Caprine arthritis encephalitis virus disease modelling review

Mathematical modelling is used in disease studies to assess the economical impacts of diseases, as well as to better understand the epidemiological dynamics of the biological and environmental factors that are associated with disease spreading. For an incurable disease such as Caprine Arthritis Encephalitis (CAE), this knowledge is extremely valuable. However, the application of modelling techniques to CAE disease studies has not been significantly explored in the literature. The purpose of the present work was to review the published studies, highlighting their scope, strengths and limitations, as well to provide ideas for future modelling approaches for studying CAE disease. The reviewed studies were divided into the following two major themes: Mathematical epidemiological modelling and statistical modelling. Regarding the epidemiological modelling studies, two groups of models have been addressed in the literature: With and without the sexual transmission component. Regarding the statistical modelling studies, the reviewed articles varied on modelling assumptions and goals. These studies modelled the dairy production, the CAE risk factors and the hypothesis of CAE being a risk factor for other diseases. Finally, the present work concludes with further suggestions for modelling studies on CAE

Small ruminant Lentivirus: a practical approach

Small ruminant lentivirus (SRLV) is a group of viruses of the Retroviridae family, shared between caprine, ovine and wild ruminants. It is responsible for a systemic infection that can affect the lungs, central nervous system, mammary gland and joints, causing chronic, insidious, and progressive diseases, seriously affecting animal health. Concurrently, it is associated with a decrease in milk production, leading to malnutrition of lambs and goat kids and to the premature slaughter of adult animals, causing substantial economic losses. This review aims to gather the latest information regarding lentivirusin small ruminants in the clinical practice, their economic importance, and diagnostic and prevention methods. Diagnosis is based on clinical, analytical, and post-mortem findings. The feasibility of imaging diagnosis is also highlighted. Preventive measures and management interventions, including the culling or segregation of positive animals, are effective options to control or even eradicate this disease. SRLV prevention strategies must be applied continuously to progressively eradicate infection

Impact of maedi-visna on sheep breeding flocks

Maedi-visna (MV), is a chronic wasting disease of sheep and goats caused by the small ruminant lentivirus (SRLV), maedi-visna virus (MVV). With no known cure or treatment, an asymptomatic period of sometimes several years and an infection that ultimately results in death, the finding that prevalence is on the rise within the UK is of great concern. In this study, a diagnostic was developed for detection and quantification of as a yet unidentified SRLV strain circulating within the UK in 2014. Identification of the viral strain was attempted to characterise this current circulating strain. Tissues and blood samples were collected from 28 seropositive rams over a period 28 months as part of a longitudinal case study after which semen harvested from 13 of these rams was used in an artificial insemination (AI) trial to estimate the risk of MVV transmission within a natural mating model. The viral strain was partially characterised at the molecular level and found to show similarities with previously reported UK strain (EV1). A qPCR assay was developed and showed successful detection of virus within both blood and tissue samples of seropositive animals but failed to detect any viral sequences with inseminated naïve ewes 7 weeks post insemination. In addition, proviral loads within blood were shown to be higher than previous reported findings. Finally, regression modelling of milk production data collected from a UK dairy flock suggested an outbreak of MVV of an unknown strain to cause a reduction in milk yield within seropositive ewes. Overall, this study demonstrates the impact of disease of a newly identified circulating strain of MVV within the UK

Surveillance and simulation of bovine spongiform encephalopathy and scrapie in small ruminants in Switzerland

BACKGROUND: After bovine spongiform encephalopathy (BSE) emerged in European cattle livestock in 1986 a fundamental question was whether the agent established also in the small ruminants' population. In Switzerland transmissible spongiform encephalopathies (TSEs) in small ruminants have been monitored since 1990. While in the most recent TSE cases a BSE infection could be excluded, for historical cases techniques to discriminate scrapie from BSE had not been available at the time of diagnosis and thus their status remained unclear. We herein applied state-of-the-art techniques to retrospectively classify these animals and to re-analyze the affected flocks for secondary cases. These results were the basis for models, simulating the course of TSEs over a period of 70 years. The aim was to come to a statistically based overall assessment of the TSE situation in the domestic small ruminant population in Switzerland. RESULTS: In sum 16 TSE cases were identified in small ruminants in Switzerland since 1981, of which eight were atypical and six were classical scrapie. In two animals retrospective analysis did not allow any further classification due to the lack of appropriate tissue samples. We found no evidence for an infection with the BSE agent in the cases under investigation. In none of the affected flocks, secondary cases were identified. A Bayesian prevalence calculation resulted in most likely estimates of one case of BSE, five cases of classical scrapie and 21 cases of atypical scrapie per 100'000 small ruminants. According to our models none of the TSEs is considered to cause a broader epidemic in Switzerland. In a closed population, they are rather expected to fade out in the next decades or, in case of a sporadic origin, may remain at a very low level. CONCLUSIONS: In summary, these data indicate that despite a significant epidemic of BSE in cattle, there is no evidence that BSE established in the small ruminant population in Switzerland. Classical and atypical scrapie both occur at a very low level and are not expected to escalate into an epidemic. In this situation the extent of TSE surveillance in small ruminants requires reevaluation based on cost-benefit analysis

Degree of technification of the sheep herd may be associated with seropositivity for the maedi-visna virus In South Brasil

Maedi-Visna (MV) is a chronic progressive multisystem disease that may be asymptomatic for several months or years, but progress rapidly, and may result in death, when signs and symptoms evolve. Viral elimination occurs mainly through direct contact with positive animal secretions. There is no vaccine or treatment, and prophylaxis is necessary for the health of the herd. The present study aimed to verify the seropositivity of MV and evaluate the factors associated with the risk in sheep herds in Paraná. A total of 1549 serum samples were collected from 90 properties. An epidemiological questionnaire was applied to each property, and the variables were analyzed using the Epi-info program and R environment. Of the 1549 samples analyzed, 22 were positive (1.4%) for the micro-AGID test in 13.3% of the properties. Our study demonstrated variables associated with the prevention and the risk of seropositivity to MVV. Conducting a breeding season, supplying concentrated feed, and separating the breeding stock before birth were factors associated with protection, whereas the previous occurrence of problems with lice, breeding on pasture, and keeping cats close to the flock were factors associated with risk. The seropositivity observed in the present study suggests the circulation of MVV in sheep herds in Paraná, which reinforces the need to implement prevention and control measures since the level of technification may be associated with the occurrence of anti-MVV antibodies in herds