Pathology of an iridescent virus in immature Culex pipiens L. (Diptera, Culicidae).

Iridovirus in Culex pipiens was reported for the first time in 2012. Later studies of horizontal transmission were performed, in which an interaction with the parasite Strelkovimermis spiculatus acting as viral vector was recognized. In the present study, we observed aspects of the pathology produced by an invertebrate iridescent virus in laboratory infected immature Cx. pipiens as well as in infected immature Cx. pipiens in the field. In the laboratory infected larvae, the infection and mortality were asynchronous. Signs of infection in larvae exposed to the virus were observed between the second and the fourth days post-exposure in 99% of the cases, while the highest daily record of visible infected larvae (52%) was observed on the third day post exposure. Moreover, 79% of confirmed virus infected larvae died in the first 10 days after exposure. The Median Lethal Time was eight days. Several tissues were found to be infected and the common sites of replication were the fat body, epidermis and epithelial derivatives, such as the imaginal discs and the tracheal epithelium. Moreover, infection in the salivary glands, gastric ceca and posterior gut have not been previously documented on other mosquito iridescent viruses.

Database of Sabethes and Haemagogus (Diptera: Culicidae) in Argentina: Sylvatic Vectors of the Yellow Fever Virus.

Yellow fever is an endemic disease in America caused by an arbovirus that circulates in the sylvatic cycle between nonhuman primates and mosquitoes of the genera Sabethes Robineau-Desvoidy and Haemagogus Williston. The main goal of this work is to report the distribution patterns of these genera in Argentina through an updated database built from published records as well as from own sample collections. These genera are represented in Argentina by a total of 18 species distributed in 14 provinces and 10 ecoregions. The ecoregions with greatest biodiversity were Paranense Forest, Yungas, Campos and Malezales. This database will also allow generating distribution maps for these mosquito genera, and their respective species in Argentina, to establish areas with high probability of viral circulation that are an essential input for vector surveillance, as a tool for public health decision-makers.

Vector competence of Aedes aegypti for different strains of Zika virus in Argentina.

The importance of Zika virus (ZIKV) has increased noticeably since the outbreak in the Americas in 2015, when the illness was associated with congenital disorders. Although there is evidence of sexual transmission of the virus, the mosquito Aedes aegypti is believed to be the main vector for transmission to humans. This species of mosquito has not only been found naturally infected with ZIKV, but also has been the subject of study in many vector competence assays that employ different strains of ZIKV around the world. In Argentina, the first case was reported in February 2016 and a total of 278 autochthonous cases have since been confirmed, however, ZIKV virus has not been isolated from any mosquito species yet in Argentina. In order to elucidate if Argentinian Ae. aegypti populations could be a possible vector of ZIKV, we conducted vector competence studies that involved a local strain of ZIKV from Chaco province, and a Venezuelan strain obtained from an imported case. For this purpose, Ae. aegypti adults from the temperate area of Argentina (Buenos Aires province) were fed with infected blood. Body, legs and saliva were harvested and tested by plaque titration on plates of Vero cells for ZIKV at 7, 11 and 14 days post infection (DPI) in order to calculate infection, transmission, and dissemination rates, respectively. Both strains were able to infect mosquitoes at all DPIs, whereas dissemination and transmission were observed at all DPIs for the Argentinian strain but only at 14 DPI for the Venezuelan strain. This study proves the ability of Ae. aegypti mosquitoes from Argentina to become infected with two different strains of ZIKV, both belonging to the Asian lineage, and that the virus can disseminate to the legs and salivary glands.

Factors Related to Aedes aegypti (Diptera: Culicidae) Populations and Temperature Determine Differences on Life-History Traits With Regional Implications in Disease Transmission.

Aedes aegypti (L.) (Diptera: Culicidae) is a vector of many medically significant viruses in the Americas, including dengue virus, chikungunya virus, and Zika virus. Traits such as longevity, fecundity, and feeding behavior contribute to the ability of Ae. aegypti to serve as a vector of these pathogens. Both local environmental factors and population genetics could contribute to variability in these traits. We performed a comparative study of Ae. aegypti populations from four geographically and environmentally distinct collection sites in Argentina in which the cohorts from each population were held at temperature values simulating a daily cycle, with an average of 25°C in order to identify the influence of population on life-history traits. In addition, we performed the study of the same populations held at a daily temperature cycle similar to that of the surveyed areas. According to the results, Aguaray is the most outstanding population, showing features that are important to achieve high fitness. Whereas La Plata gathers features consistent with low fitness. Iguazu was outstanding in blood-feeding rate while Posadas's population showed intermediate values. Our results also demonstrate that climate change could differentially affect unique populations, and that these differences have implications for the capacity for Ae. aegypti to act as vectors for medically important arboviruses.

Transmission of a pathogenic virus (Iridoviridae) of Culex pipiens larvae mediated by the mermithid Strelkovimermis spiculatus (Nematoda).

Little progress been made in elucidating the transmission pathway of the invertebrate iridescent virus (MIV). It has been proposed that the MIV has no active means to enter the mosquito larva. We have previously found that the presence of the mermithid nematode Strelkovimermis spiculatus is associated with MIV infection in Culex pipiens under field conditions. In the present study, we evaluated the transmission of MIV to C. pipiens larvae mediated by S. spiculatus and several factors involved in this pathway (mosquito instars, nematode:mosquito larva ratio, amount of viral inoculum). Our results indicate that S. spiculatus functions as an MIV vector to C. pipiens larvae and seems to be an important pathway of virus entry into this system. Moreover, TEM images of S. spiculatus exposed to the viral suspension showed no infections inside the nematode but showed that viral particles are carried over the cuticle of this mermithid. This explains the correspondence between MIV infection and the factors that affect the parasitism of S. spiculatus in C. pipiens larvae.

Vector competence of Argentine mosquitoes (Diptera: Culicidae) for West Nile virus (Flaviviridae: Flavivirus).

We examined the ability of Culex pipiens L. complex mosquitoes from Argentina to vector West Nile virus (WNV) to assess their role in the transmission of WNV in South America. Several egg rafts of Culex spp. were collected from different breeding sites in the suburbs of the city of La Plata, Argentina, and a subset of each progeny was scored with morphological and genetic species indicators. Surprisingly, we did not find Cx. pipiens form pipiens, but found evidence of genetic hybrids of Culex quinquefasciatus and Cx. pipiens f. molestus. We then used morphological traits to create two colonies predominantly composed of one of these two taxa, although some hybrids are likely to have been included in both. These colonies were used in vector competence studies using NY99 and WN02 genotype strains of WNV obtained in New York State. As controls, we also tested colonies of U.S. Cx. quinquefasciatus and Cx. pipiens f. molestus. Additional Culex larvae from three drainage ditches near the cities of La Plata and Berisso, Argentina, were identified by morphological and high-resolution molecular markers (microsatellites) as Cx. quinquefasciatus Say, Cx. pipiens form molestus, and hybrids. Results indicate that Argentinian Culex are competent but only moderately efficient vectors of WNV and are less susceptible to this virus than comparable U.S. mosquito strains. Studies of vertical transmission of NY99 virus by Cx. pipiens f. molestus hybrids from Argentina yielded a minimal filial infection rate of 1.19 from females feeding during their second and later bloodmeals.

First record of a mosquito iridescent virus in Culex pipiens L. (Diptera: Culicidae).

The mosquito iridescent viruses (MIVs) are large icosahedral DNA viruses that replicate and assemble in the cytoplasm of the host. Paracrystalline arrangements of virions that accumulate in the cytoplasm produce an iridescent color that is symptomatic of acute infections. In August 2010, we found larvae of Culex pipiens with these symptoms in suburban ditches around the city of La Plata, Argentina. Electron microscope studies, DNA sequencing, and phylogenetic analysis of the major capsid protein confirmed this as the first record of an MIV in C. Pipiens.