PDCoV) is an emergent swine coronavirus which infects cells from the small intestine and induces watery diarrhea, vomiting and dehydration, causing mortality in piglets (>40%). The aim of this study was to evaluate the antigenicity and immunogenicity of the recombinant membrane protein (M) of PDCoV (rM-PDCoV), which was developed from a synthetic gene obtained after an in silico analysis with a group of 138 GenBank sequences. A 3D model and phylogenetic analysis confirmed the highly conserved M protein structure. Therefore, the synthetic gene was successfully cloned in a pETSUMO vector and transformed in E. coli BL21 (DE3). The rM-PDCoV was confirmed by SDS-PAGE and Western blot with ~37.7 kDa. The rM-PDCoV immunogenicity was evaluated in immunized (BLAB/c) mice and iELISA. The data showed increased antibodies from 7 days until 28 days (p < 0.001). The rM-PDCoV antigenicity was analyzed using pig sera samples from three states located in “El Bajío” Mexico and positive sera were determined. Our results show that PDCoV has continued circulating on pig farms in Mexico since the first report in 2019; therefore, the impact of PDCoV on the swine industry could be higher than reported in other studies.

Background Salmonella as an important food-borne zoonotic bacterial pathogen, infection in ducks is a recessive infection, however, it can also cause high mortality and threat to food safety. Preventing and controlling the infection and transmission of Salmonella in ducks critically require rapid and sensitive detection method. Full-length Salmonella -specific protein PagN was induced and expressed in E.coil BL21 and was purified as an antigen to establish an indirect enzyme-linked immunosorbent assays (iELSA) detection kit. Results The recombinant PagN protein has a molecular weight of 43 kDa containing a His-tag, was recognized by an anti- Salmonella positive serum by Western blot assay. The optimal concentration of PagN as a coating antigen in the iELISA was 1 μg/mL, and the optimal dilution of enzyme-labeled secondary antibody was 1:4000 (0.025 μg/mL). The cutoff OD 450 value was established at 0.268. The iELISA kit showed high selectivity since no cross-reaction with E. coli, Staphylococcus aureus and Streptococcus was observed. iELISA method and Dot-blot test were performed on 100 clinical sera samples collected from duck farms, and the actual coincidence rate was 89% (89/100). 613 duck serum samples from 3 different farms were tested using established method and commercial ELISA kit. The concordance between the two methods was 94.1%. Conclusion Anti-PagN based iELISA can serve as a useful tool for diagnosis of Salmonella infection.

Background: Brucellosis is a zoonotic disease that causes substantial public health problems and endangers the development of animal husbandry in endemic areas. Early diagnosis of infected animals and humans is a crucial step in reducing the incidence of brucellosis. In this study, we designed different combinations of Brucella major outer membrane proteins (omps) including omp10, Omp16, omp19, omp25, omp31 and BP26 as antigens and evaluated their efficiency in serodiagnosis for brucellosis. The efficiency assay was conducted using the method of indirect enzyme-linked immunosorbent assay (iELISA) together with a collection of brucellosis-positive sera and healthy sera from multiple species (161 from human, 120 from goat and 144 from cattle). The diagnostic effectiveness of each omp combination was analyzed by receiver operating characteristic (ROC) curve with the software GraphPad Prism version 6.05. Results: Hie omp25/omp31/BP26 combination showed the best efficiency in diagnosis for human brucellosis. The area under the ROC curve (AUC) was 0.995 and, compared with the serum tube agglutination test (SAT) and the Rose Bengal plate agglutination test (RBPT), the positive and negative diagnostic accuracies of iELISA were 94.59% (105/111) and 100.0% (50/50), respectively. Evaluation of the 120 goat and 144 cattle serum samples showed that the best combination for diagnosing both omp31/BP26, the AUC was 0.9262 in goat and 0.9344 in cattle, and compared with those of SAT and RBPT, the positive and negative diagnostic accuracies in goat were 72.73% (48/66) and 100.0% (54/54), respectively. The positive and negative diagnostic accuracies in cattle were 79.79% (75/94) and 100.0% (50/50), respectively. Cross-reaction assays showed that omp25/omp31/BP26 and omp31/BP26 do not cross with other common pathogens. Conclusion: The results indicated that combinations of omps, as protein antigens, can be used to diagnose brucellosis with high accuracy in human, goat and cattle. Keywords: brucellosis, diagnosis, outer membrane proteins, iELISA