Field Comparison of Removed Substrate Sampling and Emergence Traps for Estimating Culicoides Orbivirus Vectors in Northern Florida.

The larval ecology of Culicoides (Diptera: Ceratopogonidae) influences their spatial distributions and the pathogens they transmit. These features are of special concern for deer farmers in Florida where epizootic hemorrhagic disease virus (EHDV) is a major source of mortality in captive herds. Rarity of larval morphological expertise leads many researchers to study larval ecology by quantifying emergence, either with field emergence traps or removing substrate from the field for observation under laboratory conditions. We investigated the comparability of these methods in Florida seepages where two recently implicated EHDV vectors, Culicoides stellifer Coquillett and Culicoides venustus Hoffman, are common. We compared the abundance and composition of emerging Culicoides collected from emergence traps with removed substrate samples (soil plugs) at three seepages. Soil plugs were sampled adjacent to the emergence trap and from underneath the trap footprint, and then monitored under laboratory conditions for 11-13 wk to compare the methods and to assess the role of incubation period for removed substrate samples. Emergence traps and removed substrate sampling largely agreed on community compositions and trends within different seepages. However, comparatively large numbers of C. stellifer emerged later than expected and well into the incubation period with emergence still occurring after 13 wk (90 d). Removed substrate samples were more similar to emergence traps at shorter incubation times. The importance of time for the capture of Culicoides in removed substrate sampling was more pronounced than we anticipated and is important from both a methodological and biological perspective.

Alphaviruses: Serological Evidence of Human Infection in Paraguay (2012-2013).

INTRODUCTION: Alphaviruses can produce febrile illness and encephalitis in dead-end hosts such as horses and humans. Within this genus, the Venezuelan Equine Encephalitis virus (VEEV) complex includes pathogenic epizootic subtypes and enzootic subtypes that are not pathogenic in horses (except subtype IE, Mexican strains), although they can cause febrile symptoms in humans. The Rio Negro virus (RNV-VEEV subtype VI) circulates in Argentina, where it was associated with undifferentiated febrile illness. Mayaro (MAYV) and Una (UNAV) viruses belong to a different group, the Semliki Forest virus complex, with confirmed circulation. OBJECTIVE: The present study aimed to determine RNV, MAYV, and UNAV seroprevalences by plaque reduction neutralization test in 652 samples of Paraguayan individuals mainly from the Central Department, between years 2012 and 2013. METHODS: Samples with antibodies titer >1:20 against RNV were also tested for Mosso das Pedras-subtype IF, subtype IAB, and Pixuna (PIXV)-subtype IV viruses that belongs to VEEV antigenic complex. RESULTS: The overall seroprevalence of RNV was 3.83%, and for UNAV it was 0.46%, and no neutralizing antibodies were detected against MAYV in the studied population. Two of the twenty-seven heterotypic samples were positive for PIXV. The 50.1% of neutralizing antibody titers against RNV were high (equal to or greater than 1/640), suggesting recent infections. The effect of age on the prevalence of RNV was negligible. CONCLUSIONS: These results bring new information about neglected alphaviruses in South America, and these data will serve as the basis for future studies of seroprevalence of other VEEV, and studies to search potential hosts and vectors of these viruses in the region.

Activity Patterns of St. Louis Encephalitis and West Nile Viruses in Free Ranging Birds during a Human Encephalitis Outbreak in Argentina.

St. Louis encephalitis virus (SLEV) (Flavivirus) is a reemerging arbovirus in the southern cone of South America. In 2005, an outbreak of SLEV in central Argentina resulted in 47 human cases with 9 deaths. In Argentina, the ecology of SLEV is poorly understood. Because certain birds are the primary amplifiers in North America, we hypothesized that birds amplify SLEV in Argentina as well. We compared avian SLEV seroprevalence in a variety of ecosystems in and around Córdoba city from 2004 (before the epidemic) and 2005 (during the epidemic). We also explored spatial patterns to better understand the local ecology of SLEV transmission. Because West Nile virus (WNV) was also detected in Argentina in 2005, all analyses were also conducted for WNV. A total of 980 birds were sampled for detection of SLEV and WNV neutralizing antibodies. SLEV seroprevalence in birds increased 11-fold from 2004 to 2005. Our study demonstrated that a high proportion (99.3%) of local birds were susceptible to SLEV infection immediately prior to the 2005 outbreak, indicating that the vertebrate host population was primed to amplify SLEV. SLEV was found distributed in a variety of environments throughout the city of Córdoba. However, the force of viral transmission varied among sites. Fine scale differences in populations of vectors and vertebrate hosts would explain this variation. In summary, we showed that in 2005, both SLEV and to a lesser extent WNV circulated in the avian population. Eared Dove, Picui Ground-Dove and Great Kiskadee are strong candidates to amplify SLEV because of their exposure to the pathogen at the population level, and their widespread abundance. For the same reasons, Rufous Hornero may be an important maintenance host for WNV in central Argentina. Competence studies and vector feeding studies are needed to confirm these relationships.