Publicação
Emergency and epidemiological surveillance of schmallenberg virus in Portugal
| Resumo: | Schmallenberg virus (SBV) is a novel Orthobunyavirus of the family Bunyaviridae which causes mild clinical signs in adults, and malformations in aborted and neonatal ruminants in Europe. This new virus was first identified in blood samples of cattle in the city of Schmallenberg in North Rhine‐Westphalia in November 2011 and since then has spread to several European countries, being transmitted by biting midges. Until the start of this doctoral thesis, no study had focused on the Portuguese territory, a circumstance that created a knowledge gap that was in need of urgent attention. To provide knowledge on SBV epidemiology in Portugal, a main goal of this work was to perform a serosurvey study to estimate the presence of immunoglobulin G (IgG) antibodies against SBV in sheep in Portugal. A stratified random sampling design was set up with the five regions of continental Portugal (North, Center, Lisboa and Vale do Tejo, Alentejo, and Algarve) and the estimated occurrence of IgG antibodies against SBV was 12.8% (95% confidence interval: 11%-15%). This thesis also aimed at ascertaining SBV circulation in Serra da Estrela, a geographical area of high altitude and low temperature, since these factors can affect the distribution of vectors and causes a deleterious effect in Culicoides development. To answer this question a 2-year prospective serological investigation was performed between 2015 and 2016, involving 168 sheep in 42 Serra da Estrela breed official farms, showing that SBV circulates at high altitudes and is endemic in sheep herds of central Portugal, even in herds with restrict circulation, with seroprevalences of 4.2% in 2015 and 6.0% in 2016 (p = 0.619). As no evidence for a change in seroprevalence was observed, with studies from Europe generally showing a decrease in SBV circulation at that time, a two year longitudinal serological investigation for Schmallenberg virus infection at the herd level was performed by using bulk-tank milk samples to better clarify the seroepidemiology of this virus in the central region of Portugal. A decrease in seroprevalence was observed with 92.6% of the bulk-tank milk samples positive in 2015, and 77.9% in 2016 (p = 0.027). Differences in the 2015/2016 seroprevalences at the herd level seems to be in agreement with reported data from other European countries. Based on the research work done and presented in this thesis, we conclude that it is further research is key and should continue to focus on the circulation of SBV in Portugal. |
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| Autores principais: | Esteves, Fernando Alexandre de Almeida |
| Assunto: | Schmallenberg virus emerging infections |
| Ano: | 2021 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Trás-os-Montes e Alto Douro |
| Idioma: | inglês |
| Origem: | Repositório da UTAD |
| Resumo: | Schmallenberg virus (SBV) is a novel Orthobunyavirus of the family Bunyaviridae which causes mild clinical signs in adults, and malformations in aborted and neonatal ruminants in Europe. This new virus was first identified in blood samples of cattle in the city of Schmallenberg in North Rhine‐Westphalia in November 2011 and since then has spread to several European countries, being transmitted by biting midges. Until the start of this doctoral thesis, no study had focused on the Portuguese territory, a circumstance that created a knowledge gap that was in need of urgent attention. To provide knowledge on SBV epidemiology in Portugal, a main goal of this work was to perform a serosurvey study to estimate the presence of immunoglobulin G (IgG) antibodies against SBV in sheep in Portugal. A stratified random sampling design was set up with the five regions of continental Portugal (North, Center, Lisboa and Vale do Tejo, Alentejo, and Algarve) and the estimated occurrence of IgG antibodies against SBV was 12.8% (95% confidence interval: 11%-15%). This thesis also aimed at ascertaining SBV circulation in Serra da Estrela, a geographical area of high altitude and low temperature, since these factors can affect the distribution of vectors and causes a deleterious effect in Culicoides development. To answer this question a 2-year prospective serological investigation was performed between 2015 and 2016, involving 168 sheep in 42 Serra da Estrela breed official farms, showing that SBV circulates at high altitudes and is endemic in sheep herds of central Portugal, even in herds with restrict circulation, with seroprevalences of 4.2% in 2015 and 6.0% in 2016 (p = 0.619). As no evidence for a change in seroprevalence was observed, with studies from Europe generally showing a decrease in SBV circulation at that time, a two year longitudinal serological investigation for Schmallenberg virus infection at the herd level was performed by using bulk-tank milk samples to better clarify the seroepidemiology of this virus in the central region of Portugal. A decrease in seroprevalence was observed with 92.6% of the bulk-tank milk samples positive in 2015, and 77.9% in 2016 (p = 0.027). Differences in the 2015/2016 seroprevalences at the herd level seems to be in agreement with reported data from other European countries. Based on the research work done and presented in this thesis, we conclude that it is further research is key and should continue to focus on the circulation of SBV in Portugal. |
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