Review/Oorsig Volume 22, Issue 04 - Page 20

Oorsig/Review Understanding Rift Valley Fever in the Republic of South Africa Melinda K. Rostal 1 , Catherine Machalaba 1 , Noam Ross 1 , Veerle Msimang 2 , Alan Kemp 2 , Assaf Anyamba 3 , Cornie van Huyssteen 4 , Robert Brand 5 , Petrus van Vuren 2 , Claudia Cordel 6 , Janusz T. Paweska 2 , William B. Karesh 1 This is the first long-term study to investigate Rift Valley fever (RVF) virus simultaneously in people and domestic and wild ruminants. Objective: To investigate how Rift Valley fever virus might spread amongst animals and people, how it is maintained in the mosquito vector, animals and/or people, during the time between outbreaks of disease, what effect climate, soil and vegetation may have on the virus and the vector, how the current level of antibodies in people and animals may affect the risk and the magnitude of an outbreak in livestock and people. MATERIALS AND METHODS Antibody determination in animals Study 1: Ruminant Cross-Sectional Study: A large-scale metapopulation survey for RVF antibodies of domestic livestock and farmed and free-ranging wildlife will be conducted during 2 separate years of the study. Three species of domestic livestock (cattle, sheep and goats) and four species of farmed and free-ranging game (springbok, blesbok, kudu and buffalo) within the study area will be appropriately handled for blood specimen collection. These surveys will indicate the overall state of prevalence of RVF virus exposure in animals in the study area. Study 2: Sheep Cohort Study a cohort of animals (sheep only) will be followed for 4 years to investigate how antibody levels against RVF virus change over time in sheep. The study sheep (n=380) were randomly assigned to one of three study groups, based on pre-determined antibody levels. Seronegative animals received one of the following treatments: modified live vaccine (group1) and no vaccine (group 2). A seropositive (previous exposure) group constitutes the third study group (group 3).Every 3 months thereafter, a blood specimen will be collected from each animal for the duration of the study (4 years). Antibody determination in people Study 3: Cross-Sectional Study in People: In co- ordination and simultaneously with study 1 the cross-sectional study in people will provide an 20 overall population level picture of the exposure risk of people having frequent contact with animals in the study area. Abattoir workers and veterinary and para-veterinary personnel from the study region were similarly recruited to participate in parallel to the farm and farm worker RVF virus surveys. Participants completed a short questionnaire about their contact with animals and potential exposure to RVF and also provided a small blood specimen for RVF virus short- and long-lived antibody testing. Additionally, farm owners and/or managers completed a second questionnaire regarding the type of animals they keep on the farm. Study 4: Cohort study (a constant group of people followed over time for 4 years): Using the results of the cross-sectional farmers/farm workers, veterinarians and abattoirs will be invited to participate. The cohort participants will be asked to complete the same questionnaire as given in study 3 and give a small blood sample on an annual basis for 4 consecutive years. Blood specimens collected will be tested for short- and long-lived antibody titres against RVF virus. The results of these studies will be used to determine the levels of previous exposure (antibody titres) to RVF virus in the study area in both people and animals. Population-level exposure information from the cross sectional studies (1 & 3) will be combined with the information on the change of antibody levels over time through the c ½‘½ΙЁΝΡΥ‘₯•ΜΝ‘••ΐ…Ή)Α•½Α±”€ Θ€˜€ΠΙ•ΝΑ•Ρ₯Ω•±δ€ΈI•ΝΥ±Ρ́™Ι½΄Ρ‘”)ΝΡՑ䁡…δ₯Ή™½Ι΄Α½±₯δ‘•₯Ν₯½ΉΜ…Ή•Ω₯‘•Ή”΄)‰…Ν•ΑΙ…Ρ₯”‰δ₯‘•ΉΡ₯™ε₯ΉœΙ₯Ν¬™…Ρ½Ί™½Θ)‘₯Ν•…Ν”…ΉΡ…ɝ•Ρ́™½ΘΑΙ•Ω•ΉΡ₯Ω”‘•…±Ρ‘…Ι”…Ή)₯΅ΑΙ½Ω•‘₯Ν•…Ν”½ΉΡΙ½°Έ)I•™•Ι•Ή•Μ…Ω…₯±…‰±”½Ή±₯Ή”)ΙΡ₯±”ΑΙ•Ν•ΉΡ•₯ΈΡ‘”…ΝΡ•ΙΈΙ•”MΡ…Ρ” ½ΉΙ•ΝΜ(ΘΐΔ؁AΙ½••‘₯ΉΜ