Mosquito Vector Activity During Inter-Epidemic Period Entomologic Surveillance

POSTER NO. 1

Arbovirus isolation from Rift Valley Fever virus vectors sampled from endemic hotspots in Kenya during inter-epidemic period.

Rosemary Sang1 2, Joel Lutomiah 1, Marion Warigia 1, Caroline Ochieng2, Philemon Cheruiyot 1, Hellen Koka 2, Albina Makio 2, Lilian O Musila 2, David Schnabel 2 and Barry R Miller 3

1 Centre for Virus Research, Kenya Medical Research Institute P.O. Box 54628, NAIROBI, Kenya. 2 United States Army Medical Research Unit Kenya, P. O. Box 606, Village Market , Nairobi, Kenya. 3 Division of Vector-Borne Infectious Diseases National Center for Zoonotic, Vector-Borne and Enteric Diseases (NZVED), Centre for Disease Control, P.O. Box 2087, 3150 Rampart Rd., Foothills Campus Fort Collins, CO 80521. National Center for Zoonotic, Vector-Borne and Enteric Diseases (NZVED)

Since the last outbreak of Rift Valley Fever (RVF), entomologic arbovirus surveillance to monitor virus transmission in the RVF virus hotspots in Garissa and Baringo district continued. The main aim was to evaluate the potential for inter-epidemic transmission of RVFV in Kenya.

This is an ongoing study where mosquitoes are collected during rainy seasons since September 2007 (only six months since the major outbreak), identified to species and screened for arboviruses. Screening methods include the use of cell culture inoculation and reverse transcription polymerase chain reaction (RT-PCR) using RVF virus specific and other arbovirus primers.

The samples identified and analysed so far have demonstrated seasonal abundance of potential vectors of RVF virus. These include the species implicated as main vectors during the last outbreak in Garissa (2006/07) such as Aedes mcintoshi (28%), Aedes ochraceous (32%) and Culex poicilipes (.06%) and in Baringo which include Mansonia uniformis and Mansonia africanus.

Although RVF virus has not been detected in any of the samples collected thus far, other viruses have been isolated comprising mainly of Alphaviruses which include multiple strains of Babanki virus, Ndumu virus and 12 unidentified Alphavirus isolates. Most of these viruses were isolated from the key RVF virus vectors implicated during the last outbreak.

The potential for RVF virus transmission between epidemics exists in Garissa and Baringo as efficient vectors of the virus identified during the last outbreak are present in reasonable abundance during the rainy season. The high activity and clustering of Alphaviruses like Babanki, Ndumu and other Alphaviruses especially during the long rains is a significant observation requiring further research to determine their impact on public and animal health and to identify the reservoir hosts. The IEP search for RVFV continues.