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Mosquitoes associated with low risk of transmission for Rift Valley fever virus in the United States
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Three of the most common mosquito species in the United States may not pose a significant risk for the transmission of Rift Valley fever virus, according to results of a new study.
Researchers examined three mosquito species: Aedes dorsalis, Aedes vexans and Culicoides sonorensis, all of which are common in the Midwestern United States. Each mosquito species was studied for its ability to serve as a potential vector for Rift Valley fever virus.
First, the researchers allowed the mosquitoes to feed on adult hamsters that had been inoculated with Rift Valley fever virus. Second, the mosquitoes were incubated for seven to 21 days at a temperature of 26·C. Following this, the mosquitoes were allowed to feed on susceptible hamsters (each with a viremia of 108.8 plaque-forming units/mL of blood). The mosquitoes were then were tested to determine infection, dissemination and transmission rates.
Low transmission
According to the researchers, none of the mosquito species tested were able to transmit Rift Valley fever virus efficiently under these lab conditions.
The results demonstrated that at 78%, the A. dorsalis species was the most susceptible to infection and had the highest dissemination rate (33%). However, this species had a salivary gland barrier and rarely transmitted Rift Valley fever virus by bite.
In contrast, 26% of the A. vexans species developed Rift Valley fever virus and 6% developed a dissemination infection. A. vexans was more likely to transmit infection by bite; about 50% of those with a disseminated infection transmitted the virus by bite.
None of the C. sonorensis species had the infection. The researchers said the results indicated that this species would not be a competent vector for Rift Valley fever virus.
Other factors
The researchers said other factors need to be considered when examining the risk of transmission for Rift Valley fever virus. “In addition to lab vector competence, factors such as seasonal density, feeding preference, longevity and foraging behavior also need to be considered when determining the role these species could play in Rift Valley fever virus transmission,” they wrote.
The researchers added that it is necessary to examine specific species of mosquitoes to better determine transmission risk. “Because mosquito control methods are often species specific, measures that are effective for one species may have little or no effect on others,” they wrote. “Thus, it is important to determine which mosquito species are capable of transmitting Rift Valley fever virus so that appropriate control measures can be instituted rapidly and efficiently, should this virus be introduced into North America.”
Turell MJ. #257.
Presented at: ASTMH 57th Annual Meeting; Dec. 7-11, 2008; New Orleans.