Sirvi Autor "Viltrop, Arvo (advisor)" järgi

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Bacillus smithii TBMI12 as a potential probiotic feed additive
(Eesti Maaülikool, 2014) Suitso, Indrek; Nurk, Allan (advisor); Viltrop, Arvo (advisor)
The purpose of the thesis was to investigate the potential of Bacillus smithii strain TBMI12 as a probiotic feed additive. For that safety, colonization, tolerance and challenge studies were performed with mice and pigs. Experiments showed that this strain is able to colonize gastrointestinal tract without harming the host or causing significant changes in the microbiota or disrupting the biodiversity of the gastrointestinal tract. Also colonization of the gastrointestinal tract with the Bacillus smithii TBMI12 endospores decreased the probability of Salmonella Enteritidis infection and decelerated the process of pathogenesis. Based on the results this strain has a potential to be probiotic feed additive.
Dynamics of the sex and age structure of wild boar population during the African swine fever epidemic in Estonia
(Eesti Maaülikool, 2024) Hietala, Annariikka Kaarina; Viltrop, Arvo (advisor)
African swine fever, a disease affecting the Suidae family, imposes significant economic losses on the pig industry. The main aim of this study was to explore the dynamics of the sex and age structure of wild boar population during the ASF epidemic in Estonia. Data was sourced from the Estonian Agriculture and Food Board, and it included data from January 2015 to December 2023 from all 15 counties in Estonia. We found that females were more likely to be found dead, but males were more likely to be hunted and killed in road accidents. These results indicated that females would be more susceptible for ASF, and males have higher value in hunting and by behavioural differences are more susceptible for road accidents. In trend analyses we observed declining proportion of females in found dead and hunted categories, which allows female population to increase even more. Were also found that female wild boars and those <1 year of age are significantly more frequently infected with ASF compared to males or other age groups respectively.
Epidemiology of African swine fever in Estonia after 2019
(Eesti Maaülikool, 2025) Uutela, Suvi Pirita; Viltrop, Arvo (advisor); Chair of Clinical Veterinary Medicine
African swine fever (ASF) poses a significant threat to both wild and domestic pig populations globally. In Estonia, detailed epidemiological analysis of ASF post-2019 has been limited. This study addresses this gap by investigating the epidemiology of ASF in Estonian wild boar populations and domestic pigs following 2019 focusing on the spatial and temporal distribution of the virus and seroprevalence across different age groups of wild boars to identify potential risk factors influencing ASF occurrence. Surveillance data from 2019 to 2024, encompassing hunted and found dead wild boar, were analyzed using descriptive statistics, regression analysis, and non-parametric tests. The study examined general trend and seasonality of ASF in wild boars as well as seroprevalence trends in different wild boar age groups. Also the associations of ASF with wild boar abundance was explored. Results indicated a significant increase in the proportion and number of polymerase chain reaction positive cases in wild boars in recent years. Seasonality analysis revealed distinct seasonal patterns in disease occurrence, particularly in hunted wild boar, with lower prevalence in the spring. Seroprevalence trend analysis suggested a declining trend in older animals, but increasing trend in the youngest age group. Spread of ASF remains active in Estonia's wild boar population, with a widespread prevalence escalation and transmission driven by complex factors beyond wild boar density. This underscores the need for enhanced monitoring and targeted interventions that incorporate spatial and temporal data, coupled with strengthened biosecurity measures across all commercial pig farms to mitigate spillover risk.
Epidemiology of African swine fever in Estonia and characterization of one virus strain
(Eesti Maaülikool, 2021) Nurmoja, Imbi; Viltrop, Arvo (advisor); Blome, Sandra (advisor); Depner, Klaus Robert (advisor); Dixon, Linda (opponent)
African swine fever (ASF) is an OIE-listed, dangerous viral disease of pigs, which has a devastating impact on animal health and the pig industry in many countries worldwide. During the period 2014–2020, ASF has been the main animal health issue in Estonia. This dissertation consists of three independent studies, which have been conducted with the aim to analyse the epidemiology of ASF and the course of the epidemic in the Estonian wild boar population, as well as in domestic pigs. In Study I, wild boar surveillance data (n = 7,015) collected from two distinct study areas from September 2014 to September 2016 were analysed. A statistically significant difference between the two areas in the temporal course of ASF seroprevalence was found. These findings indicate that ASF might have been introduced to the north-east of Estonia earlier then to the south of the country. The probability of detecting an ASF-positive animal was higher in young animals (< 1 year). Within wild boar found dead, there was a higher probability of finding an ASF-positive result compared to hunted animals. In Study II, the biological characteristics of the ASF virus strain (Est 14/WB) circulating in the wild boar population of north-east Estonia in 2014 were evaluated. Oronasal inoculation of ten young wild boar led to an acute and severe course of the disease in all infected animals. Nine animals died and one animal recovered completely from the disease. In conclusion, the ASFV strain was still found to be highly virulent. In Study III, the epidemiology of ASF in all 26 domestic pig outbreak herds that occurred in Estonia during the period 2015–2017 was retrospectively analysed. On most of the farms, the first clinical signs were mild and not ASF-specific despite the high virulence of the circulating virus. The highest mortality (29.7%) was seen on backyard farms (1–9 pigs) and the lowest (0.7%) on large commercial farms (> 1000 pigs). The spread of the virus within farms was slow and the contagiousness of the virus was relatively low. Farms of all sizes and types have been at risk. The results suggest that the increase in ASF cases in local wild boar populations is the main risk factor leading to the infection of farms; 88% of domestic outbreaks occurred in areas where ASF virus was detected in wild boar prior to the outbreak, within a radius of 15 km from the outbreak farm.
Epidemiology, impact on herd health and control of bovine herpesvirus 1 in Estonian dairy cattle herds
(Eesti Maaülikool, 2012) Raaperi, Kerli; Viltrop, Arvo (advisor); Orro, Toomas (advisor)
The objective of the present doctoral thesis was to assess the herd-level and within-herd prevalence of bovine herpesvirus 1 (BHV-1) infection in Estonian dairy cattle and estimate the sensitivity and specificity of the ELISA test for bulk tank milk (BTM) testing in detecting infected herds. The aim was to determine the risk factors related to high prevalence of the infection in herds and presence of BHV-1 among youngstock. We also aimed to clarify the role of BHV-1 in the incidence of bovine respiratory disease (BRD) in different age groups and evaluate the association between prevalence of BHV-1 and herd reproduction parameters. The last objectives were to assess the efficacy of vaccination programmes in lowering the seroprevalence of BHV-1 glycoprotein E (gE) within the herd as well as to follow the dynamics of the infection in non-vaccinating herds with uninfected replacement heifers. Prevalence study was accomplished between 2006 to 2008. One hundred and three (64 BHV-1 infected ja 39 uninfected) dairy cattle herds with more than 20 cows and with different size were selected for the study. In each of the selected herds, serum samples from a representative number of cows, and youngstock older than 6 months, were analyzed for BHV-1 antibodies. The source population used to estimate the herd level prevalence of BHV-1 consisted of all 1,205 market-oriented dairy herds. Vaccination programmes with inactivated gE marker vaccines to eradicate BHV-1 were elaborated for seven dairy herds. Five BHV-1-infected dairy herds, which had uninfected heifers (prevalence up to 5 per cent), were selected to monitor the course of the infection without control strategies. To monitor the efficacy of the vaccination, and changes in seroprevalence during the control programme, a longitudinal two year surveillance programme was carried out in those herds. Due to the moderate sensitivity of the BTM ELISA test (76.5%) it should be used with caution when making decisions about the infection status of a herd. Lower cut-off in the ELISA blocking reaction might be justified when using BTM testing in BHV-1 control programmes to be able to discover more infected herds with only a minimal loss in specificity. Twenty two percent of Estonian market-oriented dairy cattle farms are infected with BHV-1. When elaborating control programmes most of the resources should be directed to herds with more than 100 cows as those farms contain the main population infected with BHV-1. As within-herd prevalence of BHV-1 is generally high in larger herds vaccination with gE marker vaccines combined with eradication of gE positive animals is the most appropriate way to eradicate the virus in those herds. Where the within-herd prevalence is low culling of the seropositive animals without vaccination would be most cost-effective. Youngstock tested negative in 36.5% of infected herds. These herds are in more favourable situation when applying an eradication programme because it is possible to raise a BHV-1-free generation from their own herd and vaccinate youngstock just before introduction to the cow house, as long as the farmer can provide isolation facilities. The duration of vaccination programme is shorter when replacement animals are free of infection reducing the cost of eradication. In herds under control programmes it is important to be aware of the important risk factors that are related to spread of the infection within a herd. In BHV-1 positive herds more attention should be paid to possible iatrogenic transmission via the veterinarian and inseminator, and within-herd biosecurity measures should be kept in mind. Infection with bovine viral diarrhea virus (BVDV) may also be a predisposing factor for more effective viral spread. Although several infectious and management-related factors are associated with BRD in dairy calves and heifers, BHV-1 and BVDV had significant impact on the manifestation of clinical respiratory disease. BVDV contributed to the occurrence of respiratory disease signs in older youngstock. Bovine respiratory syncytial virus was related to clinical respiratory disease in adult dairy cattle. The use of control measures for these viruses may reduce the incidence of respiratory disease and improve herd health. In herds with poor reproductive performance, BHV-1 should be considered as one of the infectious risk factors, and the eradication of this virus may improve the reproductive performance of the herd. Vaccination with inactivated marker vaccine is a secure method to stop virus circulation within a herd as long as the vaccination protocol is followed precisely. On the other hand, in some herds the virus circulation may end by itself for longer periods, which may lead to self-clearance of the herd from the virus. However, aiming for eradication in herds with uninfected young-stock leaving animals unvaccinated has an unpredictable outcome – virus circulation may remain retarded or the virus may reactivate and cause an epidemic in the herd.
On-farm mortality and related risk factors in Estonian dairy and beef herds
(Eesti Maaülikool, 2020) Reimus, Kaari; Mõtus, Kerli (advisor); Viltrop, Arvo (advisor); Endres, Marcia (opponent)
On-farm mortality (unassisted death and euthanasia) of dairy cattle has increased over the last decades in several countries referring to impaired cattle welfare and affecting the economic sustainability of the sector. The aim of this thesis was to investigate the on-farm mortality rates in Estonian dairy and beef cattle and identify reasons and risk factors for mortality. Studies I and II used census cattle data of Estonian Agricultural Registers and Information Board of years 2013 and 2014. The average on-farm mortality rate was 6.95 (95% CI 6.87; 7.04) and 2.14 (95% CI 2.05; 2.23) per 100 animal-years in dairy and beef cattle, respectively. Young calves had the highest mortality rates, male cattle were more prone to death and mortality was higher in larger herds. Estonian Holstein breed cattle had higher mortality hazard compared to other dairy breeds. Calves most often die due to digestive disorders and respiratory disease. The most frequently reported reasons for on-farm mortality of adult cattle were digestive and metabolic diseases and feet disorders, also trauma and accidents were frequent causes of death in adult beef cattle. Winter months accompany the highest risk for calf mortality whereas summer is the high-risk period for cow mortality. Calving season is the risk-period for beef cattle mortality. In study III, the lactation-level records of all cows from herds with ≥ 20 cow-years enrolled in Estonian Livestock Performance Recording Ltd between years 2013 to 2015 were used. The results indicated that risk factors for mortality were mainly related to problems with calving and poor health status around parturition. In study IV, a questionnaire data of 212 dairy herds was used to analyse herd-level risk factors for on-farm mortality of calves (21-90 days of age) and cows (cattle over 24 months). Calving occurring in multiple places or systems (individual pens, group pens, tied or in pasture) as well as housing calves over two weeks of age in combined systems (single and group pens) were management factors protective for calf mortality. Not using wage labour, grazing and housing cows in free stalls and frequent hoof trimming were protective for cow on-farm mortality. We emphasise the importance of good housing and management conditions to lower the mortality rates, especially in young calves and cows during early lactation period.

Sirvi Autor "Viltrop, Arvo (advisor)" järgi

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