Towards prediction and surveillance of Murray Valley encephalitis activity in Australia

Current practices for early warning of activity of Murray Valley encephalitis and other medically-important arboviruses are reviewed with view to improvement. Data from previous papers on Culex annulirostris populations, environmental factors and virus infection rates were reanalysed and the results considered as a basis for prediction and surveillance. This goal will only be achieved with improved national cooperation, a better epidemiological understanding and greater knowledge of the bionomics of the major vector, Culex annulirostris. The improved monitoring system will utilize meteorological, serological and entomological criteria.     

Live Chimeric and Inactivated Japanese Encephalitis Virus Vaccines Differ in Their Cross-Protective Values against Murray Valley Encephalitis Virus

The Japanese encephalitis virus (JEV) serocomplex, which also includes Murray Valley encephalitis virus (MVEV), is a group of antigenically closely related, mosquito-borne flaviviruses that are responsible for severe encephalitic disease in humans. While vaccines against the prominent members of this serocomplex are available or under development, it is unlikely that they will be produced specifically against those viruses which cause less-frequent disease, such as MVEV. Here we have evaluated the cross-protective values of an inactivated JEV vaccine (JE-VAX) and a live chimeric JEV vaccine (ChimeriVax-JE) against MVEV in two mouse models of flaviviral encephalitis. We show that (i) a three-dose vaccination schedule with JE-VAX provides cross-protective immunity, albeit only partial in the more severe challenge model; (ii) a single dose of ChimeriVax-JE gives complete protection in both challenge models; (iii) the cross-protective immunity elicited with ChimeriVax-JE is durable (≥5 months) and broad (also giving protection against West Nile virus); (iv) humoral and cellular immunities elicited with ChimeriVax-JE contribute to protection against lethal challenge with MVEV; (v) ChimeriVax-JE remains fully attenuated in immunodeficient mice lacking type I and type II interferon responses; and (vi) immunization with JE-VAX, but not ChimeriVax-JE, can prime heterologous infection enhancement in recipients of vaccination on a low-dose schedule, designed to mimic vaccine failure or waning of vaccine-induced immunity. Our results suggest that the live chimeric JEV vaccine will protect against other viruses belonging to the JEV serocomplex, consistent with the observation of cross-protection following live virus infections.Murray Valley encephalitis virus (MVEV) is a mosquito-borne flavivirus belonging to the Japanese encephalitis virus (JEV) serocomplex which can cause severe, sometimes fatal, disease in humans (reviewed in references 30, 31, 32, and 42). The virus is endemic in northern Australia and Papua New Guinea, where it causes a small number of human cases of encephalitis in most years. In symptomatic patients the case fatality rate is ∼20%, and among those who recover a large number (∼50%) will suffer from neuropsychiatric sequelae. Cases of Murray Valley encephalitis are more common in children or visitors in areas of endemic disease than in adult residents, who have preexisting immunity (7, 42, 46). Sporadically, MVEV spreads to central or southern regions of Australia (e.g., the Murray Valley of southeastern Australia) and causes epidemic viral encephalitis in humans (32). There are no vaccines or antiviral agents available against MVEV, and given the relatively small number of human cases, it is unlikely that a MVEV-specific vaccine for human use will be produced. However, it has been known for many years that at least in animal models, live viral infection with other members of the JEV serocomplex will give cross-protective immunity against heterologous viruses belonging to this group (10, 17, 33, 48, 52). MVEV is genetically and antigenically closely related to JEV (82% amino acid sequence identity in the envelope [E] protein), the most important encephalitic flavivirus in terms of human disease incidence and severity (reviewed in reference 4). A number of live and inactivated JEV vaccines have been licensed or are under development (reviewed in references 2, 16, and 34). If effective and long-lasting cross-protective immunity against MVEV was induced by one of the JEV vaccines, a strong case could be made for its prophylactic use in populations at risk of MVEV infection in Australia. A further reason for investigating the suitability of JEV vaccines in the Australian context is the recent emergence of JEV in northern Australia (18, 19, 41). This has raised the prospect that JEV may become established in enzootic cycles on the Australian mainland, necessitating the use of JEV vaccines in regions where MVEV is also endemic. The impact of MVEV infection in JEV vaccine recipients in terms of disease outcome remains unknown.In contrast to its protective value against heterologous flaviviruses, cross-reactive flavivirus immunity has also been associated with infection- and/or disease-enhancing consequences in natural and laboratory settings (1, 9, 20, 39). Antibody-dependent enhancement of infection is thought to account for the more severe forms of dengue sometimes associated with secondary, heterologous dengue virus infections by a mechanism putatively involving the increased uptake of virus bound with nonneutralizing antibody into Fc receptor-bearing cells (14, 15). For the MVEV/JEV pair, it has been reported that transfer of subneutralizing concentrations of JEV-immune serum or sera from mice suboptimally immunized with inactivated JEV vaccine (JE-VAX; Biken, Japan) can prime recipient mice for a more severe disease when challenged with MVEV (3, 50). We have demonstrated this potentially detrimental effect for the first time in the context of the full complement of the vaccine-primed immune response: the administration of an experimental UV-inactivated MVEV vaccine at a suboptimal dose greatly increased the susceptibility of mice (up to 75% mortality) to challenge with a dose of JEV, which was sublethal in unvaccinated animals (29). It is not clear if this phenomenon is an inherent property of inactivated vaccines, which provide relatively poor immunity in terms of quality, magnitude, and duration in comparison to live virus infections. Here we investigate the protective value and risk of disease potentiation of a recombinant, live JEV vaccine candidate (ChimeriVax-JE) and a licensed, inactivated JEV vaccine (JE-VAX) in mouse models of MVEV and West Nile virus (WNV) encephalitis. ChimeriVax-JE is constructed from yellow fever virus 17D vaccine cDNA by replacement of the viral structural prM and E proteins with those of an attenuated JEV strain; it has been shown to protect mice and monkeys from JEV challenge (12, 36) and has undergone phase 2 and phase 3 trials for safety and efficacy in humans (35, 37).     

Epidemiology of Japanese Encephalitis in the Philippines: A Systematic Review

BackgroundJapanese encephalitis virus (JEV) is an important cause of encephalitis in most of Asia, with high case fatality rates and often significant neurologic sequelae among survivors. The epidemiology of JE in the Philippines is not well defined. To support consideration of JE vaccine for introduction into the national schedule in the Philippines, we conducted a systematic literature review and summarized JE surveillance data from 2011 to 2014.MethodsWe conducted searches on Japanese encephalitis and the Philippines in four databases and one library. Data from acute encephalitis syndrome (AES) and JE surveillance and from the national reference laboratory from January 2011 to March 2014 were tabulated and mapped.ResultsWe identified 29 published reports and presentations on JE in the Philippines, including 5 serologic surveys, 18 reports of clinical cases, and 8 animal studies (including two with both clinical cases and animal data). The 18 clinical studies reported 257 cases of laboratory-confirmed JE from 1972 to 2013. JE virus (JEV) was the causative agent in 7% to 18% of cases of clinical meningitis and encephalitis combined, and 16% to 40% of clinical encephalitis cases. JE predominantly affected children under 15 years of age and 6% to 7% of cases resulted in death. Surveillance data from January 2011 to March 2014 identified 73 (15%) laboratory-confirmed JE cases out of 497 cases tested.SummaryThis comprehensive review demonstrates the endemicity and extensive geographic range of JE in the Philippines, and supports the use of JE vaccine in the country. Continued and improved surveillance with laboratory confirmation is needed to systematically quantify the burden of JE, to provide information that can guide prioritization of high risk areas in the country and determination of appropriate age and schedule of vaccine introduction, and to measure the impact of preventive measures including immunization against this important public health threat.     

Mosquito seasonality and arboviral disease incidence in Murray Valley, southeast Australia

Abstract. Adult female mosquito populations were monitored at weekly intervals during spring-autumn (November-March) for 4 years (1991-95) using dry-ice-baited light traps at forty sites in the Murray Valley of Victoria, Australia. Among twenty species of mosquitoes collected, Culex annulirostriswas the most abundant (66.6 ± 9.3%) followed by Cx australicus(15.3 ± 7.7%). From a total of 476, 682 mosquitoes collected, nearly all were females and only 1295 (0.27%) were males. Mosquito population densities were generally higher in 1992-93 and 1993-94 seasons than in 1991-92 and 1994-95 seasons. Greatest densities of Cx annulirostrisand Cx australicusoccurred in 1992-93, coinciding with outbreaks of Ross River (RR) and Barman Forest (BF) arboviruses causing human polyarthritis. In the majority of shires, Cx australicuswas the predominant species from spring to early summer (November and December), then was replaced by Cx annulirostrisfrom mid-summer to autumn (January-April). In three shires, Aedes bancroftianusand Ae.sagaxpredominated during the early part of the season. Densities of both Cx annulirostrisand Cx australicuswere related to temperature. Cx australicusadults were found to be trapped when the mean ambient temperature exceeded 6d?C, with peak population recorded at 20d?C. Cx annulirostrisadult density increased when the mean temperature rose above 12d?C, reaching a peak during February and March when temperature exceeded 25d?C. Cx annulirostrisdeclined rapidly from April onwards, with no adult activity evident from May to November. Population densities of Aedesspp. were generally less than reported from earlier studies, possibly due to lower rainfall in spring and summer as well as reduced flood irrigation practices. In each year, a significant correlation was detected between Cx annulirostrisdensity and RR virus incidence in humans. As Cx annulirostrisis the predominant local mosquito species and feeds on a wide spectrum of hosts including man, it seems likely that Cx annulirostrisis the major vector of RR in the inland Murray Valley region.     

The First Outbreak of Eastern Equine Encephalitis in Vermont: Outbreak Description and Phylogenetic Relationships of the Virus Isolate

The first known outbreak of eastern equine encephalitis (EEE) in Vermont occurred on an emu farm in Rutland County in 2011. The first isolation of EEE virus (EEEV) in Vermont (VT11) was during this outbreak. Phylogenetic analysis revealed that VT11 was most closely related to FL01, a strain from Florida isolated in 2001, which is both geographically and temporally distinct from VT11. EEEV RNA was not detected in any of the 3,905 mosquito specimens tested, and the specific vectors associated with this outbreak are undetermined.     

Attenuation of Murray Valley Encephalitis Virus by Site-Directed Mutagenesis of the Hinge and Putative Receptor-Binding Regions of the Envelope Protein

Molecular determinants of virulence in flaviviruses cluster in two regions on the three-dimensional structure of the envelope (E) protein; the base of domain II, believed to serve as a hinge during pH-dependent conformational change in the endosome, and the lateral face of domain III, which contains an integrin-binding motif Arg-Gly-Asp (RGD) in mosquito-borne flaviviruses and is believed to form the receptor-binding site of the protein. In an effort to better understand the nature of attenuation caused by mutations in these two regions, a full-length infectious cDNA clone of Murray Valley encephalitis virus prototype strain 1-51 (MVE-1-51) was employed to produce a panel of site-directed mutants with substitutions at amino acid positions 277 (E-277; hinge region) or 390 (E-390; RGD motif). Viruses with mutations at E-277 (Ser-->Ile, Ser-->Asn, Ser-->Val, and Ser-->Pro) showed various levels of in vitro and in vivo attenuation dependent on the level of hydrophobicity of the substituted amino acid. Altered hemagglutination activity observed for these viruses suggests that mutations in the hinge region may indirectly disrupt the receptor-ligand interaction, possibly by causing premature release of the virion from the endosomal membrane prior to fusion. Similarly, viruses with mutations at E-390 (Asp-->Asn, Asp-->Glu, and Asp-->Tyr) were also attenuated in vitro and in vivo; however, the absorption and penetration rates of these viruses were similar to those of wild-type virus. This, coupled with the fact that E-390 mutant viruses were only moderately inhibited by soluble heparin, suggests that RGD-dependent integrin binding is not essential for entry of MVE and that multiple and/or alternate receptors may be involved in cell entry.     

The Severity of Murray Valley Encephalitis in Mice Is Linked to Neutrophil Infiltration and Inducible Nitric Oxide Synthase Activity in the Central Nervous System

A study of immunopathology in the central nervous system (CNS) during infection with a virulent strain of Murray Valley encephalitis virus (MVE) in weanling Swiss mice following peripheral inoculation is presented. It has previously been shown that virus enters the murine CNS 4 days after peripheral inoculation, spreads to the anterior olfactory nucleus, the pyriform cortex, and the hippocampal formation at 5 days postinfection (p.i.), and then spreads throughout the cerebral cortex, caudate putamen, thalamus, and brain stem between 6 and 9 days p.i. (P. C. McMinn, L. Dalgarno, and R. C. Weir, Virology 220:414-423, 1996). Here we show that the encephalitis which develops in MVE-infected mice from 5 days p.i. is associated with the development of a neutrophil inflammatory response in perivascular regions and in the CNS parenchyma. Infiltration of neutrophils into the CNS was preceded by increased expression of tumor necrosis factor alpha and the neutrophil-attracting chemokine N51/KC within the CNS. Depletion of neutrophils with a cytotoxic monoclonal antibody (RB6-8C5) resulted in prolonged survival and decreased mortality in MVE-infected mice. In addition, neutrophil infiltration and disease onset correlated with expression of the enzyme-inducible nitric oxide synthase (iNOS) within the CNS. Inhibition of iNOS by aminoguanidine resulted in prolonged survival and decreased mortality in MVE-infected mice. This study provides strong support for the hypothesis that Murray Valley encephalitis is primarily an immunopathological disease.     

Molecular Epidemiology and Phylogenetic Analysis of Human Adenovirus Caused an Outbreak in Taiwan during 2011

An outbreak of adenovirus has been surveyed in Taiwan in 2011. To better understand the evolution and epidemiology of adenovirus in Taiwan, full-length sequence of hexon and fiber coapsid protein was analyzed using series of phylogenetic and dynamic evolution tools. Six different serotypes were identified in this outbreak and the species B was predominant (HAdV-3, 71.50%; HAdV-7, 15.46%). The most frequent diagnosis was acute tonsillitis (54.59%) and bronchitis (47.83%). Phylogenetic analysis revealed that hexon protein gene sequences were highly conserved for HAdV-3 and HAdV-7 circulation in Taiwan. However, comparison of restriction fragment length polymorphism (RFLP) analysis and phylogenetic trees of fiber gene in HAdV-7 clearly indicated that the predominant genotype in Taiwan has shifted from 7b to 7d. Several positive selection sites were observed in hexon protein. The estimated nucleotide substitution rates of hexon protein of HAdV-3 and HAdV-7 were 0.234×10^-3 substitutions/site/year (95% HPD: 0.387~0.095×10^-3) and 1.107×10^-3 (95% HPD: 0. 541~1.604) respectively; those of the fiber protein of HAdV-3 and HAdV-7 were 1.085×10^-3 (95% HPD: 1.767~0.486) and 0.132×10^-3 (95% HPD: 0.283~0.014) respectively. Phylodynamic analysis by Bayesian skyline plot (BSP) suggested that using individual gene to evaluate the effective population size might possibly cause miscalculation. In summary, the virus evolution is ongoing, and continuous surveillance of this virus evolution will contribute to the control of the epidemic.     

The 1952 Outbreak of Encephalitis in California (A Symposium): DIFFERENTIAL DIAGNOSIS

Clinical data adequate for analysis were available in 386 laboratory-confirmed cases of arthropod-borne encephalitis — 38 St. Louis and 348 western equine. Consistently observed symptoms varied with the age of the patient. Symptoms that occurred in a high proportion of patients in each age group were:Less than one year of age: Fever and convulsions. (None had the St. Louis disease.)One through four years: Fever, headache, vomiting, drowsiness, irritability, restlessness, nuchal rigidity, tremor, and sometimes convulsions.Five through fourteen years: Headache, fever, and drowsiness. Sometimes the disease progressed no further, but if it did, nausea, vomiting, muscular pain, photophobia and limitation of neck and back flexion often were noted; and sometimes convulsions and intention tremors.Fifteen years and older: Drowsiness, lethargy, malaise, fever, stiffness at the back of the neck and, almost always, severe intractable occipital headache associated with nausea, disturbance of vision, photophobia and vertigo.The extreme difficulty of differential diagnosis on the basis of clinical observation was indicated by the wide range of diagnoses made in these cases before the invading organism was identified by laboratory studies.     

The 1952 Outbreak of Encephalitis in California (A Symposium): EPIDEMIOLOGIC ASPECTS

For the most part, epidemiologic phenomena observed in the outbreak of encephalitis in 1952 accorded with patterns that had been apparent in previous years. Ninety-seven per cent of the 414 laboratory-confirmed cases of western equine and St. Louis encephalitis in humans occurred in the 20 Central Valley counties. The cases of western equine encephalomyelitis in horses were generally scattered over the state. In the Central Valley most of the cases in horses were in animals less than two years of age; elsewhere the incidence was higher in older horses.There were no laboratory-confirmed cases of western equine or St. Louis encephalitis in humans earlier than June or later than October.In 1952 there were far more cases of western equine than of St. Louis encephalitis—a departure from the pattern in the previous seven years when there were about as many of one as of the other. No known satisfactory index is available for the prediction of the extent or type of outbreaks in humans.Approximately one-third of the cases of western equine encephalitis were in patients less than one year of age, whereas there were no cases of the St. Louis disease in patients that young.The incidence of western equine encephalitis in persons under 5 years of age was about the same for girls as for boys. In higher age brackets, males with western equine encephalitis outnumbered females 2 to 1. The corresponding ratio for St. Louis encephalitis was only 1.2 to 1.