Persistence of porcine rubulavirus in experimentally infected boars

Development of Novel Recombinant Antigens of Nucleoprotein and Matrix Proteins of Porcine orthorubulavirus: Antigenicity and Structural Prediction

Blue eye disease (BED) is a swine viral infection that affects the pork industry of Mexico. Porcine orthorubulavirus (PRV) is the etiological agent, and the hemagglutinin-neuraminidase protein (HN) is characterized as the best antigen for serological tests, although other structural proteins, including the nucleoprotein (NP) and the matrix (M) protein, have been investigated during the infection of members of the Paramyxoviridae family, generating promising results. Herein, for the first time, we successfully produced and characterized both the NP and M proteins of PRV by using a recombinant strategy in the E. coli heterologous system. The ORF of the NP and M genes were cloned in-frame with the pET-SUMO expression vector. Recombinant proteins proved to be a sensitive target to detect seroconversion at 7 days until 28 days in vaccinated mice (BALB/c) by indirect ELISAs. Immunoreactivity was also tested using porcine serum samples, in which antibodies were recognized from early stages to a persistence of PRV infection, which is indicative that these proteins contain properties similar to native antigens. The predicted tertiary structure showed that both proteins have a conserved structure that resembles those found in others Paramyxovirus. Our results pave the way for developing biotechnological tools based on these proteins for the control and prevention of BED.

Persistence and shedding of senecavirus A in naturally infected boars

Senecavirus A (SVA) infection in pigs causes vesicular disease and results in a short viremia and transient shedding of the virus, mainly in oral fluids and feces. Here we describe the consistent prolonged shedding of SVA in the semen of 2 boars, and persistence of SVA within the tonsils and testes of 3 adult boars. Two SVA-infected boars that were identified on a Minnesota sow farm in 2017 shed SVA RNA in semen for >3 mo after an outbreak of vesicular disease had occurred on the farm. SVA was isolated from 1 semen sample collected 9 d after clinical disease began on the farm. The third SVA-infected boar was identified on an Indiana sow farm in 2020. All boars had SVA RNA detected in the testes and tonsils by RT-rtPCR, with lower Ct values obtained for the testes than from the tonsils. All boars had multifocal lymphocytic orchitis with segmental degeneration and atrophy of the germinal epithelium within the seminiferous tubules. One boar also had areas of seminiferous tubule collapse and interstitial fibrosis within the testes. In all boars, in situ hybridization demonstrated the presence of SVA mRNA within cells located basally in the seminiferous tubules of the testes, and within the basal surface epithelial cells, crypt epithelial cells, and subepithelial and parafollicular lymphocytes and histiocytes of the tonsil.

Assessment of the hemagglutinating activity of the Porcine orthorubulavirus

Blue eye disease (BED) in pigs is caused by Porcine orthorubulavirus (PRV) of the Paramyxoviridae family. It is an endemic disease in swine production in the central region of Mexico and causes nervous signs and high mortality in suckling pigs, pneumonia in growing pigs, orchitis in boars and mummification during gestation. PRV hemagglutinates most red blood cells (RBCs) of domestic species. For serological diagnosis, the hemagglutination inhibition test is used, and in this test, guinea pig, bovine and chicken RBCs have been commonly used. In this investigation, hemagglutination with PRV was evaluated using the RBCs of seven domestic species (chicken, bovine, horse, pig, dog, guinea pig and rabbit). In the hemagglutination test, the following parameters were evaluated: temperature (25 °C and 37 °C), bottoms of the wells (V and U), erythrocyte concentration (0.5%, 0.75%, and 1%), and reading time (15, 30, 45, 60 and 90 min). Significant differences (P < 0.001) were found in most of the evaluated treatments. The best hemagglutination results were obtained with chicken, bovine and horse RBCs. The hemagglutination titer is higher (2 dilutions) when using chicken RBCs than when using bovine or horse RBCs. If chicken RBCs are used in the inhibition of hemagglutination, the test will be more sensitive, while it is more specific when bovine or horse RBCs are used. The hemagglutination readings are imprecise when using RBCs from dogs, pigs, guinea pigs and rabbits. RBCs from these species should not be used for the diagnosis or investigation of PRV.

From Ancient to Emerging Infections: The Odyssey of Viruses in the Male Genital Tract

The male genital tract (MGT) is the target of a number of viral infections that can have deleterious consequences at the individual, offspring, and population levels. These consequences include infertility, cancers of male organs, transmission to the embryo/fetal development abnormalities, and sexual dissemination of major viral pathogens such as human immunodeficiency virus (HIV) and hepatitis B virus. Lately, two emerging viruses, Zika and Ebola, have additionally revealed that the human MGT can constitute a reservoir for viruses cleared from peripheral circulation by the immune system, leading to their sexual transmission by cured men. This represents a concern for future epidemics and further underlines the need for a better understanding of the interplay between viruses and the MGT. We review here how viruses, from ancient viruses that integrated the germline during evolution through old viruses (e.g., papillomaviruses originating from Neanderthals) and more modern sexually transmitted infections (e.g., simian zoonotic HIV) to emerging viruses (e.g., Ebola and Zika) take advantage of genital tract colonization for horizontal dissemination, viral persistence, vertical transmission, and endogenization. The MGT immune responses to viruses and the impact of these infections are discussed. We summarize the latest data regarding the sources of viruses in semen and the complex role of this body fluid in sexual transmission. Finally, we introduce key animal findings that are relevant for our understanding of viral infection and persistence in the human MGT and suggest future research directions.

Acute neurologic disease in Porcine rubulavirus experimentally infected piglets

The objective of this study was to evaluate the clinical disease, humoral response and viral distribution of recent Porcine rubulavirus (PorPV) isolates in experimentally infected pigs. Four, 6-piglet (5-days old) groups were employed (G1-84, G2-93, G3-147, and G4-T). Three viral strains were used for the experimental infection: the reference strain LPMV-1984 (Michoacán 1984) and two other strains isolated in 2013, one in Queretaro (Qro/93/2013) and the other in Michoacán (Mich/147/2013). Each strain was genetically characterized by amplification and sequencing of the gene encoding hemagglutinin-neuroamidase (HN). The inoculation was performed through the oronasal and ocular routes, at a dose of 1×10⁶TCID₅₀/ml. Subsequently, the signs were evaluated daily and necropsies were performed on 3 different days post infection (dpi). We recorded all micro- and macroscopic lesions. Organs from the nervous, lymphatic, and respiratory system were analyzed by quantifying the viral RNA load and the presence of the infectious virus. The presence of the viral antigen in organs was evidenced through immunohistochemistry. Seroconversion was evaluated through the use of a hemagglutination inhibition test. In the characterization of gene HN, only three substitutions were identified in strain Mich/147/2013, two in strain LPMV/1984 (fourth passage) and one in strain Qro/93/2013, with respect to reference strain LPMV-84, these changes had not been identified as virulence factors in previously reported strains. Neurological alterations associated with the infection were found in all three experimental groups starting from 3dpi. Groups G1-84 and G3-147 presented the most exacerbated nervous signs. Group G2-93 only presented milder signs including slight motor incoordination, and an increased rectal temperature starting from day 5 post infection (PI). The main histopathological findings were the presence of a mononuclear inflammatory infiltrate (lymphocytic/monocytic) surrounding the ventricles in the brain and focal interstitial pneumonitis with distention of the alveolar sacs in the lungs. PorPV and RNA distribution were identified in the organs of the nervous, lymphatic, and respiratory systems of the piglets analyzed at different times (days 5, 10, and 15 PI). The viral antigen was detected in the brain and lungs in most of the assessed groups. Seroconversion was evident in groups G1-84 and G2-93. Groups G1-84 and G3-147 were the most clinically affected by the experimental infection. Both strains were isolated in the state of Michoacán. The virulence of the new isolates maintains similar characteristics to those reported more than 30 years ago.

Co-infection of classic swine H1N1 influenza virus in pigs persistently infected with porcine rubulavirus

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We analyse the co-infection of swine H1N1 influenza virus and porcine rubulavirus.

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Pigs of the co-infection group presented an increase of clinical signs.

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Interaction of two viruses infection is demonstrated in growing pigs.

Porcine rubulavirus (PorPV) and swine influenza virus infection causes respiratory disease in pigs. PorPV persistent infection could facilitate the establishment of secondary infections. The aim of this study was to analyse the pathogenicity of classic swine H1N1 influenza virus (swH1N1) in growing pigs persistently infected with porcine rubulavirus. Conventional six-week-old pigs were intranasally inoculated with PorPV, swH1N1, or PorPV/swH1N1. A mock-infected group was included. The co-infection with swH1N1 was at 44 days post-infection (DPI), right after clinical signs of PorPV infection had stopped. The pigs of the co-infection group presented an increase of clinical signs compared to the simple infection groups. In all infected groups, the most recurrent lung lesion was hyperplasia of the bronchiolar-associated lymphoid tissue and interstitial pneumonia. By means of immunohistochemical evaluation it was possible to demonstrate the presence of the two viral agents infecting simultaneously the bronchiolar epithelium. Viral excretion of PorPV in nasal and oral fluid was recorded at 28 and 52 DPI, respectively. PorPV persisted in several samples from respiratory tissues (RT), secondary lymphoid organs (SLO), and bronchoalveolar lavage fluid (BALF). For swH1N1, the viral excretion in nasal fluids was significantly higher in single-infected swH1N1 pigs than in the co-infected group. However, the co-infection group exhibited an increase in the presence of swH1N1 in RT, SLO, and BALF at two days after co-infection. In conclusion, the results obtained confirm an increase in the clinical signs of infection, and PorPV was observed to impact the spread of swH1N1 in analysed tissues in the early stage of co-infection, although viral shedding was not enhanced. In the present study, the interaction of swH1N1 infection is demonstrated in pigs persistently infected with PorPV.

Molecular and epidemiological studies of Porcine rubulavirus infection - an overview

Porcine rubulavirus-La Piedad-Michoacan-Mexico virus (PorPV-LPMV) was identified as the causative agent of a viral disease that emerged spontaneously in Mexican swine in the 1980s. Since the report of the initial outbreak of the disease, only one full-length genome from a strain isolated in 1984 (PorPV-LPMV/1984) has been sequenced; sequence data are scarce from other isolates. The genetic variation of this virus that has spread throughout the main endemic region of Mexico is almost a complete mystery. The development of molecular techniques for improved diagnostics and to investigate the persistence, molecular epidemiology, and the possible reservoirs of PorPV are needed. Together, this will provide greater knowledge regarding the molecular genetic changes and useful data to establish new strategies in the control of this virus in Mexico.

Porcine semen as a vector for transmission of viral pathogens

Different viruses have been detected in porcine semen. Some of them are on the list of the World Organization for Animal Health (OIE), and consequently, these pathogens are of socioeconomic and/or public health importance and are of major importance in the international trade of animals and animal products. Artificial insemination (AI) is one of the most commonly used assisted reproductive technologies in pig production worldwide. This extensive use has enabled pig producers to benefit from superior genetics at a lower cost compared to natural breeding. However, the broad distribution of processed semen doses for field AI has increased the risk of widespread transmission of swine viral pathogens. Contamination of semen can be due to infections of the boar or can occur during semen collection, processing, and storage. It can result in reduced semen quality, embryonic mortality, endometritis, and systemic infection and/or disease in the recipient female. The presence of viral pathogens in semen can be assessed by demonstration of viable virus, nucleic acid of virus, or indirectly by measuring serum antibodies in the boar. The best way to prevent disease transmission via the semen is to assure that the boars in AI centers are free from the disease, to enforce very strict biosecurity protocols, and to perform routine health monitoring of boars. Prevention of viral semen contamination should be the primary focus because it is easier to prevent contamination than to eliminate viruses once present in semen. Nevertheless, research and development of novel semen processing treatments such as single-layer centrifugation is ongoing and may allow in the future to decontaminate semen.

Long-term RNA persistence of porcine rubulavirus (PorPV-LPMV) after an outbreak of a natural infection: the detection of viral mRNA in sentinel pigs suggests viral transmission

The persistence of porcine rubulavirus (PorPV-LPMV) in five pigs that had survived an outbreak of a natural infection was determined. After the resolution of the outbreak, each animal was housed in an isolation pen together with one sentinel pig. Approximately every 2 months thereafter one group of animals was euthanized and tissue samples taken for virological and serological analysis. Infectious virus was not isolated from any samples; antibodies to PorPV-LPMV were detected in convalescent pigs by virus neutralisation test and blocking ELISA but not in sentinel pigs. PorPV-LPMV mRNA of the nucleoprotein (NP) and phosphoprotein (P) genes was detected by a nested polymerase chain reaction (nPCR) in samples of trigeminal and optic nerves, cervical spinal cord, tonsils, salivary gland, lung and pancreas from convalescent pigs. mRNA was also detected in the midbrain, corpus callosum, or olfactory bulb in four out of five pigs by nRT-PCR, this result was confirmed by the sequencing of a 260bp PCR product of P gene region. The highest average viral copies/μg of total RNA occurred in the olfactory bulb and pancreas tissues of convalescent pigs and midbrain, tonsil and pancreas of sentinel pigs housed with the convalescent pigs. Satellitosis and gliosis of the midbrain, olfactory bulb, corpus callosum, medulla oblongata or choroid plexus were microscopically observed in four convalescent pigs. The control pig remained negative in all tests. The results indicate that PorPV-LPMV mRNA persists and induces a durable humoral immune response in pigs that have recovered from a natural infection. After a possible reactivation of the virus, it was transmitted to sentinel pigs in contact with the convalescent pigs.

Viral antibody dynamics in a chiropteran host

Bats host many viruses that are significant for human and domestic animal health, but the dynamics of these infections in their natural reservoir hosts remain poorly elucidated. In these, and other, systems, there is evidence that seasonal life-cycle events drive infection dynamics, directly impacting the risk of exposure to spillover hosts. Understanding these dynamics improves our ability to predict zoonotic spillover from the reservoir hosts. To this end, we followed henipavirus antibody levels of >100 individual E. helvum in a closed, captive, breeding population over a 30-month period, using a powerful novel antibody quantitation method. We demonstrate the presence of maternal antibodies in this system and accurately determine their longevity. We also present evidence of population-level persistence of viral infection and demonstrate periods of increased horizontal virus transmission associated with the pregnancy/lactation period. The novel findings of infection persistence and the effect of pregnancy on viral transmission, as well as an accurate quantitation of chiropteran maternal antiviral antibody half-life, provide fundamental baseline data for the continued study of viral infections in these important reservoir hosts.

Respiratory disease in growing pigs after Porcine rubulavirus experimental infection

The aim of this study was to analyze the pathogenicity and distribution of Porcine rubulavirus (PorPV) in the respiratory tract of experimentally infected pigs. Nine 6-week-old pigs were infected with PorPV and examined clinically. Blood, nasal swab, and tissue samples were collected on different days post-infection (DPI). The humoral immune responses and viral loads were evaluated. The infected pigs exhibited an increase in the respiratory clinical signs. In addition, the excretion of PorPV was extended to 23 DPI in the nasal fluid. The distribution of PorPV in the respiratory tract tissues was extended until the end of the experiment; soft palate tonsil and lymph nodes exhibited high viral loads. The major microscopic lesions observed in the lungs corresponded to interstitial pneumonia and hyperplasia of the associated lymphoid tissue. In conclusion, PorPV infection causes a pneumonic disease characterized by a prolonged virus excretion and high viral load in the lymphoid tissues.