In the early 1980s, a highly contagious viral hemorrhagic fever in rabbits (Oryctolagus cuniculus) emerged, causing a very high rate of mortality in these animals. Since the initial occurrence of the rabbit hemorrhagic disease virus (RHDV), several hundred million rabbits have died after infection. The emergence of genetically-different virus variants (RHDV GI.1 and GI.2) indicated the very high variability of RHDV. Moreover, with these variants, the host range broadened to hare species (Lepus). The circulation of RHDV genotypes displays different virulences and a limited induction of cross-protective immunity. Interestingly, juvenile rabbits (<9 weeks of age) with an immature immune system display a general resistance to RHDV GI.1, and a limited resistance to RHDV GI.2 strains, whereas less than 3% of adult rabbits survive an infection by either RHDV GI.1. or GI.2. Several not-yet fully understood phenomena characterize the RHD. A very low infection dose followed by an extremely rapid viral replication could be simplified to the induction of a disseminated intravascular coagulopathy (DIC), a severe loss of lymphocytes—especially T-cells—and death within 36 to 72 h post infection. On the other hand, in animals surviving the infection or after vaccination, very high titers of RHDV-neutralizing antibodies were induced. Several studies have been conducted in order to deepen the knowledge about the virus’ genetics, epidemiology, RHDV-induced pathology, and the anti-RHDV immune responses of rabbits in order to understand the phenomenon of the juvenile resistance to this virus. Moreover, several approaches have been used to produce efficient vaccines in order to prevent an infection with RHDV. In this review, we discuss the current knowledge about anti-RHDV resistance and immunity, RHDV vaccination, and the further need to establish rationally-based RHDV vaccines.

Inactivated strain-specific vaccines have been successfully used to control rabbit haemorrhagic disease (RHD) caused by RHDV-2 in the rabbit industry. It is unknown whether and how vaccination of breeding does contributed to protect the population of young susceptible rabbit kits. The present study investigates whether the immunity against RHDV-2 produced by vaccination of breeding does is transmitted to their progeny and its dynamic once inherited by kits. For this purpose, New Zealand female rabbits of 8–9 weeks of age were allocated into 2 groups of 40 subjects each and bred during 6 reproductive cycles. The first experimental group was vaccinated with a commercially available inactivated vaccine against RHDV-2 whereas the second group was inoculated with PBS. Moreover, the present study was also meant to identify the mechanisms of transmission of that maternal immunity. For this reason, rabbit kits of vaccinated and non-vaccinated breeding does were cross-fostered before milk uptake. The RHDV-2 antibody response was monitored in the blood serum of breeding does and of their kits by competition ELISA (cELISA) and solid-phase ELISA (spELISA). Since it has been clearly demonstrated that cELISA positive rabbits are protected from RHD, we avoided the resorting of the challenge of the kits with RHDV-2. Results showed that RHDV-2 antibodies were inherited by kits up to one year from vaccination of breeding does. Once inherited, the maternally derived antibody response against RHDV-2 lasted at least until 28 days of life. Finally, the study also elucidated that the major contribution to the maternal derived immunity against RHDV-2 in kits was provided during gestation and probably transmitted through transplacental mechanisms although lactation provided a little contribution to it. The present study contributed to elucidate the characteristics of the maternal antibody immunity produced by vaccination and its mechanisms of transmission.

Early detection and treatment of cases of Leishmania infantum infection are critical in controlling the spread of the disease in dogs. Several serological methods are available to support the diagnosis of canine leishmaniosis. The immunofluorescence antibody test (IFAT) and enzyme-linked immunosorbent assay (ELISA) are the main tests used by clinicians. High antibody levels are associated with severe parasitism and disease and are diagnostic of clinical leishmaniosis. Conversely, the presence of low antibody levels is not necessarily indicative of disease and may be more difficult to detect by serological tests. The aim of this study was to evaluate and compare the diagnostic performance of four commercially available serological tests, including ELISAs (CIVTEST® CANIS LEISHMANIA short and standard protocols), LEISHMANIA-ELISA DOG®, ELISA/S7® and MegaFLUO®LEISH IFAT, for the detection of specific antibodies against L. infantum antigens in dogs in different states of infection. Canine sera samples from seropositive sick infected dogs (n = 75), seropositive apparently healthy dogs (n = 48), and seronegative apparently healthy dogs from a high endemic area (Cadiz, n = 40) and seronegative apparently healthy dogs from very low endemic area of L. infantum infection (Asturias, n = 40) were classified based on the results of an in-house UAB ELISA as a reference test. The positive percent of agreement (PPA) and negative percent of agreement (NPA) observed for each test were as follows: CIVTEST® standard (93.4 %, 100 %) on 202 samples tested, CIVTEST® short (84.4 %, 100 %) on 202 samples tested, LEISHMANIA-ELISA DOG® (81.8 %, 72.2 %) on 138 samples tested, ELISA/S7® (34.8 %, 45 %) on 195 samples tested and MegaFLUO®LEISH IFAT (100 %, 100 %) on 203 samples tested, respectively. The accuracy was as follows: CIVTEST® standard (0.96), CIVTEST® short (0.91), LEISHMANIA-ELISA DOG® (0.77), ELISA/S7® (0.39), and MegaFLUO®LEISH IFAT (1). The Cohen´s Kappa index (K) from best to worst was: MegaFLUO®LEISH IFAT (K = 1), CIVTEST® standard (K = 0.92), CIVTEST® short (K=0.81), LEISHMANIA-ELISA DOG® (K =0.54), and ELISA/S7® (K=-0.19). Finally, the area under the receiver operating characteristic curve (AUC-ROC), in the ELISAs test, ordered from the maximum to the minimum value was: CIVTEST® short (1), CIVTEST® standard (0.99), LEISHMANIA-ELISA DOG® (0.87), and S7® (0.37). In conclusion, this study demonstrated that the diagnostic performance of the commercially available ELISA tests against L. infantum antigen can vary widely. Moreover, it highlights the fact that CIVTEST® CANIS LEISHMANIA is a reliable test to support the diagnosis of canine leishmaniosis in clinical settings.

Oseltamivir is a common therapy against influenza A virus (IAV) infections. The acquisition of oseltamivir resistance (OR) mutations, such as H275Y, hampers viral fitness. However, OR H1N1 viruses have demonstrated the ability to spread throughout different populations. The objective of this work was to compare the fitness of two strains of OR (R6 and R7) containing the H275Y mutation, and a wild-type (F) pandemic influenza A (H1N1) 2009 (pdm09) virus both in vitro and in vivo in mice and to select one OR strain for a comparison with F in ferrets. R6 showed faster replication and pathogenicity than R7 in vitro and in mice. Subsequently, R6 was selected for the fitness comparison with the F strain in ferrets. Ferrets infected with the F virus showed more severe clinical signs, histopathological lung lesions, and viral quantification when compared to OR R6-infected animals. More importantly, differential viral kinetics correlated with differential pro-inflammatory host immune responses in the lungs of infected ferrets, where OR-infected animals developed a protective higher expression of type I IFN and Retinoid acid Inducible Gene I (RIG-I) genes early after infection, resulting in the development of milder disease. These results suggest the presence of early specific viral-host immune interactions relevant in the development of influenza-associated lung pathology.

Neonatal diarrhea causes significant economic losses in swine production by reducing average daily weight gain (ADWG) and increasing piglet mortality, with Clostridioides difficile (CD) and Clostridium perfringens type A (CPA) being the most common causes. The aim of this study was to evaluate the efficacy of a new commercial vaccine against these agents to minimize diarrhea, pre-weaning mortality, and its negative consequences on weight performance in suckling piglets under field conditions. The study consisted of two randomized, double-blind, negative-controlled field trials (Study A and B) focusing on clinically healthy pregnant sows from commercial pig farms experiencing recurrent neonatal diarrhea. In the meta-analysis of both farms, the control group showed lower performance compared to the vaccine group (least squares means differences) for ADWG (−14.5 g/day, p < 0.001), body weight (−0.33 kg, p < 0.001), and underweight piglets at weaning (6.94%, p = 0.011). The number of piglets with diarrhea (9.76%, p < 0.001) and the percentage of piglets treated with antibiotics for diarrhea (6.09%, p = 0.016) were lower in vaccinated animals compared to controls. No significant differences in pre-weaning mortality were observed. The results of this study suggest that the new commercial vaccine against CD and CPA reduces the incidence of neonatal diarrhea and the associated use of antibiotics, while positively impacts the growth performance of suckling piglets.