Fernando S. Flores

Vertical transmission of St. Louis encephalitis virus in Culex quinquefasciatus (Diptera: Culicidae) in Córdoba, Argentina.

Arbovirus vector transmission is interrupted when vector abundance decreases or disappears in temperate regions during the winter season. Although the primary overwintering mechanism for many arboviruses in nature remains unknown, vertical transmission is one potential mechanism. Vertical transmission functions as an overwintering mechanism for St. Louis encephalitis virus (SLEV) in temperate areas of Argentina, where SLEV is endemic. The aim of this project was to detect vertical transmission of SLEV in Culex quinquefasciatus mosquitoes. Under laboratory conditions, SLEV vertical transmission (3.4 minimum infection rates) was detected in larvae (1:256) and adults F₁ (1:406). There were no positive larvae for SLEV among over 2011 analyzed individuals collected in nature. This is the first study to confirm experimental vertical transmission of SLEV in Cx. quinquefasciatus populations from Argentina, though additional overwintering mechanisms (e.g., nontraditional vectors such as ticks and nondiapausing female mosquitoes) should be considered.

Transmission of endemic St Louis encephalitis virus strains by local Culex quinquefasciatus populations in Córdoba, Argentina

BACKGROUND St Louis encephalitis virus (SLEV) is a re-emerging human pathogen widely distributed in the American continent. Although it is not fully understood, the SLEV transmission network may involve Culex quinquefasciatus mosquitoes as vectors and Columbidae species as hosts. METHODS To calculate infection rates, we inoculated Cx. quinquefasciatus mosquitoes from Córdoba, Argentina by feeding them on viremic chicks. RESULTS We observed differences in infection rate among the viral strains, the highest rate (78/87 mosquitoes, 90.8%) being seen in strain 78V-6507. After re-feeding on susceptible chicks, mosquitoes were able to transmit the virus. CONCLUSION Our findings suggest that Cx. quinquefasciatus populations are susceptible to and able to transmit different SLEV strains.

Intertwined arbovirus transmission activity: reassessing the transmission cycle paradigm.

Arboviruses are emerging/reemerging infectious agents worldwide. The factors within this scenario include vector and host population fluctuations, climatic changes, anthropogenic activities that disturb ecosystems, an increase in international flights, human mobility, and genetic mutations that allow spill-over phenomenon. Arboviruses are maintained by biologic transmission among vectors and hosts. Sometimes this biological transmission is specific and includes one vector and host species such as Chikungunya (CHIKV), Dengue (DENV), and urban Yellow Fever (YFV). However, most of the arboviruses are generalist and they use many vectors and hosts species. From this perspective, arboviruses are maintained through a transmission network rather than a transmission cycle. This allows us to understand the complexity and dynamics of the transmission and maintenance of arboviruses in the ecosystems. The old perspective that arboviruses are maintained in close and stable transmission cycles should be modified by a new more integrative and dynamic idea, representing the real scenario where biological interactions have a much broader representation, indicating the constant adaptability of the biological entities.

Ticks (Acari: Ixodidae) on wild birds in north-central Argentina

Ixodid ticks were collected from wild birds in five ecoregions in north-central Argentina, namely: Selva de las Yungas, Esteros del Iberá, Delta e Islas del Paraná, Selva Paranaense and Chaco Seco. A total of 2199 birds belonging to 139 species, 106 genera, 31 families and 11 orders were captured, but ticks were collected only from 121 birds (prevalence=5.5%) belonging to 39 species (28.1%) and three Orders: Tinamiformes (Tinamidae) and Falconiformes (Falconidae) in Selva de las Yungas and Passeriformes (Conopophagidae, Corvidae, Emberizidae, Furnariidae, Icteridae, Parulidae, Thamnophilidae, Thraupidae, Troglodytidae, Turdidae) for all ecoregions. The following tick species were found: Haemaphysalis juxtakochi, Haemaphysalis leporispalustris, Ixodes pararicinus plus Amblyomma sp. and Haemaphysalis sp. in Selva de las Yungas; Amblyomma triste and Ixodes auritulus in Delta e Islas del Paraná; Amblyomma dubitatum, A. triste and Amblyomma sp. in Esteros del Iberá; Amblyomma ovale and Amblyomma sp. in Selva Paranaense, and Amblyomma tigrinum in Chaco Seco. Amblyomma dubitatum was found for the first time on Passeriformes, while the records of A. ovale on avian hosts are the first for Argentina. Birds are also new hosts for I. pararicinus females. Besides 2 larvae and 1 nymph, and 1 larvae found on Tinamidae (Tinamiformes) and Falconidae (Falconiformes), respectively, all other ticks (691 larvae, 74 nymphs and 2 females) were found on Passeriformes with a relevant contribution of the family Turdidae. Birds are important hosts for I. pararicinus as shown by a prevalence of 45% while all others prevalence were below 15%. All the species of Amblyomma and Haemaphysalis found on birds in Argentina have been also detected on humans and are proven or potential vectors for human diseases. Therefore, their avian hosts are probable reservoirs of human pathogens in Argentina.

St. Louis Encephalitis virus mosquito vectors dynamics in three different environments in relation to remotely sensed environmental conditions.

In Argentina the St. Louis Encephalitis virus (SLEV) is an endemic and widely distributed pathogen transmitted by the cosmopolitan mosquito Culex quinquefasciatus. During two outbreaks in Córdoba city, in 2005 and 2010, Culex interfor was also found infected, but its role as vector of SLEV is poorly known. This mosquito species is distributed from central Argentina to southern Brazil. The primary aim of this study was to analyze the population dynamic of Cx. interfor and Cx. quinquefasciatus in three different environments (urban, suburban and non-urban) in relation to remotely sensed environmental data for vegetation (NDVI and NDWI) and temperature (brightness temperature). Cx. quinquefasciatus and Cx. interfor were found at the three sampled sites, being both the most abundant Culex species, with peaks in early and midsummer. Temporal distribution patterns of both mosquito species were highly correlated in a non-urban area of high SLEV risk transmission. Cx. quinquefasciatus and Cx. interfor were associated with the most urbanized site and the non-urban environment, respectively; high significant correlations were detected between vegetation indices and abundance of both mosquito species confirming these associations. These data provide a foundation for building density maps of these two SLEV mosquito vectors using remotely sensed data to help inform vector control programs.

Rickettsial infection in ticks infesting wild birds from two eco-regions of Argentina

Several tick-borne Rickettsia species are recognized human pathogens in Argentina. Here we evaluated rickettsial infection in ticks collected on passerine birds during 2011-2012 in two eco-regions of Argentina. The ticks were processed by molecular analysis through polymerase chain reaction (PCR) detection and DNA sequencing of fragments of two rickettsial genes, gltA and ompA. A total of 594 tick specimens (532 larvae and 62 nymphs), representing at least 4 species (Amblyomma tigrinum, Ixodes pararicinus, Haemaphysalis juxtakochi, Haemaphysalis leporispalustris), were evaluated. At least one A. tigrinum larva, collected on Coryphospingus cucullatus in Chaco Seco, was infected with Rickettsia parkeri, whereas at least 12 larvae and 1 nymph of I. pararicinus, collected from Troglodytes aedon, Turdus amaurochalinus, Turdus rufiventris, C. cucullatus and Zonotrichia capensis, were infected with an undescribed Rickettsia agent, genetically related to several rickettsial endosymbionts of ticks of the Ixodes ricinus complex. R. parkeri is a recognized human pathogen in several American countries including Argentina, where a recent study incriminated A. tigrinum as the potential vector of R. parkeri to humans. Birds could play an important role in dispersing R. parkeri-infected A. tigrinum ticks. Additionally, we report for the first time a rickettsial agent infecting I. pararicinus ticks.

Environmental Surveillance of Enteroviruses in Central Argentina: First Detection and Evolutionary Analyses of E14

Environmental surveillance is an effective approach to investigate the circulation of human enteroviruses in the population. Enteroviruses E14, CVA9, E-6, E16, E20, E25, E13, and CVA24 were detected in sewage and a watercourse in central Argentina. E14 was the most frequent serotype and was found for the first time in environmental samples in our region. Phylogenetic and coalescence analyses showed at least two recent introduction events.

The presence of Argas keiransi Estrada-Peña, Venzal & González- Acuña, 2003 (Acari: Argasidae) in Argentina

Abstract Forty-two larvae of Argas keiransi (Acari: Argasidae) were collected from the Chimango Caracara, Milvago chimango (Falconiformes: Falconidae), at three localities in La Pampa Province, Argentina. Ticks were determined by a combination of palpal segment IV as long as or longer than the other palpal segments, absence of a trumpet-shaped sensillum extending from the capsule of Haller´s organ into the lumen of the tarsus, length of dorsal plate between 180 and 240 μm, length of hypostome between 180 and 205 μm, dental formula 2/2 in the basal third, 2/2 or 3/3 apically, and length of posterolateral setae between 45 and 50 μm. Morphological determination was confirmed by analysis of sequences of the mitochondrial 16S rRNA gene. The results of this work constitute the first Argentinean record of A. keiransi, which has previously been reported only from Chile.

Wild birds as host of Borrelia burgdorferi sensu lato in northwestern Argentina

Borrelia burgdorferi sensu lato (s. l.) spirochetes are associated with a wide range of vectors and hosts. Birds are important hosts in the ecology of some hard ticks (Ixodidae) in northwestern Argentina, where B. burgdorferi s.l. have been detected in Ixodes pararicinus. We evaluated Borrelia infection in ticks collected from wild birds by molecular analysis through the presence of Borrelia DNA (by nested-PCR targeting the fla gene). A total of 381 ticks (357 larvae and 24 nymphs) belonging to four species (I. pararicinus, Haemaphysalis juxtakochi, Haemaphysalis leporispalustris and Amblyomma sp.) were collected. Partial sequences of the fla gene of Borrelia (100% identical to Borrelia sp. haplotype I from Argentina) were detected in 9 of 70 tick pools (6 pools of larvae and 1 pool of nymphs of I. pararicinus, and in 2 pools of H. juxtakochi larvae) collected on Turdus rufiventris, Syndactila rufosuperciliata and Troglodytes aedon. The results of this study suggest that resident birds have reservoir capacity for Borrelia sp. haplotype I.

Evaluation of Argentinean Bird Species as Amplifying Hosts for St. Louis Encephalitis Virus (Flavivirus, Flaviviridae)

St.Louis encephalitis virus (SLEV) is an emerging human pathogen flavivirus in Argentina. Recently, it has reemerged in the United States. We evaluated the role as amplifying host of six resident bird species and analyzed their capacity as host during the 2005 encephalitis outbreak of SLEV in Córdoba. Eared Dove, Picui Ground Dove, and House Sparrow were the three species with highest host competence index. At a city level, Eared Dove and Picui Ground Dove were the most important amplifying hosts during the 2005 SLEV human outbreak in Córdoba city. This finding highlighted important differences in the SLEV ecology between Argentina and the United States. Characterizing and evaluating the SLEV hosts contribute to our knowledge about its ecology and could help us to understand the causes that promote its emergence as a human pathogen in South America.