West Nile virus poses a serious threat to Galápagos wildlife

22 September 2011 by Tamera Jones

The unique wildlife of the Galápagos Islands could be at risk from West Nile virus if measures to enforce biosecurity aren't rigorously adhered to, researchers have warned.

Marine iguana

Marine iguana

They came to their conclusion after finding that mosquitoes accidentally introduced to the islands in the 1980s are capable of spreading the potentially deadly virus.

The virus most commonly affects birds, but can also infect mammals, reptiles and people.

West Nile virus hasn't yet made its way to the islands, but scientists are concerned that if it gets in, the islands' fragile animal populations could suffer. Soon after the virus arrived in North America in 1999 - via New York - it quickly spread west and south, leading to declines in several bird populations, most noticeably in birds like crows.

"The situation in North America demonstrates the potential risk. A lot of the islands' wildlife has also evolved in isolation, so animals likely haven't built up much immunity to new diseases like West Nile virus," explains Gillian Eastwood who's based at the Institute of Zoology, and studied the mosquitoes during her PhD project also at the University of Leeds.

The main thing is to stop invasive species like mosquitoes getting to the islands in the first place.

- Gillian Eastwood, Institute of Zoology

The virus comes from Africa, but increased air and boat travel around the world means it now exists on six continents. Its quick spread has led to its classification as an emerging infectious disease.

While the virus has showed up in some countries in South America, whether or not the virus has got as far as Ecuador - the gateway to the - isn't yet clear.

Recent studies show that the likely route into the Galápagos for mosquitoes that often carry the virus - Culex quinquefasciatus - is via aeroplane. With visitor numbers to the island increasing from 41,000 in 1991 to more than 160,000 at the last count, there's a very real risk of the disease spreading to the islands.

But the ability of mosquitoes to transmit diseases can vary. "We didn't know if this particular strain of mosquito could transmit West Nile virus," says Eastwood.

So, she and colleagues from the New York State Department of Health, the University of Leeds and the Zoological Society of London (ZSL) measured how well the C. quinquefasciatus mosquitoes in the Galápagos could pick up and transmit West Nile virus in the lab under conditions you'd find in the wild.

Their results confirmed that the mosquito can indeed carry the virus. "There's no doubt that West Nile virus poses a serious threat to the survival of the Galápagos' iconic wildlife," says Professor Andrew Cunningham from ZSL, who was involved in the study.

Eastwood recommends that the spread of more C. quinquefasciatus mosquitoes be controlled. "The main thing is to stop invasive species like mosquitoes getting to the islands in the first place. Tourism is great for the local economy, but biocontrol needs to be taken very seriously," she says.

Flights that arrive into the Galápagos are fumigated, but not all transport to the islands is. "It's important that all incoming transport is included, like military aircraft and boats for example," adds Eastwood.

She says one of the next things is to understand exactly where the mosquitoes are getting their blood meals from to see which wildlife is most at risk. This would also give scientists clues about how the virus might circulate in the population. "We need to look more at how the virus interacts with different hosts, understand other mosquito species in the Galápagos islands and see if the disease is on mainland Ecuador at all."

The study is published in the American Journal of Tropical Medicine & Hygiene.

'West Nile Virus Vector Competency of Culex quinquefasciatus Mosquitoes in the Galapagos Islands' - Gillian Eastwood, Laura D Kramer, Simon J Goodman and Andrew A Cunningham. The American Journal of Tropical Medicine & Hygiene, 2011 vol. 85 no. 3 426-433, doi: 10.4269/ajtmh.2011.10-0739