Western equine encephalitis in avian populations in North Dakota, 1975

The involvement of wild birds in western equine encephalitis (WEE) and St. Louis encephalitis (SLE) virus activity in the Red River valley area of North Dakota (USA) during a WEE epidemic was investigated in August 1975. Free-ranging birds were captured with mist nets and nestlings by hand. Virologic and serologic results indicated that a similar rate of WEE virus activity occurred throughout Richland County and between permanent and summer resident birds. The rate of SLE virus activity in the birds of Richland County was lower than for WEE virus, but the SLE antibody prevalence was greater in rural areas than within urban locations. Seven of the nine WEE virus isolations were from nestling birds of four different species; the remaining two from adults of two different species. Overall prevalence of neutralizing (N) antibody against WEE virus was 5% in nestling and 14% in adult birds but was the opposite for N antibody against SLE virus, 17% in nestling and 5% in adult birds. Differences between the two viruses in the presence and persistence of maternal N antibody or differential mortality in nestling birds may have caused the disparity in antibody prevalences.     

Cache Valley virus: isolations from mosquitoes in Saskatchewan, 1972-1974.

Eighteen isolations of Cache Valley virus (Bunyaviridae) were obtained from a total of 113,694 mosquitoes collected in Saskatchewan during the summers of 1972 to 1974. Most of the isolations were from mosquitoes collected during August. Culiseta inornata, the most abundant mosquito (38% of total collected), had the highest minimum vector-infection rate (0.83 isolations per 1000 mosquitoes). The virus was also isolated from Culex tarsalis and Aedes vexans. It is indicated in the isolations that the prairie grasslands of the province are enzootic for Cache Valley virus.     

Role of peridomestic birds in the transmission of St. Louis encephalitis virus in southern California

In response to the 1984 St. Louis encephalitis (SLE) epidemic in the Los Angeles Basin of southern California (USA), an investigative program was initiated to evaluate the interactive components of the SLE virus transmission cycle. From 1987 through 1996 (10 yr), 52,589 birds were bled and their sera tested for SLE and western equine encephalomyelitis (WEE) virus antibodies by the hemagglutination inhibition (HAI) test. Eighty-three percent of the birds tested were house finches (Carpodacus mexicanus) (48.7%) and house sparrows (Passer domesticus) (34.6%); 1.1% of these birds were positive for SLE antibodies. Prevalence of WEE antibodies was negligible. The analysis of 5,481 sera from rock doves (Columbia livia) yielded 3.6% SLE positives and 0.4% WEE positives. Collection sites were maintained as study sites when identified as positive bird, mosquito, and SLE virus activity localities; others were abandoned. Serial serum samples from 7,749 banded house sparrows and 9,428 banded house finches from these selected sites demonstrated year-round SLE virus transmission. One location exhibited significant numbers of house finches undergoing annual SLE seroconversion and a number of seroconversion-reversion-reconversion sequences suggesting either viral reinfection from mosquitoes or recrudescence by latent virus. A proportion of both bird species also lived for longer than 1 yr, thus, increasing the possibility of virus carry-over from autumn to spring. Assessment of concurrently collected mosquitoes indicated no correlative association between mosquito populations and SLE seroconversion and reconversion. European house sparrows introduced in the 1800's may have provided a supplemental link to the existing SLE virus enzootic cycle involving endemic house finches. Meteorological factors are reviewed as possible important correlates of SLE epidemics. The house finch/house sparrow serosurveillance system is also evaluated for use as an "Early Warning" indicator of SLE virus activity.     

Evaluation of the Epidemic Potential of Western Equine Encephalitis Virus in the Northeastern United States

The problem of evaluating the epidemic potential of western equine encephalitis in the northeastern United States is presented and possible reasons are discussed for the present lack of human and horse cases of this disease even though increased numbers of isolations of the virus have been obtained in the East during recent years. Epidemiologic factors of vector bionomics and virus strain variations are considered. It is concluded that while this virus strain can no longer be regarded as uncommon in the Northeast, the evidence indicates there is little potential for epidemic expression of this agent in the human and horse population. This appears to be due to differences in the bionomics of the mosquito Culiseta melanura, which serves as the primary enzootic vector in the northeastern United States and in the bionomics of Culex tarsalis that is the vector in the western region of the United States. Other limiting factors in the epidemic potential may be variations between virus strains located in the East and West.     

Salmonella infections in a marsupial, the quokka (Setonix brachyurus), in relation to seasonal changes in condition and environmental stress

An unusual abundance of Salmonella infections was studied in an island population of a wild marsupial, the quokka (Setonix brachyurus), which experiences starvation in summer associated with significant mortality. The frequency of infections was found to vary seasonally over most parts of the island, with high infection rates (70 to 100%) in summer and low infection rates (0 to 30%) in winter. In some samples, there was an average of as many as two isolations per animal, and up to five isolations were made from a single animal. By the end of summer, virtually all animals excreted Salmonella spp., with a median rate of excretion of approximately 3,000 Salmonella organisms per g of feces. The seasonal changes occurred over intervals of only weeks. The infections are believed to be associated with disruption of the digestive physiology of the animals caused by the poor quality of feed available in summer. This conclusion was supported by a quantitative study of the infections and by a field manipulation experiment which delayed the initiation of the infections as long as a food supplement was available. The proliferation of Salmonella spp. is discussed in terms of the ecology of the quokka and of the use of Salmonella spp. as indicators of environmental stress acting on the animals.     

Salmonella infections in a marsupial, the quokka (Setonix brachyurus), in relation to seasonal changes in condition and environmental stress.

An unusual abundance of Salmonella infections was studied in an island population of a wild marsupial, the quokka (Setonix brachyurus), which experiences starvation in summer associated with significant mortality. The frequency of infections was found to vary seasonally over most parts of the island, with high infection rates (70 to 100%) in summer and low infection rates (0 to 30%) in winter. In some samples, there was an average of as many as two isolations per animal, and up to five isolations were made from a single animal. By the end of summer, virtually all animals excreted Salmonella spp., with a median rate of excretion of approximately 3,000 Salmonella organisms per g of feces. The seasonal changes occurred over intervals of only weeks. The infections are believed to be associated with disruption of the digestive physiology of the animals caused by the poor quality of feed available in summer. This conclusion was supported by a quantitative study of the infections and by a field manipulation experiment which delayed the initiation of the infections as long as a food supplement was available. The proliferation of Salmonella spp. is discussed in terms of the ecology of the quokka and of the use of Salmonella spp. as indicators of environmental stress acting on the animals.     

Chronic infections of Haplosporidium nelsoni (MSX) in the oyster Crassostrea virginica

Oysters inhabiting areas enzootic for the parasite Haplosporidium nelsoni (MSX) are exposed to infective particles each summer, and it is often difficult to distinguish newly acquired lesions from older infections. To study long-term parasitism without the complication of new infections, MSX-infected oysters were moved from Delaware Bay to a disease-free area on the New Jersey coast. Because infections seen after the transfer were acquired in Delaware Bay during a known infective period, it was possible to determine how long oysters remained infected and how they were affected by chronic parasitism. Chronic infections displayed the same seasonal cycle (high levels in winter and late spring, low levels in summer and early spring) that occurs in enzootic areas with annual reinfection. Within individual oysters, chronic MSX became localized, relapsed into general infections, and then became localized again in a sequence that was probably controlled by temperature. Some experimental oysters survived with MSX for at least 4 years. Hemocytosis persisted in these oysters, and their poor condition suggested that chronically infected individuals would have lowered resistance to additional stress.     

European red squirrel population dynamics driven by squirrelpox at a gray squirrel invasion interface

Infectious disease introduced by non‐native species is increasingly cited as a facilitator of native population declines, but direct evidence may be lacking due to inadequate population and disease prevalence data surrounding an outbreak. Previous indirect evidence and theoretical models support squirrelpox virus (SQPV) as being potentially involved in the decline of red squirrels (Sciurus vulgaris) following the introduction of the non‐native gray squirrel (Sciurus carolinensis) to the United Kingdom. The red squirrel is a major UK conservation concern and understanding its continuing decline is important for any attempt to mitigate the decline. The red squirrel–gray squirrel system is also exemplary of the interplay between infectious disease (apparent competition) and direct competition in driving the replacement of a native by an invasive species. Time series data from Merseyside are presented on squirrel abundance and squirrelpox disease (SQPx) incidence, to determine the effect of the pathogen and the non‐native species on the native red squirrel populations. Analysis indicates that SQPx in red squirrels has a significant negative impact on squirrel densities and their population growth rate (PGR). There is little evidence for a direct gray squirrel impact; only gray squirrel presence (but not density) proved to influence red squirrel density, but not red squirrel PGR. The dynamics of red SQPx cases are largely determined by previous red SQPx cases, although previous infection of local gray squirrels also feature, and thus, SQPV‐infected gray squirrels are identified as potentially initiating outbreaks of SQPx in red squirrels. Retrospective serology indicates that approximately 8% of red squirrels exposed to SQPV may survive infection during an epidemic. This study further highlights the UK red squirrel – gray squirrel system as a classic example of a native species population decline strongly facilitated by infectious disease introduced by a non‐native species. It is therefore paramount that disease prevention and control measures are integral in attempts to conserve red squirrels in the United Kingdom.     

Eastern equine encephalitis in the United States, 1971: Past and prologue

During 1971, surveillance for equine encephalitis in the United States was increased due to an epizootic of Venezuelan equine encephalomyelitis. Of 1,982 specimens from 1,551 equines, 76 isolates of eastern equine encephalitis (EEE) virus were recovered from 67 individuals. The virus was isolated from 50/176 brains, 8/74 spleens, 14/1,127 sera, and 4/147 whole bloods from infected equines in 12 of the 31 states bounded by or east of the Mississippi River and in Texas and Iowa; no specimens were received from 9 of these 31 states. Thus, EEE virus was isolated from equines in 12 of 22 of these states. Determinations of antibody to EEE and western equine encephalitis (WEE) viruses indicated a relatively high prevalence of infection with EEE virus in the eastern USA and similarly high prevalence of antibody to WEE virus in the western USA. These data indicate that equine infections with EEE virus in the eastern USA are considerably more common than previous surveillance data have suggested. Increased surveillance and submission of specimens to diagnostic laboratories for diagnosis of EEE virus infections in equines are suggested so that a greater proportion of the thousands of unspecified equine encephalitis cases occurring in the United States each year can be laboratory confirmed.     

Isolation of Western Equine Encephalomyelitis (Wee) Virus From Mosquitoes In Saskatchewan, 1962

Saskatchewan, in the summer of 1962, was the scene of an extensive outbreak of western equine encephalomyelitis (WEE) in horses. The results of mosquito survey work showed Culiseta inornata and Culex tarsalis respectively to be the two most abundant mosquito species during midsummer. These species are those reported to be most commonly associated with outbreaks of WEE. Five hundred and sixty-four pools of mosquitoes were examined for the presence of WEE virus. Six pools, three of C. tarsalis and one each of C. inornata, Aedes flavescens and Aedes dorsalis, yielded WEE virus. Positive mosquitoes were from St. Walburg (C. inornata), Saskatoon (C. tarsalis - two, A. dorsalis - one), Outlook (C. tarsalis) and Kisbey (A. flavescens).     

Results of the 20-year study of tick-borne encephalitis in Crimea

The history of tick-borne encephalitis (TBE) study in the Crimea was retraced and the possibility of introduction of TBE virus to the Crimea in the process of the acclimatization of vertebrates from areas enzootic for TBE is discussed. The foci of TBE were found throughout the whole of the mountain forest zone of the Crimea and coincided with the habitat area of lxodes ricinus, the main vector of TBE. Such ticks as Dermacentor reticulatus, D. marginatus and Hyalomma marginatum were also found to take part in the circulation of the virus. Among the residents of the mountain forest zone, 13.9% were found to have immunity to TBE, testifying to the wide contact of the population with the pathogen. TBE morbidity had pronounced seasonal character and the morbidity rate was low with the prevalence of mild clinical forms. The characteristic feature of the virus population was polymorphism: strains identical to the Far-Eastern strains Sofyin (about 60-70%) and strains differing in their antigenic structure circulated here.     

Red Squirrel Middens Influence Abundance but Not Diversity of Other Vertebrates

Some animals modify the environment in ways that can influence the resources available to other species. Because red squirrels (Tamiasciurus hudsonicus) create large piles of conifer-cone debris (middens) in which they store cones, squirrels concentrate resources that might affect biodiversity locally. To determine whether other animals are attracted to midden sites beyond their affinity for the same resources that attract red squirrels, we assessed associations between middens, mammals, and birds at population and community levels. We surveyed 75 middens where residency rates of red squirrels varied during the previous five years; sampling along this residency gradient permitted us to evaluate the influence of resources at middens beyond the influence of a resident squirrel. At each location, we quantified vegetation, landscape structure, abundance of conifer cones, and midden structure, and used capture–recapture, distance sampling, and remote cameras to quantify presence, abundance, and species richness of mammals and birds. Red squirrels and the resources they concentrated at middens influenced mammals and birds at the population scale and to a lesser extent at the community scale. At middens with higher residency rates of red squirrels, richness of medium and large mammals increased markedly and species richness of birds increased slightly. After accounting for local forest characteristics, however, only species richness of medium-to-large mammals was associated with a red squirrel being resident during surveys. In areas where red squirrels were resident during surveys or in areas with greater amounts of resources concentrated by red squirrels, abundances of two of four small mammal species and two of four bird species increased. We conclude that the presence of this ecosystem modifier and the resources it concentrates influence abundance of some mammals and birds, which may have implications for maintaining biodiversity across the wide geographic range inhabited by red squirrels and other larderhoarding animals.     

Spatial Evaluation and Modeling of Dengue Seroprevalence and Vector Density in Rio de Janeiro,Brazil

Background

Rio de Janeiro, Brazil, experienced a severe dengue fever epidemic in 2008. This was the worst epidemic ever, characterized by a sharp increase in case-fatality rate, mainly among younger individuals. A combination of factors, such as climate, mosquito abundance, buildup of the susceptible population, or viral evolution, could explain the severity of this epidemic. The main objective of this study is to model the spatial patterns of dengue seroprevalence in three neighborhoods with different socioeconomic profiles in Rio de Janeiro. As blood sampling coincided with the peak of dengue transmission, we were also able to identify recent dengue infections and visually relate them to Aedes aegypti spatial distribution abundance. We analyzed individual and spatial factors associated with seroprevalence using Generalized Additive Model (GAM).

Methodology/Principal Findings

Three neighborhoods were investigated: a central urban neighborhood, and two isolated areas characterized as a slum and a suburban area. Weekly mosquito collections started in September 2006 and continued until March 2008. In each study area, 40 adult traps and 40 egg traps were installed in a random sample of premises, and two infestation indexes calculated: mean adult density and mean egg density. Sera from individuals living in the three neighborhoods were collected before the 2008 epidemic (July through November 2007) and during the epidemic (February through April 2008). Sera were tested for DENV-reactive IgM, IgG, Nested RT-PCR, and Real Time RT-PCR. From the before–after epidemics paired data, we described seroprevalence, recent dengue infections (asymptomatic or not), and seroconversion. Recent dengue infection varied from 1.3% to 14.1% among study areas. The highest IgM seropositivity occurred in the slum, where mosquito abundance was the lowest, but household conditions were the best for promoting contact between hosts and vectors. By fitting spatial GAM we found dengue seroprevalence hotspots located at the entrances of the two isolated communities, which are commercial activity areas with high human movement. No association between recent dengue infection and household''s high mosquito abundance was observed in this sample.

Conclusions/Significance

This study contributes to better understanding the dynamics of dengue in Rio de Janeiro by assessing the relationship between dengue seroprevalence, recent dengue infection, and vector density. In conclusion, the variation in spatial seroprevalence patterns inside the neighborhoods, with significantly higher risk patches close to the areas with large human movement, suggests that humans may be responsible for virus inflow to small neighborhoods in Rio de Janeiro. Surveillance guidelines should be further discussed, considering these findings, particularly the spatial patterns for both human and mosquito populations.     

Spatial pattern of abundance of the mosquito,Ochlerotatus albifasciatus,in relation to habitat characteristics

Ochlerotatus albifasciatus (Macquart) (Diptera: Culicidae) is the main vector of the western equine encephalomyelitis (WEE) virus and potentially of other arboviruses in Argentina. Surges of adult population abundance during the rainy season are a nuisance, affecting milk and beef production. Larvae develop in short periods in shallow temporary ground pools on fresh or brackish water. Although adults seem to disperse long distances from larval habitats, little is known about their habitat preferences. This work studied factors affecting the spatial pattern of adult Oc. albifasciatus abundance. Adult mosquitoes were collected using CDC miniature light traps baited with CO2 at 28 sites located to the south of Mar Chiquita Lagoon, from November 1997 to April 1998. Each site was typified according to its predominating vegetation cover, potential breeding site occurrence, land slope and cattle density. The spatial and temporal patterns of abundance suggested that Oc. albifasciatus prefers prairies and natural grasslands subject to periodic flooding vs. woodland and farm land. A discriminant function based on the proximity to potential larval habitats, distance to woodland and land slope accurately classified 95% of the data categorized as having an average high (>500 mosquitoes) or low (<500 mosquitoes) abundance, and was validated using six sites located away from the study area. An analysis of the temporal variation of mosquito abundance highlighted the influence of the dynamics of the larval habitats on adult mosquito abundance.     

Effects of influenza, mumps, and western equine encephalitis viruses on fetal rhesus monkeys (Macaca mulatta).

Pregnant Rhesus monkeys were infected via instillation of influenza, mumps and western equine encephalomyelitis viruses respectively into the amniotic sacs at approximately 90 days gestation to determine if fetal infections would occur. Virus was recovered from fetal tissues after seven days in 100% of the exposed animals. Thus, the viruses are capable of causing fetal infection. Rhesus monkey fetuses were inoculated with influenza, mumps and WEE viruses by the direct intracerebral route at approximately 90 days gestation to determine possible teratogenicity of the viruses. influenza virus caused no malformations or measurable fetal effects. Mumps virus resulted in significant fetal mortality. WEE virus resulted in a 100% incidence of encephalitis and hydrocephalus. Thus, mumps and WEE viruses are teratogens in primates and are potential teratogens of man.     

A systematic review into the suitability of urban refugia for the Eurasian red squirrel Sciurus vulgaris

1. Urban growth and intensification are projected to increase as the global human population increases. Historically, urban areas have been disregarded as suitable wildlife habitat, but it is now known that these areas can be biodiverse and that wildlife species can adapt to the environmental conditions. One such urban-dwelling species is the Eurasian red squirrel Sciurus vulgaris, which has suffered population declines in several countries throughout its range in recent decades.
2. The current published literature was systematically reviewed to determine whether or not urban habitats are suitable refugia for red squirrels, through identifying and discussing key topics regarding the urban ecology of red squirrels.
3. Urban environments can support higher population densities of red squirrels than rural areas, probably due to the widespread and reliable provision of anthropogenic supplemental food alongside natural food sources. The availability and quality of urban greenspaces are important determinants of the suitability of urban habitats for red squirrels, as they provide natural food sources and nesting sites. Despite the barriers present in urban landscapes (e.g. roads), red squirrels can still disperse and maintain gene flow at the population level.
4. Road traffic accidents appear to be a significant cause of mortality in some urban red squirrel populations, and seasonal peaks of mortality occur during the autumn months. Diseases (e.g. squirrelpox virus) can also be a significant cause of mortality, although effects differ between populations and depend on whether grey squirrels Sciurus carolinensis are present. Many of the predation events that affect red squirrels appear to be due to free-ranging domestic and feral cats Felis catus, although there is currently little evidence to suggest that predation is a limiting factor for urban red squirrel populations.
5. We conclude that urban areas can be suitable refugia for red squirrels, provided that high-quality greenspaces are maintained. Mitigation measures may also be necessary to reduce population mortality and to prevent disease outbreaks.

     

Multiyear and seasonal hepatitis A morbidity in different population age groups in certain areas

At the areas with high activity of hepatitis A (HA) epidemic process the duration of epidemic cycles was shown to differ, the intervals between the peaks of morbidity increasing in older age groups. The beginning of seasonal rises exceeding the average annual HA morbidity level in different age groups was found to depend on the activity of the epidemic process. At the areas with the highest activity of the epidemic process children aged 1-2 years were the first to be affected by the seasonal rise of HA. Stable direct correlation between HA morbidity levels at the beginning of seasonal rises and some markers indicative of unfavorable sanitary conditions (the size of the fly population, the purity of water samples deviating from the requirement of the Government Standard) during the preceding year was demonstrated.     

Breeding ecology and seasonal abundance of the giant water bug Appasus japonicus (Heteroptera, Belostomatidae)

Males of the giant water bug Appasus (= Diplonychus) japonicus Vuillefroy (Belostomatidae: Heteroptera) carry egg masses on their back, but little is known about the relationship between seasonal abundance and breeding ecology of the species. In the present study, therefore, a field survey based on a mark-and-recapture census was carried out at three survey points within a rice paddy area (0.3 km²) where A. japonicus forms a meta-population in northern Okayama, Japan. We investigated the body size, seasonal abundance, dispersion, egg mass size (number of eggs within one egg mass), number of egg masses and the total eggs carried on the back of each male as fundamental parameters of the population and breeding. Significant differences in egg mass size, number of egg masses, and total number of eggs that males carried was found among the survey points. The present results suggested the possibility that the differences in breeding parameters of A. japonicus were influenced by differences in environmental factors among the microhabitats. These results are discussed in conjunction with previous reports on seasonal abundance and breeding systems in Belostomatidae bugs.     

Atlantic Bluefin Tuna in the Gulf of Maine, I: Estimation of Seasonal Abundance Accounting for Movement, School and School-Aggregation Behaviour

Direct assessment of the abundance of highly migratory pelagic species, such as tuna, is rarely available and most indices are based on catch information. We estimate the seasonal abundance of North Atlantic bluefin tuna, Thunnus thynnus, in the Gulf of Maine (GOM) from a 3-year aerial survey conducted with commercial spotter pilots, while also utilizing findings from analyses of tracking and tagging data. We apply statistical correction and calibration to seasonal abundance estimates accounting for measured changes in horizontal and vertical movement behaviour, size, shape and aggregation of bluefin tuna schools. Our approach relies on ecological knowledge of bluefin tuna to extrapolate survey observations across areas not sampled by correcting survey abundance estimates based on range of movement search pattern and depth preference. We demonstrate how separate findings obtained through the analysis of data collected across different spatial and temporal scales can be integrated to correct and calibrate estimates of population abundance. We obtain fitted estimates of seasonal abundance of bluefin tuna in the GOM during 1994–1996 in the range of 45,000–51,000 individuals. If tuna behaviour is not accounted for, we estimate that the base or residual survey precision would be 4–7% determined from analysis of recent spotter survey data in the study region. We estimate the precision in estimating seasonal abundance accounting for tuna behaviour to lie within a range of 1,301–3,302%. Under hypothetical future improvements in survey design that achieve a precision of 20% in transect length and placement, we calculate net-precision to lie within a range of 82–93%. This calculation assumes reducible uncertainty in school size estimation and irreducible uncertainty in movement and school-aggregation behaviour. We infer that survey precision could be further reduced by 43–32% to attain 10–50% in which a 3–8 years adaptive survey design may reliably detect a seasonal abundance trend.     

Molecular epizootiology and evolution of vesicular stomatitis virus New Jersey.

Vesicular stomatitis virus (VSV) has been shown previously to be capable of undergoing rapid mutational change during sequential experimental infections in various tissue culture cell systems (J. Holland, K. Spindler, F. Horodyski, E. Grabau, S. Nichol, and S. Vandepol, Science 215:1577-1585, 1982). The present study was undertaken to determine the degree of genetic diversity and evolution of the virus under natural infection conditions and to gain insight into the epizootiology of the disease. Between 1982 and 1985, numerous outbreaks of VSV of the New Jersey serotype were reported throughout regions of the United States and Mexico. A T1 RNase fingerprint analysis was performed on the RNA genomes of 43 virus isolates from areas of epizootic and enzootic virus activity. This indicates that virus populations were genetically relatively homogeneous within successive U.S. virus epizootics. The data included virus isolates from different epizootic stages, geographical locations, host animals, and host lesion sites. In contrast, only distant genome RNA T1 fingerprint similarities were observed among viruses of the different U.S. epizootics. However, Mexican viruses isolated before or concurrent with U.S. epizootics had very similar RNA genome fingerprints, suggesting that Mexico may have been the possible origin of virus initiating recent U.S. VSV New Jersey outbreaks. Comparison of T1 fingerprints of viruses with enzootic disease areas revealed a greater extent of virus genetic diversity in these areas relative to that observed in epizootic areas. The evolutionary significance of these findings and their relationship to experimental data on VSV evolution are discussed.