19 February 2013

Kenya: Researchers Identify Animal Skin Odours That Control RVF

Researchers from Icipe have identified skin odours from animals which allow mosquitoes to find and obtain blood meal from preferred hosts.

The discovery is a key milestone in the fight against the Rift Valley Fever virus, which is transmitted in animals by mosquito vectors.

The skin odours known as aldehydes have been discovered in sheep, goats, cows and donkeys. The discovery will be instrumental in resolving challenges in the fight against RVF.

The study, which has been published in the Neglected Tropical Diseases journal, will help identify effective tools for monitoring mosquito vectors distribution, through developing more efficient trapping systems.

In the last 20 years, epidemics of the disease have occurred at irregular intervals with hundreds of thousands of infections in people as well as livestock.

"The findings will enhance the ability of national programmes to predict the likelihood of an outbreak of the disease, which will enable them respond in a timely manner," reads the report.

The 1997/8 RVF outbreak in Kenya, Somalia and Tanzania, was the largest ever recorded in Sub Saharan Africa, with 100,000 people being affected and 450 deaths reported in Kenya alone.

Traditionally RVF vectors have been monitored using Centre for Disease Control light traps that are baited with carbon dioxide.

"Such traps generally target a wide spectrum of mosquito species and also trap a wide range of non-target insect species," reads the report, which faults light traps, which it says are not effective during the low vector density and during RVF inter-epidemic periods.

The re-emergence of the disease could pose a huge threat to livestock and human health beyond the region. It also presents a potential threat due to global environmental, demographic and societal changes and trade.

The researchers warn that if not controlled, RVF can lead to trade sanctions, travel warnings or restrictions such as animal culling, which could result in declining public confidence in Kenya's animal products.

Once RVF is known to be circulating in an animal herd, the World Organisation for Animal Health places a three-year export embargo on those animals.

Viral activity among mosquito species during inter-epidemic periods is said to remain undetected, and is believed to produce varied results that cannot be applied.

The researchers found that combining a blend of aldehydes with CDC carbon dioxide-baited traps without the light bulb can increase the number of mosquito vectors that are captured.

The traps can also be used for the surveillance of mosquitoes during the outbreak period when mosquito populations, as well as the transmission of the virus is low.

"As a result, the trapping system developed would provide adequate numbers of mosquitoes for virus detection."

When combined with climate data, says the report, the tool can improve prediction of potential outbreaks.

In the last 20 years, spates of the disease have occurred at irregular intervals with hundreds of thousands of infections in people as well as in livestock.

In its control, surveillance of mosquitoes is advantageous as it provides the earliest evidence of transmission in an area. It also helps in identifying the potential risk to humans.

Surveillance further allows emergency control operations to be set in motion in readiness for epidemics.

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