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BackgroundIn northern Europe, bluetongue (BT) caused by the BT virus (BTV), serotype 8, was first notified in August 2006 and numerous ruminant herds were affected in 2007 and 2008. However, the origin and the time and place of the original introduction have not yet been determined.Methods and Principal FindingsFour retrospective epidemiological surveys have been performed to enable determination of the initial spatiotemporal occurrence of this emerging disease in southern Belgium: investigations of the first recorded outbreaks near to the disease epicenter; a large anonymous, random postal survey of cattle herds and sheep flocks; a random historical milk tank survey of samples tested with an indirect ELISA and a follow-up survey of non-specific health indicators. The original introduction of BTV into the region probably occurred during spring 2006 near to the National Park of Hautes Fagnes and Eifel when Culicoides become active.Conclusions/SignificanceThe determination of the most likely time and place of introduction of BTV8 into a country is of paramount importance to enhance awareness and understanding and, to improve modeling of vector-borne emerging infectious diseases.

A seroprevalence study carried out between June and September 2016 in the Belgian sheep population showed a significant increase in overall (from 25% to 62%) and between-herd (from 60% to 96%) seroprevalence against Schmallenberg virus (SBV) during this period, indicating the most extensive recirculation of SBV since its original emergence in 2011. SBV recirculation was confirmed by the detection of SBV RNA-positive Culicoides obsoletus complex midges collected in the region of Antwerp in August 2016, reaching a minimum infection rate of 3%. The recirculation of SBV in the largely unprotected ruminant population during summer 2016 will likely cause an increase in the number of arthrogryposis-hydranencephaly cases in newborn ruminants during the coming months.

Control of bovine viral diarrhoea (BVD) in Belgium is currently implemented on a voluntary basis at herd level and mainly relies on detection and culling of persistently infected (PI) animals. The present field study was conducted during the winter of 2010/2011 to assess the performances of diagnostic assays used in the testing scheme for BVD as proposed by the two Belgian regional laboratories. Individual blood samples were collected from 4972 animals, and individual samples from the same herd were pooled (maximum of 30 individual samples per pool) and screened for the presence of Bovine Viral Diarrhoea Virus (BVDV)-specific RNA using a commercial real-time RT-PCR test (ADIAGENE). Individual samples from positive pools were then tested in parallel with the same RT-PCR test and with an antigen-capture ELISA test (IDEXX) to detect viremic animals. This study demonstrated that individual results differed according to the type of assay used (P < 0.001): 140 animals (2.8%) were positive by RT-PCR and 72 (1.4%) by antigen-ELISA. A second blood sample was taken 40 days later from 74 PCR positive animals to detect persistent viremia: 17 (23%) of these were still PCR positive and considered to be PI and the 57 that no longer tested positive were assumed to be transiently infected (TI) animals. All PI animals were positive also by antigen-ELISA at both time points. Among TI animals, 10 (16%) were positive by antigen-ELISA at the first but none at the second sampling. A highly significant difference in cycle threshold (Ct ) values obtained by RT-PCR was observed between PI and TI animals. ROC analysis was performed to establish thresholds to confirm with high probability that an animal is PI, based on the result of RT-PCR test performed on a single individual blood sample.

BackgroundPertussis, also known as whooping cough, is a vaccine-preventable respiratory disease caused by Bordetella pertussis infection, against which Senegalese children are immunized with the diphtheria-tetanus-whole cell pertussis vaccine (DTwP). Seroepidemiology of pertussis has been widely described in industrialized countries, but rare are the studies referring to it in developing countries.MethodsWe conducted a longitudinal survey in Northern Senegal to investigate the epidemiology of B. pertussis by evaluating the IgG antibody (Ab) response against pertussis toxin (PT). A cohort of 410 children aged 1 to 9 from five villages in the Middle Senegal River Valley were followed-up for 18 months. During that period, five visits were made to assess the immunological status of the children.Principal FindingsPT-specific IgG responses were significantly different according to age. Until the age of 3, there was a decrease in the Ab response, which then increased in the older groups. Assessment of IgG antibodies to PT (IgG-PT) suggested evidence of recent exposures to the pathogen. Surprisingly, in one of the five villages the average Ab response to PT was very low at all ages during the first 6 months of the study. At the third visit, IgG-PT concentrations peaked to very high levels, to slightly decline at the end of the survey. This indicates an outbreak of B. pertussis, whereas in the other villages a pertussis endemic profile could be observed.ConclusionsPertussis is endemic in Northern Senegal despite the introduction of vaccination. The circulation of the bacteria seems to differ between geographic locations and over time. A more complete understanding of the epidemiology of pertussis and its environmental determinants could provide information to adapt vaccination programs.

Abstract. To evaluate immunity to vaccine-preventable diseases according to nutritional status, a longitudinal study was conducted in Senegalese children ages 1-9 years old. A linear regression analysis predicted that weight for age was positively associated with immunoglobulin G (IgG) response to tetanus toxoid in children born during the rainy season or at the beginning of the dry season. A relationship between village, time of visits, and levels of antibodies to tetanus showed that environmental factors played a role in modulating humoral immunity to tetanus vaccine over time. Moreover, a whole-blood stimulation assay highlighted that the production of interferon-γ (IFN-γ) in response to tetanus toxoid was compromised in stunted children. However, the absence of cytokine modulation in response to Mycobacterium tuberculosis-purified protein derivatives and phytohemagglutinin suggests that the overall ability to produce IFN-γ was preserved in stunted children. Therefore, these results show that nutritional status can specifically alter the efficacy of long-lasting immunity to tetanus.

We performed a thorough fit-for-purpose evaluation of commercial ELISAs for the detection of bovine viral diarrhea virus (BVDV)-specific antibodies in serum and in milk by testing 2 panels of well-characterized serum and milk samples. Sixteen ELISAs from 9 different manufacturers, available on the Belgian market at the time of our study, were assessed for their diagnostic and analytical sensitivity (DSe and ASe, respectively), diagnostic specificity (DSp), and repeatability relative to the virus neutralization (VN) test considered to be the gold standard assay. Using serum as a matrix, DSe was much lower for competitive (c)ELISAs (min. 45%, max. 65%) than for indirect (i)ELISAs (min. 85%, max. 100%), partly because of the lower detection of positive samples from vaccinated animals included in the panel. ASe was also better for iELISAs; DSp was >95% for all but 2 ELISAs. Repeatability, expressed as coefficients of variation (CV) of optical densities, was generally good, although 3 ELISAs had a mean CV >10%. With milk samples, as observed for serum, DSe was lower for cELISAs (min. 57%, max. 75%) than for iELISAs (min. 61%, max. 89%), and DSp was high for all ELISAs (min. 94%, max. 100%). Both DSe and ASe were lower when testing milk samples compared to serum samples. These results confirm that serologic monitoring of BVDV-free herds should be performed using serum samples of unvaccinated animals to avoid interference of vaccination and to maximize the chance of detecting seroconversion linked to BVDV infection. Further investigations using a larger collection of field samples are recommended.

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