Experimental study of the susceptibility of a European Aedes albopictus strain to dengue virus under a simulated Mediterranean temperature regime

Dengue virus (DENV) has re-emerged in Europe driven by the geographic expansion of the mosquito species Aedes albopictus and Aedes aegypti (Diptera: Culicidae) and the introduction of the virus by viraemic travellers. In the present study, the vector competence (VC) of Ae. albopictus collected in Catalonia (northeast Spain) was evaluated for two different DENV strains, DENV-1 and DENV-2, the serotypes responsible for all outbreaks of dengue that have occurred in Europe. Mosquitoes were reared under environmental conditions mimicking the mean temperature and humidity recorded in July on the Mediterranean coast of Catalonia. Mosquitoes were fed on an artificial infectious bloodmeal and, at 14 days post-exposure, infection, disseminated infection and transmission rates (IR, DIR, TR) and transmission efficiency (TE) were determined by testing the virus in the body, legs and saliva. The tested Ae. albopictus strain was found to be susceptible to both DENV-1 and DENV-2 and to be able to transmit DENV-1. This is the first time that the VC of Ae. albopictus for DENV has been tested in Europe in this specific context (i.e. mimicking the Mediterranean temperature and humidity recorded in Catalonia in July). This study confirms the potential of Ae. albopictus to start autochthonous DENV transmission cycles in the Mediterranean basin.

Emergence and spread of highly pathogenic avian influenza A(H5N8) in Europe in 2016-2017

Circulation of highly pathogenic avian influenza (HPAI) viruses poses a continuous threat to animal and public health. After the 2005-2006 H5N1 and the 2014-2015 H5N8 epidemics, another H5N8 is currently affecting Europe. Up to August 2017, 1,112 outbreaks in domestic and 955 in wild birds in 30 European countries have been reported, the largest epidemic by a HPAI virus in the continent. Here, the main epidemiological findings are described. While some similarities with previous HPAI virus epidemics were observed, for example in the pattern of emergence, significant differences were also patent, in particular the size and extent of the epidemic. Even though no human infections have been reported to date, the fact that A/H5N8 has affected so far 1,112 domestic holdings, increases the risk of exposure of humans and therefore represents a concern. Understanding the epidemiology of HPAI viruses is essential for the planning future surveillance and control activities.

Assessing the variability in transmission of bovine tuberculosis within Spanish cattle herds

In Spain, despite years of efforts to eradicate bovine tuberculosis (bTB), the disease is still endemic, with some areas of high prevalence. In this context, the surveillance and control plans may need to be re-evaluated, and understanding the dynamics of bTB spread within Spanish herds may help to develop new strategies for reducing the time for detection of infected herds and for the elimination of bTB from the herds already infected. Here, we developed a compartmental stochastic model to simulate bTB within-herd transmission, fed it with epidemiological data from 22 herds (obtained from a previous work) and carried out parameter inference using Approximate Bayesian Computing methods We also estimated the "Within-herd transmission potential Number" (R_h), i.e. the average number of secondary cases generated by a single animal infected introduced into a totally susceptible herd, considering different scenarios depending on the frequency of controls. The median global values obtained for the transmission parameters were: for the transmission coefficient (β), 0.014 newly infected animals per infectious individual per day (i.e. 5.2 per year), for the rate at which infected individuals become infectious (α), 0.01 per day (equivalent to a latent period of 97 days), and for the rate at which infected individuals become reactive to the skin test (α₁), 0.08 per day (equivalent to a period of 12 days for an infected animal to become reactive). However, the results also evidenced a great variability in the estimates of those parameters (in particular β and α) among the 22 herds. Considering a 6-month interval between tests, the mean R_h was 0.23, increasing to 0.82 with an interval of 1 year, and to 2.01 and 3.47 with testing intervals of 2 and 4 years, respectively.

Epidemiology and spatio-temporal analysis of West Nile virus in horses in Spain between 2010 and 2016

During the last decade, West Nile virus (WNV) outbreaks have increased sharply in both horses and human in Europe. The aims of this study were to evaluate characteristics and spatio-temporal distribution of WNV outbreaks in horses in Spain between 2010 and 2016 in order to identify the environmental variables most associated with WNV occurrence and to generate high-resolution WNV suitability maps to inform risk-based surveillance strategies in this country. Between August 2010 and November 2016, a total of 403 WNV suspected cases were investigated, of which, 177 (43.9%) were laboratory confirmed. Mean values of morbidity, mortality and case fatality rates were 7.5%, 1.6% and 21.2%, respectively. The most common clinical symptoms were as follows: tiredness/apathy, recumbency, muscular tremor, ataxia, incoordination and hyperaesthesia. The outbreaks confirmed during the last 7 years, with detection of WNV RNA lineage 1 in 2010, 2012, 2013, 2015 and 2016, suggest an endemic circulation of the virus in Spain. The spatio-temporal distribution of WNV outbreaks in Spain was not homogeneous, as most of them (92.7%) were concentrated in western part of Andalusia (southern Spain) and significant clusters were detected in this region in two non-consecutive years. These findings were supported by the results of the space-time scan statistics permutation model. A presence-only MaxEnt ecological niche model was used to generate a suitability map for WNV occurrence in Andalusia. The most important predictors selected by the Ecological Niche Modeling were as follows: mean annual temperature (49.5% contribution), presence of Culex pipiens (19.5% contribution), mean annual precipitation (16.1% contribution) and distance to Ramsar wetlands (14.9% contribution). Our results constitute an important step for understanding WNV emergence and spread in Spain and will provide valuable information for the development of more cost-effective surveillance and control programmes and improve the protection of horse and human populations in WNV-endemic areas.

Understanding Spatio-Temporal Variability in the Reproduction Ratio of the Bluetongue (BTV-1) Epidemic in Southern Spain (Andalusia) in 2007 Using Epidemic Trees

Andalusia (Southern Spain) is considered one of the main routes of introduction of bluetongue virus (BTV) into Europe, evidenced by a devastating epidemic caused by BTV-1 in 2007. Understanding the pattern and the drivers of BTV-1 spread in Andalusia is critical for effective detection and control of future epidemics. A long-standing metric for quantifying the behaviour of infectious diseases is the case-reproduction ratio (R_t), defined as the average number of secondary cases arising from a single infected case at time t (for t>0). Here we apply a method using epidemic trees to estimate the between-herd case reproduction ratio directly from epidemic data allowing the spatial and temporal variability in transmission to be described. We then relate this variability to predictors describing the hosts, vectors and the environment to better understand why the epidemic spread more quickly in some regions or periods. The R_t value for the BTV-1 epidemic in Andalusia peaked in July at 4.6, at the start of the epidemic, then decreased to 2.2 by August, dropped below 1 by September (0.8), and by October it had decreased to 0.02. BTV spread was the consequence of both local transmission within established disease foci and BTV expansion to distant new areas (i.e. new foci), which resulted in a high variability in BTV transmission, not only among different areas, but particularly through time, which suggests that general control measures applied at broad spatial scales are unlikely to be effective. This high variability through time was probably due to the impact of temperature on BTV transmission, as evidenced by a reduction in the value of R_t by 0.0041 for every unit increase (day) in the extrinsic incubation period (EIP), which is itself directly dependent on temperature. Moreover, within the range of values at which BTV-1 transmission occurred in Andalusia (20.6°C to 29.5°C) there was a positive correlation between temperature and R_t values, although the relationship was not linear, probably as a result of the complex relationship between temperature and the different parameters affecting BTV transmission. R_t values for BTV-1 in Andalusia fell below the threshold of 1 when temperatures dropped below 21°C, a much higher threshold than that reported in other BTV outbreaks, such as the BTV-8 epidemic in Northern Europe. This divergence may be explained by differences in the adaptation to temperature of the main vectors of the BTV-1 epidemic in Andalusia (Culicoides imicola) compared those of the BTV-8 epidemic in Northern Europe (Culicoides obsoletus). Importantly, we found that BTV transmission (R_t value) increased significantly in areas with higher densities of sheep. Our analysis also established that control of BTV-1 in Andalusia was complicated by the simultaneous establishment of several distant foci at the start of the epidemic, which may have been caused by several independent introductions of infected vectors from the North of Africa. We discuss the implications of these findings for BTV surveillance and control in this region of Europe.

Serological Follow-up of Tuberculosis in a Wild Boar Population in Contact with Infected Cattle

There is an increasing concern in several European countries over the role that tuberculosis (TB)-infected wild boar may play in the progress of bovine TB eradication campaigns. In 2004, as a consequence of the detection of a TB focus in wild boar from a National Game Reserve (NGR) located in southern Catalonia, a surveillance programme based on post-mortem inspection for detection of macroscopic TB-like lesions (TBLL) was initiated in the affected area. The source of infection for wild boar was linked to a tuberculous cattle herd located in the same area. Besides, the results of the surveillance programme in wild boar were used for the validation of an indirect enzyme-linked immunosorbent assay (ELISA) specific for Mycobacterium tuberculosis complex (MTBC) IgG antibodies. Using this ELISA, a seven-year serological study of MTBC in wild boar from the NGR was conducted in 173 animals (93 adults, 44 juveniles-yearlings and 36 piglets) culled between 2004 and 2010. ELISA results and presence of TBLL showed excellent agreement for adult and juvenile wild boar (Kappa index = 0.85; 95% CI: 0.76-0.95). Of the thirty-eight adults, yearlings and juveniles classified as positives by the ELISA, 34 (89%) showed TBLL at necropsy. In contrast, none of the ELISA-positive wild boar piglets (n = 20) showed TBLL, suggesting the detection of early antibody responses to the infection. Overall, this study contributes to the knowledge of wild boar humoral responses to MTBC. The results also highlight the usefulness of this serological test for wild boar TB surveillance.

Ecological surveillance for West Nile in Catalonia (Spain), learning from a five-year period of follow-up

To enhance early detection of West Nile virus (WNV) transmission, an integrated ecological surveillance system was implemented in Catalonia (north-eastern Spain) from 2007 to 2011. This system incorporated passive and active equine surveillance, periodical testing of chicken sentinels in wetland areas, serosurveillance wild birds and testing of adult mosquitoes. Samples from 298 equines, 100 sentinel chickens, 1086 wild birds and 39 599 mosquitoes were analysed. During these 5 years, no acute WNV infection was detected in humans or domestic animal populations in Catalonia. WNV was not detected in mosquitoes either. Nevertheless, several seroconversions in resident and migrant wild birds indicate that local WNV or other closely related flaviviruses transmission was occurring among bird populations. These data indicate that bird and mosquito surveillance can detect otherwise silent transmission of flaviviruses and give some insights regarding possible avian hosts and vectors in a European setting.

Assessment of the risk of a bluetongue outbreak in Europe caused by Culicoides midges introduced through intracontinental transport and trade networks

The importation of infected hosts and the arrival of windborne infected Culicoides (Diptera: Ceratopogonidae) were considered unlikely mechanisms for bluetongue virus (BTV) incursion into a BTV-free area during the recent BTV serotype 8 (BTV-8) epidemic in northern Europe. Therefore, alternative mechanisms need to be considered. Air, sea and land transport networks continue to expand, and an important consequence of this is vector-borne pathogen importation. One important aspect of bluetongue (BT) epidemiology not yet addressed is the potential movement of infected Culicoides via transport and trade networks. Therefore, a risk assessment model was constructed to assess the probability of a BTV outbreak as a consequence of the introduction of Culicoides via these networks. The model was applied to calculate the risk for a BTV-8 epidemic in Spain in 2007 caused by the introduction of Culicoides from affected northern European countries. The mean weighted annual risk for an outbreak caused by transportation of a single vector from an affected northern European country varied from 1.8 × 10(-7) to 3.0 × 10(-13), with the highest risks associated with Culicoides imported from Belgium, the Netherlands, Germany and France. For this mechanism to pose a significant risk to BTV-free countries, a large number of vectors would have to be transported.

Monitoring bluetongue disease (BTV-1) epidemic in southern Spain during 2007

On the 25th of July 2007, bluetongue virus (BTV) serotype 1 was detected in Andalusia, southern Spain for the first time. A total of 4436 farms infected with BTV-1 were confirmed during that year: 3162 in sheep flocks, 113 in goat flocks, 7 in cattle herds and 1154 in mixed farms (sheep, goat and/or cattle in the same farm). The most common clinical signs were: fever, depression, lethargy, facial edema, and salivation (observed in more than 70% of the infected farms). Lesions in oral mucosa, lameness and dyspnea were also frequently observed. Median morbidity rate in sheep and goat flocks were 6.3% and 2.7% respectively. Median mortality rate was 2.2% in sheep flocks and 1.2% in goat flocks. Median case fatality rate was 29.8% in sheep flocks and 45% in goat flocks. Morbidity and mortality rates were not significantly higher in sheep flocks than in goat flocks (p>0.05), whereas case fatality rate was significant higher in goat flocks compared to sheep flocks (p<0.05). Neither clinical signs nor mortality were observed in cattle herds. The spatial distribution of the risk of BTV infection over Andalusia by municipality was evaluated by means of a hierarchical Bayesian model. The results evidenced that the risk was not homogeneous over the territory, being higher in the western part of the region. The likelihood of BTV infection was increased between 1.01 and 1.16 times by an increase of 10,000 domestic ruminants, and between 1.01 and 1.69 times by the presence of red deer (Cervus elaphus) in the municipality.

Assessment of different surveillance systems for avian influenza in commercial poultry in Catalonia (North-Eastern Spain)

Compulsory surveillance programmes for avian influenza (AI) have been implemented in domestic poultry and wild birds in all the European Member States since 2005. The implementation of these programmes is complex and requires a close evaluation. A good indicator to assess their efficacy is the sensitivity (Se) of the surveillance system. In this study, the sensitivities for different sampling designs proposed by the Spanish authorities for the commercial poultry population of Catalonia were assessed, using the scenario tree model methodology. These samplings were stratified throughout the territory of Spain and took into account the species, the types of production and their specific risks. The probabilities of detecting infection at different prevalences at both individual and holding level were estimated. Furthermore, those subpopulations that contributed more to the Se of the system were identified. The model estimated that all the designs met the requirements of the European Commission. The probability of detecting AI circulating in Catalonian poultry did not change significantly when the within-holding design prevalence varied from 30% to 10%. In contrast, when the among-holding design prevalence decreased from 5% to 1%, the probability of detecting AI was drastically reduced. The sampling of duck and goose holdings, and to a lesser extent the sampling of turkey and game bird holdings, increased the Se substantially. The Se of passive surveillance in chickens for highly pathogenic avian influenza (HPAI) and low pathogenicity avian influenza (LPAI) were also assessed. The probability of the infected birds manifesting apparent clinical signs and the awareness of veterinarians and farmers had great influence on the probability of detecting AI. In order to increase the probability of an early detection of HPAI in chicken, the probability of performing AI specific tests when AI is suspected would need to be increased.

Brotes de fiebre aftosa en Europa (1991-2005)

La fiebre aftosa (FA) ha sido considerada durante muchos años como la enfermedad animal más importante debido a sus consecuencias sanitarias y económicas. Actualmente la enfermedad es endémica en varios países, especialmente de África y Asia. Por el contrario, Europa es una zona libre, si bien se siguen produciendo epidemias de forma esporádica. Europa erradicó la fiebre aftosa por medio de campañas de vacunación profiláctica que finalizaron en 1991. A partir de esa fecha la prevención de epidemias se basa en el control de las importaciones de animales y sus productos. Si bien las medidas establecidas han conseguido en general mantener fuera de Europa el virus de fiebre aftosa, varios países se vieron afectados por epidemias de esta enfermedad entre 1991 y 2005. En este trabajo se revisan las epidemias más importantes agrupadas por el origen del brote: introducción de productos contaminados o de animales infectados. A pesar de las estrictas medidas de control establecidas en Europa, el riesgo de introducción del virus de la FA en Europa no es despreciable, como lo demuestran las distintas epidemias ocurridas en los últimos años.

Immunization with H1, HASPB1 and MML Leishmania proteins in a vaccine trial against experimental canine leishmaniasis

The protective capabilities of three Leishmania recombinant proteins – histone 1 (H1) and hydrophilic acylated surface protein B1 (HASPB1) immunized singly, or together as a protein cocktail vaccine with Montanide™, and the polyprotein MML immunized with MPL^®-SE adjuvant – were assessed in beagle dogs. Clinical examination of the dogs was carried out periodically under blinded conditions and the condition of the dogs defined as asymptomatic or symptomatic. At the end of the trial, we were able to confirm that following infection with L. infantum promastigotes, five out of eight dogs immunized with H1 Montanide™, and four out of eight dogs immunized with either the combination of HASPB1 with Montanide™ or the combination of H1 + HASPB1 with Montanide™, remained free of clinical signs, compared with two out of seven dogs immunized with the polyprotein MML and adjuvant MPL^®-SE, and two out of eight dogs in the control group. The results demonstrate that HASPB1 and H1 antigens in combination with Montanide™ were able to induce partial protection against canine leishmaniasis, even under extreme experimental challenge conditions.