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 coordination and simultaneously with study 1 the cross-sectional study in people will provide an
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 cohort studies sheep and people ( 2 & 4 respectively ). Results from the study may inform policy decisions and evidencebased practice by identifying risk factors for disease and targets for preventive healthcare and improved disease control .
References available online
Article presented in the Eastern Free State Congress 2016 Proceedings
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