The need to apply vaccines in different species – small ruminants
2012 • 1 10 Foot and mouth disease (FMD) has been successfully controlled and eliminated in many parts of the world using conventional disease control measures, including vaccination of domestic animals. Potent vaccines have also been the mainstay in controlling outbreaks in non-enzootic regions. Several characteristics of FMD complicate the use of vaccines to control the disease. Not only are there seven serotypes, with little cross-protection between the serotypes, but genetic and antigenic variants occur within these serotypes. In addition, FMD virus can infect over 70 cloven-hoofed species, many of which are free-living wild animals. The role of sheep and goats in the epidemiology of the disease is poorly understood and perceived differently in different parts of the world. This perception is reflected in the vaccination policies applied in these countries. Cattle are generally the species of choice in vaccination programmes, while sheep and goats are vaccinated in only a small number of countries, and then mostly either for strategic purposes or as part of a routine disease control programme. The general assumption is that sheep and goats do not play a significant role in the spread of the disease or as sentinel animals to detect clinical disease. However, this assumption does not hold true for all circumstances or under all epidemiological conditions. This paper describes the potential circumstances under which the vaccination of small livestock should be considered to mitigate the risk of viral spread or to contain an outbreak of the disease. The need to apply vaccines in different species – small ruminants
Quantification of foot and mouth disease virus excretion and transmission within groups of lambs with and without vaccination.
Sheep are well known to be susceptible for foot and mouth disease virus (FMDV), but it is unknown whether the infection can spread and persist in a sheep population. We therefore quantified virus transmission by performing experiments with FMD virus strain O/NET/2001 in groups of lambs. We used six groups of four lambs each, in which half of each group was inoculated and the other half was contact-exposed. To quantify the effectiveness of a single vaccination we also included six groups of four lambs each, vaccinated with O Manisa vaccine, 14 days prior to inoculation. Oropharyngeal fluid was obtained with a swab (OPF-swab), and blood samples were collected daily to determine virus excretion and serological response. We calculated the transmission rate beta (the number of new infections per day per infectious animal), and the reproduction ratio R (the number of secondary infections caused by one infectious individual). The mean daily virus excretion and the number of days the lambs excreted virus in the OPF differed significantly between vaccinated and non-vaccinated lambs. The transmission rate beta in the unvaccinated groups was 0.105 (95% confidence limit 0.044; 0.253) per day. The duration of the infectious period (T) was 21.11 (95% confidence limit 10.6; 42.1) days. With the final size of infection we estimated the reproduction ratio R in the non-vaccinated groups to be 1.14 (0.3; 3.3), and in vaccinated groups 0.22 (0.01; 1.78). Virus transmission as quantified by the final size did not differ statistically between the vaccinated and the non-vaccinated groups of lambs. In conclusion, FMDV seems able to persist in a sheep population, although the reproduction ratio was only slightly larger than one. As a consequence, vaccination might only have a small effect on transmission, in spite of the fact that virus excretion and duration of virus excretion is significantly reduced after vaccination.
Genetics of the phenotypic evolution in sheep: a molecular look at diversity-driving genes
Background After domestication, the evolution of phenotypically-varied sheep breeds has generated rich biodiversity. This wide phenotypic variation arises as a result of hidden genomic changes that range from a single nucleotide to several thousands of nucleotides. Thus, it is of interest and significance to reveal and understand the genomic changes underlying the phenotypic variation of sheep breeds in order to drive selection towards economically important traits. Review Various traits contribute to the emergence of variation in sheep phenotypic characteristics, including coat color, horns, tail, wool, ears, udder, vertebrae, among others. The genes that determine most of these phenotypic traits have been investigated, which has generated knowledge regarding the genetic determinism of several agriculturally-relevant traits in sheep. In this review, we discuss the genomic knowledge that has emerged in the past few decades regarding the phenotypic traits in sheep, and our ultimate aim is to encourage its practical application in sheep breeding. In addition, in order to expand the current understanding of the sheep genome, we shed light on research gaps that require further investigation. Conclusions Although significant research efforts have been conducted in the past few decades, several aspects of the sheep genome remain unexplored. For the full utilization of the current knowledge of the sheep genome, a wide practical application is still required in order to boost sheep productive performance and contribute to the generation of improved sheep breeds. The accumulated knowledge on the sheep genome will help advance and strengthen sheep breeding programs to face future challenges in the sector, such as climate change, global human population growth, and the increasing demand for products of animal origin.