RESUMEN
African horse sickness (AHS) and equine encephalosis (EE) are Culicoides-borne viral diseases that could have the potential to spread across Europe if introduced, thus being potential threats for the European equine industry. Both share similar epidemiology, transmission patterns and geographical distribution. Using stochastic spatiotemporal models of virus entry, we assessed and compared the probabilities of both viruses entering France via two pathways: importation of live-infected animals or importation of infected vectors. Analyses were performed for three consecutive years (2010-2012). Seasonal and regional differences in virus entry probabilities were the same for both diseases. However, the probability of EE entry was much higher than the probability of AHS entry. Interestingly, the most likely entry route differed between AHS and EE: AHS has a higher probability to enter through an infected vector and EE has a higher probability to enter through an infectious host. Consequently, different effective protective measures were identified by 'what-if' scenarios for the two diseases. The implementation of vector protection on all animals (equine and bovine) coming from low-risk regions before their importation was the most effective in reducing the probability of AHS entry. On the other hand, the most significant reduction in the probability of EE entry was obtained by the implementation of quarantine before import for horses coming from both EU and non-EU countries. The developed models can be useful to implement risk-based surveillance.
Asunto(s)
Enfermedad Equina Africana/epidemiología , Ceratopogonidae/virología , Enfermedades Transmisibles Emergentes/veterinaria , Enfermedades Transmisibles Importadas/veterinaria , Insectos Vectores/virología , Infecciones por Reoviridae/veterinaria , Enfermedad Equina Africana/transmisión , Enfermedad Equina Africana/virología , Animales , Enfermedades Transmisibles Emergentes/epidemiología , Enfermedades Transmisibles Emergentes/transmisión , Enfermedades Transmisibles Emergentes/virología , Enfermedades Transmisibles Importadas/epidemiología , Enfermedades Transmisibles Importadas/transmisión , Enfermedades Transmisibles Importadas/virología , Francia/epidemiología , Caballos , Probabilidad , Cuarentena , Infecciones por Reoviridae/epidemiología , Infecciones por Reoviridae/transmisión , Infecciones por Reoviridae/virología , RiesgoRESUMEN
BACKGROUND: African horse sickness (AHS) is a major, Culicoides-borne viral disease in equines whose introduction into Europe could have dramatic consequences. The disease is considered to be endemic in sub-Saharan Africa. Recent introductions of other Culicoides-borne viruses (bluetongue and Schmallenberg) into northern Europe have highlighted the risk that AHS may arrive in Europe as well. The aim of our study was to provide a spatiotemporal quantitative risk model of AHS introduction into France. The study focused on two pathways of introduction: the arrival of an infectious host (PW-host) and the arrival of an infectious Culicoides midge via the livestock trade (PW-vector). The risk of introduction was calculated by determining the probability of an infectious animal or vector entering the country and the probability of the virus then becoming established: i.e., the virus's arrival in France resulting in at least one local equine host being infected by one local vector. This risk was assessed using data from three consecutive years (2010 to 2012) for 22 regions in France. RESULTS: The results of the model indicate that the annual risk of AHS being introduced to France is very low but that major spatiotemporal differences exist. For both introduction pathways, risk is higher from July to October and peaks in July. In general, regions with warmer climates are more at risk, as are colder regions with larger equine populations; however, regional variation in animal importation patterns (number and species) also play a major role in determining risk. Despite the low probability that AHSV is present in the EU, intra-EU trade of equines contributes most to the risk of AHSV introduction to France because it involves a large number of horse movements. CONCLUSION: It is important to address spatiotemporal differences when assessing the risk of ASH introduction and thus also when implementing efficient surveillance efforts. The methods and results of this study may help develop surveillance techniques and other risk reduction measures that will prevent the introduction of AHS or minimize AHS' potential impact once introduced, both in France and the rest of Europe.
Asunto(s)
Enfermedad Equina Africana/transmisión , Ceratopogonidae/fisiología , Comercio , Modelos Biológicos , Enfermedad Equina Africana/economía , Enfermedad Equina Africana/epidemiología , Animales , Bovinos , Equidae , Factores de RiesgoRESUMEN
Current knowledge does not allow the prediction of when low pathogenic avian influenza virus (LPAIV) of the H5 and H7 subtypes infecting poultry will mutate to their highly pathogenic phenotype (HPAIV). This mutation may already take place in the first infected flock; hence early detection of LPAIV outbreaks will reduce the likelihood of pathogenicity mutations and large epidemics. The objective of this study was the development of a model for the design and evaluation of serological-surveillance programmes, with a particular focus on early detection of LPAIV infections in layer chicken flocks. Early detection is defined as the detection of an infected flock before it infects on average more than one other flock (between-flock reproduction ratio Rf<1), hence a LPAI introduction will be detected when only one or a few other flocks are infected. We used a mathematical model that investigates the required sample size and sampling frequency for early detection by taking into account the LPAIV within- and between-flock infection dynamics as well as the diagnostic performance of the serological test used. Since layer flocks are the target of the surveillance, we also explored whether the use of eggs, is a good alternative to sera, as sample commodity. The model was used to refine the current Dutch serological-surveillance programme. LPAIV transmission-risk maps were constructed and used to target a risk-based surveillance strategy. In conclusion, we present a model that can be used to explore different sampling strategies, which combined with a cost-benefit analysis would enhance surveillance programmes for low pathogenic avian influenza.
Asunto(s)
Pollos , Brotes de Enfermedades/veterinaria , Virus de la Influenza A/patogenicidad , Gripe Aviar/diagnóstico , Animales , Glicoproteínas Hemaglutininas del Virus de la Influenza/metabolismo , Virus de la Influenza A/metabolismo , Gripe Aviar/epidemiología , Gripe Aviar/virología , Países Bajos/epidemiología , Vigilancia de la Población , Factores de Riesgo , Factores de TiempoRESUMEN
Many biological systems experience a periodic environment. Floquet theory is a mathematical tool to deal with such time periodic systems. It is not often applied in biology, because linkage between the mathematics and the biology is not available. To create this linkage, we derive the Floquet theory for natural systems. We construct a framework, where the rotation of the Earth is causing the periodicity. Within this framework the angular momentum operator is introduced to describe the Earth's rotation. The Fourier operators and the Fourier states are defined to link the rotation to the biological system. Using these operators, the biological system can be transformed into a rotating frame in which the environment becomes static. In this rotating frame the Floquet solution can be derived. Two examples demonstrate how to apply this natural framework.
Asunto(s)
Modelos Biológicos , Periodicidad , Animales , Ritmo Circadiano , Enfermedades Transmisibles/epidemiología , Enfermedades Transmisibles/transmisión , Vectores de Enfermedades , Análisis de Fourier , Humanos , Modelos Lineales , Conceptos Matemáticos , Dinámica Poblacional , Estaciones del AñoRESUMEN
After a massive epidemic of Bluetongue virus serotype 8 (BTV-8) among ruminants in 2006-2007 in the European Union (EU), the Netherlands started a voluntary emergency vaccination campaign in May 2008, subsidized by the EU. At the start of a new campaign in 2009, without subsidized vaccination, we investigated by mail survey the motives of farmers and hobby holders to vaccinate against BTV-8 in 2008 and 2009. Mean vaccine uptake in 2008 was: 73% in sheep, 71% in cattle, 43% in goat farms and 67% in hobby holdings. Top-5 motives pro-vaccination were: prevention of production loss; subsidized vaccination; recommendation by practitioner; welfare reasons; contribution to the eradication campaign. Top-5 motives against vaccination were: vaccination costs; absence of clinical BT-problems; presumed low infection risk; balance between vaccination costs and loss without vaccination; bad experience with earlier vaccination campaigns. Willingness to vaccinate was significantly lower in 2009: 42% in sheep, 58% in cattle, 19% in goat farms and 49% in hobby holdings. Measures to stimulate vaccination among those that did not want to vaccinate in 2009 were: subsidized vaccination; possibility to vaccinate their own animals; more information on efficacy/safety of vaccine and why animals had to be vaccinated again; availability of a BT vaccine combined with vaccine(s) against other diseases.
Asunto(s)
Animales Domésticos/inmunología , Virus de la Lengua Azul/inmunología , Lengua Azul/epidemiología , Lengua Azul/prevención & control , Vacunación/estadística & datos numéricos , Vacunas Virales/administración & dosificación , Animales , Bovinos , Recolección de Datos , Cabras , Humanos , Países Bajos/epidemiología , Ovinos , Encuestas y CuestionariosRESUMEN
This study calculates the financial consequences of the bluetongue serotype 8 (BTV8) epidemics of 2006 and 2007 in the Netherlands. We constructed a deterministic economic model that is compatible with the Dutch livestock production systems for cattle, sheep and goats. Two hundred cattle farms and 270 sheep farms were infected with BTV8 in the epidemic of 2006, whereas 30,417 cattle farms, 45,022 sheep farms and 35,278 goat farms were estimated to be infected in the epidemic of 2007. The net costs (costs minus benefits) of the BTV8 epidemic of 2006 (BT2006) was estimated at 32.4 million Euros. The net costs of the BTV8 epidemic of 2007 (BT2007) was valued at 164-175 million Euros, depending on the mortality and morbidity rates for cattle used. The losses account for 2%, 10% and 11% of the gross value of the primary production within Dutch pasture-based livestock farming that equals 1.6 billion Euros. Control measures accounted for 91% of the net costs of the BT2006, while diagnostic costs represented 7%. By contrast, for the BT2007 92% of the net costs were in the form of production losses and veterinary treatment fees, while only 6% were related to control measures. Furthermore, the control costs dropped from 29,630 in BT2006 to 10,990 in BT2007 mainly due to the costly indoor housing that was not obligatory during the BT2007 epidemic. The cattle sector suffered 88% and 85% of the net costs for the BT2006 and BT2007, respectively; the highest of all sectors.
Asunto(s)
Virus de la Lengua Azul/clasificación , Lengua Azul/epidemiología , Enfermedades de los Bovinos/epidemiología , Brotes de Enfermedades/veterinaria , Enfermedades de las Cabras/epidemiología , Agricultura/economía , Animales , Lengua Azul/economía , Lengua Azul/virología , Virus de la Lengua Azul/genética , Bovinos , Enfermedades de los Bovinos/economía , Enfermedades de los Bovinos/virología , Enfermedades de las Cabras/economía , Enfermedades de las Cabras/virología , Cabras , Modelos Económicos , Países Bajos/epidemiología , Sensibilidad y Especificidad , Serotipificación , OvinosRESUMEN
The expected time to extinction of a herpes virus is calculated from a rather simple population-dynamical model that incorporates transmission, reactivation and fade-out of the infectious agent. We also derive the second and higher moments of the distribution of the time to extinction. These quantities help to assess the possibilities to eradicate a reactivating infection. The key assumption underlying our calculations is that epidemic outbreaks are fast relative to the time scale of demographic turnover. Four parameters influence the expected time to extinction: the reproduction ratio, the reactivation rate, the population size, and the demographic turn-over in the host population. We find that the expected time till extinction is very long when the reactivation rate is high (reactivation is expected more than once in a life time). Furthermore, the infectious agent will go extinct much more quickly in small populations. This method is applied to bovine herpes virus (BHV) in a cattle herd. The results indicate that without vaccination, BHV will persist in large herds. The use of a good vaccine can induce eradication of the infection from a herd within a few decades. Additional measures are needed to eradicate the virus from a whole region within a similar time-span.
Asunto(s)
Enfermedades de los Bovinos/virología , Brotes de Enfermedades/veterinaria , Infecciones por Herpesviridae/veterinaria , Herpesvirus Bovino 1/fisiología , Modelos Biológicos , Animales , Bovinos , Enfermedades de los Bovinos/epidemiología , Infecciones por Herpesviridae/epidemiología , Infecciones por Herpesviridae/virología , Análisis Numérico Asistido por Computador , Dinámica Poblacional , Activación Viral , Latencia del VirusRESUMEN
Our aim was to provide additional estimates of main parameters for the transmission of foot-and-mouth disease virus (FMDV) strain O Taiwan (3/97). We used the data of previous experiments in non-vaccinated and vaccinated pigs and combined the data of experiments with the same treatment(s). First, we quantified the reproduction ratio R for the various groups using a final-size method. Our final-size results predicted that vaccination with a four-fold vaccine dose (but not with a single dose) at 1 week before inoculation (-7 dpi) would reduce R compared to the non-vaccinated group. Secondly, we used the daily results of virus excretion to quantify the transmission rate beta (by using generalized linear modelling), and the infectious period T (by using survival analysis). We used the estimates of beta and T to estimate R more precisely as compared to the final-size method and also for the groups for which a finite estimate could not be obtained using a final-size method. Our modelling results predicted that beta for non-vaccinated, for single-dose and four-fold-dose groups would be 6.1 (3.7, 10)day(-1), 2.0 (1.0, 4.0)day(-1) and 0.4 (0.1, 1.4)day(-1), T at 6.5 (5.7, 7.3), 5.3 (4.7, 6.0) and 2.3 (0.9, 5.7) days and R at 40 (21, 74), 11 (4.9, 24) and 1.0 (0.1, 7.8), respectively. These results predicted that both vaccination with a four-fold vaccine dose and with a single dose at -7 dpi would reduce beta, T and R significantly as compared to the non-vaccinated pigs, thereby showing that vaccination will reduce transmission of FMDV significantly already 1 week post vaccination.
Asunto(s)
Transmisión de Enfermedad Infecciosa/veterinaria , Virus de la Fiebre Aftosa/inmunología , Fiebre Aftosa/prevención & control , Fiebre Aftosa/transmisión , Enfermedades de los Porcinos/prevención & control , Enfermedades de los Porcinos/transmisión , Animales , Virus de la Fiebre Aftosa/clasificación , Países Bajos , Porcinos , Vacunación/veterinaria , Vacunas Virales/administración & dosificaciónRESUMEN
The efficacy of the procedures in use at the two rendering plants in the Netherlands was assessed on a laboratory-scale using procedures that simulated the pressure cooking part of the rendering process. A pool of bovine spongiform encephalopathy (BSE)-infected brainstem from the United Kingdom and a pool of scrapie-infected brainstem from Dutch sheep were used to spike the rendering materials. The mixtures were subjected to various time-temperature combinations of hyperbaric heat treatment related to the conditions used in Dutch rendering plants in the early 1990s, and to the combination of 20 minutes at 133 degrees C required by the EU Directive on rendering of 1996. The efficacy of the procedures in inactivating BSE or scrapie infectivity was measured by titrating the materials before and after heat treatment in inbred mice, by combined intracerebral and intraperitoneal inoculations at limiting dilutions. Two independent series of experiments were carried out. The design of the study allowed for minimum inactivations of up to 2.2 log (2.0 in the second series) to be measured in the diluted infective material and 3.1 log in the undiluted material. After 20 minutes at 133 degrees C there was a reduction of BSE infectivity of about 2.2 log in the first series (with some residual infectivity detected), and in the second series more than 2.0 log (with no residual infectivity detected). With undiluted brain material there was an inactivation of about 3.0 log (with some residual infectivity detected). With the same procedure, scrapie infectivity was reduced by more than 1.7 log in the first series and by more than 2.2 log in the second series. With undiluted brain material there was an inactivation of more than 3.1 log. In each case no residual scrapie infectivity was detected. The BSE agent consistently appeared to be more resistant to heat inactivation procedures than the scrapie agent, particularly at lower temperatures and shorter times.