Foot-and-Mouth Disease Seroprevalence in Cattle in Eritrea.

Information about seroprevalence of foot-and-mouth disease (FMD) and virus serotypes in Eritrea is unavailable, but is very important as it may guide the choice of intervention measures including vaccination to be implemented. We carried out a cross-sectional study from February to June 2011 in Eritrea with a two-stage cluster design, sampling cattle in 155 villages with the objective of determining the seroprevalence of FMD in four administrative regions of the country. We analysed cattle sera (n = 2429) for FMD virus antibodies using the non-structural ELISA (NS ELISA) and virus neutralization test (VNT). The overall seroprevalence was 26% and 30% for the NS ELISA and VNT, respectively. FMD virus serotypes O (14%) and A (11%) were the most prevalent. Gash Barka showed the highest (39%) seroprevalence both in NS ELISA and VNT compared to the other three administrative regions. Strategic FMD virus vaccination with type O and A (matching circulating strains) in combination of zoo-sanitary measures would be the best control option for Eritrea which could be started in areas where the disease is less endemic.

Transmission characteristics and optimal diagnostic samples to detect an FMDV infection in vaccinated and non-vaccinated sheep.

We wanted to quantify transmission of FMDV Asia-1 in sheep and to evaluate which samples would be optimal for detection of an FMDV infection in sheep. For this, we used 6 groups of 4 non-vaccinated and 6 groups of 4 vaccinated sheep. In each group 2 sheep were inoculated and contact exposed to 2 pen-mates. Viral excretion was detected for a long period (>21 days post-inoculation, dpi). Transmission of FMDV occurred in the non-vaccinated groups (R0=1.14) but only in the first week after infection, when virus shedding was highest. In the vaccinated groups no transmission occurred (Rv<1, p=0.013). The viral excretion of the vaccinated sheep and the viral load in their pens was significantly lower than that of the non-vaccinated sheep. FMDV could be detected in plasma samples from 12 of 17 infected non-vaccinated sheep, for an average of 2.1 days, but in none of the 10 infected vaccinated sheep. In contrast, FMDV could readily be isolated from mouth swab samples from both non-vaccinated and vaccinated infected sheep starting at 1-3 dpi and in 16 of 27 infected sheep up till 21 dpi. Serologically, after 3-4 weeks, all but one of the infected sheep were detected using the NS-ELISA. We conclude that vaccination of a sheep population would likely stop an epidemic of FMDV and that the use of mouth swab samples would be a good alternative (instead of using vesicular lesions or blood samples) to detect an FMD infection in a sheep population both early and prolonged after infection.

Intradermal vaccination of pigs against FMD with 1/10 dose results in comparable vaccine efficacy as intramuscular vaccination with a full dose.

The aim of this study was to investigate whether intradermal (ID) vaccination against foot-and-mouth disease (FMD) is suitable as an alternative for the usually used intramuscular (IM) route. We compared vaccine efficacy in groups of pigs in which vaccine administration differed with respect to antigen payload of the vaccine, administrated volume and administration route. When compared with pigs that were IM vaccinated with a full dose vaccine with a standard antigen payload, pigs vaccinated ID with 1/10 dose of the same vaccine were equally protected against clinical disease and subclinical virus shedding. The ID vaccinated pigs were protected against virus shedding at a significant lower VN-titre as compared to IM vaccinated pigs, suggesting that immune responses other than neutralising antibodies also contributed to protection. We conclude that the ID route might be a good alternative for IM application, as ID application might induce a very efficient immunological response against FMD and, moreover, because the dose required by the ID route is lower compared to the IM route, ID application may reduce the production costs per dose of FMD vaccine markedly.

Comparison of immune responses after intra-typic heterologous and homologous vaccination against foot-and-mouth disease virus infection in pigs.

This study compares the immune responses and protection induced by intra-typic heterologous vaccination with that induced by homologous vaccination against challenge with foot-and-mouth disease virus (FMDV). Humoral and cell-mediated immune responses and protection against challenge with FMDV O Taiwan were examined in a non-vaccinated group, a group vaccinated with O Taiwan FMD vaccine and a group vaccinated with O Manisa FMD vaccine. Five pigs from each group were challenged with FMDV type O Taiwan 14 days after vaccination and five other pigs were contact-exposed to the inoculated pigs. Both homologous and heterologous vaccination protected against challenge with FMDV O Taiwan at 2 weeks after vaccination. In the heterologous vaccinated group, cross-neutralizing antibody titres against O Taiwan could be detected although the ratio 'r(1)' was 0.4, which was significantly smaller than the critical r-value. Cell-mediated immune responses were detected after both homologous and heterologous vaccination. Virus-induced in vitro lymphocyte (cross-) proliferation and production of both a Th1-type (IFN-gamma) and a Th2-type (IL-10) cytokine response were demonstrated in cultures of peripheral blood mononuclear cells (PBMC). The findings show that heterologous (emergency) vaccination can prevent clinical disease and shedding of virus. The induction of the cell-mediated immune responses after (heterologous) vaccination needs more research but data on these responses might provide additional tools for both vaccine choice and vaccine development.

Vaccination of pigs two weeks before infection significantly reduces transmission of foot-and-mouth disease virus.

The objective of this study was to investigate whether and at what time interval could vaccination reduce transmission of foot-and-mouth disease virus (FMDV) among pigs. Reduction of virus transmission by vaccination was determined experimentally. Transmission of FMDV was studied in three groups of ten pigs: one non-vaccinated group and two groups that were vaccinated 7 days (-7 dpi) and 14 days before inoculation (-14 dpi), respectively. Five randomly selected pigs from each group were inoculated with FMDV type O Taiwan, while the other five pigs left in the groups were exposed to the inoculated pigs by direct contact. Clinical signs were recorded, virus isolation and RT-PCR were carried out on oropharyngeal fluid (OPF), and the neutralizing antibody titres and the antibody response against non-structural (NS) proteins of FMDV were determined. No virus transmission was observed in the -14 dpi group, whereas virus transmission was observed in all contact pigs affecting both the non-vaccinated and the -7 dpi group. The reproduction ratio R in the -14 dpi vaccinated group was significantly lower than that of the non-vaccinated group. This study confirms the potential of vaccination as an important tool to reduce transmission of FMDV.

Isotype specific ELISAs to detect antibodies against swine vesicular disease virus and their use in epidemiology.

Isotype specific ELISAs to detect antibodies against swine vesicular disease, which may help to estimate the moment of infection, were developed and validated on sera from pigs experimentally infected with four different isolates of swine vesicular disease virus. Virus specific IgM antibodies could be detected from days 3-49 and occasionally up to day 91 after infection. IgG1 antibodies were first detected at day 8 and IgG2 at day 11. IgA antibodies coincided with IgG1 antibodies, but antibody titres varied widely. From the results obtained with the sera from the experimentally infected pigs, we calculated the day at which 50% of the pigs had become positive (D50). A D50 of 5, 4, 12, 12 and 24 days was calculated, respectively, for the appearance of antibodies in the virus neutralization test, the IgM, total IgG, IgG1 and IgG2 ELISA. A D50 of 49 days was calculated for the disappearance of IgM antibodies. The isotype specific ELISAs proved to be valuable tools to study the epidemiology of the disease.