Serological evidence of widespread exposure of Grenada fruit bats to chikungunya virus.

Antibody detection against selected potentially zoonotic vector-borne alphaviruses and flaviviruses was conducted on sera from bats from all six parishes in Grenada, West Indies. Sera were tested for (i) antibodies to flaviviruses West Nile virus, St. Louis encephalitis virus, Ilhéus virus, Bussuquara virus (BSQV), Rio Bravo virus and all four serotypes of dengue virus (DENV) by plaque reduction neutralization test (PRNT); (ii) antibodies to alphaviruses western equine encephalitis virus, Venezuelan equine encephalitis virus and eastern equine encephalitis virus by epitope-blocking enzyme-linked immunosorbent assay (ELISA); and (iii) antibodies to the alphavirus chikungunya (CHIKV) by PRNT. Two species of fruit bats were sampled, Artibeus jamaicensis and Artibeus lituratus, all roosting in or within 1,000 m of human settlements. Fifteen (36%) of the 42 bats tested for neutralizing antibodies to CHIKV were positive. The CHIKV-seropositive bats lived in localities spanning five of the six parishes. All 43 bats tested for epitope-blocking ELISA antibody to the other alphaviruses were negative, except one positive for Venezuelan equine encephalitis virus. All 50 bats tested for neutralizing antibody to flaviviruses were negative, except one that had a BSQV PRNT80 titre of 20. The CHIKV serology results indicate that bats living close to and within human settlements were exposed to CHIKV in multiple locations. Importantly, bats for this study were trapped a year after the introduction and peak of the human CHIKV epidemic in Grenada. Thus, our data indicate that bats were exposed to CHIKV possibly during a time of marked decline in human cases.

Evaluation of Simultaneous Transmission of Chikungunya Virus and Dengue Virus Type 2 in Infected Aedes aegypti and Aedes albopictus (Diptera: Culicidae).

The simultaneous transmission of chikungunya virus (CHIKV) and dengue viruses (DENV) has been a major public health concern because of their sympatric distribution and shared mosquito vectors. Groups of Aedes aegypti (L.) and Aedes albopictus (Skuse) were orally infected with 1.5 × 10(5) PFU/ml of CHIKV and 3.2 × 10(6) FFU/ml of DENV-2 simultaneously or separately in inverse orders and evaluated for dissemination and transmission by qRT-PCR. Simultaneous dissemination of both viruses was detected for all groups in Ae. aegypti and Ae. albopictus while cotransmission of CHIKV and DENV-2 only occurred at low rates after sequential but not simultaneous infection.

Modulation of Anopheles gambiae gene expression in response to o'nyong-nyong virus infection.

To determine if gene expression of An. gambiae is modulated in response to o'nyong-nyong virus (ONNV) infection, we utilized cDNA microarrays including about 20 000 cDNAs. Gene expression levels of ONNV-infected female mosquitoes were compared to that of the uninfected control females harvested at 14 days postinfection. In response to ONNV infection, expression levels of 18 genes were significantly modulated, being at least two-fold up- or down-regulated. Quantitative real-time PCR analysis (qRT-PCR) further substantiated the differential expression of six of these genes in response to ONNV infection. These genes have similarity to a putative heat shock protein 70, DAN4, agglutinin attachment subunit, elongation factor 1 alpha and ribosomal protein L35. One gene, with sequence similarity to mitochondrial ribosomal protein L7, was down-regulated in infected mosquitoes. The expression levels and annotation of the differentially expressed genes are discussed in the context of host/virus interaction including host translation/replication factors, and intracellular transport pathways.

Molecular characterization of California serogroup viruses isolated in Russia.

Nucleotide sequencing was used to characterize unidentified California (CAL) serogroup virus isolates from Russia. These viruses were isolated from mosquitoes and humans during epidemiologic investigations on the role of CAL serogroup viruses in the increased incidence of arboviral encephalitis in Russia. Most of the isolates were identified serologically as snowshoe hare (SSH), Inkoo (INK), and Tahyna (TAH) viruses, but some of the isolates were difficult to classify serologically, suggesting that they could be reassortant viruses. There is evidence that at least 2 of these viruses are not reassortant viruses. Sequence analysis revealed that the Russian viruses differ from other Eurasian and North American CAL serogroup viruses in all of the segments analyzed. They are most closely related to SSH virus. Whether they differ sufficiently to be considered a new group of SSH-like viruses remains to be determined.

Typing of LaCrosse, snowshoe hare, and Tahyna viruses by analyses of single-strand conformation polymorphisms of the small RNA segments.

Single-strand conformation polymorphism analysis was developed to differentiate the small RNA segments of three California serogroup bunyaviruses. The small RNA segments of La Crosse, snowshoe hare, and Tahyna viruses were reverse transcribed and PCR amplified. The cDNAs were then denatured, rapidly chilled to promote intrastrand reassociation, separated electrophoretically on a nondenaturing gel at room temperature, and silver stained. The resulting single-strand conformation polymorphism patterns were specific for the respective viruses. This molecular technique offers great potential for virus typing and taxonomic studies.