Evaluation of the Control of West Nile Virus in Ontario: Did Risk Patterns Change from 2005 to 2012?

The goal of this study was to evaluate and compare the risk distribution of human cases of West Nile virus (WNV) disease in Ontario in 2005 to 2012. The objectives were to: map the risk distribution of WNV in 2005 and 2012, identify clusters of human WNV disease and determine whether the clusters are significantly different between the years 2005 and 2012. West Nile virus surveillance data were used to calculate empirical Bayesian smoothed estimates of disease incidence in southern Ontario for 2005 and 2012. Choropleth maps were generated to visualize the spatial risk distribution, and the spatial scan test was performed to identify clusters of disease. Following identification of clusters for 2005 and 2012, a Poisson model was applied to the 2012 human WNV incidence adjusted for the smoothed human WNV incidence rate from 2005 and the scan test was repeated. Two significant clusters were identified in both the year 2005 and 2012. In 2005, the primary cluster was located in the Windsor‐Essex and Chatham‐Kent public health units (PHUs). For 2012, the primary cluster was identified in the Golden Horseshoe area. A cluster analysis for 2012 adjusted for those identified in 2005 resulted in one significant cluster in the Windsor‐Essex PHU. In 2012, the Windsor‐Essex PHU remained as a high‐risk area for human WNV disease when compared with the rest of southern Ontario. Although overall risk may change from year to year, public health programming should be employed to decrease the relative risk of WNV in this area.     

West Nile virus: North American experience

West Nile virus, a mosquito‐vectored flavivirus of the Japanese encephalitis serogroup, was first detected in North America following an epizootic in the New York City area in 1999. In the intervening 11 years since the arrival of the virus in North America, it has crossed the contiguous USA, entered the Canadian provinces bordering the USA, and has been reported in the Caribbean islands, Mexico, Central America and, more recently, South America. West Nile virus has been reported in over 300 species of birds in the USA and has caused the deaths of thousands of birds, local population declines of some avian species, the clinical illness and deaths of thousands of domestic horses, and the clinical disease in over 30 000 Americans and the deaths of over 1000. Prior to the emergence of West Nile virus in North America, St. Louis encephalitis virus and Dengue virus were the only other known mosquito‐transmitted flaviviruses in North America capable of causing human disease. This review will discuss the North American experience with mosquito‐borne flavivirus prior to the arrival of West Nile virus, the entry and spread of West Nile virus in North America, effects on wild bird populations, genetic changes in the virus, and the current state of West Nile virus transmission.     

Clinical West Nile virus infection in 2 horses in western Canada

Two horses had a history of ataxia and weakness or recumbency. One recovered and was diagnosed with West Nile virus (WNV) infection by serologic testing. The other was euthanized; it had meningoencephalomyelitis, WNV was detected by polymerase chain reaction. West Nile virus infection is an emerging disease. Year 2002 is the first year in which cases have been seen in Saskatchewan.     

上海地区禽与马血清中西尼罗病毒抗体的调查

西尼罗病毒病是一种以鸟类为中间宿主、以马为终末宿主的人兽共患病,给全球公共卫生带来严重威胁。本文用ELISA方法对上海地区禽和马中西尼罗病毒的血清学进行了调查,结果显示,在所调查的2005年到2009年14类95份禽血清和7个区341份马血清中,禽和马的抗体阳性率分别为5.26%和0%。结果表明,该病在上海已通过禽类开始广泛传播,虽尚未发现终末宿主感染,但已存在一定隐患。因此,应进一步监测该病的流行与传播情况。     

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.     

Recent rapid changes in the spatio‐temporal distribution of West Nile Neuro‐invasive Disease in Italy

In Italy, the first human case of West Nile Virus (WNV) infection was reported in 2008 and, since then, the number of cases has been steadily increasing. In this study, we describe the temporal and spatial pattern of WNV infection risk among humans in Italy, focusing on the human cases of West Nile Neuro‐invasive Disease (WNND) observed between 2008 and 2017. Incidence rates are estimated for each year and province under study. The incidence temporal trend is estimated using Poisson regression, and a spatio‐temporal cluster detection analysis is performed to detect high‐risk areas. In total, 231 WNND cases were notified in Italy between 2008 and 2017. The annual incidence rates increased during the study period (annual percentage change: 11.7%; 95%CI: ?0.9%; 26.1%). A geographical spread of the disease was observed during the study period throughout Northern Italy, with an increasing number of affected provinces. Provinces close to the Po River (the main river in the north of Italy) and the Oristano province (in the Sardinia Island) experienced the highest incidence rates during the study period. Our study shows a gradual, but rapid spread of WNND across Northern Italy from east to west and suggests the hypothesis that provinces close to Po River might present ecological and climatic conditions favourable to the virus circulation.     

Prediction of human cases of West Nile virus by equine cases, Saskatchewan, Canada, 2003

In 2003, an outbreak of West Nile virus (WNV) occurred in Saskatchewan, Canada from July to September. One-hundred thirty-three horse cases and 947 human cases were recorded and data were analyzed retrospectively for evidence of clustering to determine if clinical infection in the horse population could be used to estimate human risk of infection with WNV. Kulldorff's scan statistic was used to identify spatial-temporal clusters in both the human and horse cases. In most areas, human clusters were not preceded by horse clusters. In one area, a significant cluster of horse cases preceded human cases by 1 week; however, 1 week does not provide sufficient time for human-health authorities to act and provide advance warning for the public.     

West Nile virus: lessons from the 21st century

Introduction: West Nile virus (WNV) first appeared in the United States in 1999, causing illness and death in birds, horses, and humans. While the initial outbreak of this sometimes deadly viral disease was limited to the northeastern United States, the virus had an inexorable migration across the continental United States over the next 3 years, causing huge losses among the affected species. The purpose of this review is to present currently available information regarding the epi‐demiology, diagnosis, treatment, and prevention of WNV infection. Veterinarians, particularly those in an emergency practice, serve as an important source of reliable information regarding this disease for animal owners and the public in general. Data sources: Data sources used for the preparation of this review include computer‐based searches of PubMed and Commonwealth Agricultural Bureaux (CAB) abstracts. A search in PubMed using ‘West Nile’ retrieved 1468 ‘hits’ or references, while a similar search in CAB abstracts produced 815 references. Additional information was obtained from various meeting proceedings, particularly data presented in abstract form, and from the Centers for Disease Control (CDC) website dedicated to WNV. Human data synthesis: Prior to the mid‐1990s, reported large‐scale epidemics of WNV infection in humans predominantly presented as acute, mild, febrile disease, sometimes associated with lymphadenopathy and skin rash. The recent large epidemic in the United States, in contrast, has prominently featured encephalitis, particularly among the elderly. Additionally, polio‐encephalomyelitis‐like complications resulting in long‐term neurologic sequelae have been reported. There are many WNV‐permissive native avian and mosquito hosts in the Unites States and there appear to be few limitations to the spread of the disease in the United States. It is expected that the virus will be identified in all 48 continental states, Mexico, and Canada by the end of 2003. Veterinary data synthesis: The horse is the animal species most affected by the recent WNV epidemic in the United States, and losses to the equine industry have been large and unprecedented. A United States Department of Agriculture (USDA)‐approved vaccine against WNV has been in use in horses since 2001 and appears to be effective in limiting the incidence of disease in well‐vaccinated populations. WNV infection has been documented in other species of mammals, including camelids (alpaca/llamas) and dogs, and veterinarians should include WNV as a differential diagnosis for animals presenting with clinical signs consistent with central nervous system infection. A large concern exists for endangered bird populations, particularly birds of prey, whether in zoos or in the wild.     

上海闵行地区犬和猫中西尼罗河病毒病血清学调查

西尼罗病毒病是一种外来的新发性的虫媒人兽共患病,近年来已经成为全球公共卫生的新威胁。采用ELISA对上海市闵行地区犬和猫中西尼罗河病毒的血清学调查结果显示,在所调查的7个地区中,犬和猫中的抗体阳性率分别达到4.6%和15.5%。本调查数据和分析为制定科学、合理的防控对策提供了技术依据。     

Investigation of an outbreak of encephalomyelitis caused by West Nile virus in 136 horses

OBJECTIVE: To describe an outbreak of encephalomyelitis caused by West Nile virus (WNV) in horses in northern Indiana. DESIGN: Case series. ANIMALS: 170 horses. PROCEDURES: Horses with clinical signs suggestive of encephalomyelitis caused by WNV were examined. Date, age, sex, breed, and survival status were recorded. Serum samples were tested for anti-WNV antibodies, and virus isolation was attempted from samples of brain tissue. Climate data from local weather recording stations were collected. An epidemic curve was constructed, and case fatality rate was calculated. RESULTS: The most common clinical signs were ataxia, hind limb paresis, and muscle tremors and fasciculations. Eight horses had been vaccinated against WNV from 2 to 21 days prior to the appearance of clinical signs. West Nile virus was isolated from brain tissue of 2 nonvaccinated horses, and anti-WNV IgM antibodies were detected in 132 nonvaccinated horses; in 2 other nonvaccinated horses, anti-WNV antibodies were detected and WNV was also isolated from brain tissue. Thirty-one (22.8%) horses died or were euthanatized. The peak of the outbreak occurred on September 6, 2002. Ambient temperatures were significantly lower after the peak of the outbreak, compared with prior to the peak. CONCLUSIONS AND CLINICAL RELEVANCE: The peak risk period for encephalomyelitis caused by WNV in northern Indiana was mid-August to mid-September. Reduction in cases coincided with decreasing ambient temperatures. Because of a substantial case fatality rate, owners of horses in northern Indiana should have their horses fully protected by vaccination against WNV before June. In other regions of the United States with a defined mosquito breeding season, vaccination of previously nonvaccinated horses should commence at least 4 months before the anticipated peak in seasonal mosquito numbers, and for previously vaccinated horses, vaccine should be administered no later than 2 months before this time.     

Wild birds as sentinels for multiple zoonotic pathogens along an urban to rural gradient in greater Chicago, Illinois

Wild birds are important in the maintenance and transmission of many zoonotic pathogens. With increasing urbanization and the resulting emergence of zoonotic diseases, it is critical to understand the relationships among birds, vectors, zoonotic pathogens, and the urban landscape. Here, we use wild birds as sentinels across a gradient of urbanization to understand the relative risk of diseases caused by three types of zoonotic pathogens: Salmonella pathogens, mosquito-borne West Nile virus (WNV) and tick-borne pathogens, including the agents of Lyme disease and human anaplasmosis. Wild birds were captured using mist nets at five sites throughout greater Chicago, Illinois, and blood, faecal and ectoparasite samples were collected for diagnostic testing. A total of 289 birds were captured across all sites. A total of 2.8% of birds harboured Ixodes scapularis--the blacklegged tick--of which 54.5% were infected with the agent of Lyme disease, and none were infected with the agent of human anaplasmosis. All infested birds were from a single site that was relatively less urban. A single bird, captured at the only field site in which supplemental bird feeding was practised within the mist netting zone, was infected with Salmonella enterica subspecies enterica. While no birds harboured WNV in their blood, 3.5% of birds were seropositive, and birds from more urban sites had higher exposure to the virus than those from less urban sites. Our results demonstrate the presence of multiple bird-borne zoonotic pathogens across a gradient of urbanization and provide an assessment of potential public health risks to the high-density human populations within the area.     

Environmental risk factors for equine West Nile virus disease cases in Texas

West Nile Virus (WNV) was first detected in the Texas equine population during June 2002. Infection has since spread rapidly across the state and become endemic in the equine population. Environmental risk factors associated with equine WNV attack rates in Texas counties during the period 2002 to 2004 were investigated. Equine WNV attack rates were smoothed using an empirical Bayesian model, because of the variability among county equine populations (range 46−9,517). Risk factors investigated included hydrological features (lakes, rivers, swamps, canals and river basins), land cover (tree, mosaic, shrub, herbaceous, cultivated and artificial), elevation, climate (rainfall and temperature), and reports of WNV-positive mosquito and wild bird samples. Estimated county equine WNV attack rate was best described by the number of lakes, presence of broadleaf deciduous forest, presence of cultivated areas, location within the Brazos River watershed, WNV-positive mosquito status and average temperature. An understanding of environmental factors that increase equine WNV disease risk can be used to design and target disease control programs.     

新疆地区蚊类携带西尼罗病毒情况调查研究

为查明新疆地区蚊体内携带西尼罗病毒的情况,从2005年-2007年每年的7月~10月采集新疆不同地区的蚊子共计16000余只,并提取总RNA,通过RT-nest PCR的方法检测样品中西尼罗病毒。结果表明,调查样品中没有检测到西尼罗病毒,但不能就此推测新疆是否存在西尼罗病毒,至少对新疆地区和全国制定针对不同动物和人的积极防御政策有重要的公共卫生学意义。     

West Nile Virus in North‐Eastern Italy, 2011: Entomological and Equine IgM‐Based Surveillance to Detect Active Virus Circulation

Since 2008, West Nile Virus (WNV) has expanded its range in several Italian regions, and its yearly recurrence suggests the virus may have become endemic in some areas. In 2011, a new plan based also on the detection of IgM antibodies was implemented in the north‐eastern Italian regions of Veneto and Friuli Venezia Giulia, aiming to early detect WNV infections in areas where the virus had already circulated during the previous summers, and in adjacent zones. From July to November 2011, 1880 sera from 521 equine premises were screened by a commercial IgM capture ELISA. Mosquitoes were captured by CDC‐CO₂ traps at 61 locations in the two regions. Collected mosquitoes were identified, pooled by species/date/location and examined by real‐time RT‐PCR and sequencing. Passive surveillance was carried out on clinically affected horses and non‐migratory wild birds found dead. IgM sero‐positive equines were detected in 19 holdings, five in the area with WNV circulation (AWC) and 14 in the surveillance area (SA); 10 more horse premises tested positive to further serological controls within 4 km of the positive holdings. A total of 85 398 mosquitoes of 15 species were collected and 2732 pools examined. Five Culex pipiens pools tested positive for the presence of WNV. Passive surveillance on non‐migratory wild birds allowed detection of the virus only in one found dead collared dove (Streptopelia decaocto), of 82 birds sampled. The WNV belonged to the lineage 2, which had been isolated for the first time in Italy earlier in 2011. By the first week of October, nine human cases had been confirmed in the same area. The implementation of a protocol combining IgM screening of horses with surveillance on mosquito vectors proved to be valuable for early detecting WNV circulation.     

Seroprevalence and molecular characterization of West Nile Virus in Egypt

West Nile Virus (WNV) is a flavivirus, mosquito-borne infection and have public health importance worldwide. WNV infection have highly significant impact on animal and human health. The virus has been detected serologically in Egypt among equids. Therefore, the aim of the present study to investigate the serological situation of WNV among horse in north of Egypt and identification of WNV in vector. The serological survey was conducted on 500 serum samples that collected from horses from four governorates at north of Egypt. The infection rate was non-significant differed between four localities and the highest rate was reported in Qalyubia governorate (25.5 %) in comparison with other areas. Moreover, the WNV RNA was detected in mosquitoes and the obtained WNV sequence showed high similarity with Eg101 strain and characterized as lineage 1. The obtained findings confirm the circulation of WNV in mosquitoes and animals in Egypt.     

西尼罗河病毒病的研究进展

西尼罗河病毒病是由西尼罗河病毒(West Nile Virus,WNV)引起的一种人畜共患传染病,病原是一种虫媒病毒,可导致西尼罗河热和致死性的西尼罗河脑炎。自发现以来,西尼罗河病毒病曾在世界上多个国家暴发,给畜牧业和人类生命安全造成了巨大的危害。我国目前尚无该病的发生,但是防治技术储备是必要的。本文对西尼罗河病毒病的流行病学、病原学、致病机制、临床症状和病理剖检变化、诊断方法和候选疗法进行综述,为西尼罗河病毒病的防控提供资料。