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Zinga Virus: A Strain of Rift Valley Fever Virus

Rift Valley fever (RVF), an arthropod-borne viral disease, has caused widespread epizootics in domestic animals and epidemics in humans in sub-Saharan Africa and, in 1977 and 1978, in Egypt (1). In humans, RVF virus (RVFV) infection is associated with febrile illness, which may be complicated by encephalitis, blinding retinitis, or fatal hemorrhage (2). Zinga virus, originally isolated from mosquitoes and humans in the Central African Republic (C.A.R) (3,4), produces a disease similiar to RVF, but was believed to be a serologically ungrouped arthropod-borne virus. Although RVFV was previously known to be indigenous to Nigeria (5,6), isolations of Zinga from mosquitoes collected in Senegal, Madagascar, and Guinea, and from infected humans in Senegal, further extend the confirmed range of RVFV activity in West Africa (7).

While testing antisera to African viruses in an enzyme-linked immunosorbent assay using RVFV as antigen, the Yale Arbovirus Research Unit detected a cross-reaction between Zinga virus hyperimmune antisera and RVFV. The relationship between RVF and Zinga viruses was determined using three monoclonal antibodies, each highly specific for different antigenic sites on three structural proteins found in all RVFV strains that have been examined. In indirect fluorescent antibody tests, each monoclonal antibody reacted to either RVFV or Zinga virus antigen with identical titers. Plaque reduction neutralization tests with reference hyperimmune antisera confirmed that the prototype strain of Zinga virus (Institut Pasteur strain Ar B 1976) was serologically identical to RVFV.

Because of its threat to humans and to animal production, research on RVFV in the United States is restricted to high containment laboratories. During the last few years, Zinga virus has been studied in many laboratories in North America, Europe, and Africa, and numerous Zinga infections have resulted from laboratory accidents (7). Any laboratory with Zinga virus in its collection should be aware that it is a strain of RVFV and represents a substantial biohazard to people and animals. Reported by JM Meegan, PhD, RE Shope MD, Yale Arbovirus Research Unit, Yale University School of Medicine, New Haven, Connecticut; CJ Peters, MD, US Army Medical Research Institute for Infectious Diseases, Frederick, Maryland; JP Digoutte, MD, Institut Pasteur de Dakar, Dakar, Senegal; Animal and Plant Health Inspection Svc, US Dept of Agriculture; Special Pathogens Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The discovery that Zinga virus cannot be differentiated from RVFV is important to laboratorians who may have been working with Zinga, unaware of its pathogenic potential, and to public health and agriculture officials concerned with RVF control in livestock. Documentation that the geographic range of RVF includes much of West Africa should alert physicians to consider RVF in the differential diagnosis of dengue-like illnesses or hemorrhagic fever in travelers returning from that area. Since the onset of meningoencephalitis and retinitis may occur late in RVF, clinicians should be aware that these complications may be the presenting features of RVF in a returning traveler.

RVF is primarily an arthropod-borne viral disease of man, sheep, goats, and cattle. In epizootics, the infection results in significant mortality among adult animals, and abortion rates and mortality rates in young animals approach 100%. The 1977 epidemic in completely susceptible human populations of Egypt resulted in an estimated 20%-30% attack rate in epidemic areas, with a case-fatality ratio of 3% (8). Thus, RVF has proven to be a disease of both economic significance and public health importance.

Importation of RVF into the United States is regarded as a threat to the livestock industry and to human public health. Although animals imported from areas known to have enzootic RVF are quarantined before entry, viremic travelers could introduce the virus, since indigenous mosquitoes may serve as vectors. Because of these potential threats and the many documented cases of laboratory-acquired RVF, work with this virus is restricted to laboratories with high-containment facilities. The U.S. Department of Agriculture (USDA) has developed contingency plans to respond to and control an RVF outbreak.

Importation regulations for laboratory strains of RVF and other exotic etiologic agents and vectors are a joint responsibility of the US Public Health Service and USDA. Under the Foreign Quarantine Regulations (42CFR Section 71.156), a permit is required for importation and subsequent domestic transport of such agents and vectors. Adherence to these regulations rests on the good faith of laboratorians. The potential usefulness of such regulation is shown in this instance in which Zinga could be traced to two laboratories in the United States. Other laboratories that have Zinga should contact the Animal and Plant Health Inspection Service of the USDA (301-436-8017) for instructions on proper disposal.

References

  1. Peters CJ, Meegan JM. Rift Valley fever. In: JH Steele, ed. Handbook Series in Zoonoses, Sect. B, Vol. 1, Viral Zoonoses. Boca Raton, Florida: CRC Press, 1981:403-20.

  2. Meegan JM, Shope, RE. Emerging concepts on Rift Valley fever. Perspectives in Virology 1981;11:267-387.

  3. Digoutte JP, Cordellier R, Robin Y, Pajot FX, Geoffroy B. Zinga virus (Ar B 1976), a new arbovirus isolated in the Central African Republic. Ann Microbiol (Inst Pasteur) 1974;125B:107-18.

  4. Digoutte JP, Jacobi JC, Robin Y, Gagnard VJ. Zinga virus infection in man. Bull Soc Pathol Exot 1974;67:451-7.

  5. Ferguson W. Identification of Rift Valley fever in Nigeria. Bulletin of Epizootic Diseases of Africa 1959;7:317-8.

  6. Fagbami AH, Tomori O, Kemp GE. A survey of Nigerian domestic and wild animals for neutralizing antibody to indigenous Rift Vally fever. Nigerian Veterinary Journal 1973;2:45-8.

  7. Digoutte JP. Viruses identified from 1963-1981. Rapport Sur Le Fonctionnement Technique de L'Institut Pasteur de Dakar. 1981.

  8. El-Akkar AM. Rift Valley fever outbreak in Egypt, October-December 1977. Journal of the Egyptian Public Health Association 1978;53:123-128.

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