Rift Valley Fever Surveillance in Mobile Sheep Flocks in the Nile Delta

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  • * Ain Shams University Research and Training Center on Vectors of Disease
  • | ** Epidemiology and Biometry Section, Microbiology and Infectious Disease Program, Clinical Epidemiological Studies Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland
  • | U.S. Naval Medical Research Unit No. 3, Cairo, Egypt
  • | U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, Maryland

Rift Valley fever (RVF) surveillance was carried out in the Nile Delta by monitoring mobile and stationary sheep flocks for antibodies to RVF virus. Sheep are known to be susceptible to RVF virus infection and experienced severe morbidity in 1977 and 1978 when RVF was epidemic in Egypt. Four hundred six sheep in 32 flocks were surveyed during 1984. Twenty-four sheep from 7 flocks had antibodies to RVF virus detected by hemagglutination inhibition and plaque reduction neutralization tests. Antibodies were found primarily in sheep > 3 years of age, although 1- and 2-year-old sheep were included in the sample. No seroconversion was observed among 177 seronegative sheep that were bled successively for a period of 10 months. These results indicate that epizootic RVF was probably not present in the Nile Delta during 1984.