Asymptomatic West Nile Virus Infection Research Articles

A Preliminary Study of Proinflammatory Cytokines and Depression Following West Nile Virus Infection.

West Nile virus (WNV) is a neurotropic flavivirus that can cause acute febrile illness leading to neuroinvasive disease. Depression is a well-described outcome following infection, but the underlying pathogenic mechanisms are unknown. Proinflammatory cytokines play important roles in WNV infection, but their role in depression post-WNV remains unstudied. This research aimed to retrospectively evaluate associations between proinflammatory cytokines and new onset depression in a WNV cohort. Participants with asymptomatic WNV infection were significantly less likely to report new onset depression when compared to those with symptomatic disease. Participants with encephalitis and obesity were significantly more likely to report new onset depression post-infection. Based on univariate analysis of 15 antiviral or proinflammatory cytokines, depression was associated with elevated MCP-1 and decreased TNFα, whereas G-CSF was significantly elevated in those with a history of neuroinvasive WNV. However, no cytokines were statistically significant after adjusting for multiple comparisons using the Bonferroni method. While symptomatic WNV infection, encephalitis, and obesity were associated with new onset depression following infection, the role of proinflammatory cytokines requires additional studies. Further research involving paired acute-convalescent samples, larger sample sizes, and additional data points would provide additional insight into the impact of the inflammatory response on WNV-mediated depression.

Enhancement of Zika virus infection by antibodies from West Nile virus seropositive individuals with no history of clinical infection

BackgroundRecent outbreaks of Zika Virus (ZIKV) infection and associated microcephaly has raised multiple scientific questions. The close antigenic relatedness between flaviviruses makes diagnosis of specific infection difficult. This relatedness also raises the potential of Antibody Dependent Enhancement (ADE) via cross reactive antibodies to flaviviruses like West Nile Virus (WNV) and Dengue Virus (DENV). Asymptomatic WNV infections are endemic throughout the US creating a large proportion of the population that is seropositive for WNV antibodies. Whether these sero-positive individuals potentially carry ZIKV enhancing antibodies remains unknown.ResultsSerum samples obtained from human subjects with symptomatic or asymptomatic WNV infection from a WNV endemic region in Texas were tested for their ability to enhance or neutralize ZIKV infection. Sero-surveillance data demonstrated a ~ 7% prevalence for WNV antibodies in the population. Sera from both symptomatic and asymptomatic WNV seropositive donors effectively neutralized WNV and to some extent DENV infection. Interestingly, WNV+ sera failed to inhibit ZIKV while significantly enhancing infection. Conversely, ZIKV specific sera effectively neutralized ZIKV, with ADE only evident at lower concentrations. The enhancement of ZIKV via WNV antibody positive sera was likely due to non-neutralizing Envelope (E) antibodies as seen with monoclonal ZIKV E antibodies.ConclusionsOverall, our findings suggest that WNV antibodies in the sera significantly enhance ZIKV infection in Fc receptor positive cells with limited neutralization activity. Further studies in more relevant models of ADE will be needed to confirm the relevance of these findings in vivo.

West Nile virus in California, 2003-2018: A persistent threat.

The California Arbovirus Surveillance Program was initiated over 50 years ago to track endemic encephalitides and was enhanced in 2000 to include West Nile virus (WNV) infections in humans, mosquitoes, sentinel chickens, dead birds and horses. This comprehensive statewide program is a function of strong partnerships among the California Department of Public Health (CDPH), the University of California, and local vector control and public health agencies. This manuscript summarizes WNV surveillance data in California since WNV was first detected in 2003 in southern California. From 2003 through 2018, 6,909 human cases of WNV disease, inclusive of 326 deaths, were reported to CDPH, as well as 730 asymptomatic WNV infections identified during screening of blood and organ donors. Of these, 4,073 (59.0%) were reported as West Nile neuroinvasive disease. California’s WNV disease burden comprised 15% of all cases that were reported to the U.S. Centers for Disease Control and Prevention during this time, more than any other state. Additionally, 1,299 equine WNV cases were identified, along with detections of WNV in 23,322 dead birds, 31,695 mosquito pools, and 7,340 sentinel chickens. Annual enzootic detection of WNV typically preceded detection in humans and prompted enhanced intervention to reduce the risk of WNV transmission. Peak WNV activity occurred from July through October in the Central Valley and southern California. Less than five percent of WNV activity occurred in other regions of the state or outside of this time. WNV continues to be a major threat to public and wild avian health in California, particularly in southern California and the Central Valley during summer and early fall months. Local and state public health partners must continue statewide human and mosquito surveillance and facilitate effective mosquito control and bite prevention measures.

Prevalence and molecular epidemiology of West Nile and Usutu virus infections in Croatia in the 'One health' context, 2018.

In 2018, Croatia reported the largest outbreak of West Nile virus (WNV) infections as well as the re-occurrence of human Usutu virus (USUV) infections. For the first time, fatal WNV and USUV infections were detected in wild birds. We analysed epidemiological characteristics and molecular epidemiology of WNV and USUV infections detected during 2018 transmission season. From April to November, 178 patients with neuroinvasive disease and 68 patients with febrile disease were tested for WNV and USUV. Viral RNA was detected in cerebrospinal fluid (CSF) and urine samples using a real-time RT-PCR. Positive samples were tested by nested RT-PCR and nucleotide sequencing. IgM/IgG antibodies were detected in serum/CSF samples using ELISA with confirmation of cross-reactive samples by virus neutralization test (VNT). WNV neuroinvasive disease was confirmed in 54 and WNV fever in seven patients from 10 continental Croatian counties. Areas affected in 2018 were those in which cases occurred in previous seasons, while in three areas human cases were reported for the first time. Phylogenetic analysis of six strains from patients residing in different geographic areas showed circulation of WNV lineage 2. In three patients, neuroinvasive USUV infection was confirmed by RT-PCR or VNT. Sequence analysis of one detected strain revealed USUV Europe 2 lineage. During the same period, a total of 2,574 horse and 1,069 poultry serum samples were tested for WNV antibodies using ELISA. Acute asymptomatic WNV infection (IgM antibodies) was documented in 20/0.7% horses. WNV IgG antibodies were found in 307/11.9% horses and in 125/12.7% poultry. WNV RNA was detected in two goshawks and USUV RNA was detected in one blackbird from north-western Croatia. In the Zagreb area, 3,670 female mosquitoes were collected. One Culex pipiens pool collected in July tested positive for USUV RNA. Our results highlight the importance of continuous multidisciplinary 'One health' surveillance of these emerging arboviruses.

The role of IgG avidity determination in diagnosis of West Nile virus infection

Purpose: West Nile virus (WNV) IgM antibodies have been shown to persist for up to 500 days or even longer in some patients. Therefore, additional tests are needed to confirm primary infection. The aim of this study was to analyze the value of IgG avidity in diagnosis of symptomatic and asymptomatic WNV infection. Methods & Materials: A total 54 WNV IgM and/or IgG positive serum samples collected from 39 patients with neuroinvasive disease (meningitis/encephalitis/myelitis) and 15 asymptomatic persons were tested for WNV IgG avidity. Serological tests were performed using a commercial enzyme-linked immunosorbent assay (Euroimmun, Lübeck, Germany) and confirmed by virus neutralization test. Avidity index (AI) was calculated and expressed as percentage using the extinction values with and without urea treatment. The interpretation of AI results was determined as follows: AI < 40% = low avidity antibodies indicating acute primary infection; AI 40-60% = borderline avidity indicating recent (post-acute) infection; AI > 60% = high avidity antibodies indicating past WNV infection. Results: WNV IgM antibodies were detected in 47/87.0% samples: 39/100% patients with neuroinvasive disease and 8/53.3% asymptomatic subjects. Recent WNV infection was documented by low/borderline AI in 44/93.6% IgM positive samples. In 3/6.4% IgM positive samples, high AI was detected indicating persisting IgM antibodies from a previous infection. All 7 IgM negative samples showed high AI. In 33/84.6% patients with WNV neuroinvasive disease tested within 30 days after onset of symptoms AI was low. Six patients (15.4%) tested 34-50 days after disease onset showed borderline AI (42-60%) indicating earlier maturation of WNV IgG antibodies. Conclusion: The results of this study indicate that IgG avidity differentiates current/recent WNV infection from persistent IgM antibodies both in patients with WNV neuroinvasive disease and asymptomatic persons. Since many patients showed rapid avidity maturation, a low IgG avidity is indicative of WNV infection within the previous month.

Diagnostic significance of immunoglobulin G avidity in symptomatic and asymptomatic West Nile virus infection.

West Nile virus (WNV) immunoglobulin M (IgM) antibodies have been shown to persist for up to 500 days in certain patients. To evaluate the usefulness of immunoglobulin G (IgG) avidity assessment in the diagnosis of WNV infection, we analyzed 54 WNV IgM- and/or IgG-positive serum samples from 39 patients with neuroinvasive disease and 15 asymptomatic cases tested during a seroprevalence investigation. Serological tests (WNV IgM/IgG antibody detection, IgG avidity) were performed using commercially available enzyme-linked immunosorbent assays. WNV IgM antibodies were detected in 47 (87%) samples. Acute/recent WNV infection was confirmed based on low/borderline avidity index (AI) in 44 IgM-positive samples (93.6%). In three IgM-positive samples (6.4%), high IgG AIs were detected, thus indicating persisting IgM antibodies from previous infections. All IgM-negative samples showed high AIs. Patients with WNV neuroinvasive disease tested within 30 days showed low AIs. In six patients tested 34-50 days after disease onset, AI was borderline (42%-60%), suggesting earlier WNV IgG maturation. Samples with the highest IgM values were associated with the lowest AIs (Spearman's rho coefficient -0.767, p < 0.001). Our results indicate that IgG avidity differentiates current/recent WNV infection from persistent IgM seropositivity from the previous WNV transmission season both in patients with WNV neuroinvasive disease and in asymptomatic persons. A strong negative correlation between IgM antibody levels and AI indicates that in cases with very high IgM levels, determination of IgG avidity may not be necessary. As many patients showed rapid avidity maturation, low IgG avidity is indicative of WNV infection within the previous month.

First evidence of simultaneous occurrence of West Nile virus and Usutu virus neuroinvasive disease in humans in Croatia during the 2013 outbreak.

We report on first evidence of simultaneous occurrence of West Nile virus (WNV) and Usutu virus (USUV) neuroinvasive infection in humans in Croatia during the transmission season 2013. From June to December 2013, a total of 95 patients with clinically suspected WNV infection (WNV fever and neuroinvasive disease) were tested for WNV IgM/IgG antibodies using enzyme-linked immunosorbent assay. Twenty-six reactive samples were further tested by virus neutralization test for confirmation. WNV neuroinvasive infection was confirmed in 20 patients, while in three patients USUV neutralizing antibodies were detected. Cases occurred during the 11-week interval (from 24 July to 07 October 2013). Both WNV and USUV cases were distributed in three north-western Croatian counties. In addition to human cases, recent asymptomatic WNV infection (detection of IgM antibodies) was recorded in 9/3,460 (0.3 %) tested sentinel horses. Infected animals were recorded in two eastern and one north-western county. Our results indicate co-circulation of WNV and USUV in Croatia. WNV infection could be misdiagnosed with other emerging infectious diseases presenting with neurological symptoms such as USUV infection.

First Outbreak of West Nile Virus Neuroinvasive Disease in Humans, Croatia, 2012

Between September 6 and 21, 2012, seven human cases of West Nile virus (WNV) neuroinvasive infection were laboratory confirmed in Croatia. The median patient age was 62 years (range 48-77). Five patients presented with meningoencephalitis and two patients with meningoencephalitis followed by acute flaccid paralysis. Four of them had an underlying disease (hypertension). Using enzyme-linked immunosorbent assay (ELISA), WNV-specific immunoglobulin M (IgM) and IgG antibodies of low avidity were detected in six patients, whereas one showed only IgM antibodies. All samples were confirmed using plaque-reduction neutralization and microneutralization tests. Five patients recovered fully. Before human cases were reported, acute asymptomatic WNV infection was demonstrated by detection of IgM antibodies in sentinel horses. Moreover, an increased WNV IgG seropositivity in horses was detected in counties where human cases occurred. Adulticidal and larvicidal treatments were administered immediately in the respective places of residence. The end of the warm season contributed to the fact that there were no new cases of WNV disease recorded.

Quantitative and qualitative differences in CD4+ T cell responses for subjects with symptomatic and asymptomatic West Nile virus infection (P6125)

Abstract The West Nile virus (WNV), a mosquito-borne flavivirus, induces a wide range of clinical manifestations in humans. While the majority of infections are essentially asymptomatic, a small percentage of inflections lead to neuroinvasive disease with symptoms ranging from mild disorientation to paralysis and death. Increased risk of symptomatic infection in immunosuppressed subjects could suggest that lack of effective immune responses against WNV may lead to worse outcomes. In this study, we utilized HLA class II tetramers to characterize the epitope specificity, frequency, and phenotype of WNV-specific T cells in subjects who had previously documented WNV infection. CD4+ T cell epitopes were present within all WNV fever proteins allowing broad characterization of WNV-specific responses. Ex vivo tetramer analysis revealed that WNV-specific CD4+ T cells were present at significantly higher frequencies in subjects with symptomatic infection than in those with no symptoms. CD4+ T cells had a memory phenotype in all WNV infected subjects, exhibited varying levels of activation, and produced multiple cytokines, including interferon-γ and IL-17. T cells from symptomatic subjects had a distinct phenotype, producing higher levels of Th2 cytokines after re-activation in vitro. Therefore, quantitative and qualitative differences in CD4+ T cell responses toward WNV are associated with neuroinvasive disease.

West Nile virus transmission through organ transplantation in north-eastern Italy: a case report and implications for pre-procurement screening

West Nile virus (WNV) transmission through organ transplantation occurs rarely and screening of organ donors for WNV infection remains controversial. This report describes the case of WNV encephalitis in a kidney recipient and the case of asymptomatic WNV infection in the organ donor, both observed at Treviso Hospital, northeastern Italy. After briefly reviewing the literature, we discuss the implications for WNV screening. We reviewed medical, laboratory and epidemiological records at our hospital, and the literature concerning cases of organ-transmitted WNV infections and WNV screening of organ donors in Italy and worldwide. The kidney recipient was the first confirmed case of WNV infection notified in northeastern Italy in 2011, and the first case of WNV infection in a cluster of four transplant recipients who acquired the infection from a common organ donor. The organ donor, whose WNV infection was only retrospectively diagnosed by IgM detection, represents the index case of a WNV outbreak in the Treviso Province. Screening of her blood prior to organ recovery did not show detectable levels of WNV nucleic acid with the use of quantitative real-time polymerase chain reaction. This report emphasizes that transplant-acquired WNV neuroinvasive disease can be particularly severe. We suggest that pre-procurement screening of organ donors by testing blood with both WNV IgM capture ELISA and a sensitive nucleic acid testing should be adopted during the transmission season in the present Italian epidemiological setting.

Tregs control the development of symptomatic West Nile virus infection in humans and mice

West Nile virus (WNV) causes asymptomatic infection in most humans, but for undefined reasons, approximately 20% of immunocompetent individuals develop West Nile fever, a potentially debilitating febrile illness, and approximately 1% develop neuroinvasive disease syndromes. Notably, since its emergence in 1999, WNV has become the leading cause of epidemic viral encephalitis in North America. We hypothesized that CD4+ Tregs might be differentially regulated in subjects with symptomatic compared with those with asymptomatic WNV infection. Here, we show that in 32 blood donors with acute WNV infection, Tregs expanded significantly in the 3 months after index (RNA+) donations in all subjects. Symptomatic donors exhibited lower Treg frequencies from 2 weeks through 1 year after index donation yet did not show differences in systemic T cell or generalized inflammatory responses. In parallel prospective experimental studies, symptomatic WNV-infected mice also developed lower Treg frequencies compared with asymptomatic mice at 2 weeks after infection. Moreover, Treg-deficient mice developed lethal WNV infection at a higher rate than controls. Together, these results suggest that higher levels of peripheral Tregs after infection protect against severe WNV disease in immunocompetent animals and humans.

West Nile virus infection in Veneto region, Italy, 2008-2009

We report here an update on human cases of West Nile virus (WNV) infection in Veneto region, northeastern Italy. In addition to two cases of WNV neuroinvasive disease notified through a surveillance programme started in September 2008, further four cases were retrospectively identified (in May 2009) by investigating patients with aseptic meningoencephalitis of unknown aetiology occurring in Veneto region in June-September 2008. All six patients had symptom onset in August-September 2008 and were resident in a wetland area close to the Po river delta in Rovigo province. Further five cases of asymptomatic WNV infection, including four residents of the same area in Rovigo, were identified in a seroprevalence study in farm workers from Veneto region. To date, no human cases have been notified in 2009.

West Nile virus: An emerging infection in transfusion medicine

West Nile virus (WNV) is an enzootic disease affecting birds which was introduced to the eastern United States in 1999 and has since spread rapidly across the country. Humans and other mammals are tangential hosts, acquiring the disease from the bite of an infected mosquito. In 2002, WNV was responsible for the largest outbreak of viral meningoencephalitis ever seen in the U.S., claiming thousands of victims. Despite these frightening numbers, WNV infection of humans is usually asymptomatic or results in a relatively mild febrile illness. WNV has not only challenged public health officials but has stimulated great interest among blood bankers. It has become clear that blood donated by people with asymptomatic WNV infection or clinically mild disease can transmit WNV to recipients, causing severe morbidity and mortality. To protect the blood supply from WNV, blood collection agencies are now testing donated blood for WNV using nucleic acid amplification tests. Although this effort will significantly decrease the incidence of transfusion-transmitted WNV, risk of infection remains, and new testing methods will likely need to be developed.