Immunoglobulin M antibody capture enzyme-linked immunosorbent assay for diagnosis of St. Louis encephalitis

Evaluation of a SARS-CoV-2 Capture IgM Antibody Assay in Convalescent Sera

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for a global pandemic with over 152 million cases and 3.19 million deaths reported by early May 2021. Understanding the serological response to SARS-CoV-2 is critical to determining the burden of infection and disease (coronavirus disease 2019 [COVID-19]) and transmission dynamics. We developed a capture IgM assay because it should have better sensitivity and specificity than the commonly used indirect assay. Here, we report the development and performance of a capture IgM enzyme-linked immunosorbent assay (ELISA) and a companion indirect IgG ELISA for the spike (S) and nucleocapsid (N) proteins and the receptor-binding domain (RBD) of S. We found that among the IgM ELISAs, the S ELISA was positive in 76% of 55 serum samples from SARS-CoV-2 PCR-positive patients, the RBD ELISA was positive in 55% of samples, and the N ELISA was positive in 15% of samples. The companion indirect IgG ELISAs were positive for S in 89% of the 55 serum samples, RBD in 78%, and N in 85%. While the specificities for IgM RBD, S, and N ELISAs and IgG S and RBD ELISAs were 97% to 100%, the specificity of the N IgG ELISA was lower (89%). RBD-specific IgM antibodies became undetectable by 3 to 6 months, and S IgM reached low levels at 6 months. The corresponding IgG S, RBD, and N antibodies persisted with some decreases in levels over this time period. These capture IgM ELISAs and the companion indirect IgG ELISAs should enhance serologic studies of SARS-CoV-2 infections. IMPORTANCE Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has inflicted tremendous loss of lives, overwhelmed health care systems, and disrupted all aspects of life worldwide since its emergence in Wuhan, China, in December 2019. Detecting current and past infection by PCR or serology is important to understanding and controlling SARS-CoV-2. With increasing prevalence of past infection or vaccination, IgG antibodies are less helpful in diagnosing a current infection. IgM antibodies indicate a more recent infection and can supplement PCR diagnosis. We report an alternative method, capture IgM, to detect serum IgM antibodies, which should be more sensitive and specific than most currently used methods. We describe this capture IgM assay and a companion indirect IgG assay for the SARS-CoV-2 spike (S), nucleocapsid (N), and receptor-binding domain (RBD) proteins. These assays can add value to diagnostic and serologic studies of coronavirus disease 2019 (COVID-19).

Zika virus infection in asymptomatic persons in Myanmar, 2018

BACKGROUND

Zika virus (ZIKV) is a mosquito-borne flavivirus. Outbreaks of ZIKV infection have occurred in Africa, Southeast Asia, the Pacific Islands, the Americas and the Caribbean. Although most ZIKV infections are asymptomatic, cases of neurological manifestations have been described. The aim of the present study was to identify the prevalence of ZIKV infection among the asymptomatic persons in Myanmar in 2018.

METHODS

A total of 284 serum samples from apparently healthy persons were collected from Yangon, Myanmar in 2018. They were analysed for ZIKV infection by immunoglobulin M (IgM) capture enzyme-linked immunosorbent assay (ELISA), IgG indirect ELISA, 50% focus reduction neutralization test, real-time reverse transcription polymerase chain reaction (RT-PCR) and conventional RT-PCR.

RESULTS

Of the 284 apparently healthy persons, 31.3% were positive for the presence of IgM against ZIKV and 94.3% were positive for anti-flavivirus IgG. Among the ZIKV IgM-positive samples, we confirmed ZIKV infection in 15.8% of asymptomatic persons by neutralization test and real-time RT-PCR.

CONCLUSIONS

We conclude that ZIKV infection was increasing among asymptomatic persons in the same area in Myanmar during 2018 compared with 2017. It is highly recommended to strengthen the surveillance system for ZIKV to prevent possible outbreaks.

Congenital Zika Virus Infection in a Birth Cohort in Vietnam, 2017-2018

To detect congenital ZIKV infection (CZI) in a birth cohort and among high-risk neonates in Vietnam, we collected umbilical cord blood plasma samples of newly delivered babies and peripheral plasma samples of high-risk neonates in Nha Trang, central Vietnam, between July 2017 and September 2018. Samples were subjected to serological and molecular tests. Of the 2013 newly delivered babies, 21 (1%) were positive for Zika virus (ZIKV) IgM and 1,599 (79%) for Flavivirus IgG. Among the 21 ZIKV IgM-positives, 11 were confirmed to have CZI because their plasma samples had anti-ZIKV neutralization titers ≥ 4 times higher than those against dengue virus (DENV)-1 to 4 and Japanese encephalitis virus (JEV) and were tested for the ZIKV RNA positive by real-time reverse transcription–PCR. Therefore, the incidence of CZI in our birth cohort was approximately 0.5%. Of the 150 high-risk neonates, three (2%) and 95 (63%) were positive for ZIKV IgM and Flavivirus IgG antibodies, respectively. None of the three ZIKV IgM-positives had ≥ 4 times higher anti-ZIKV neutralization titers than those against DENV-1 to 4 and JEV, and were therefore considered as probable CZI. Our results indicate that CZI is not rare in Vietnam. Although those with confirmed CZI did not show apparent symptoms suspected of congenital Zika syndrome at birth, detailed examinations and follow-up studies are needed to clarify the CZI impact in Vietnam. This is the first report of CZI cases in a birth cohort in Asia.

The longitudinal health economic impact of viral encephalitis in the United States

Introduction. Previous studies of viral encephalitis have focused on acute costs, estimating incidence at 7.3 per 100 000 and total US annual charges at $2 billion in 2010.Aim. We aim to quantify the most updated longitudinal health economic impact of viral encephalitis in the USA from 2008 to 2015.Methodology. Data on patients diagnosed with viral encephalitis were obtained from the Truven Health Analytics MarketScan database. Patients with a primary diagnosis of viral encephalitis, from herpetic viruses and other viral aetiologies (e.g. West Nile fever) were included in the analysis. Data concerning healthcare resource utilization, inpatient mortality, length of stay and accrued healthcare costs were collected for up to 5 years.Results. Among 3985 patients with continuous enrolment for 13 months prior to the encephalitis diagnosis, more non-herpes simplex encephalitis (61.7 %) than herpes simplex encephalitis (HSE; 38.3 %) cases were recorded, with the majority concentrated in the southern USA (29.2 %). One-year inpatient mortality was 6.2 %, which over a 5-year period rose to 8.9 % for HSE and 5.8 % for all other viral encephalitides. HSE resulted in longer cumulative stays in the hospital (11 days vs. 4 days; P=0.0025), and accrued 37 % higher first-year costs, after adjusting for known confounders [P<0.001, cost ratio=1.37, 95 % confidence interval (1.20, 1.57)]. Additionally, HSE was associated with greater 5-year cumulative median charges ($125 338 vs. $82 317, P=0.0015).Conclusion. The health economic impact and long-term morbidity of viral encephalitis in the USA are substantial.

Specific diagnostic method for St. Louis encephalitis virus using a non-structural protein as the antigen

St. Louis encephalitis virus (SLEV) is a mosquito-borne re-emerging flavivirus in Argentina. It is currently necessary to develop specific serological tests that can efficiently discriminate the flaviviruses that circulate in our country. The immunoassays to diagnose SLEV lack specificity because they are based on the detection of structural viral proteins and the human immunoglobulins produced during infection against these proteins cross-react with other flaviviruses. Here, we describe an enzyme-immunoassay designed to detect human IgG antibodies specific to the viral non-structural protein NS5. The results indicate that NS5 is a promising antigen useful to discriminate SLEV from other circulating flaviviruses.

Clinical and epidemiological features of West Nile virus equine encephalitis in New South Wales, Australia, 2011

BACKGROUND

Between February and June 2011, more than 300 horses with unexplained neurological disease were observed in New South Wales, Australia. A virulent strain of West Nile virus (WNV_NSW2011 ), of Australian origin, was shown to be the cause of many of these cases.

METHODS

We reviewed the clinical descriptions provided by veterinary practitioners and the associated laboratory results. Although there was a range of clinical signs described, ataxia was the only sign that was consistently described in laboratory-confirmed cases.

RESULTS

WNV was detected in brain samples by real-time reverse transcription PCR assay and virus isolation. For serological confirmation of clinical cases, an equine IgM ELISA specific for WNV was shown to be the most effective tool.

CONCLUSION

A state-wide serological survey undertaken after the outbreak indicated that, contrary to expectation, although infection had been widespread, the seroprevalence of antibodies to WNV was very low, suggesting that there could be a significant risk of future disease outbreaks.

Diagnostic approach to encephalitis and meningoencephalitis in adult returning travellers

BACKGROUND

Encephalitis and meningoencephalitis are severe, sometime life-threatening infections of the central nervous system. Travellers may be exposed to a variety of neurotropic pathogens.

AIMS

We propose to review known infectious causes of encephalitis in adults acquired outside Europe, and how to identify them.

SOURCES

We used Pubmed and Embase, to search the most relevant publications over the last years.

CONTENT

Microbiologic tests and radiological tools to best identify the causative pathogen in travellers presenting with encephalitis and ME are presented in this narrative review, as well as a diagnostic approach tailored to the visited area and types of exposures.

IMPLICATIONS

This review highlights the diagnostic difficulties inherent to exotic causes of central nervous system infections, and attempts to guide clinicians with respect to which microbiological tests to consider, in addition to brain MRI, when approaching a returning traveller presenting with encephalitis.

Comparison of enzyme-linked immunosorbent assay systems using rift valley fever virus nucleocapsid protein and inactivated virus as antigens

Background

Rift Valley Fever (RVF) is a mosquito-borne viral zoonosis. To detect RVF virus (RVFV) infection, indirect immunoglobulin G (IgG) and immunoglobulin M (IgM) enzyme linked immunosorbent assays (ELISAs) which utilize recombinant RVFV nucleocapsid (RVFV-N) protein as assay antigen, have reportedly been used, however, there is still a need to develop more sensitive and specific methods of detection.

Methods

RVFV-N protein was expressed in Escherichia coli (E. coli) and purified by histidine-tag based affinity chromatography. This recombinant RVFV-N (rRVFV-N) protein was then used as antigen to develop an IgG sandwich ELISA and IgM capture ELISAs for human sera. Ninety six serum samples collected from healthy volunteers during the RVF surveillance programme in Kenya in 2013, and 93 serum samples collected from RVF-suspected patients during the 2006–2007 RVF outbreak in Kenya were used respectively, to evaluate the newly established rRVFV-N protein-based IgG sandwich ELISA and IgM capture ELISA systems in comparison with the inactivated virus-based ELISA systems.

Results

rRVFV-N protein-based-IgG sandwich ELISA and IgM capture ELISA for human sera were established. Both the new ELISA systems were in 100% concordance with the inactivated virus-based ELISA systems, with a sensitivity and specificity of 100%.

Conclusions

Recombinant RVFV-N is a safe and affordable antigen for RVF diagnosis. Our rRVFV-N-based ELISA systems are safe and reliable tools for diagnosis of RVFV infection in humans and especially useful in large-scale epidemiological investigation and for application in developing countries.

Incorporation of IgG Depletion in a Neutralization Assay Facilitates Differential Diagnosis of Zika and Dengue in Secondary Flavivirus Infection Cases

Zika virus (ZIKV) has emerged as a major global public health concern due to its link as a causative agent of human birth defects. Laboratory diagnosis of suspected ZIKV infections by serological testing of specimens collected a week or more after symptom onset primarily relies on detection of anti-ZIKV-specific IgM antibodies by enzyme-linked immunosorbent assay coupled with detection of ZIKV-specific neutralizing antibody by neutralization tests. A definitive diagnosis based on serological assays is possible during primary ZIKV infections; however, due to the cross-reactivity of antibodies elicited during flaviviral infections, a definitive diagnosis is not always possible, especially among individuals who have previously been exposed to closely related flaviviruses, such as dengue virus (DENV). Here, we investigated the neutralizing IgM antibody profiles of 33 diagnostic specimens collected from individuals with suspected primary and secondary flaviviral infections acquired when visiting areas experiencing active ZIKV transmission in 2015 and 2016. Specimens collected between 1 day and 3 months postexposure were tested for ZIKV and dengue virus type 1 (DENV1) and type 2 (DENV2) by the plaque reduction neutralization test (PRNT) before and after IgG depletion. We found that IgG depletion prior to neutralization testing had little effect in differentiating samples from individuals with secondary infections taken less than 3 weeks postexposure; however, IgG depletion significantly reduced the cross-reactive neutralizing antibody titers and increased the percentage of cases discernible by PRNT from 15.4% (95% confidence interval [CI], 4.3 to 42.2%) to 76.9% (95% CI, 49.7 to 91.8%) for samples collected between roughly 3 and 12 weeks postexposure. These results highlight the potential of IgG depletion to improve the specificity of PRNT for better confirmation and differential diagnosis of flavivirus infections.

Seroepidemiology of arbovirus in communities living under the influence of the lake of a hydroelectric dam in Brazil

Abstract Introduction The arbovirus proposes an important problem of public health in Brazil, especially in the Amazon, due to its capacity to cause outbreaks with high levels of morbidity-mortality in humans as well as in animals. Objective This paper had the objective to estimate the prevalence of antibodies to arbovirus in communities that live under the influence of the artificial lake of UHE Tucuruí in the State of Pará, Brazil. Method The analytical transversal study has selected 657 blood serum samples of individuals over 18, both genders, residents at the Sustainable Development Reserves (SDR) in the region of the lake of UHE Tucuruí. The epidemiological information has been registered in an instrument especially designed for such a study and the blood samples were collected in two periods of high and low tide of the lake. The blood serum tests were performed by the method of hemagglutination inhibition (HI). Results The results revealed a prevalence of positive antibodies to arbovirus of 85.0%, being 84.1% related to Flavivirus (vaccine strain of YFV), 25.5% related to Alphavirus and 34.6% to Bunyavirus. The results of serum prevalence to arbovirus between the periods of high tide and low tide have revealed significance amongst the Alphavirus, not observed in the other families. Conclusion In general, the data from this paper have suggested that the anthropoid actions on the environment of the lake have become determinant factors for the prevalence of arboviral antibodies.

Detection of Zika Virus Infection in Myanmar

Zika virus (ZIKV), an emerging mosquito-borne flavivirus, causes a dengue-like infection that has recently caught global attention. The infection, which also includes some birth defects, has been documented in the Americas, Pacific Islands, and some parts of Africa and Asia. There are no published reports on local ZIKV transmission in Myanmar. In this study, a total of 462 serum samples from patients and asymptomatic persons were collected in Myanmar from 2004 to 2017. They were analyzed for ZIKV infection by immunoglobulin M capture enzyme-linked immunosorbent assay (ELISA), immunoglobulin G indirect ELISA, neutralization test, real-time polymerase chain reaction (PCR), and conventional PCR. Our study confirmed ZIKV infection in 4.9% of patients with clinical dengue symptoms and in 8.6% of persons who were asymptomatic. This is the first report on ZIKV infection in Myanmar and it suggests the occurrence of ZIKV infection in two geographically distinct sites in this country since at least 2006.

Following the Yellow Brick Road

Charles Calisher was fascinated by microorganisms from the time he was in high school. He attended Stuyvesant High School in New York City, Philadelphia College of Pharmacy and Science (now University of the Sciences) (BS), then University of Notre Dame in South Bend, Indiana (MS), and finally Georgetown University, in Washington, DC (PhD), the latter while employed at a commercial biological house. He was hired by the US Communicable Disease Center (now the Centers for Disease Control and Prevention) in Atlanta, Georgia, was transferred to its Fort Collins laboratories in 1973, and retired from there in 1992. After traveling the world a bit, Calisher joined the faculty of Colorado State University in 1993, then semiretired as professor emeritus in 2010. During all those years, he developed from a would-be virologist to an arbovirologist-epidemiologist, identifying scores of newly recognized viruses from throughout the world and helping to investigate disease outbreaks and epidemics. His interests (always primarily arboviruses but now also rodent-borne viruses and bat-borne viruses) continue to expand, and he continues to be involved in various aspects of virology and to assist and annoy journal editors and others in regard to viral taxonomy.

Application of recombinant severe fever with thrombocytopenia syndrome virus nucleocapsid protein for the detection of SFTSV-specific human IgG and IgM antibodies by indirect ELISA

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging disease that was first reported in China in 2011. It is caused by SFTS virus (SFTSV) which is a member of the Phlebovirus genus in the Bunyaviridae family. SFTSV has been classified as a BSL3 pathogen. There is a need to develop safe and affordable serodiagnostic methods for proper clinical management of infected patients.

Methods

The full length nucleocapsid (N) gene of SFTSV Yamaguchi strain was amplified by RT-PCR and cloned to an expression vector pQE30. The recombinant (r) SFTSV-N protein was expressed by using Escherichia coli (E. coli) expression system and purified under native conditions. rSFTSV-N protein based indirect IgG and IgM enzyme linked immunosorbent assay (ELISA) systems were established to detect specific human IgG and IgM antibodies, respectively. One hundred fifteen serum samples from clinically suspected-SFTS patients were used to evaluate the newly established systems and the results were compared with the total antibody detecting sandwich ELISA system.

Results

The native form of recombinant (r) SFTSV-N protein was expressed and purified. Application of the rSFTSV-N protein based indirect IgG ELISA to the 115 serum samples showed results that perfectly matched those of the total antibody sandwich ELISA with a sensitivity and specificity of 100 %. The rSFTSV-N protein based indirect IgM ELISA missed 8 positive samples that were detected by the total antibody sandwich ELISA. The sensitivity and specificity of rSFTSV-N-IgM capture ELISA were 90.59 and 100 %, respectively.

Conclusions

The rSFTSV-N protein is highly immunoreactive and a good target for use as an assay antigen in laboratory diagnosis. Its preparation is simpler in comparison with that used for the total antibody sandwich system. Our rSFTSV-N protein-based IgG and IgM ELISA systems have the advantage of distinguishing two types of antibodies and require small volume of serum sample only. They are safe to use for diagnosis of SFTS virus infection and especially fit in large-scale epidemiological investigations.

Application of West Nile virus diagnostic techniques

West Nile virus (WNV) is an enveloped RNA virus in the family Flaviviridae and belongs to Japanese encephalitis virus serocomplex group. The WNV has a wide geographic distribution that includes Africa, Europe, Asia, America and Australia. Recently, it has re-emerged as an important pathogenic organism, illustrated by the series of WNV outbreaks in North America and in Europe. Several hundred people are sacrificed by WNV infection every year. WNV can infect many mammals, birds, reptiles and amphibians. A variety of diagnoses for WNV infection have been developed, such as virus isolation, nucleotide amplification, antigen detection and serology. Flaviviruses, including WNV, share common nucleotide sequences and antigenic epitopes. Understanding these properties that can influence cross-reactivity is important for accurate diagnosis, especially because areas with multiple flaviviruses are currently expanding. Herein, the authors outline the different diagnostic methods for detecting WNV infection as well as important considerations in using these methods.

Human arboviral encephalitis

Worldwide, arboviral illnesses constitute the most important international infectious threat to human neurological health and welfare. Before the availability of effective immunizations, approximately 50,000 cases of Japanese encephalitis occurred in the world each year, one-fifth of which cases proved lethal and a much larger number were left with severe neurological handicaps. With global climate change and perhaps other factors, the prevalences of some arboviral illnesses appear to be increasing. Arboviral illnesses, including Japanese encephalitis, tick-borne encephalitis, Yellow fever, and others, are emerging as possible global health care threats because of biological warfare. This chapter will review ecology, pathophysiology, diagnosis, management, and outcome of the forms of arboviral encephalitis that are of greatest importance in North America, together with some of the most important arboviral encephalitides prevalent in other parts of the world.

Detection of West Nile virus

West Nile virus (WNV; Flavivirus, Flaviviridae) is a spherical enveloped virion containing single-stranded, positive-sense RNA, approximately 11 kb in length. The virus is the most widely distributed flavivirus in the world. Genetic analysis reveals two major lineages of virus, I and II, and several possible newly recognized lineages. Lineage I strains are most commonly associated with outbreaks of neurologic disease, although lineage II virus has led to large epidemics of fever, as in South Africa in 1974. Infection with WNV leads to a wide range of diseases from mildly febrile to severely neurologic, but asymptomatic -infections occur most frequently. Approximately one in 140 infected individuals develop neurologic -disease. The virus is maintained in an enzootic cycle, where it is transmitted between ornithophilic mosquitoes of the Culex genus and predominantly passeriform birds. Equines and humans are considered incidental hosts since they do not mount high enough viremia for mosquitoes to become infected -following feeding. Laboratory diagnosis of WNV infection is predominantly serological, although -caution is advised because of the high degree of cross-reactivity among flaviviruses. Field specimens, especially mosquitoes and dead birds, collected as part of surveillance programs, are tested for the presence of viral nucleic acid, viral antigen, or infectious virus. Rapid test protocols have been developed in response to the expansion of WNV in the United States. Since WNV is classified as a Biosafety Level-3 (BSL-3) agent by CDC, it is recommended that once this virus is identified in a diagnostic specimen, all infectious virus should be handled in a BSL-3 laboratory in Class II biosafety cabinets by laboratory staff who are trained to work at this level of containment. Assay protocols are described and the necessary equipment and supplies listed.

North American encephalitic arboviruses

Arboviruses continue to be a major cause of encephalitis in North America, and West Nile virus neuroinvasive disease is now the dominant cause of encephalitis. Transmission to humans of North American arboviruses occurs by infected mosquitoes or ticks. Most infections are asymptomatic or produce a flulike illness. Rapid serum or cerebrospinal fluid IgM antibody capture ELISA assays are available to diagnosis the acute infection for all North American arboviruses. Unfortunately, no antiviral drugs are approved for the treatment of arbovirus infection and current therapy is supportive.

Reliable detection of St. Louis encephalitis virus by RT-nested PCR

INTRODUCTION

St. Louis encephalitis virus (SLEV) is a re-emerging arbovirus in South America, with reported cases in humans in Argentina and Brazil. This fact indicates that there is an urgent need to increase the current knowledge about this virus in order to control and prevent future cases. Exhaustive epidemiological and laboratory investigation is required to ensure fast, accurate identification of the viral agent and allow prompt surveillance action by health authorities. Herein, we report the development of a species-specific RT-nested PCR to detect SLEV.

MATERIAL AND METHODS

After selecting the SLEV genomic region providing the greatest information on the natural genetic variability of this virus, degenerated oligonucleotide primers were designed to amplify a 234-bp fragment of the envelope gene from nine SLEV strains (Parton, BeH356964, SPAN11916, AN9275, AN9124, 78V6507 and 3 SLEV strains obtained from naturally infected mosquito pools).

RESULTS

The method was able to identify the genome of all the SLEV strains tested and did not amplify unrelated RNA viruses, such as yellow fever virus, Ilheus virus, dengue-2 virus, Bussuquara virus, West Nile virus, Japanese encephalitis virus and Murray Valley encephalitis virus. The method was specific and sensitive, with a lower detection limit of < 10 plaque-forming units.

CONCLUSION

This molecular assay is a reliable procedure with a wide spectrum for detecting the natural diversity of SLEV and may be useful for ecological studies, clinical and laboratory settings and virological surveillance.

Human outbreak of St. Louis encephalitis detected in Argentina, 2005

BACKGROUND

An outbreak of flavivirus encephalitis occurred in 2005 in Córdoba province, Argentina.

OBJECTIVES

To characterize the epidemiologic and clinical features of that outbreak and provide the serologic results that identified St. Louis encephalitis virus (SLEV) as the etiologic agent.

STUDY DESIGN

From January to May 2005, patients with symptoms of encephalitis, meningitis, or fever with severe headache were evaluated and an etiologic diagnosis achieved by detection of flavivirus-specific antibody sera and cerebrospinal fluid.

RESULTS

The epidemic curve of 47 cases showed an explosive outbreak starting in January 2005 with one peak in mid-February and a second peak in mid-March; the epidemic ended in May. Cases occurred predominantly among persons 60 years and older. Nine deaths were reported. SLEV antibodies, when detected in 47 patients studied, had a pattern characteristic of a primary SLEV infection.

CONCLUSIONS

Even though isolated cases of St. Louis encephalitis have been reported in Argentina, this is the first description of a large SLEV encephalitis outbreak in Argentina.

Recombinant truncated nucleocapsid protein as antigen in a novel immunoglobulin M capture enzyme-linked immunosorbent assay for diagnosis of severe acute respiratory syndrome coronavirus infection

We report the development of an immunoglobulin M (IgM) antibody capture enzyme-linked immunosorbent assay (MAC-ELISA) for severe acute respiratory syndrome coronavirus (SARS-CoV) by using recombinant truncated SARS-CoV nucleocapsid protein as the antigen. The newly developed MAC-ELISA had a specificity and sensitivity of 100% as evaluated by using sera from healthy volunteers and patients with laboratory-confirmed SARS. Using serial serum samples collected from SARS patients, the times to seroconversion were determined by IgM antibody detection after SARS-CoV infection. The median time to seroconversion detection was 8 days (range, 5 to 17 days) after disease onset, and the seroconversion rates after the onset of illness were 33% by the first week, 97% by the second week, and 100% by the third week. Compared with the results of our previous report on the detection of IgG, the median seroconversion time by IgM detection was 3 days earlier and the seroconversion rate by the second week after the illness for IgM was significantly higher than by IgG assay. Our results indicating that the IgM response appears earlier than IgG after SARS-CoV infection in consistent with those for other pathogens. Our newly developed MAC-ELISA system offers a new alternative for the confirmation of SARS-CoV infection.

Duplex microsphere-based immunoassay for detection of anti-West Nile virus and anti-St. Louis encephalitis virus immunoglobulin m antibodies

West Nile (WN) virus was introduced into the United States in 1999, when the first human cases of WN fever and encephalitis appeared in New York City. From there, the virus has spread throughout North America, in some areas cocirculating with the related flavivirus St. Louis encephalitis (SLE) virus. Public health laboratories currently use an immunoglobulin M (IgM) antibody capture enzyme-linked immunosorbent assay (MAC-ELISA) as a primary test for human serodiagnosis, followed by a confirmatory plaque-reduction neutralization test (PRNT). The MAC-ELISAs take 2 days to perform; therefore there is a need for a more rapid test. This report describes a duplex microsphere-based immunoassay (MIA) that shortens the test processing time to about 4.5 h. The assay employs two sets of microspheres coupled to a single flavivirus group-reactive antibody, which are used to capture the WN and SLE viral antigens independently. Immunoglobulin G-depleted serum is concurrently assayed for IgM antibodies to each of the viral antigens. The results are standardized and classified by using quadratic discriminant analysis so that a single result, anti-WN IgM-positive, anti-SLE IgM-positive, negative, or nonspecific, can be determined. The duplex MIA results compared favorably to those of the plaque-reduction neutralization test and MAC-ELISA. The assay proved to be reproducible, produced accurate classifications as to the infecting virus, and was specific.

Yellow fever outbreak, Imatong, southern Sudan

In May 2003, the World Health Organization received reports about a possible outbreak of a hemorrhagic disease of unknown cause in the Imatong Mountains of southern Sudan. Laboratory investigations were conducted on 28 serum samples collected from patients in the Imatong region. Serum samples from 13 patients were positive for immunoglobulin M antibody to flavivirus, and serum samples from 5 patients were positive by reverse transcription–polymerase chain reaction with both the genus Flavivirus–reactive primers and yellow fever virus–specific primers. Nucleotide sequencing of the amplicons obtained with the genus Flavivirus oligonucleotide primers confirmed yellow fever virus as the etiologic agent. Isolation attempts in newborn mice and Vero cells from the samples yielded virus isolates from five patients. Rapid and accurate laboratory diagnosis enabled an interagency emergency task force to initiate a targeted vaccination campaign to control the outbreak.

Dengue virus serotyping based on envelope and membrane and nonstructural protein NS1 serotype-specific capture immunoglobulin M enzyme-linked immunosorbent assays

Envelope and membrane (E/M) and nonstructural protein NS1 serotype-specific capture Immunoglobulin M (IgM) enzyme-linked immunosorbent assays (ELISAs) were developed to differentiate four dengue virus serotypes. A total of 93 anti-dengue virus IgM-positive serum samples collected between days 5 and 45 of illness from 59 confirmed dengue patients were analyzed. The results showed that positive serotype specificity could be identified for 86.1 and 47.6% of serum samples tested for E/M-specific IgM antibodies versus 83.3 and 42.9% of serum samples tested for NS1-specific IgM antibodies from patients with primary and secondary dengue virus infections, respectively. Dual analyses with both E/M and NS1 serotype-specific capture IgM ELISAs showed that positive serotype specificity could be correctly identified for 98.6 and 61.9% of all of the primary and secondary serum samples tested, respectively. These findings suggested that E/M and NS1 serotype-specific capture IgM ELISAs have the potential to be of use in dengue virus serotyping.

Newer viral encephalitides

BACKGROUND

Viral encephalitis occurs in epidemic settings or is sporadic. New encephalitis patterns reflect the roles that biologic reservoirs and vectors play in determining virus-human interactions. "New" viral encephalitis can also result from human host modifications that increase susceptibility to neuroinvasive viral infection.

REVIEW SUMMARY

Three human viruses, Nipah virus, Human Herpesvirus-6, and West Nile virus, present examples of how "new" viral encephalitides emerge in a specific geographic region or clinical setting. Nipah virus encephalitis emerged after the molecular evolution of a new zoonotic viral genus within the Paramyxovirinae family. Human herpesvirus-6 encephalitis has emerged in the immune suppressed human host harboring this ubiquitous but typically benign herpesvirus. West Nile virus encephalitis has emerged in the Western hemisphere after apparent abrupt translocation of this mosquito-borne virus to a distant geographic region with immunologically naive avian and human hosts.

CONCLUSION

While the clinical features of these viral encephalitides are somewhat distinct, they each emerged as the result of human-derived factors that altered the biologic dynamic between humans and their viral pathogens.

Persistence of virus-reactive serum immunoglobulin m antibody in confirmed west nile virus encephalitis cases

Twenty-nine laboratory-confirmed West Nile virus (WNV encephalitis patients were bled serially so that WNV-reactive immunoglobulin (Ig) M activity could be determined. Of those patients bled, 7 (60%) of 12 had anti-WNV IgM at approximately 500 days after onset. Clinicians should be cautious when interpreting serologic results from early season WNV IgM-positive patients.

Antigenic Structure of Flavivirus Proteins

The increased activity of Dengue virus in the tropical regions of the world and the recent movement of West Nile virus from the eastern to the western hemisphere emphasize the fact that vector-borne flaviviruses are medically important emerging infectious diseases. These facts warrant continued efforts to decode all facets of flavivirus immunology. This chapter reviews current understanding of the antigenic fine structure of flaviviral structural and nonstructural (NS) proteins and their involvement in B- an T-cell host responses. The virion structural glycoprotein E elicits both virus-neutralizing antibodies and antiviral Th-cell responses. Consistent with the current hypothesis of the MHC class I pathway of protein processing, immunodominant flaviviral Tc-cell epitopes mainly reside on the NS proteins. To prepare effective and inexpensive subunit vaccines, we will need to continue to better understand these structure-function relationships of flavivirus proteins.

Performance characteristics of an in-house assay system used to detect West Nile Virus (WNV)-specific immunoglobulin M during the 2001 WNV season in the United States

During the 2001 U. S. West Nile virus (WNV) season, 163 specimens were reactive in an in-house WNV-specific immunoglobulin M (IgM) screening enzyme-linked immunosorbent assay (ELISA) and were referred to either the Centers for Disease Control and Prevention or the appropriate state public health laboratory (CDC/SPHL) for additional testing. CDC/SPHL supplied results for 124 specimens that could be further evaluated in-house: 70 specimens were nonreactive in the CDC/SPHL WNV-specific IgM screening assay, and 54 specimens were reactive. These specimens were used to evaluate a modified in-house WNV-specific IgM ELISA that incorporated background subtraction to identify nonspecific reactivity and thus improve assay specificity. Of the 70 CDC/SPHL nonreactive samples, 49 (70%) were nonreactive in the modified ELISA; of the 54 CDC/SPHL reactive samples, 51 (94%) were reactive in the modified ELISA. Confirmatory studies performed by CDC/SPHL indicated that 38 CDC/SPHL screen-reactive specimens represented true WNV infection; all 38 specimens were reactive in the modified in-house WNV-specific IgM ELISA. These findings demonstrate that an in-house ELISA system for WNV-specific IgM effectively identifies patients with WNV infection.

Transient CD4/CD8 ratio inversion and aberrant immune activation during dengue virus infection

The immune status after dengue virus infection was studied in dengue patients from an outbreak of serotype 3 dengue virus infection in the southern part of Taiwan during November and December 1998. Consecutive blood samples from 29 dengue patients, of whom 21 had dengue fever and 8 had dengue hemorrhagic fever/dengue shock syndrome, were collected, and the immunophenotypes of the peripheral blood mononuclear cells were determined by flow cytometry. The early activation marker CD69 appeared on lymphocytes and monocytes at day 4 after the onset of fever, and declined afterward. However, a transient reverse in the CD4/CD8 ratio occurred at days 6-10 after the onset of fever. The CD4/CD8 ratio inversion was manifested in 10 of 29 dengue patients and was encountered more frequently in dengue hemorrhagic fever/dengue shock syndrome than in dengue fever patients. Analysis of the clinical blood cell count of these 10 cases showed that increase of immature neutrophils developed at fever days 5-6, CD4(dim) or CD8(dim) monocytosis at days 6-7, and atypical lymphocytosis at days 8-10 after the onset of fever. Serum IL-6 was found at either day 7 or day 9-11. The PHA-stimulated T-cell response was depressed as well. These changes in immune parameters indicate aberrant immune activation during dengue virus infection and might be involved in the pathogenesis of dengue virus infection.

Use of immunoglobulin m cross-reactions in differential diagnosis of human flaviviral encephalitis infections in the United States

To define the virus specificity of the immunoglobulin M (IgM) antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA) among the medically important members of the Japanese encephalitis (JE) virus serocomplex of flaviviruses, 103 IgM-positive human serum samples from patients with confirmed West Nile (WN) virus, St. Louis encephalitis (SLE) virus, or JE virus infections were assembled and simultaneously tested against all three viral antigens in a standardized MAC-ELISA. Of the serum samples tested, 96 (93%) showed higher positive-to-negative absorbance ratios (P/Ns) with the infecting virus antigen compared to those obtained with the other two virus antigens. Of the seven specimens with higher P/Ns with heterologous virus antigens, six were from patients with SLE virus infections (the serum samples had higher levels of reactivity with WN virus antigen) and one was from a patient with a JE virus infection (this serum sample also had a higher level of reactivity with WN virus antigen). Not surprisingly, similar virus specificity was observed with WN virus-elicited IgM in cerebrospinal fluid. As shown in previous studies, a subset of these specimens was even less reactive in the MAC-ELISA with dengue virus, a member of a different flavivirus serocomplex. The degree of virus cross-reactivity did not appear to be related to days postonset, at least during the first 40 days of infection. Infections with WN virus could be correctly distinguished from infections with SLE virus on the basis of the observed anti-viral IgM cross-reactivities alone 92% of the time. Infections with SLE virus resulted in antibody that was more cross-reactive, so identification of SLE virus as the infecting agent by use of MAC-ELISA cross-reactivity alone was more problematic.

Persistence of arboviruses and antiviral antibodies in vertebrate hosts: its occurrence and impacts

The recent isolation of West Nile virus from a bird in mid-winter in New York immediately raised, as one of a few explanations, the possibility of long-term persistence of arboviruses in vertebrate hosts. Although it was a highly popular topic for research many years ago, generally it has since been neglected and its meaning under appreciated. This comprehensive survey of literature worldwide uncovered, contrary to the general perception that it is a rather infrequent phenomenon, a large number of important observations involving all groups of arboviruses that have been accumulating over the years without drawing much attention. In this review, the data and observations were analysed in terms of the occurrence, role in natural transmission, mechanisms and genesis of persistence, source of problems in research and impact. The outcome of the analyses clearly demonstrates that asymptomatic, long-term infection in the absence of viraemia with or without the induction of neutralising antibody, the most frequent characteristics of arboviral persistence, presents a serious question about the validity of some of the past animal experiments that were conducted without the consideration of such a possibility. Likewise, significant impacts are felt on diverse fields ranging from epidemiology to diagnostic virology and from veterinary medicine to agricultural commerce. Published in 2001 by John Wiley & Sons, Ltd.

Antibody to the nonstructural protein NS1 of Japanese encephalitis virus: potential application of mAb-based indirect ELISA to differentiate infection from vaccination

An indirect enzyme-linked immunosorbent assay (ELISA) was developed to detect and differentiate the antibody responses to Japanese encephalitis (JE) virus nonstructural protein NS1 between infected and vaccinated individuals. The results showed that all convalescent sera from JE patients contained NS1-specific IgG antibodies, while 65 and 40% of these sera showed detectable NS1-specific IgM and IgA antibodies, respectively. Specificity analysis showed that NS1-specific IgM and IgA antibodies from JE patients do not cross-react to dengue virus NS1 glycoprotein, while IgG antibodies from 10% of JE patients showed significant cross-reaction to dengue virus NS1 glycoprotein. To differentiate infection from vaccination, the immune sera from 24 children vaccinated with inactivated JE vaccine were analyzed. The data showed that none of these immune sera had detectable NS1-specific IgG antibodies. The results demonstrated the potential application of JE NS1-specific indirect ELISA to differentiate infection from vaccination.

[Serological survey on arbovirus infection in residents of an ecological reserve]

OBJECTIVE

Serological inquires conducted in the Ribeira Valley, S. Paulo State, Brazil, showed an intense circulation of pathogenic arboviruses in the region. The goal was to verify the prevalence of arboviral infections in people living at the local ecological, and its potential association with these population' individual and familiar characteristics.

METHODS

The study was carried out among 182 persons of 58 families to identify the presence of antibodies to the following viruses: Rocio (ROC), Ilheus (ILH), Eastern equine encephalitis virus (EEE), Western equine encephalitis virus (WEE), Venezuelan equine encephalitis virus (VEE) and St. Louis encephalitis virus (SLE). Inhibition hemagglutination test and plaque reduction neutralization test were the laboratory assays of choice. MAC-ELISA was used to identify IgM antibodies to ROC, ILH and EEE viruses.

RESULTS

The prevalence of antibodies was 26.9% (21. 4% to alphavirus and 12.6% to flavivirus). There were no antibodies to WEE virus. IgM antibodies were not observed suggesting no recent infection in study population. Among the characteristics investigated, age, occupation, place of birth and the habit of going into the forest were shown to be statistically associated with arboviral infection (p<0.05).

CONCLUSIONS

It was observed an intense circulation of pathogenic arboviruses, especially VEE. It seems the habit of going into the forest is the most important factor to this population exposure to the mosquito vectors of arboviruses. The results suggest the need of further investigation to clarify the role of birds as arbovirus infection amplificators indoors.

Standardization of immunoglobulin M capture enzyme-linked immunosorbent assays for routine diagnosis of arboviral infections

Immunoglobulin M antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA) is a rapid and versatile diagnostic method that readily permits the combination of multiple assays. Test consolidation is especially important for arthropod-borne viruses (arboviruses) which belong to at least three virus families: the Togaviridae, Flaviviridae, and Bunyaviridae. Using prototype viruses from each of these families and a panel of well-characterized human sera, we have evaluated and standardized a combined MAC-ELISA capable of identifying virus infections caused by members of each virus family. Furthermore, by grouping antigens geographically and utilizing known serological cross-reactivities, we have reduced the number of antigens necessary for testing, while maintaining adequate detection sensitivity. We have determined that a 1:400 serum dilution is most appropriate for screening antiviral antibody, using a positive-to-negative ratio of >/=2.0 as a positive cutoff value. With a blind-coded human serum panel, this combined MAC-ELISA was shown to have test sensitivity and specificity that correlated well with those of other serological techniques.

Detection of anti-arboviral immunoglobulin G by using a monoclonal antibody-based capture enzyme-linked immunosorbent assay

Monoclonal antibody (MAb)-based capture enzyme-linked immunosorbent assays (ELISAs) for the detection of anti-arboviral immunoglobulin G (IgG ELISAs) were developed for a comprehensive array of medically important arboviruses from the Alphavirus, Flavivirus, and Bunyavirus genera. Tests were optimized and standardized so that maximum homology could be maintained among working parameters for the different viral agents, enabling a wide range of viruses to be easily tested for at one time. MAbs were screened for suitability as capture vehicles for antigens from the three genera. The final test configuration utilized group-reactive MAbs eastern equine encephalitis virus 1A4B-6, dengue 2 virus 4G2, and La Crosse encephalitis virus 10G5.4 to capture the specific inactivated viral antigens. Serum IgG was detected by using alkaline phosphatase-conjugated anti-human IgG (Fc portion). A dilution of 1:400 was chosen as the universal screening serum dilution, with endpoint titrations of serum samples testing positive eliminating occasional false-positive results. IgG ELISA results correlated with those of the standard plaque-reduction neutralization assays. As expected, some test cross-reactivity was encountered within the individual genera, and tests were interpreted within the context of these reactions. The tests were standardized for laboratory diagnosis of arboviral infections, with the intent that they be used in tandem with the corresponding IgM antibody-capture ELISAs.

O'nyong-nyong fever in south-central Uganda, 1996-1997: clinical features and validation of a clinical case definition for surveillance purposes

O'nyong-nyong (ONN) fever, caused by infection with a mosquito-borne central African alphavirus, is an acute, nonfatal illness characterized by polyarthralgia. During 1996-1997, south-central Uganda experienced the second ONN fever epidemic ever recognized. Among 391 persons interviewed and sampled, 40 cases of confirmed and 21 of presumptive, well-characterized acute, recent, or previous ONN fever were identified through active case-finding efforts or during a household serosurvey and by the application of clinical and laboratory criteria. Among confirmed cases, the knees and ankles were the joints most commonly affected. The median duration of arthralgia was 6 days (range, 2-21 days) and of immobilization was 4 days (range, 1-14 days). In the majority, generalized skin rash was reported, and nearly half had lymphadenopathy, mainly of the cervical region. Viremia was documented in 16 cases, primarily during the first 3 days of illness, and in some of these, body temperature was normal. During this epidemic, the combination of fever, arthralgia, and lymphadenopathy had a specificity of 83% and a sensitivity of 61% in the identification of cases of ONN fever and thus could be useful for surveillance purposes.

Aspergillosis in children with cancer: A 34-year experience

A retrospective review of medical records, microbiology and pathology laboratory records, and nosocomial infection surveillance data was undertaken to describe the experience with culture-documented aspergillus infection in pediatric cancer patients at our facility. Sixty-six patients were identified from a 34-year period. The most common underlying diagnosis was leukemia. Risk factors included neutropenia, immunosuppression, and prior antibiotic therapy. On the basis of clinical presentation, 23 patients were believed to have disseminated disease and 43 to have localized disease. The lung was the most frequently affected organ. Despite aggressive medical and surgical management, overall mortality was 85% within the first year after diagnosis. Patients who presented with disease in sites other than the lungs fared better than patients with initial pulmonary involvement (P=.0014). Aspergillosis continues to be associated with poor outcome. Development of improved medical and adjuvant therapies, including surgery, is warranted.

Dengue haemorrhagic fever in children in the 1996 Delhi epidemic

An epidemic of dengue haemorrhagic fever (DHF) occurred in Delhi in 1996. A total of 240 children between the age of 4 months to 13 years of either sex, admitted in one hospital, were evaluated. Two hundred and sixteen (90%) children were from Delhi. A clinical diagnosis of dengue fever (DF) was made in 25 (10%), dengue fever with unusual bleeding (DFB) in 22 (9%), DHF in 80 (33%) and dengue shock syndrome (DSS) in 113 (47%) of the children strictly according to the WHO classification. The age peaked at 8 years. There was no association between various grades of severity of illness and age-groups though girls suffered from more severe illness. No association between severity of malnutrition and severity of illness was observed. Tourniquet test was positive in 40% with DF, 18% with DFB, 62% with DHF and 64% with DSS. In DSS haematemesis was present in 55 (49%), epistaxis in 39 (35%), melaena in 27 (24%) and ecchymosis in 34 (30%) patients. Children diagnosed as DFB had haematemesis and epistaxis in 12 (55%) and 10 (45%) respectively. Intravenous fluid requirement was clearly less in DFB patients than in DHF/DSS patients. Unusual clinical features in the form of jaundice were present in 7 (6%), hepatic encephalopathy in 6 (5%) and dengue encephalopathy in 6 (5%) patients. Dengue 2 virus was isolated from 10 of the 50 patients for whom viral culture was done on C6/36 clone of Aedes albopictus cell line. Eighteen patients suffering from DSS died giving an overall case fatality of 7.5%. The mortality rate in DHF/DSS was 9.3%. It is further suggested that DFB is a distinct entity. Most patients could be classified by the WHO classification if a retrospective packed cell volume was used to assess haemoconcentration. We suggest that development of area-specific criteria for diagnosis and management is desirable.

Diagnosis and prevention of equine infectious diseases: present status, potential, and challenges for the future

The frequent transfers of horses, whether on a permanent or temporary basis, make strict control of infectious diseases essential. Such control needs a reliable and rapid means to accurately diagnose the relevant diseases. Indirect diagnosis based on antibody detection remains certainly the best method to secure the epidemiologic surveillance of the diseases at regional, national, or even world level, while direct diagnosis is the only way to diagnose a new outbreak. New diagnostic methods resulting from advances in biochemistry, molecular biology, and immunology are now available. As far as antibody detection is concerned, the new methods are mainly based on immunoassays, especially ELISAs. Regarding the identification of the pathogens, while isolation is still of importance, much progress has been made with immunocapture tests including capture ELISA based on monoclonal antibodies. DNA probes and amplification tests such as PCR or RT-PCR are representing a real breakthrough. Factors common to all of these tests are specificity, sensitivity, rapid implementation, and quick results. Such tests are, however, often still at the development stage. They absolutely need to be validated under multicentric evaluations prior to being used on a larger scale. At the same time there is an obvious need for the standardization of the reagents used. The technical and economic impact of a false (either positive or negative) diagnosis justifies such an harmonization which could effectively be achieved worldwide under the aegis of the Office International des Epizooties (OIE), which is itself the primary source of disease information. Vaccines are also essential for the control of equine infectious diseases. Most vaccines used in the prevention of viral or bacterial diseases are inactivated adjuvanted vaccines, which may cause unacceptable side effects. Also, their efficacy can sometimes be questioned. Subunit vaccines, when available, represent significant advances especially with regards to safety. Greater progress is expected from the use of new technologies taking advantage of recent developments in molecular biology (recombinant DNA technology) and in immunology (immunomodulators). Significant results have been obtained with subunit vaccines or with live vectored vaccines using recombinant DNA technology. Good results are on the way to be achieved with genetic (or naked-DNA) vaccines. It is therefore possible to expect the availability of a new generation of vaccines in the rather short term. Such vaccines will not only be safer and more efficacious, but they will also make it possible to differentiate vaccinated from infected animals, which will contribute to better control of the infection. Whatever the quality of the vaccines of the future may be, vaccination alone will never be sufficient to control infectious diseases. It is therefore essential to keep on making the animal owners and their veterinarians aware of the importance of the management and the hygiene in the diseases control and to organize them under "Common Codes of Practice."

The first major outbreak of dengue hemorrhagic fever in Delhi, India

India An outbreak of dengue hemorrhagic fever/dengue shock syndrome (DHS/DSS) occurred in 1996 in India in and near Delhi. The cause was confirmed as dengue virus type 2, by virus cultivation and indirect immunofluorescence with type-specific monoclonal antibodies. This is the largest such outbreak reported from India, indicating a serious resurgence of dengue virus infection.

Lymphocytic 2',5'-oligoadenylate synthetase activity increases prior to the appearance of neutralizing antibodies and immunoglobulin M and immunoglobulin G antibodies after primary and secondary immunization with yellow fever vaccine

Primary and secondary immunizations with live, attenuated yellow fever virus vaccine (17D strain) were performed in order to study the course of appearance of virus-neutralizing antibodies and immunoglobulin M (IgM) and IgG antibodies directed against the virus and the interferon-dependent enzyme 2',5'-oligoadenylate synthetase (2',5'AS) activity, determined in homogenates of peripheral B and T lymphocytes. From cellular ATP, this enzyme generates 2',5'-oligoadenylates which mediate degradation of viral mRNA by stimulation of a latent RNase. By day 4 after the first immunization, the earliest and highest 2',5'AS activity was present in the T-lymphocyte fraction. By day 7, the enzyme activity was highest in the B-lymphocyte fraction. Virus-neutralizing antibodies appeared on day 7, and IgM antibodies were present on day 12. After the second immunization, performed 2 years +/- 2 months later, the only significant increase in 2',5'AS activity was observed in the T-lymphocyte fraction. Virus-neutralizing antibodies were present from day 1, whereas no IgM antibodies were detected. By day 12, 80% of the vaccines were IgG positive. In the primary and secondary (memory) immune responses, 2',5'AS activity is expressed in the T-lymphocyte fraction prior to the appearance of antibodies directed against the virus and may serve as an early and sensitive marker of an ongoing virus infection which is otherwise difficult to detect. No change in conventional laboratory analysis parameters, such as in differential blood cell counts or total IgA, IgG, and IgM, disclosed the immune activity in either the primary or the secondary immunization.

Medically important arboviruses of the United States and Canada

Of more than 500 arboviruses recognized worldwide, 5 were first isolated in Canada and 58 were first isolated in the United States. Six of these viruses are human pathogens: western equine encephalitis (WEE) and eastern equine encephalitis (EEE) viruses (family Togaviridae, genus Alphavirus), St. Louis encephalitis (SLE) and Powassan (POW) viruses (Flaviviridae, Flavivirus), LaCrosse (LAC) virus (Bunyaviridae, Bunyavirus), and Colorado tick fever (CTF) virus (Reoviridae, Coltivirus). Their scientific histories, geographic distributions, virology, epidemiology, vectors, vertebrate hosts, transmission, pathogenesis, clinical and differential diagnoses, control, treatment, and laboratory diagnosis are reviewed. In addition, mention is made of the Venezuelan equine encephalitis (VEE) complex viruses (family Togaviridae, genus Alphavirus), which periodically cause human and equine disease in North America. WEE, EEE, and SLE viruses are transmitted by mosquitoes between birds; POW and CTF viruses, between wild mammals by ticks; LAC virus, between small mammals by mosquitoes; and VEE viruses, between small or large mammals by mosquitoes. Human infections are tangential to the natural cycle. Such infections range from rare to focal but are relatively frequent where they occur. Epidemics of WEE, EEE, VEE, and SLE viruses have been recorded at periodic intervals, but prevalence of infections with LAC and CTF viruses typically are constant, related to the degree of exposure to infected vectors. Infections with POW virus appear to be rare. Adequate diagnostic tools are available, but treatment is mainly supportive, and greater efforts at educating the public and the medical community are suggested if infections are to be prevented.