Serological survey of veterinarians to assess the zoonotic potential of three emerging swine diseases in Mexico.

We conducted an immunological assay of blood samples taken from 85 swine-specialist veterinarians attending the Congress of the Mexican Association of Swine Specialist Veterinarians in Mexico in 2011. Serum samples were assayed for Porcine rubulavirus (PorPV), Encephalomyocarditis virus (EMCV) and Leptospira spp. antibodies. Using a hemagglutination inhibition test, we registered 2.3% and 27% seropositivity for PorPV and EMCV, respectively. Using viral neutralization tests, we registered 5.8% and 47% seropositivity for PorPV and EMCV, respectively. For Leptospira spp., we registered a seropositivity of 38.8%. The variables (sex, age, years of exposure, number of visited farms, biosecurity level and region) showed no significant effect (P > 0.05) on the seropositivity for EMCV, PorPV and Leptospira spp. except for number of visited farms on HI seropositivity for EMCV (P < 0.05; odds ratio: 1.38). The data obtained provide information on the epidemiology of emerging diseases with zoonotic potential in occupational risk groups.

Comparative study of the pathogenic properties of a Belgian and a Greek encephalomyocarditis virus (EMCV) isolate for sows in gestation.

Thirteen conventional sows were inoculated between 61 and 92 days of gestation with a Belgium or a Greek EMCV isolate to investigate the difference in pathogenicity of both strains for sows in gestation. The Belgian EMCV strain was isolated from the offspring of a sow with productive failure and without myocardial lesions. The Greek strain was isolated from a 3-month-old pig with prominent myocardial lesions. The present study demonstrates a transplacental virus transmission with fetal death following an infection of the sows in gestation with both isolates. The fetal pathogenicity was more severe with the Greek strain than with the Belgian isolate. No myocardial lesions were noticed.

Involvement of the IRF-1 transcription factor in antiviral responses to interferons.

The mechanisms underlying interferon (IFN)-induced antiviral states are not well understood. Interferon regulatory factor-1 (IRF-1) is an IFN-inducible transcriptional activator, whereas IRF-2 suppresses IRF-1 action. The inhibition of encephalomyocarditis virus (EMCV) replication by IFN-alpha and especially by IFN-gamma was impaired in cells from mice with a null mutation in the IRF-1 gene (IRF-1-/- mice). The IRF-1-/- mice were less resistant than normal mice to EMCV infection, as revealed by accelerated mortality and a larger virus titer in target organs. The absence of IRF-1 did not clearly affect replication of two other types of viruses. Thus, IRF-1 is necessary for the antiviral action of IFNs against some viruses, but IFNs activate multiple activation pathways through diverse target genes to induce the antiviral state.

Reproductive failure in sows following experimental infection with a Belgian EMCV isolate.

In this study, a transplacental infection with fetal death was demonstrated following inoculation of pregnant sows with a Belgian encephalomyocarditis virus (EMCV) isolate. Eight multiparus sows were inoculated between 60 and 92 days of gestation with this EMCV-isolate to investigate its ability to cause reproductive failure in sows. Virus persistence and antibody titre in their offspring were also studied. Only the two sows inoculated at 60 days of gestation showed premature farrowing, but all sows seroconverted to EMCV. Virus was recovered from the offspring of all sows at the time of farrowing, but not from every piglet born. One month after birth EMCV could be isolated from all the piglets examined. These results can help in a better understanding of the spread of the disease in piggeries.

Persistence of the D variant of encephalomyocarditis virus in the ICR-Swiss mouse.

The D variant of encephalomyocarditis virus (EMCV-D) is used in the murine model to study virus-induced, acute-onset diabetes mellitus (IDDM) and myocarditis. In this model, viral replication and disease occur within seven days post infection (p.i.), and by Day 10 p.i., no infectious virus is detectable. The present study examined the possibility that EMCV-D persists in ICR-Swiss mice after the acute infection is resolved. The data show that viral antigen is detected at 28 days p.i. within the pancreatic islets of 8/10 males and 13/14 females, and within the heart valves of all animals tested. Histologic examination of the organs at 28 days p.i. suggests the development of chronic obstructive pancreatitis, and shows almost fully healed lesions in the myocardium. These observations indicate that the murine model for the study of EMCV-D induced IDDM may be extended to investigate chronic pancreatitis and heart-valve disease.

Experimental encephalomyocarditis virus infection in pigs.

A field isolate of Encephalomyocarditis (EMC) virus was inoculated intravenously into 8 pigs. Four animals died at post inoculation day (PID) 2, the remaining being sacrificed at PID 5, 7, 11 and 15. Two control, in-contact pigs were sacrificed at PID 19. Virus was isolated from leucocytes and nasal swabs until PID 4, from rectal swabs until PID 2 and, in the pigs found dead at PID 2, from several organs. EMC virus was further isolated from brain and spleen of the pig sacrificed at PID 7. One of the 2 control pigs became infected: virus was isolated from nasal swabs at days 6 and 7 and from leucocytes at day 4 of the experiment. Serum-neutralizing (SN) antibody was detected in the injected pigs starting from PID 4; two days later, it was also revealed in the infected, in-contact control. To our knowledge, this is the first report of an experimental transmission of EMC virus infection in pigs by contact exposure.