Serological evidence of West Nile virus infection in human populations and domestic birds in the Northwest of Morocco

West Nile virus (WNV) was recently detected in Culex pipiens mosquitoes in Morocco. The aim of this study was to evaluate the seroprevalence of WNV in humans and in domestic birds in two regions of Morocco by the detection of IgG antibodies. Blood samples were obtained from 91 human patients and 92 domestic birds from September to December 2019. All study samples were tested using competitive enzyme-linked immunosorbent assay (cELISA) and WNV neutralization tests (VNT) were performed on positive sera. Of all samples, 4 (4.39 %) humans and 4 (4.34 %) birds were found to be seropositive for flaviviruses by the cELISA test. The VNT revealed that three of the four human samples detected positive by cELISA contained neutralizing antibodies against WNV. Two bird samples were confirmed positive by VNT. These results show a significant seroprevalence of anti-WNV antibodies and therefore suggest the active circulation and exposure of human and bird populations in the northwest of Morocco.     

Absence of humoral response in flamingos and red-tailed hawks to experimental vaccination with a killed West Nile virus vaccine

Sixteen Chilean flamingos, Phoenicopterus chiles, and 10 red-tailed hawks, Buteo jamacensis, were vaccinated in the pectoral muscle with 0.2 ml of a commercially produced killed West Nile virus vaccine intended for use in horses. Half the birds of each species received a booster vaccination 3 weeks after the first injection. Three weeks after the booster vaccination, none of 13 birds surveyed had detectable antibody to West Nile virus.     

Serological evidence of West Nile virus circulation in Portugal

The circulation of West Nile virus in Portugal was assessed by serological surveys conducted during 2004-2010 in horses and birds. The detection of WNV antibodies in both species in all the years covered by the study as well as the presence of anti-WNV IgM in symptomatic horses that had not traveled outside the country, support the notion that WNV circulates in Portugal.     

Pathology and tissue tropism of natural West Nile virus infection in birds: a review

West Nile virus (WNV) is a globally distributed arthropod-borne flavivirus capable of infecting a wide variety of vertebrates, with birds as its natural reservoir. Although it had been considered a pathogen of little importance for birds, from the 1990’s, and especially after its introduction in the North American continent in 1999, thousands of birds have succumbed to West Nile infection. This review summarizes the pathogenesis and pathology of WNV infection in birds highlighting differences in lesion and antigen distribution and severity among bird orders and families. Despite significant species differences in susceptibility to infection, WNV associated lesions and viral antigen are present in the majority of organs of infected birds. The non-progressive, acute or more prolonged course of the disease accounts for part of the differences in lesion and viral antigen distribution and lesion severity. Most likely a combination of host variables and environmental factors in addition to the intrinsic virulence and pathogenicity of the infecting WNV strain influence the pathogenesis of the infection.     

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.     

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.     

Pathologic and immunohistochemical findings in naturally occuring West Nile virus infection in horses

The pathologic and peroxidase immunohistochemical features of West Nile flavivirus (WNV) infection were compared in four horses from the northeastern United States and six horses from central Italy. In all 10 animals, there were mild to severe polioencephalomyelitis with small T lymphocyte and lesser macrophage perivascular infiltrate, multifocal glial nodules, neutrophils, and occasional neuronophagia. Perivascular hemorrhages, also noted macroscopically in two animals, were observed in 50% of the horses. In the four American horses, lesions extended from the basal nuclei through the brain stem and to the sacral spinal cord and were more severe than the lesions observed in the six Italian horses, which had moderate to severe lesions mainly in the thoracolumbar spinal cord and mild rhombencephalic lesions. WNV antigen was scant and was identified within the cytoplasm of a few neurons, fibers, glial cells, and macrophages. WNV infection in horses is characterized by lesions with little associated antigen when compared with WNV infection in birds and some fatal human infections and with other important viral encephalitides of horses, such as alphavirus infections and rabies.     

Attempts to detect West Nile virus in wild birds in Poland

The aim of the study was to attempt the detection of West Nile virus (WNV) in wild birds in Poland. Forty-eight species of 1912 wild birds were used for the investigations. The birds were derived from various locations in Poland from early spring till late autumn of the years 2009-2011. The brain samples were homogenised and cellular RNA was isolated. Two methods (RT-PCR and nested RT-PCR) were used. The presence of WNV RNA was not detected in the samples examined. Additionally, a short analysis of the epizootiological situation regarding the presence of WNV in Poland is presented.     

Serologic evidence of West Nile virus infection in three wild raptor populations

We assayed for West Nile virus (WNV) antibodies to determine the presence and prevalence of WNV infection in three raptor populations in southeast Wisconsin during 2003-04. This study was conducted in the framework of ongoing population studies that started before WNV was introduced to the study area. For 354 samples, 88% of 42 adult Cooper's hawks (Accipiter cooperii), 2.1% of 96 nestling Cooper's hawks, 9.2% of 141 nestling red-tailed hawks (Buteo jamaicensis), and 12% of 73 nestling great horned owls (Bubo virginianus) tested positive for WNV antibodies by the constant virus-serum dilution neutralization test. Samples that tested positive for WNV antibodies were collected across a wide variety of habitat types, including urban habitats (both high and low density), roads, parking areas, recreational areas, croplands, pastures, grasslands, woodlands, and wetlands. Based on the increased prevalence and significantly higher WNV antibody titers in adults compared with nestlings, we suggest that nestlings with detectable antibody levels acquired these antibodies through passive transmission from the mother during egg production. Low levels of WNV antibodies in nestlings could serve as a surrogate marker of exposure in adult raptor populations. Based on breeding population densities and reproductive success over the past 15 yr, we found no apparent adverse effects of WNV infections on these wild raptor populations.     

Clinical findings, lesions, and viral antigen distribution in great gray owls (Strix nebulosa) and barred owls (Strix varia) with spontaneous West Nile virus infection

West Nile Virus (WNV) infection manifests itself clinically a nd pathologically differently in various species of birds. The clinicopathologic findings and WNV antigen tissue distribution of six great gray owls (Strix nebulosa) and two barred owls (Strix varia) with WNV infection are described in this report. Great gray owls usually live in northern Canada, whereas the phylogenetically related barred owls are native to the midwestern and eastern United States and southern Canada. Naturally acquired WNV infection caused death essentially without previous signs of disease in the six great gray owls during a mortality event. Lesions of WNV infection we re dominated by hepatic and splenic necrosis, with evidence o f disseminatedintravascular coagulation in the great gray owls. WNV antigen was widely distributed in th e organs of the great gray owls and appeared totarget endothelial cells, macrophages, and hepatocytes. The barred owls represented two sporadic cases. They had neurologic disease with mental dullness that led to euthanasia. These birds had mild to moderate lymphoplasmacytic encephalitis with glial nodules and lymphoplasmacytic pectenitis. WNV antigen was sparse in barred owls and only present in a few brain neurons and renaltubular epithelial cells. The cause of the different manifestations of WNV disease in these fairly closely related owl species is uncertain.     

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.     

West Nile virus-associated mortality events in domestic Chukar partridges (Alectoris chukar) and domestic Impeyan pheasants (Lophophorus impeyanus)

West Nile virus (WNV) infection was diagnosed in captive juvenile chukars (Alectoris chukar), and captive juvenile Impeyan pheasants (Lophophorus impeyanus) on the basis of necropsy, histopathology, polymerase chain reaction, and immunohistochemistry. The chukars were kept in a game bird farm that experienced two outbreaks with approximately 25% mortality in hundreds of chukars between September and October 2002 and during the same months in 2003. The submitted pheasants were part of a group of 15 juvenile Impeyan pheasants that all died within approximately 2 wk at the end of August 2002. The macroscopic lesions in the pheasants were dominated by mucosal hemorrhage at the proventricular to ventricular junction and cecal ulcers, whereas the gross lesions in the chukar partridges were nonspecific. The predominant microscopic lesion in the chukar partridges was myocardial necrosis, whereas fibrinous and necrotizing splenitis was prominent in the pheasants. Viral antigen was usually widespread in animals of both species. Spontaneously occurring WNV infection should be considered a differential diagnosis in cases of mortality among select species of galliform birds.